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Composite Structures
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ISSN (Print) 0263-8223
Published by Elsevier Homepage  [3161 journals]
  • Hybrid approaches for aircraft primary structure repairs
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): J. Wang, A Baker, P. ChangAbstractCurrently bonded repairs can only be permitted on those aircraft primary structures suffering cracks/damages having a residual strength well exceeding the design limit load prior to application of the bonded repairs. This paper focuses on the approaches to meet the certification requirement by combining a bonded patch with other methods that enhance residual strength of the damaged structures. An overview of the recent research in this area conducted by Defence Science and Technology Group and its research partner organisations is presented. The outcomes from six individual research programs indicated the hybrid repair methods are promising for primary structure repair applications. Significant residual strength increases were achieved through optimum damage removal and/or inclusion of alternative load paths. These methods also provide significant additional fatigue life post premature bond failure that would allow any possible bond-line defect/damage to be identified by NDI means long before a catastrophic failure. The adhesive bond in the hybrid repairs was proven to provide significant benefit in enhancing the static strength and fatigue resistance. Key issues for the application of these hybrid repair methods and future research directions are also discussed.
  • Static and fatigue load performance of a pultruded GFRP deck panel
           reinforced with steel wires
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): Hyeong-Yeol Kim, Sang-Yoon LeeAbstractThis paper presents an experimental study of the quasi-static and fatigue load performance of a pultruded GFRP (glass fiber-reinforced polymer) deck panel that can be used to furnish the roadway surface of temporary detour bridges. The flanges of the GFRP deck panel were reinforced with uniformly spaced steel wires to increase the flexural stiffness of the panel. A total of nine full size GFRP deck panel specimens were tested under static and fatigue loadings. The load-deflection behavior and ultimate strength of the deck specimens were compared with those of the unreinforced specimens. The test results were also compared with the results of finite element analysis. The steel reinforcement of the steel reinforced GFRP panels was only 2.5% of the cross-sectional area of the GFRP composite. The test results indicated that, at the design load level, the flexural stiffness of the steel reinforced GFRP panels was approximately 12.3% greater than that of the unreinforced GFRP panels. The test results further revealed that the fatigue loading up to 120% of the design load did not influence the stiffness of the steel reinforced GFRP deck panel.
  • Thermo-structural Design of a Ceramic Matrix Composite Wing Leading Edge
           for a Re-entry Vehicle
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): Michele Ferraiuolo, Roberto Scigliano, Aniello Riccio, Emanuele Bottone, Marco RennellaAbstractThe design of the wing leading edge of re-entry vehicles is a very challenging task since severe aerothermal loads are encountered during the re-entry trajectory. Hence, advanced materials and structural concepts need to be adopted to withstand the elevated thermal gradients and stresses. Furthermore, particular attention must be paid to the design of hot areas and connections between hot and cold areas of the structure, where the presence of major thermal gradients associated to significant thermal expansion coefficients variations, can lead to damage onset and failure. In order to face this issues, Ceramic Matrix Composites are generally employed as passive hot structures due of their capability to operate at elevated temperatures retaining acceptable mechanical properties. In the present work a novel thermo-structural concept of an hypersonic wing leading edge is introduced and verified by means of an advanced finite element thermo-structural model.
  • Mechanical modelling of the micromegas detectors for the atlas new small
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): F. Rossi, J. Elman, B. Jose, on behalf of the NSW Working Group at CEA Paris-SaclayAbstractIn order to benefit from the expected high luminosity performance provided by the Phase-I upgraded LHC at CERN, the New Small Wheel (NSW) will be installed in the ATLAS detector during the Long Shutdown 2. The ATLAS NSW will be equipped with a new technology for the detection of muons: the MicroMegas (MM) detectors. They consist of different panels made of composite materials and when charged particles traverse the drift space, the gas is ionized and electrons are liberated; the avalanche of electrons takes place in the amplification region after the mesh and they are detected by read-out strips to reconstruct the trajectory of muons produced after the collision. Very tight mechanical tolerances are given in the design phase and they must be preserved from the panel construction to the final operation in the ATLAS cavern.In this paper the construction procedure of these very precise particle detectors is described and the mechanical modelling to predict their mechanical behaviour is presented. Finally, the experimental tests done to validate the numerical models are discussed.
  • Energy absorption analysis for tapered multi-cell tubes improved by foams:
           theoretical development and numerical simulation
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): H. Saeidi Googarchin, M. Pasandidehpoor, A. Mahmoodi, M.H. ShojaeefardAbstractIn this paper, Energy absorption characteristics of tapered multi-cell tubes improved by foams are studied. For the energy absorption process, a theoretical formulation is developed to represent the mean crush load of the foam-filled tubes considering a combination of mean crush loads due to non-filled tube, the foam-filler, and a frictional resistance between them (interaction effects). The formulation is based on the assumptions including equivalent segmented non-tapered single-cell tubes as well as a parallel resisting force of the contributors (non-filled tubes, foam-filler, and interaction effects). Moreover, an extensive numerical analysis on the crushing of the foam-filled tapered multi-cell tubes, with a taper angle ranging from 0 to 7 degrees, a wall thickness ranging from 0.25 to 3 mm, and a cell number ranging from 11 to 10×10, is conducted to evaluate the effects of side wall tapering, cross section’s division into multiple cells and wall thickness enlargement on the crashworthiness characteristics. Analyses indicate that there are significant enhancements in the energy absorption behavior of the foam-filled tubes with respect to the non-filled ones. As a special case, the force-displacement results obtained in the numerical simulation are verified against those experimentally observed and reported in the literature for a foam-filled non-tapered single-cell tube.
  • Mechanical, Morphological, Structural and Dynamic Mechanical Properties of
           Alkali Treated Ensete Stem Fibers Reinforced Unsaturated Polyester
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): Tolera A. Negawo, Yusuf Polat, Feyza N. Buyuknalcaci, Ali Kilic, N. Saba, M. JawaidAbstractPresent study deals the surface morphology and structural composition analysis of alkali (NaOH) treated 2.5% 5.0% and 7.5wt. % Ensete stem fiber obtained from the Ethiopian Ensete ventricosum plant. Treated Ensete fibers reinforced unsaturated polyester (UP) composites were characterized in terms of tensile, flexural, surface morphology and dynamic mechanical properties. Mechanical test results revealed that 5.0 wt.% alkali treated Ensete fibers/UP composites showed 14.5% and 43.5% increase in flexural strength and Young's modulus respectively, with relative to untreated Ensete fibers/UP composites. Storage and loss modulus value also highest for 5.0 wt.% alkali treated Ensete fibers/UP composites. Moreover, a positive shift in glass transition temperature (Tg) of composites after alkali treatment and tensile fracture surface morphology indicates better interfacial interaction in treated Ensete fibers/UP composites. Overall we concluded that 5.0 wt.% treated Ensete fibers satisfactorily and effectively improved mechanical, morphological and dynamic properties of UP for various engineered and hi-tech applications.
  • Electrochemical Performance of Corroded Reinforced Concrete Columns
           Strengthened with Fiber Reinforced Polymer
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): Hongjun Liang, Shan Li, Yiyan Lu, Jiyue Hu, Zhenzhen LiuAbstractExternal bonding of fiber reinforced polymers (FRP) has been widely used to strengthen corroded reinforced concrete columns. During the application of FRP, the variations of electrochemical parameters, such as corrosion current density and charge transfer resistance, have a significant effect on the understanding of anti-corrosion protection mechanism of FRP. Therefore, this study conducted the electrochemical measurements of corroded reinforced concrete wrapped with FRP. The considered variables included pre-corrosion degrees (1%, 3%, and 6% theoretical mass losses) and anti-corrosion protection methods (non-protection, carbon FRP wrapping, glass FRP wrapping, and epoxy coating). The measurements included half-cell potential, linear polarization, and electrochemical impedance spectroscopy (EIS). By analyzing the variation of the above electrochemical parameters in the whole exposure period, it was concluded that FRP wrapping cannot stop the elicited corrosion response but were effective to reduce the corrosion rates, and the main contributor was the epoxy used as an adhesive between concrete and FRP. Moreover, clear inductive loops were observed in Nyquist plots. According to the fitting results, the inductance values were significantly larger for FRP wrapped specimens and less corroded specimens. The inductance may be owing to the difficulties for diffusion of corrosion products.
  • Fatigue crack growth characterization in adhesive CFRP joints
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): I. Floros, K. TserpesAbstractAdhesive joints find an increasing use in lightweight structures, which is proportional to the evolution of carbon fiber-reinforced plastics (CFRPs). Understanding of fatigue crack growth behavior in adhesive CFRP joints is essential for the efficient maintenance and repair of existing joints and the design of new joints. Here, the fatigue crack growth behavior of adhesive CFRP joints under Mode-I, Mode-II and Mixed-Mode I+II loading conditions is characterized experimentally by means of Mode-I fatigue fracture toughness tests, Mode-II fatigue fracture toughness tests and the Mixed-Mode fatigue lap shear test. For the three different tests, the Double Cantilever Beam (DCB), the End-Notch Flexure (ENF) and the Cracked Lap Shear (CLS) specimens are used, respectively. Crack growth versus number of cycles is reported and modified Paris-laws are derived. The DCB specimens failed in cohesive failure mode while the ENF and CLS specimens in adhesive. The crack growth in the DCB specimens was more stable and showed a smaller scatter among the different specimens than the ENF specimens. Crack propagation with number of cycles in CLS specimen was almost linear. The results reported herein suggest a full experimental characterization of fatigue crack growth behavior of the considered aerospace CFRP/adhesive material system and can be proved very useful in the development and validation of fatigue crack growth simulation models.
  • Matrix-graded and fibre-steered composites to tackle stress concentrations
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): David Stanier, Arjun Radhakrishnan, Ian Gent, Sree Shankhachur Roy, Ian Hamerton, Prasad Potluri, Fabrizio Scarpa, Milo Shaffer, Dmitry S. IvanovAbstractThis paper studies the feasibility of improving structural performance of composites in the presence of stress concentrators. Matrix grading through local deposition of additive-enhanced matrices and fibre steering by varying fibrous architecture are examined independently and in combination on a glass-fibre triaxial braided composite subjected to open hole tensile test. Stiffened and toughened matrices were incorporated through precise point-wise injections of liquid reactive resin into dry preforms (Liquid Resin Printing). Fibre steering was implemented by varying the braiding angle along the length of the braided sleeve. It has been shown that these novel forms of architecture modification enable a significant improvement in composite strength through a variety of deformation mechanisms. This includes local stiffening of composite in the direct vicinity of the stress concentrator and damage accumulation away from the stress concentrators. The experimental observations are explained by using simple finite-element models.
  • Experimental and finite element analysis of the long-term behaviour of
           GFRP-concrete hybrid beams fabricated using adhesive bonding
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): Alachek Ibrahim, Reboul Nadège, Jurkiewiez BrunoAbstractThis paper presents experimental and numerical investigations about the short- and long-term behaviour of a hybrid beam consisting of a GFRP pultruded profile bonded by an epoxy adhesive joint to a reinforced concrete slab. The experimental program included flexural creep tests on GFRP I-profiles and on hybrid beams subjected to constant loads. The deflections and the longitudinal strains were measured in natural environmental conditions and recorded for time durations up to 3500 h. Also, three-dimensional models, based on the incremental form of the linear viscoelastic theory, were proposed to study the evolution of strains and stresses over time for the structures. The results of the sustained-load test show that creep deflections on the order of 27-37% of the initial static deflections were observed for the hybrid beams after about 5 months of loading. It is also found that, for the hybrid beam, the rapid degradation of bond strength, resulted from the combined effect of environmental conditions and applied loading, leads to debonding and subsequently a brutal failure. Furthermore, the finite-element analysis is found to be able to simulate the long-term behaviour of the hybrid beam and help understand the complex changes in the stress state that occur over time.
  • Nonlinear vibration of piezoelectric sandwich nanoplate with a
           functionally graded porous core with consideration of flexoelectric effect
    • Abstract: Publication date: Available online 18 September 2018Source: Composite StructuresAuthor(s): S. Zeng, B.L. Wang, K.F. WangAbstractThe porous materials become a new class of advanced engineering material due to their excellent advantage such as low specific weight, efficient capacity of energy dissipation, reduced thermal and electrical conductivity, enhanced recyclability and machinability. In this study, the nonlinear vibration of piezoelectric sandwich nanoplates with a functionally graded (FG) porous core under electrical load is presented. The piezoelectric effect, flexoelectric effect and von Karman type large deformation are simultaneously taken into account. Results show that the piezoelectric and flexoelectric effects of the material reduce the vibration frequency of the sandwich nanoplate even there is no applied voltage on the piezoelectric layer. The natural frequency of the sandwich structure with porous core can be adjusted by controlling the porosity distribution and porous coefficients of the porous material, and the applied voltages on the piezoelectric layer.
  • Quantification of epistemic uncertainty in laminated composite plates
           under static and in-plane loads using trigonometric shear deformation
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Sambhaji Lore, Suganyadevi Sarangan, B.N. SinghAbstractIn the present study, epistemic uncertainty is quantified for bending and buckling analysis of laminated composite plates using evidence theory. By employing vertex and uniform sampling methods the degree of confidence of the failure analysis is carried out in terms of belief and plausibility. Dempster’s rule of combination is used when the analysis subjected to more number of experts under vertex and sampling methods. To proceed the uncertainty quantification for the composite plates a trigonometric higher order shear deformation theory is assessed by analytical and finite element formulation. Numerical examples are carried out to illustrate the effectiveness of the proposed methods for failure analysis based evidence theory of real engineering problems. Considering various parameters such as size of focal element, uncertain variables as material and geometric parameters, more number of uncertain variables and more number experts for each uncertain variable the quantification is executed. From the numerical examples, it is observed that for quantifying the epistemic uncertainty employing more experts for uncertain variables is the favorable choice.
  • The effect of off-axis angles on the mesoscale deformation response and
           failure behavior of an orthotropic textile carbon-epoxy composite
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Jishen Yang, Xiaoguang Yang, Hanxing Zhu, Duoqi Shi, Xindong Chen, Hongyu QiAbstractThe deformation response and failure behavior of an orthotropic textile carbon-epoxy composite were investigated under off-axis tensile loading. Digital image correlation (DIC) was utilized to effectively capture the full-field and mesoscale strain distribution. The macroscale mechanical performance was strongly sensitive to the fiber bundles orientation relative to the loading direction. Based on the experimental data, a quantitative relation between the rotation angle and off-axis angle was established, and a negative correlation between the failure strength and the rotation angle was observed. The underlying failure mechanisms of the specimens with different off-axis orientations were analyzed using scanning electron microscopy (SEM) and DIC techniques. The load-bearing mechanisms were different between the on- and off-axis cases. High local shear strain eventually resulted in the brushy shear-type fracture in the off-axis case, and the local micro cracks developed during the loading caused the reduction and imbalance of local load-bearing capacity.
  • 3D-wave propagation in generalized thermoelastic functionally graded disks
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Ayoob Entezari, Matteo Filippi, Erasmo Carrera, Mohammad Ali KouchakzadehAbstractThis paper explores the capabilities of refined finite elements for 3D analysing of thermoelastic waves propagation in disks made of functionally graded materials. Based on the Lord-Shulman generalized theory of thermoelasticity, the field equations are written according to the three-dimensional formalism of the Carrera Unified Formulation (CUF). The system of the coupled equations is solved in the Laplace domain and, then, converted in the time domain by using numerical inverse Laplace transform. For a functionally graded disk exposed to thermal shock load, the time histories of displacement, temperature and stress fields are reported for different gradation laws. Propagation and reflection of the thermoelastic waves are illustrated as well. Comparisons with analytical solutions demonstrated the significant rate of convergence and the accuracy of the presented finite elements.
  • A study on the energy absorption capacity of braided rod composites
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Yuqiu Yang, Khalil Ahmed, Ruiyun Zhang, Ruohua Liu, Gabriel Fortin, Hiroyuki Hamada, Yan MaAbstractComposite materials are becoming popular among automobile manufacturers because of their high strength, light weight, and controlled crushing mechanisms. Many composite structures have been designed and developed as energy absorption components in automobiles until now. Following the trend, in this study UD and braided UD glass fiber rods were manufactured as an energy absorption component for the automotive industry and their energy absorption capability was measured by quasi-static compression testing. In order to fully understand the crushing mechanisms, the effect of braiding layers, braiding technique, taper angle, single and multiple rods and their separation on the energy absorption capability was investigated. Braided UD rods absorbed more energy compared to the MFW (multifilament wounded) rods, while tapering one side of the rod greatly influenced the crushing distance, yield point, and load bearing capabilities. Additionally, the mean load of three BR-1L rods was almost three times higher than that of a single rod however, it was influenced by varying the distance among them. The aim of this research was to collect more data about the crashworthiness of composite rods under different parameters and to gain a better understanding for future research work.
  • Numerical studies on stability and load capacity of compressed channel
           section columns made of composite reinforced with flax fibers
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Mariusz Urbaniak, Adrian Gliszczyński, Łukasz BorkowskiAbstractIn this article, the results for compressed channel section profiles made of glass and flax fiber reinforced polymer were presented. Six symmetric arrangements of layers were tested: [0/−45/45/90]s, [90/−45/45/0]s, [90/0/90/0]s, [0/90/0/90]s, [45/−45/45/−45]s, [45/−45/90/0]s. The study concerns the buckling and failure modes and loads determination. To obtain load capacity of analyzed structures the ANSYS program based on finite element method was employed. Linear (LBA) and nonlinear buckling analyses (NBA) with an implementation of the progressive failure algorithm (PFA) with the Hashin criterion as the damage onset criterion, were performed. Structures made of natural fibers were characterized by small differences in relation to the successive buckling loads, similar load carrying capacity values determined for the implementation of successive buckling modes and, in opposition to GFRP channel section profiles, by a lack of or a small range of deformations in the postbuckling stage. Wherefore, the obtained results with results for analogous profiles made of GFRP were compared. Furthermore, the effect of laying the laminate layers on the magnitude of the critical force and the occurrence of a specific failure mechanism depending on the number of degraded layers were presented.
  • Length-scale effect in dynamic problems for thin biperiodically stiffened
           cylindrical shells
    • Abstract: Publication date: 1 December 2018Source: Composite Structures, Volume 205Author(s): Barbara Tomczyk, Anna LitawskaAbstractThe objects of consideration are thin linearly elastic Kirchhoff-Love-type circular cylindrical shells having a periodically microheterogeneous structure in circumferential and axial directions (biperiodic shells). The aim of this contribution is to formulate and discuss a new mathematical averaged model for the analysis of selected dynamic problems for these shells. This, so-called, general combined asymptotic-tolerance model is derived by applying a certain extended version of the known tolerance (non-asymptotic) modelling procedure. This version is based on a new notion of weakly slowly-varying functions. Contrary to the starting exact shell equations with highly oscillating, non-continuous and periodic coefficients, governing equations of the proposed combined model have constant coefficients depending also on a cell size. Hence, this model can be applied to study the effect of a microstructure size on dynamic behaviour of the shells (the length-scale effect). An important advantage of this model is that it makes it possible to analyse micro-dynamics of biperiodic shells independently of their macro-dynamics. The differences between the proposed general combined model and the corresponding known less accurate standard combined model derived by means of the more restrictive concept of slowly-varying functions are discussed. As an example there are determined and analysed cell-depending micro-vibrations of the biperiodic shells under consideration.
  • Analysis of isotropic and composite laminated plates and shells using a
           differential quadrature hierarchical finite element method
    • Abstract: Publication date: Available online 5 September 2018Source: Composite StructuresAuthor(s): Yang Wu, Yufeng Xing, Bo LiuAbstractA p-version curved composite laminated shell element has been developed using the modified high order bases of a differential quadrature hierarchical finite element method (DQHFEM). The theoretical model of the shell is based on a layerwise theory with linear expansion in each layer. Exact geometry is established using the CAD technique of Non-Uniform Rational B-splines. As a result, the FEM discretization errors of geometry are eliminated. To solve the coupling difficulty of elements with different parameterization that commonly exists in complicated models, a novel method based on interpolation on arc length coordinates is proposed in this work. Even though the computational efficiency based on a layerwise theory is not as fast as those based on the equivalent single-layer theory, it produces as accurate results as the 3D theory and uses less DOFs as well as less input data than the 3D model. Additionally, because of the high convergence rate of the p-version FEM and the exact representation of the geometric model, the present elements are expected to produce more accurate results than the conventional h-version flat shell elements with the same number of DOFs. Numerical examples are provided to illustrate the accuracy as well as versatility of the present elements.
  • Stability analysis of multi-layered plates subjected to partial edge
           compression with and without initial imperfection
    • Abstract: Publication date: Available online 5 September 2018Source: Composite StructuresAuthor(s): Loc V. Tran, Seung-Eock KimAbstractThis paper studies buckling and post-buckling behaviours of multi-layered plates under in-plane compression based on Reissner-Mindlin plate theory. The governing equations are derived from a kinematic nonlinearity based on the von-Kármán assumptions and are thereafter discretized by isogeometric analysis (IGA), which utilizes the NURBS basis functions. For the symmetrically laminated plates, stability analysis consists of three steps: pre-buckling, buckling and post-buckling analyses. In fact, the pre-buckling stresses must be first determined in the pre-buckling analysis and become an important factor in accurate estimation of the critical buckling and post-buckling loads. Otherwise, in the imperfect or unsymmetrically stacked plates, there is no buckling bifurcation phenomenon. The Newton-Rapshon method is hence adopted to solve the geometrically nonlinear problem. Numerical examples are supplied to investigate the effect of an initially geometrical imperfection, which is possible imperfection type such as sine-type, global-type or local-type imperfection, on the post-buckling response of the plates.
  • Material tailoring for reducing stress concentration factor at a circular
           hole in a functionally graded material (FGM) panel
    • Abstract: Publication date: Available online 3 September 2018Source: Composite StructuresAuthor(s): G.J. Nie, Z. Zhong, R.C. BatraAbstractBy assuming that Young’s modulus and Poisson’s ratio of a linearly elastic and isotropic material vary along the radial direction in a panel with a circular hole and deformed by a far field uniaxial tensile traction, we first analytically find the stress concentration factor, K, at the hole. The problem is solved by superposing solutions of two problems – one of uniform biaxial tension and the other of pure shear. The solutions of the first and the second problem are, respectively, in terms of hypergeometric functions and Frobenius series. Subsequently, we analytically study the material tailoring problem for uniform biaxial tension, and give explicit variation of Young’s modulus to achieve a prespecified K. For the panel loaded by a far field uniaxial tensile traction, we show that the K can be reduced by a factor of about 8 by appropriately grading Young’s modulus and Poisson’s ratio in the radial direction. By plotting K versus the two inhomogeneity parameters, we solve the material tailoring problem for a panel loaded with a far field uniaxial traction. The analytical results should serve as benchmarks for verifying the accuracy of approximate/numerical solutions for an inhomogeneous panel.
  • Modeling, Simulation, and Experiments of High Velocity Impact on Laminated
    • Abstract: Publication date: Available online 25 August 2018Source: Composite StructuresAuthor(s): M. Schwab, M. Todt, J. Tauchner, D. Schlie, H.E. PettermannAbstractHigh velocity impact on laminated composite panels is investigated by modeling, simulation, and experiments. Impact velocities of 100, 200, and 300m/s are considered and normal as well as oblique impacts are studied. FEM simulations are conducted to design three different laminate configurations to achieve the cases of a reflecting, almost stucking, and fully perforating impactor, respectively. Within a domain where material nonlinarities are expected the shell-based ply-scale approach is used. Every ply is modeled by a layer of shell elements which are connected via cohesive zone elements. Both element types are assigned nonlinear constitutive laws to capture their mechanical behavior appropriately. Outside this domain, a single layer of composite shell elements is used. Corresponding laminated plates are produced and tested using a gas gun setup, where energy absorption and damage patterns are assessed.The comparison of simulations and experiments shows excellent agreement. The three cases are predicted well, and also the damage patterns and the energy absorptions match very well.
  • Mechanical performance of GFRP-profiled steel sheeting composite sandwich
           beams in four-point bending
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Fubin Zhang, Weiqing Liu, Zhibin Ling, Hai Fang, Dandan JinAbstractThis study proposed a novel GFRP-profiled steel sheeting composite sandwich beam (GPSS beam) composed of glass fiber reinforced polymer (GFRP) skins, a lightweight polyurethane (PU) foam core and a 0.9-mm-thick profiled steel sheeting. The interaction between the GFRP skins and the profiled steel sheeting was enhanced by the use of stainless steel core rivets. The flexural performance of the GPSS beams was studied through experimental and analytical methods. Eight beam specimens, including a control specimen, were tested in 4-point bending tests to verify the efficiency of the profiled steel sheeting to improve the stiffness, ultimate load-bearing capacity and energy dissipation capacity of the beams. Test results demonstrated that the bending stiffness and ultimate load-bearing capacity can increase up to 306% and 158%, respectively compared to those of the control specimen. The energy dissipation ability of GPSS beams was increased greatly by using stainless steel core rivets. Additionally, unlike the control specimen, the GPSS beams collapsed in a ductile manner. Analytical formulas for predicting the bending stiffness and ultimate load-bearing capacity of GPSS beams were proposed and captured these effects reasonably accurately. The flexural stiffness of the GPSS beams with the profiled steel sheeting were equivalent to those of the same size RC beams with a moderate to heavy reinforcement ratio of 1.0–2.4%, but the GPSS beams were 25.5–65.1% higher in ultimate load-bearing capacity and 5–8 times lighter in weight.
  • Isogeometric analysis and design of variable-stiffness aircraft panels
           with multiple cutouts by level set method
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Peng Hao, Chen Liu, Xuanxiu Liu, Xiaojie Yuan, Bo Wang, Gang Li, Manhong Dong, Liang ChenAbstractFor composite panels with cutouts, curvilinear fiber path can adjust the in-plane stiffness distribution to increase the buckling resistance, but it results in huge computational cost for the buckling analysis when FEA is employed. In this study, variable-stiffness panels with cutouts are analyzed via isogeometric method, where cutouts are represented by the level set method. The method for suppressing artificial buckling modes is proposed to improve the prediction accuracy. Moreover, the analytical sensitivity is derived to facilitate fiber path optimization, and a new bi-level optimization framework considering manufacturing constraints is established. Finally, the proposed method is verified by variable-stiffness aircraft panel with multiple cutouts, which can not only provide an accurate prediction of buckling load, but also exhibit high convergence rate and low computational cost for fiber path optimization.
  • Micro-CT analysis of the orientation unevenness in randomly chopped strand
           composites in relation to the strand length
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Yi Wan, Ilya Straumit, Jun Takahashi, Stepan V. LomovAbstractMulti-sample X-ray micro-computed tomography (micro-CT) is used for the statistical analysis of the internal geometry of randomly oriented strands (ROS) composite – ultra-thin chopped carbon fiber tape reinforced thermoplastics (UT-CTT) with different tape lengths. The accuracy of the micro-CT measurements and their quantification for the local fiber orientation is assessed and the statistical significance of the observed trends in the fiber orientation is confirmed. The effect of tape length on structure morphology and orientation concentration is investigated. Increasing the tape length decreases the number of internal structure irregularities (scattered fiber clusters and out-of-plane fiber disturbance for instance) present in UT-CTT.
  • The Walsh series method for free vibration analysis of functionally graded
           cylindrical shells
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Jianyu Fan, Jin Huang, Zhang Juxiang, Zhang JieAbstractIn this paper, a novel numerical method based on the Walsh series (WS) is proposed for free vibrations of functionally graded material (FGM) cylindrical shells. Based on the first order shear deformation theory, the governing equations of the FGM cylindrical shells are derived via the Hamilton’s principle. After converting the governing equations into a set of ordinary differential equations (ODEs) by the separation of variables, the proposed Walsh series method (WSM) is utilized to transform the ODEs to algebraic equation sets, which results to a standard linear eigenvalue problem. The natural frequencies of the FGM cylindrical shell are calculated by solving the obtained algebraic equations. The convergence and accuracy analyses of the present method are performed by comparing the obtained results with those available in the existing literature. The results show that the solution of the proposed WSM is stably converged with the numerical convergence rate close to 2 and the good agreement of the obtained results with those in the available literature is also observed. Finally, the parametric study is conducted to investigate the effects of several geometrical and material parameters of the FGM cylindrical shells with various boundary conditions on the natural frequencies.
  • Nonlinear dynamic analysis of composite piezoelectric plates with graphene
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Xiangying Guo, Pan Jiang, Wei Zhang, Jie Yang, Sritawat Kitipornchai, Lin SunAbstractThis paper studies the nonlinear dynamical characteristic of a composite plate made of new three-phase materials which include the graphene (GP) combined with macro fiber composite (MFC) in the polymer. The GP is supposed to be uniformly dispersed in the upper and lower surfaces of the composite laminated plate with 1–3 mode of macro fiber. The cross-ply MFC composite laminated plate is subjected to transversal excitations. The constitutive laws for the MFC-GP composite material are obtained based on the rule of mixture for multi-components of composite material. The nonlinear governing equations of motion of the MFC-GP plate are derived by Hamilton’s principle and the von Kármán geometrical kinematics. Galerkin’s approach is employed to discretize the partial differential governing equations into a two-degree-of-freedom nonlinear system. Then, stability analysis is conducted to investigate the influences of various parameters on natural frequencies of the MFC-GP plate, with a particular focus on the effects of GP volume fraction, initial conditions and damping coefficients on nonlinear vibration behaviours of the composite plate.
  • Impact and after-impact properties of nanocarbon aerogels reinforced
           epoxy/carbon fiber composite laminates
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Tsung-Han Hsieh, Yau-Shian Huang, Feng-Xiang Wang, Ming-Yuan ShenAbstractNano-carbon aerogels (NCAs) have three-dimensional structures, and high porosities. They show promise as innovative materials because of their attractive properties such as high electrical conductivity, high-porosity structures, and high surface areas, which suggest that the material properties of polymer-based composites can be improved. In this study, NCAs were used to reinforce epoxy/carbon fiber composite (CFRP) laminates to investigate the impact and after-impact properties of the composites under three different impact energies 20, 25, and 30 J.The experimental results showed that the impact resistance properties of the CFRP laminates steadily improved with NCAs at the addition of 0.3 wt%. In addition, the damage to the NCAs/CFRP laminates at the low impact energy of 20 J was observed by nondestructive evaluation, including ultrasonic inspection (C-scan) and thermographic analysis, to understand the delamination behavior of the NCAs/CFRP laminate.
  • Design, manufacturing and structural testing of all-composite FRP bridge
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Tomasz Siwowski, Maciej Kulpa, Mateusz Rajchel, Pawel PonetaAbstractNowadays FRP composites have been used in many bridge applications due to their excellent strength and durability characteristics. Footbridges seem to be the most often application of the FRP composites in bridge engineering. After the comprehensive survey of existing FRP footbridges the innovative idea of FRP composite structural system for typical footbridges with the span length of 15–25 m has been proposed in the paper. The basic structural element of the footbridge is a main box girder with the U-shape cross-section covered with the sandwich deck, and made of hybrid glass – carbon composites by the VARTM infusion. The comprehensive static tests have been carried out in the laboratory to evaluate the actual stiffness, ultimate strength and failure modes of the large scale prototype girder. The prototype FRP girder exhibited satisfying structural behaviour during the test and reasonable agreement with the predictions from the FE design analysis.
  • Design and nonlinear structural responses of multi-bolted joint composite
           box-beam for sectional wind turbine blades
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Zhiwen Qin, Jihui Wang, Ke Yang, Guangan Yu, Yu Xu, Jianzhong XuAbstractThis paper deals with the nonlinear structural responses of multi-bolted joint box-beam under inadequate preload, the composite box-beam was designed to refer to a real blade. The simplified analytical, solid-shell finite element and experimental methods were jointly conducted to investigate additional bolt loads, clamped loads, and deflections of the sectional box-beam under flap-wise bending loads. The validation of the finite element model is confirmed by the good prediction of the natural frequencies, strains of composite spar caps and the additional bolt loads of the sectional box-beam. The numerical model shows superior precision in describing the structural responses of the sectional box-beam even after separation. The simplified analytical method offers a conservative solution to calculate bolt loads. The global movement at the divided section will not appear ideally due to continuous increase of the total clamped load. The slight jump of clamped load in PS implies the probability of residual deflection of the sectional box-beam. Meanwhile, the relative movement tends to brings about the bolt preload reduction in the case of periodic loading, and then fatigue failure rapidly under on-going reduction of preloads. This study provides a deep insight into the fatigue strength of bolted joint for sectional rotor blades.
  • Experimental study on delamination growth of stiffened composite panels in
           compression after impact
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Tian Ouyang, Wei Sun, Zhidong Guan, Riming Tan, Zengshan LiAbstractThe purpose of this paper was to investigate the failure behaviors of composite stiffened panels with skin low-velocity impact (LVI) damage under axial compression. Barely visible impact damage (BVID) was introduced into the L-shaped and T-shaped stiffened panels within the skin between stiffeners. Compression after impact (CAI) tests were performed and delamination growth of specimens was observed directly. The results show that there are two types of delamination growth processes, which are unstable and stable respectively. Due to the restriction effect of the stiffener, the delamination growth is easier to initiate in the outer sublaminates on the smooth side of the skin compared to the ones on the stiffener side. In addition, according to the thermal-deply result, adjacent impact delaminations can be connected by matrix cracks, which results in a larger area of the sublaminate. It is revealed that buckling of the sublaminates and subsequent transverse delamination propagation in large area are the triggers leading to the final failure of the stiffened panel.
  • Thermal and mechanical buckling analysis of FG carbon nanotube reinforced
           composite plates using modified couple stress theory and isogeometric
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Amir Farzam, Behrooz HassaniAbstractThis paper investigates the thermal and mechanical buckling analysis of functionally graded carbon nanotube reinforced composite (FG-CNTRC) plates by using isogeometric analysis (IGA) based on modified couple stress theory (MCST). A refined hyperbolic shear deformation theory is used for buckling analysis, which satisfies free transverse shear stress conditions on the top and bottom surfaces of plate without a need for shear correction factor. The material properties of carbon nanotube reinforced composite plates are assumed to be temperature-dependent. For numerical analysis the IGA method using B-Spline or Non-Uniform Rational B-Spline (NURBS) functions is employed. The obtained results are compared with those available in the literature. Also, the influence of different parameters on mechanical and thermal buckling analysis is investigated. These parameters include material length scale parameter, boundary conditions, aspect and length-to-thickness ratios of plate, different types of FG-CNTRC distribution, volume fraction of CNTs and temperature dependency.
  • A level-set-based strategy for thickness optimization of blended composite
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): F. Farzan Nasab, H.J.M. Geijselaers, I. Baran, R. Akkerman, A. de BoerAbstractAn approach is presented for the thickness optimization of stiffened composite skins, which guarantees the continuity (blending) of plies over all individual panels. To fulfill design guidelines with respect to symmetry, covering ply, disorientation, percentage rule, balance, and contiguity of the layup, first a stacking sequence table is generated. Next, a level-set gradient-based method is introduced for the global optimization of the location of ply drops. The method aims at turning the discrete optimization associated with the integer number of plies into a continuous problem. It gives the optimum thickness distribution over the structure in relation to a specific stacking sequence table. The developed method is verified by application to the well-known 18-panel Horseshoe Problem. Subsequently, the proposed method is applied to the optimization of a composite stiffened skin of a wing torsion box. The problem objective is mass minimization and the constraint is local buckling.
  • Reduced modal state-space approach for low-velocity impact analysis of
           sandwich beams
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Mojtaba Lezgy-Nazargah, Ehsan EtemadiAbstractThe convergence problems of nonlinear dynamic impact analysis may be in some extent overcome by using the linear forms of contact laws. However, the full-scale finite element analysis of structures with linearized contact laws need high computational efforts. In this study, an efficient reduced modal state-space approach with low computational cost was introduced to predict the dynamic structural response of sandwich beams. A one degree of freedom spring-mass system was used to model the dynamics of projectile. Furthermore, the fully dynamic equations of the sandwich beam were obtained using a new high-order finite element formulation. The dimensions of the dynamic system were reduced based on the method of truncated combination of modes. Finally, the reduced dynamic equations were solved in the framework of state-space approach. The results obtained from the present formulation were compared with the available analytical and numerical results and good agreements found between them.
  • In-plane and out-of-plane buckling of architected cellular plates:
           Numerical and experimental study
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): H. Niknam, A.H. AkbarzadehAbstractIn this article, the nature of instability in architected cellular materials is explored through computational modelling and experimental testing. The in-plane and out-of-plane buckling as two major instability mechanisms in cellular materials are distinguished and the effects of their microarchitectural parameters on the buckling behavior are demonstrated. Different architected cellular materials in the form of cellular plates are analysed with a finite element method (FEM) by eigen buckling and nonlinear analyses, while a few samples of elastomeric architected cellular materials are prototyped and experimentally tested to corroborate our numerical predictions for the buckling load. We show that an appropriate gradient of cell architecture within the cellular plates could lead to an increase in both out-of-plane and in-plane buckling loads. The experimental tests conducted on the casted cellular plates with uniform and graded microarchitectures, made of a two-component silicone elastomer, confirm that different buckling mode shapes can be observed by tailoring the microarchitectures of cellular plates. This idea can pave the path for devising advanced reconfigurable materials, for shape matching and energy absorption applications, whose mode shapes and resistance to buckling can be programmed based on the desirable functionalities without compromising their total mass.
  • Experimental and analytical characterizations of finite interlaminar crack
           growth of 2D woven textile composites
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): W. Xu, Z.Z. Guo, Y. Yu, J. Xiong, Y. GaoAbstractDue to the weave structure of woven textile composites, unstably finite crack growths are observed in the quasi-static interlaminar fracture tests for unidirectional woven textile composites. The unstable crack growth speed and finite crack growth length are up to 60 m/s and 24 mm, respectively. A double compliances method is used to measure the fracture toughnesses for the static and dynamic crack growths. It is found that the double compliances method is very accurate and much simpler than the ASTM standard methods for determining the static fracture toughness. With the help of a high speed camera and the double compliances method, the fracture toughness of the unstable crack is given in this paper.
  • The pull-out behavior of straight and hooked-end steel fiber from hybrid
           fiber reinforced cementitious composite: Experimental study and analytical
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Fangqian Deng, Xiaoxiao Ding, Yin Chi, Lihua Xu, Li WangAbstractThis paper deals with the interfacial bonding performance of the steel fiber in the steel-polypropylene hybrid fiber reinforced cementitious composite. 42 groups of straight and hooked-end steel fiber specimens are investigated by the single-sided pull-out tests. The whole pull-out load-slip responses are captured, and the effects of hybrid fiber dosage, matrix strength and fiber embedded length are analyzed. Furthermore, the interfacial bonding mechanism and fiber reinforcing mechanism are revealed based on SEM images. Results show that the addition of hybrid fibers in the matrix contributes significantly to increasing the maximum and residual pull-out load as well as improving the pull-out energy dissipation capacity. The polypropylene fiber content is found to be the dominant factor for the variation of interfacial properties. For straight steel fiber, the enhancing effect of hybrid fiber on the chemical adhesion force is more pronounced than that on the sliding frictional force. For hooked-end steel fiber, the contribution of hybrid fiber is not significant on the hook mechanical interlocking. Finally, a theoretical model is developed to predict the pull-out behavior with the hybrid fiber effect taken into account. The predictions provide satisfactory correlation to the experimental results from both the current study and previous work.
  • Nonlinear buckling analysis of variable stiffness composite plates based
           on the reduced order model
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Ke Liang, Qin Sun, Yongjie ZhangAbstractThe variable-stiffness fiber composite plates which have an enhanced design flexibility, largely rely on laminate optimizations to maximize the buckling performance. The corresponding computational efficiency becomes a key issue, in particular when the nonlinear structural behavior is considered. The finite element method based on a full nonlinear analysis is a standard technique for nonlinear structural analysis, however the high computational complexities generated from both the incremental-iterative procedure and the very refined mesh needed for the discrete modeling of curved fibers, are still a decisive cost factor on modern computers. In this work, the Koiter-Newton method is further extended to nonlinear buckling analysis, including the pre and post buckling stage, of variable stiffness composite plates. A four-node quadrilateral element based on the classical laminated plate theory is developed in framework of the von Kármán kinematics, for the finite element implementation of the proposed asymptotic method. The reduced order model, with or without imperfections, is constructed using the improved Koiter’s asymptotic expansion, for both the symmetrical and unsymmetrical laminates. The nonlinear response curve of loaded structure can be traced automatically, using the nonlinear predictor and corrections both generated from the reduced order model. This leads to a fairly large step size in the path-tracing process, compared to that for the classical Newton method. The reduced order model largely reduces the computational burden produced by the high-density FE mesh for the varied fiber path. Numerical results indicate the overall high quality and efficiency of the proposed method.
  • Improved genetic algorithm for optimization design of a three-dimensional
           braided composite joint
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Ziyang Tian, Ying Yan, Yang Hong, Fangliang Guo, Jinxin Ye, Jie LiAbstractIn this study, we develop an algorithm for the optimization design of a three-dimensional (3D) braided composite joint. The design is a typical optimization problem with high computational expense in terms of objective evaluation and a highly dimensional design domain. The algorithm is established in the framework of a Genetic Algorithm (GA) that integrates the Steepest Descend Method (SDM), and it is improved according to the characteristics of the abovementioned problem. A Structural Strength Computational Model (SSCM) for the mechanical performance analysis of the joint is also developed to evaluate the optimization objective, and the model is experimentally verified. Results show that structural strength increases significantly after optimization. During optimization, the coupling relationship between stress distribution and material properties leads to the problem of nonlinearity and multimodality. The GA searches globally, which prevents the result from locally converging, and provides excellent initial solutions for the SDM. Then, the SDM searches locally with high-efficiency and increases the accuracy of the solutions. This method is precise and efficient for the abovementioned optimization problem.
  • A cohesive network approach for modelling fibre and matrix damage in
           composite laminates
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): M.W. Joosten, Q.D. Yang, M. Blacklock, C.H. WangAbstractIn the current study a high fidelity analysis approach is used to predict the failure process of notched composite structures. Discrete cracking is explicitly modelled by incorporating cohesive interface elements along potential failure paths. These elements form an interconnected network to account for the interaction between interlaminar and intralaminar failure modes. Finite element models of these configurations were created in the commercial analysis software ABAQUS and a user defined material subroutine (UMAT) was used to describe the behaviour of the cohesive elements. The material subroutine ensured that the model remained stable despite significant damage, which is a significant challenge for implicit damage simulations. Two analysis approaches were adopted using either the as-measured or modified (in-situ) ply strengths. Both approaches were capable of closely predicting the mean ultimate strength for a range of hole diameters. However, using the measured ply properties resulted in extensive matrix cracking in the surface ply which caused a deviation from the experimentally measured surface strain. The results demonstrate that high fidelity physically based modelling approaches have the ability to complement or replace certain experimental programs focussed on the design and certification of composite structures.
  • Meta-tensegrity: Design of a tensegrity prism with metal rubber
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Yanhong Ma, Qicheng Zhang, Yousef Dobah, Fabrizio Scarpa, Fernando Fraternali, Robert E. Skelton, Dayi Zhang, Jie HongAbstractA tensegrity structure involves the presence of elements withstanding pure compression, and others under pure tension only. Metal rubber is introduced into a tensegrity prism strut to create a mechanical metamaterial with energy absorption and tuneable dynamic properties. In this work we describe the design and development of the meta-tensegrity structure with particular emphasis on the evaluation of parameters such as the structural size, the metal rubber stiffness, the initial internal force and the external compression load. Prototypes of tensegrity prisms with and without metal rubber inserts have been assembled and subjected to quasi-static loading. The model used to design the meta tensegrity prism has been then modified to take into account specific manufacturing and internal dissipation mechanisms typical of this configuration. The updated model provides a better comparison with the experimental results. Both the theoretical and experimental data show that the introduction of the metal rubber within the tensegrity configuration contributes to improve significantly the energy absorption, and to reduce the stiffness of the whole tensegrity structure.
  • Additive manufacturing of woven carbon fibre polymer composites
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Andrew N. Dickson, Keri-Ann Ross, Denis P. DowlingAbstractA novel technique for the fabrication of woven composites using additive manufacturing (AM) is presented and evaluated. To-date fibre reinforced composites deposited by AM exhibit highly anisotropic properties as the individual layers do not interact, this study helps address this by printing of a 0/90 woven structure into one layer to aid in stress distribution. A fibre path generator was created utilising Gcode to emulate the weft-warp components of a woven construction using a continuous carbon fibre filament. This new pathing technique also allows for a woven structure to be integrated with features (such as notches) previously only possible through destructive machining processes. In order to evaluate the performance of the printed composites, open hole tensile studies were carried out in which 6 mm holes were routed into the composite structure and the resulting part’s mechanical performance were compared with specimens which had been die punched as well as an unnotched control group. The latter exhibited strengths equivalent to 49% that of unnotched specimen. In contrast the specimens with woven holes exhibited strengths which were 44% higher, just 7% lower than the strength achieved for the unnotched specimens. Digital image correlation (DIC) analysis also demonstrated significantly reduced strain concentration around the printed hole perimeter, compared with that for the die punched hole.
  • Evaluation on the interval values of tolerance fit for the composite
           bolted joint
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Chao Chen, Dean Hu, Qiming Liu, Xu HanAbstractThe bolted joint has frequently been used to join different components together for the composite materials. However, the effect of tolerance fit on mechanical properties of the composite bolted joint is still ambiguous. In this paper, a three-dimensional numerical model is established and validated by reference experiment for the single-lap composite bolted joint. Then the High Dimension Model Representation (HDMR) using Sobol method is employed to analyse the global sensitivity of tolerance fit, bolt clamping force and friction of contact interfaces. The sensitivity index indicates that the tolerance of composite hole is the most crucial parameter for the mechanical properties of composite bolted joint. Finally, the interval values of tolerance behaviours between bolt shank and laminate hole are investigated numerically based on Six Sigma analysis. The tolerance is analysed by considering the influences of perfect fit, clearance fit and interference fit on mechanical properties. This work provides a meaningful reference for selecting the tolerance fit for the composite bolted joint.
  • Optimizing mechanical properties of bio-inspired composites through
           functionally graded matrix and microstructure design
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Zhongliang Yu, Junjie Liu, Wenqing Zhu, Xiaoding WeiAbstractInspired by biological composites, the brick-and-mortar microstructure has been adopted in many synthetic composites to achieve improved material strength and toughness. Recently, introducing gradient in the matrix property is found to be a novel approach to provide additional enhancements in composites’ mechanical performance. In this study, we present a theoretical approach to investigate the mechanical properties of the brick-and-mortar composites in which the shear modulus of the matrix varies periodically. Using the parabolic distribution of the shear modulus as an example, we show that the shear stress concentration along the interface can be greatly suppressed, and the material elastic limit and resilience can be improved. Further, we identified two critical aspect ratios of the brick-and-mortar unit cell that optimize the elastic limit and resilience of composites. From analyses and numerical calculations, formulae for these two critical aspect ratios are obtained and validated by finite element simulations.
  • Flexural behaviour of hardwood and softwood beams with mechanically
           connected GFRP plates
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Marco Corradi, Thuc P. Vo, Keerthan Poologanathan, Adelaja Israel OsoferoAbstractThe use of Glass Fiber Reinforced Polymers (GFRP) can delay or prevent tension failure in timber beams under loading and highly reduce tensile stresses. In this paper, the problem of reversibility, compatibility, and poor performance at high temperatures, of “traditional” organic adhesives was mitigated through the use of metal connectors. The flexural behaviour of hardwood and softwood beams reinforced by mechanically connected GFRP plates, has been studied through series of experimental investigations and numerical modelling. The experimental program included strengthening and testing of a total of 91 beams (50 hardwood and 41 softwood). Each beam was loaded above its service load until complete failure. Different strengthening layouts and quantity of metal connectors were used. The increment in capacity and stiffness is the main focus of this paper and effects of strengthening on deflection, failure load and failure mode, strain, and beam ductility were discussed in details. The combination of different GFRP configurations with appropriate amount of metal connectors, led to the doubling of the maximum load carrying capacity of the beams.
  • Manufacturing of a composite wing with internal structure in one cure
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Jacob B. Patterson, Joachim L. GrenestedtAbstractThe need for faster and more accurate manufacturing methods for composite parts continues to grow. Co-curing composite structures can decrease manufacturing time by eliminating secondary operations such as grinding, jigging, bonding, and fastening while creating lighter and more accurate parts. As a demonstrator for co-curing techniques, a six-meter carbon fiber wing for a high-altitude and high-speed dynamically soaring unmanned aerial vehicle (UAV) was designed and manufactured in one cure cycle. Two wing-skin molds were created using low density tooling board, with the mold geometry directly machined into the material, reducing tool manufacturing time and cost. An aluminum insert was used to create a trailing edge cavity while maintaining a simple parting line of the wing tool. Three removable forms made of polystyrene foam inside of the wing cavity were used to position six internal webs and, after curing and removal of the forms, resulted in a hollow wing with internal webs. The resulting wings showed some defects in the wing skins but overall produced structurally sound parts. The method shows great potential for creating complex composite parts using only a single cure cycle with little finishing work and no secondary bonding, resulting in high precision at a relatively low cost.
  • A mechanical degradation model for bidirectional natural fiber reinforced
           composites under hydrothermal ageing and applying in buckling and
           vibration analysis
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): K.F. Wang, B.L. WangAbstractNatural fiber reinforced composites may have a great potential applications in the automotive and aerospace industries. Hydrothermal ageing in natural fiber reinforced composites leads to significantly degradation of their mechanical properties. This paper proposes a theoretical model for predicting the mechanical responses of bidirectional natural fiber reinforced composites under hydrothermal loading. Nine elastic coefficients of orthotropic composites after hydrothermal reaction and moisture absorption are obtained. Based on the present model, closed-form solutions for buckling load and frequency of a simply supported composite plate are derived. It is found that the elastic module and buckling load decrease monotonously with time, and approaches to a certain value with time. However, the frequency decreases with time firstly, and then increases with time, finally approaches to a certain value with time. In addition, the degradation of elastic modulus, buckling load and frequency for the composites with high fiber content are larger than those with low fiber content. This research may be helpful for designing natural fiber reinforced composites for applications in humid environments.
  • Guiding and splitting Lamb waves in coupled-resonator elastic waveguides
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Yan-Feng Wang, Ting-Ting Wang, Jin-Ping Liu, Yue-Sheng Wang, Vincent LaudeAbstractWe investigate experimentally Lamb wave propagation in coupled-resonator elastic waveguides (CREWs) formed by a chain of cavities in a two-dimensional phononic crystal slab with cross holes. Wide complete bandgaps, extending from 53 to 88 kHz, are first measured in a finite phononic crystal slab sample. A straight waveguide and a wave splitting circuit with 90° bends are then designed, fabricated and measured. Elastic Lamb waves are excited by a piezoelectric patch attached to one side of the phononic slab and detected using a scanning vibrometer. Strongly confined guiding and splitting at waveguide junctions are clearly observed for several guided waves. Numerical simulations are found to be in excellent agreement with experimental results and allow for the identification of the involved resonant cavity modes. The influence on the dispersion of guided waves of the slab thickness and of the hole length is also investigated. The results have implications for the design of innovative phononic devices with strong confinement and tailorable dispersion.
  • Dynamic response and research of 3D braided Carbon Fiber Reinforced
           Plastics subjected to ballistic impact loading
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Yongqi Yang, Li Zhang, Licheng Guo, Wei Zhang, Jiuzhou Zhao, Wenbo XieAbstractThe damage mechanism of braided composites under ballistic impact condition is of paramount importance. In the present work, an experimental study was carried out to analyze the deformation failure mechanisms of 3D braided Carbon Fiber Reinforced Plastics (CFRPs) subjected to ballistic impact loading. A two camera system was adapted to study the damage initiation and propagation of 3D braided CFRPs under ballistic impact simultaneously, as well as the whole-field displacement field and strain field. Moreover, the energy absorption mechanism of 3D braided CFRPs was studied. Finally both C-Scan and digital microscope technique were used to observe different failure patterns on the surface of 3D braided CFRPs under ballistic impact. The typical deflection curves and damage modes were obtained. The results show that the absorbed energy and the incident velocity have a liner relationship approximately.
  • Experimental vibration response of homogeneous beam models damaged by
           notches and strengthened by CFRP lamina
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): R. Capozucca, E. MagagniniAbstractUndamaged and damaged simply supported homogeneous in scale beams were investigated by free vibration. The damage of beams was obtained by notches; two different types of damage have been considered in the paper: concentrated damage on the midspan section of beams and diffused damage in a middle zone. The analysis of free vibration of specimens was carried out also by verifying response using numerical modelling by the finite element method (FEM). Two beam models, one with double concentrated notches and one with diffused damage, strengthened by epoxy resin in the notches and with one unidirectional CFRP lamina at the intrados were subjected to cycles of bending loading. After each cycle of static loading the free vibration response was experimentally evaluated considering the beam hinge at the ends. The envelope of frequency response functions (FRFs) obtained by the dynamic experimental tests was elaborated and the changes of natural frequency values are then correlated to the damage degree both to non-strengthened beam and to the strengthened beam models also damaged by static loading.Comparison of experimental and theoretical frequency values is shown and discussed to validate nondestructive monitoring based on vibration tests and the behavior of homogeneous beam strengthened by CFRP lamina.
  • Cyclic behavior of diagonally reinforced slender HPFRCC coupling beams
           with reduced diagonal and transverse reinforcement
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Sang Whan Han, Jin Wook Kang, Chang Seok LeeAbstractSlender diagonally reinforced coupling beams (DRCBs) have been increasingly used for coupled shear wall systems in high-rise buildings, which can reduce the height of buildings and associated construction costs. However, in practice, it is difficult to make slender DRCBs according to current design provisions due to heavy reinforcement congestion. To alleviate the reinforcement congestion problem and improve the cyclic behavior of the coupling beams, High Performance Fiber-Reinforced Cementitious Composite (HPFRCC) DRCBs with new reinforcement arrangements or a reduced amount of reinforcement have been developed. The objective of this study is to explore the cyclic behavior of slender DRCBs made of HPFRCC with polyvinyl alcohol (PVA) fibers. Experimental tests were conducted with six DRCB specimens with a length-to-height (ln/h) of 3.5 to investigate the effect of the HPFRCC and the amount of diagonal and transverse reinforcement on the cyclic behavior of slender DRCBs. In this study, an empirical equation for predicting the shear strength of slender HPFRCC DRCBs was also proposed, considering the contributions of the HPFRCC and the amounts of diagonal and transverse reinforcements. The proposed equation was verified by using HPFRCC DRCB specimens with ln/h ranging from 2.0 to 3.5.
  • Investigating the effects of fluid intrusion on Nomex® honeycomb sandwich
           structures with carbon fiber facesheets
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Garam Kim, Ronald Sterkenburg, Waterloo TsutsuiAbstractHoneycomb sandwich construction is commonly used in aircraft structures to make parts with a superior strength to weight ratio. Nomex® honeycomb core is used extensively for flooring, skin panels, fairings, engine cowlings, and flight controls. Honeycomb sandwich structures are prone to fluid ingression due to their thin facesheets which get damaged easily by impact or erosion. The purpose of this research was to determine how the mechanical properties of honeycomb sandwich structures were affected if the structure was saturated by a fluid such as water, fuel, hydraulic fluid, or engine oil. The authors focused on the lasting effect on the sandwich structure when aircraft fluids ingress into the structure. The test panels were made of carbon fiber prepreg, and they were bonded to a 12.7 mm thick Nomex® honeycomb core material. The specimens were soaked in water, fuel, hydraulic fluid, or engine oil for 45 days. After the soak period, the specimens were removed from the fluids and left to drain for 30 days. The specimens including the control group were tested with a four-point loading test and impact test in accordance with ASTM standards.
  • The development of multiscale models for predicting the mechanical
           response of GNP reinforced composite plate
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): O. Aluko, S. Gowtham, G.M. OdegardAbstractA multiscale analysis was developed for the evaluation of graphene nanoplatelet (GNP)/carbon fiber/epoxy materials and the laminated composite plate. Computational molecular dynamic and micromechanics were utilized in the modeling and simulation of the material systems to characterize their elastic behavior when subjected to thermo-mechanical loadings. In this investigation, the approach for analyzing the structures of graphene/carbon fiber/epoxy composite at various length scales was documented. The methodology employed for evaluating the thermomechanical loadings was also specified. The predicted results at various length scales showed that the addition of GNP into the material system does not only increase the elastic moduli of the material at evaluated temperatures, but it also improves the mechanical integrity of the laminated composite plates.
  • Kalman Filter based Neutral Axis tracking for damage detection in
           composites structures under changing axial loading conditions
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Rohan Soman, Wieslaw OstachowiczAbstractStructural Health Monitoring (SHM) systems allow early detection of damage which allows maintenance planning and reduces the maintenance cost.Several researchers have proposed use of Neutral Axis (NA) location as a damage sensitive feature. It has been shown that through proper signal processing, NA location is insensitive to measurement noise and ambient temperature changes. This paper presents a methodology for successful NA tracking under changing axial loading conditions. The novel methodology is validated using numerical data as well as experimental results.This paper demonstrates the development of a Kalman Filter (KF) based NA tracking strategy under different loading conditions. The methodology was employed on a composite beam instrumented with fiber optic strain sensors. The stable NA tracking under changing loading conditions allows the application of the NA as a damage sensitive feature. The change in NA location is used to detect delamination in the beam. The method has been validated through a numerical model and experiments. The results show that the novel formulation of the KF for NA tracking allows more robust use of NA location as a damage sensitive feature in a wider range of applications.
  • Structural integrity of glass/epoxy composites embedded in cement or
           geopolymer mortars
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): A.M. Amaro, M.I.M. Pinto, P.N.B. Reis, M.A. Neto, S.M.R. LopesAbstractThe main goal of the present work is to study the mechanical response of glass/epoxy composites when exposed to cement and geopolymer (metakaolin) mortars, as it happens in Civil Engineering applications. For this purpose, specimens were embedded into mortar followed by a period of curing, which was done under the air laboratory environment. For cement, curing was also performed inside a container filled with water. The specimens were removed from the mortars after 30, 60 or 90 days of curing and then tested. Three point bending (3 PB) tests, tensile and transverse impact tests were carried out. The degradation was evaluated, both by the residual mechanical properties and by the failure damage mechanisms. In terms of 3 PB, and comparatively to the control samples, decreases around 29.5%, 31.3% and 37.9% were found after 90 days of exposure to cement, cement with water and metakaolin mortar, respectively. The same comparison for the impact strength reveals decreases about 39%, 40.1% and 44.3% for impacts in tensile mode, while these values are 7%, 11.6% and 63.1% for impacts in transverse mode, respectively. Therefore, the exposure to both cementitious and geo-polymeric matrices affects significantly the mechanical properties, but their effects are strongly dependent of the exposure time. Finally, it was possible to conclude that the worst results are obtained with the metakaolin mortar.
  • Compression properties of a novel foam-core sandwich cylinder reinforced
           with stiffeners
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Jie Tao, Feng Li, Ruijie Zhu, Dongdong Zhang, Jianbang LiuAbstractTo obtain a strong and weight-efficient cylindrical shell, a novel foam-core sandwich cylinder was proposed with glass fibre-reinforced plastic (GFRP) stiffeners inserted between the faces and the foam core. This novel cylinder possessed the advantages of both stiffened cylinders and sandwich cylinders to resist buckling. A cost-effective vacuum-assisted resin infusion (VARI) method was used to manufacture the structure. We performed axial compression tests on two representative samples to investigate the compression strength and failure modes of the novel structure. Thereafter, a theoretical model was developed to predict the collapse strengths associated with three typical failure modes. The analytically predictions showed great agreement with the experimentally observed failure mode and load. Results indicated that, benefitting from the combination advantage of stiffened cylinder and sandwich cylinder, this novel cylinder can resist or postpone various buckling failure, instead failing via face crushing with high strength. Combined with the simplified manufacturing technology, this novel cylinder is a desirable alternative in engineering structures.
  • Wing twisting by elastic instability: A purely passive approach
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): F. Runkel, U. Fasel, G. Molinari, A.F. Arrieta, P. ErmanniAbstractThe design of morphing structures requires attaining concurrently light-weight, load-carrying and shape adaptable systems that minimize complexity, actuation requirements and part count. Exploiting the external loads to produce local stiffness variations induced by elastic instabilities offers the potential to activate shape deformations purely passively. Following this approach, we present the structural response study of wings capable of attaining compliant buckling-induced twisting deformations. The structure is designed such that a specific level of aerodynamic load triggers the elastic instability in a shear web part of the wing box. The buckling-induced variation in effective shear stiffness, resulting from the development of a stable, reversible diagonal tension field, leads to a twisting deformation. The structural behaviour is characterized by two drastically different mechanical responses, delimited by the onset of elastic instability. The influence of the buckling component design on the attainable change in spanwise angle of attack is investigated for the specific case of a finite composite wing structure under aerodynamic loads. The type of composite material, its thickness, and the fibre orientation are the considered design parameters. The buckling-induced variation in twist angle, and the corresponding aerodynamic pressure redistribution on the wing, is exploited for achieving load alleviation, reducing the global lift coefficient and decreasing the wing root bending moment.
  • Lamb wave interaction with composite delamination
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Rajendra Kumar Munian, D. Roy Mahapatra, S. GopalakrishnanAbstractElastic guided wave based evaluation is useful to detect delamination in composites. This paper reports a detailed account of guided wave interaction with delamination in laminated composites modeled using time domain spectral finite element (TSFE) method. Wave scattering due to different delamination positions is studied. Wave field near the delamination in different layer-wise positions is investigated, which is useful to further characterize and correlate the far field wave packet carrying the parametric signature of delamination. Off-axis delamination in composite laminate creates an asymmetry in the elastodynamic stress transfer. It leads to wave mode conversions. Sensitivity of the delamination to the wavelengths is studied. The outcome of this study indicates potential possibilities to use frequency-wavelength information to discriminate various sizes of delamination. Energy of the scattered waves and dissipation/conversion of the wave energy due to the defects depend on the resonance characteristics of the sub-laminates. Wave scattering effect due to length-wise multiple delaminations and edge delamination is also analyzed. The resonance patterns in the signals are analyzed with reference to the defect quantification problem.
  • Material characterization of filament-wound composite pipes
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): William Toh, Long Bin Tan, Kwong Ming Tse, Anthoni Giam, Karthikayen Raju, Heow Pueh Lee, Vincent Beng Chye TanAbstractIn obtaining mechanical properties of filament-wound fibre reinforced plastic pipes, standardized tests are often used to obtain bulk properties. Being a laminated composite, individual layers of the lamina will behave differently and therefore pipe-level characterizations are usually unable to fully describe the localised responses in detail. Unlike flat composite layups, obtaining unidirectional ply properties in cylindrical filament-wound composites is not as straight-forward. In this work, the composite pipe stress homogenization theory was applied in reverse to obtain the corresponding ply properties in the filament-wound pipe through successive iterations towards experimentally obtained bulk properties. Initial estimates of ply properties were obtained through a combination of extensive literature search and applications of micromechanics theories. With the iterated ply properties, finite element models simulating the tests used to obtain bulk properties were performed to validate the accuracy of the material properties. In addition, additional validation was performed on a smaller pipe section to evaluate the scalability of using ply properties across pipes of different dimensions. It was found that the ply properties obtained was able to accurately predict the responses for pipes of various dimensions.
  • Composite “1.2361 tool steel – Ti – TiO2” structure and its
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Aleksandr Fomin, Ivan Egorov, Andrey Shchelkunov, Marina Fomina, Vladimir Koshuro, Igor RodionovAbstractThe composite “1.2361 tool steel – Ti – TiO2” structure was prepared by resistance welding (RW) with subsequent induction heat treatment (IHT). RW of tool steel with titanium was performed at an electric power in the range of 3.5–4 kW with the pulse duration of 0.25–1.0 s. IHT was performed at the temperatures in the range of 950–1600 °C for 5–60 s for titanium inserts, and the temperature of the steel substrate did not exceed the melting point (about 1370 °C). At the electric power of 3.5 kW with the pulse duration not more than 0.5 s, Fe–Ti transition area of the weld joint with the moderate hardness about 4.0 ± 0.5 GPa (410 ± 50 HV1) was formed. According to the results of scanning electron microscopy with energy dispersive X-ray analysis (EDX) and Vickers hardness test, titania coatings with high hardness about 2500 ± 250 HV1 and 950 ± 50 HV5 were formed on titanium surface after IHT at 1500 ± 50 °C for 30 ± 10 s. Preliminary results on the cuttability tests of the experimental replaceable cutting inserts were obtained, according to which the composite “1.2361 tool steel – Ti – TiO2” structure enabled the fine turning of X40Cr13 steel (43 HRC or 415 HV).
  • FRP Strengthening of Web Panels of Steel Plate Girders against Shear
           Buckling Part-I: Static Series of Tests
    • Abstract: Publication date: Available online 3 September 2018Source: Composite StructuresAuthor(s): Zaid Al-Azzawi, Tim Stratford, Michael Rotter, Luke BisbyAbstractThe result of an experimental programme investigating a novel technique to strengthen web plates against breathing fatigue is presented in this paper; the programme was divided into five phases, including: (1) the development of a novel preformed corrugated FRP panel for strengthening thin-walled steel plate girder webs against buckling, (2) selecting the adequate adhesive and epoxy using double-lap shear and tension specimens, (3) producing the FRP panel, and (4, 5) testing its performance in two main experimental series; the initial (static) series and the final (cyclic) series. Only the initial series which involved tests on 13 steel plates strengthened with the proposed preformed corrugated FRP panel and subjected to in-plane shear will be reported in this paper. This series investigated the performance of different forms of strengthening under static load, in preparation for a subsequent series of cyclic tests to investigate their fatigue performance. Test results showed the efficiency of the technique at increasing the stiffness of the strengthened specimens in comparison to the unstrengthened ones and reducing the critical stresses which will serve as a precursor for the anticipated increase in the fatigue life of the girders.
  • Characterisation of smart CFRP composites with embedded PZT transducers
           for nonlinear ultrasonic applications
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Christos Andreades, Pooya Mahmoodi, Francesco CiampaAbstractEmbedded piezoelectric lead zirconate titanate (PZT) transducers in carbon fibre reinforced plastic (CFRP) composites are typically electrically insulated by interlaying materials such as polyimide Kapton films between the PZT and the laminate ply. However, the presence of polymeric films may cause debonding at the layer interface, thus reducing the structural performance. This paper proposes an alternative insulation technique in which PZTs are covered by a thin patch of woven E-glass fibre fabric for enhanced adhesion with the surrounding epoxy matrix. An analysis of variance on experimental test results showed that the compressive, flexural and interlaminar shear strengths of plain CFRP specimens were equal to the means of the smart CFRP composite (0.41 
  • Study of dynamic behavior of a composite laminated material manufactured
           of the bark of Lata’s Palm “Bactris Guineensis”
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Alberto D. Pertuz, German A. Diaz, Daniel G. Chavez, Fausto A. GarciaAbstractThe use of alternative lignocellulosic raw materials for development of new engineering composite materials is researched. The study is based on the Lata’s palm “Bactris Guineensis” bark as the main constituent for glued laminated composite material manufacturing. Static mechanical properties as well as fatigue behaviors were studied, since in these types of loads a wide range of engineering dynamic applications can be envisaged. Tensile and hardness testing were performed for the characterization of static and mechanical properties. Additionally, fatigue testing was used to analyze the durability behavior of the composite materials obtained and the fracture surface was analyzed by SEM microscopy. Vickers hardness and tensile resistance at the exterior bark demonstrated that it is the hardest and most resistant zone with 27,5 Vickers and 354 MPa values respectively. During fatigue testing, the temporary life zone was obtained from the stress vs. number of cycles curve (S vs Nf). The Basquin’s equation parameters were found (S=A·Nfb), with: A = 321 MPa. and b = −0,060. Finally, in order to evaluate the potential use of glued laminated Lata’s Palm as a composite material constituent its mechanical characterization was performed.
  • Performance of a hybrid GFRP-concrete beam subject to low-velocity impacts
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Zongjun Li, Amar Khennane, Paul J. Hazell, Alex M. RemennikovAbstractIn the present study, the impact behaviour of a hybrid beam consisting of a rectangular hollow GFRP pultruded profile filled with concrete is studied. The hollow pultruded GFRP box profile not only provides tensile strength but also protects the concrete block inside from suffering chemical attacks. The concrete on the other hand provides the system with bulk size and structural stability. A series of beams were subjected to low-velocity impacts by using a high capacity drop weight machine. A nonlinear finite element model was developed and calibrated to analyse the failure of the beams. In particular, it was used to reveal the failure modes, the cracking pattern, and damage sequences within the concrete hidden inside the pultruded profile. The calibrated finite element model was subsequently used to analyse hybrid beams of similar size to prestressed concrete railway sleepers. The numerical simulations revealed that in terms of the maximum load, the hybrid beam outperforms the prestressed concrete sleeper. Indeed, if the proposed beam is to be used as a railway sleeper, it needs to display better or equal dynamic properties to existing railway sleepers.
  • A three dimensional elasticity model for free vibration analysis of
           functionally graded micro/nano plates: Modified strain gradient theory
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): H. Salehipour, A. ShahsavarAbstractThe different applications of micro/nano scale structures increase daily, and using new developed theories accounting size-reduction effect can be useful to study mechanical behaviors of such structures. The size dependent theory of modified strain gradient is capable for considering micro/nano structures. In the current work a new model based on the modified strain gradient and three dimensional elasticity theories is developed for free vibration of functionally graded (FG) micro/nano plates, and an exact analytical solution is carried out for extracting the natural frequencies of it. The present three-dimensional elasticity model contains three length scale parameters. Analytical solution is based on the state space method. In order to achieve the analytical solution, the distribution of material properties through the plate thickness follows an exponential law. Finally, some exact numerical results are tabulated for both homogeneous and FG plates that can be used as an exact three dimensional elasticity benchmark for validate other two dimensional models.
  • Snapthrough and free vibration of bistable composite laminates using a
           simplified Rayleigh-Ritz model
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Samir A. EmamAbstractThe snapthrough and free vibration response of bistable cross-ply [90n/0n] composite laminates is investigated. Thin unsymmetric composite laminates possess more than one equilibrium position when cooled to room temperature due to the difference in thermal expansion of the plies. Bistable cross-ply laminates have cylindrical shapes at room temperature provided appropriate side-length-to-thickness ratio is used. The laminate is modelled according to the classical lamination plate theory taking into account the von Karman geometric nonlinearity. The strains and displacements are approximated via a simplified Rayleigh-Ritz model that depends on only four time-dependent parameters for the general dynamic response. The simplified model is validated against experimental and finite element results and an acceptable agreement is obtained. The laminate’s length-to-thickness ratio is key to assess the existence of bistability. The model is used to investigate the snapthrough response of an 8-ply [904/04] laminate that is subjected to three loading schemes: concentrated moments, normal forces, and tangential forces. The variations of the principal curvatures and the lateral displacement of the laminate with the applied forces are shown. The significance of the force location is also found a crucial element in finding the snapthrough force. The free vibration that takes place in the vicinity of a stable equilibrium position is studied and the variation of the fundamental frequency with the laminate size is presented.
  • Health monitoring of timber beams retrofitted with carbon fiber composites
           via the acoustic emission technique
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Francisco J. Rescalvo, Elisabet Suarez, Ignacio Valverde-Palacios, Juan Manuel Santiago-Zaragoza, Antolino GallegoAbstractThis paper proposes a methodology for monitoring of timber beams retrofitted with CFRP (Carbon Fiber Reinforced Polymer) via the acoustic emission technique (AE). The work proposes the use of multi-resonant sensors linearly distributed along the element. The spectral energy of the located AE events is proposed to separate the signals into two groups, depending on the predominant frequency band, between two resonant bands of the used sensor. To avoid the influence of the attenuation, the spectral energy is corrected by the attenuation curves empirically determined. By means of bending tests on beams with two retrofitting layouts, it is demonstrated how the signals grouped into the high-frequency group are located at the areas where the final CFRP-wood delamination took place or where the final failure of the element is concentrated. This result is very promising for health monitoring of retrofitted timber elements in real scenarios.
  • Reanalysis assisted metaheuristic optimization for free vibration problems
           of composite laminates
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Xiangcheng Li, Hu Wang, Guangyao LiAbstractThe metaheuristic optimization methods have been widely used in complex composite material design. However, it is still difficult to apply these methods to complicated problems due to expensive cost of evaluations. Therefore, to reduce the expensive cost of finite element (FE) analysis in the composite laminate optimization problems, the surrogate assisted optimization (SAO) method has been well developed. However, considering the low accuracy of surrogate model for complicated cases, the SAO is always difficult to converge to the global optimum. In this study, a fast and accurate solver, the reanalysis algorithm is extended to vibration problem and integrated to improve the efficiency of metaheuristic optimization of composite laminates instead of surrogate model. In the proposed method, the shifting method is used in each iterative step. To validate the performance of suggested method, several numerical examples are presented. The results demonstrate that reanalysis assisted particle swarm optimization (RPSO) is much more efficient for free vibration problems of composite laminates than the PSO. Moreover, such strategy can be extended to other metaheuristic algorithms easily.
  • Asymptotic equivalence of DKMT and MITC3 elements for thick composite
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Irwan Katili, Imam Jauhari Maknun, Jean-Louis Batoz, Andi Makarim KatiliAbstractThis paper presents in a unified and comparative manner, the formulation of two triangular plate bending composite elements, i.e. DKMT and MITC3 which are published in 1993 and 2004. Both elements have 3 nodes and 5 dof per node (three displacements and two rotations), taking into account transverse shear effects. There are valid for thin to thick composite plates, and give good results in classical benchmark and patch tests. The numerical results using DKMT element show the optimal and uniform convergence for thin and thick plates with an advantage for DKMT compare to MITC3 due to semi quadratic interpolation for the rotation variables The present paper contains new convergence analysis based on the s-norm tests for sandwich plates considering uniform and distorted meshes, and for symmetric and non symmetric composite plates with 3 and 9 layers. As the novelty and main contribution of this article, we propose the shear projection method in the element formulations to show the asymptotic equivalence of DKMT and the MITC3 for thick to thin composite plates.
  • Assessment of delaminated smart composite laminates via system
           identification and supervised learning
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Asif Khan, Heung Soo KimAbstractThis paper proposes the synergetic integration of system identification and artificial intelligence for the detection and assessment of delamination damages in smart composite laminates. An electromechanically coupled mathematical model is developed for the healthy and delaminated smart composite laminates on the basis of improved layerwise theory, higher order electric potential field and finite element method. A discriminative feature space is constructed for the healthy and delaminated structures via system identification from their structural vibration responses. The discriminative features are used for the training and cross-validation of various supervised machine learning classifiers and an optimal classifier is identified. The optimal classifier is employed to make predictions on unseen test delamination cases, and its predictions are validated via a dimensionality reduction tool. The obtained results show that the proposed technique could be employed as a reliable tool for nondestructive evaluation of smart composite laminates.
  • Thermo-elastic analysis of multilayered plates and shells based on 1D and
           3D heat conduction problems
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): S. Brischetto, R. TorreAbstractThe present work shows a generic 3D exact shell solution for the thermo-mechanical analysis of a heterogeneous group of one- and multi-layered isotropic, composite and sandwich structures. Plates, cylinders, cylindrical and spherical shells can be investigated using orthogonal mixed curvilinear coordinates. The 3D equilibrium equations for spherical shells automatically degenerate in those for simpler geometries. The elastic part of the proposed 3D model is based on a consolidated layer-wise exact solution which uses the exponential matrix method to solve the equilibrium differential equations through the thickness direction. The closed-form solution is obtained assuming simply-supported boundary conditions and harmonic forms for displacement and temperature fields. The temperature amplitudes are imposed at the top and bottom external surfaces in steady-state conditions. Therefore, the temperature profile can be evaluated through the thickness direction in three different ways: – calculation of the temperature profile via the steady-state 3D Fourier heat conduction equation; – evaluation of the temperature profile using the steady-state simplified 1D version of the Fourier heat conduction equation; – a priori assumed linear temperature profile through the entire thickness direction ranging from the bottom temperature value to the top temperature value. Once the temperature profile is defined at each thickness coordinate, it is considered as a known term in the 3D differential equilibrium equations. The obtained system consists in a set of non-homogeneous second order differential equilibrium equations which can be solved introducing appropriate mathematical layers. After a reduction to a first order differential equation system, the exponential matrix method is used to calculate both the general and the particular solutions. The effects of the temperature field on the static response of plates and shells are evaluated in terms of displacements and stresses. The proposed solution will be validated using reference results available in the literature. Then, new analyses will be presented for different thickness ratios, geometries, lamination schemes, materials and temperature values at the external surfaces. Results will demonstrate the importance in the 3D shell model of both the correct definition of the elastic part and the appropriate evaluation of the temperature profile through the thickness of the structure. .
  • Design and experimental analysis of a novel wedge anchor for prestressed
           CFRP plates using pre-tensioned bolts
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Huawen Ye, Changmeng Liu, Suwei Hou, Tianqi Wang, Xinshun LiAbstractA novel friction-based wedge anchor system was developed experimentally and numerically for the prestressed carbon fiber reinforced polymer (CFRP) plates with several commercial widths and thicknesses. A simple analytical model was first developed to investigate the CFRP compression distribution. Both static and fatigue tests were then conducted to determine the anchor performance. The effects of the barrel and wedge thickness, the wedge shape and contact surface (corrosion and cross knurling) were investigated experimentally on the anchor behavior. The design parameters of the new anchor were recommended through the pull-off experiments, and this anchor can be capable of not only anchoring at least 90% of the CFRP plate specified strength of 2000 MPa statically, but also maintaining the stress level of 900 MPa under a fatigue stress range of 100 MPa. Both the simulation of the CFRP stress distribution and a sensitivity analysis were also conducted on finite element numerical models. The numerical analysis shows that the barrel flexural deformation occurs across the CFRP width, and leads to the bimodal stress distribution across the CFRP plate width. The stress sensitivity results show the stress distribution is significantly sensitive to the wedge shape and contact surface, the bolt pretension and the CFRP width.
  • Numerical estimation of stress intensity factors in cracked functionally
           graded piezoelectric materials – A scaled boundary finite element
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): A.L.N. Pramod, Ean Tat Ooi, Chongmin Song, Sundararajan NatarajanAbstractThe stress intensity factors and the electrical displacement intensity factor for functionally graded piezoelectric materials (FGPMs) are influenced by: (a) the spatial variation of the mechanical property and (b) the electrical and mechanical boundary conditions. In this work, a semi-analytical technique is proposed to study the fracture parameters of FGPMs subjected to far field traction and electrical boundary conditions. A scaled boundary finite element formulation for the analysis of functionally graded piezoelectric materials is developed. The formulation is linearly complete for uncracked polygons and can capture crack tip singularity for cracked polygons. These salient features enable the computation of the fracture parameters directly from their definition. Numerical examples involving cracks in FGPMs show the accuracy and efficiency of the proposed technique.
  • An efficient two-dimensional shear-lag model for the analysis of patched
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Ralph Kussmaul, Markus Zogg, Paolo ErmanniAbstractFiber patch placement (FPP) is a manufacturing technique for variable stiffness composites. In the FPP approach, a structural component is assembled from a multitude of discrete fiber patches, thus allowing for an easy tailoring of the layup to the local load state. However, due to the discontinuous fibers at the patch edges, complex stress distributions occur in patched laminates. To date, an efficient method for the analysis of patched laminates on macro-scale does not exist. This article introduces a 2D planar shear-lag model (SLM) based on thin-plate mechanics and a simplified interlaminar shear stress formulation. It is shown how the governing partial differential equation system is assembled and how boundary conditions are set. The model is solved numerically using the Finite Element Method. For verification the 2D SLM is compared to a full 3D linear-elastic solution. It can be shown that the SLM allows for accurate prediction of stress fields disturbed by interrupted fibers with considerably improved numerical efficiency. An application example shows that the SLM resolves the effects of discontinuities significantly better than a state-of-the-art shell element modeling approach. As a consequence, a substantial progress in the design of patch laminated structures is achieved.
  • Modeling the postbuckling behavior of thermal-resistant ultrathin films
           attached to glass substrate
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Yang Zhang, Gen Li, David Hui, K.M. LiewAbstractThis paper investigates the postbuckling behavior of a novel glass-protection film system under thermal environment using the element-free kp-Ritz method. The governing formulation is derived based on the first-order shear deformation plate theory considering small strains and the nonlocal elasticity theory which takes small scale effect into account. The modified Newton-Raphson method incorporated with the arc-length continuation technique is used to trace the nonlinear response of the film-foundation system. The influences of boundary conditions, nonlocal parameters, geometry and elastic foundation on the nonlinear response of glass-protection film are examined. The results show that adhesion force between graphene sheets (GSs) film and the elastic substrate can significantly enhance thermal buckling resistance of GSs film. It is also concluded that van der Waals forces between GSs film lead to consistent post-buckling behavior of individual GSs. Present study can provide suggestions on firefighting design, such as setting alarm temperature based on transition temperature.
  • Fabrication and design of electromagnetic wave absorber composed of carbon
           nanotube-incorporated cement composites
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): I.W. Nam, J.H. Choi, C.G. Kim, H.K. LeeAbstractIn the present study, an electromagnetic (EM) wave absorber was fabricated with a multi-walled carbon nanotube (MWNT)-incorporated cement composite and the absorbing capability of the absorber was assessed. To disperse MWNTs in a cement matrix, composites were fabricated under a low flow condition of the fresh mixture, and silica fume (SF) was added to explore the influence of SF addition on MWNT distribution. The electrical conductivity of the composite was evaluated to examine the MWNT distribution and the complex permittivity was determined to study the EM characteristics of the composite. The conductivity results demonstrated that SF addition of 10 wt% led to the greatest enhancement. Meanwhile, the absorber was designed on the basis of complex permittivity at a frequency point of 9.4 GHz, and SF0-M1.0 type (no SF addition and MWNT content of 1.0 wt%) and SF10-M0.6 type (SF content of 10 wt% and MWNT content of 0.6 wt%) were employed. The experimental assessment of the absorbing capability demonstrated that the −10 dB bandwidths of SF0-M1.0 and SF10-M0.6 type absorbers were 2.5 GHz and 3.2 GHz, respectively. In addition, the absorbing capability derived from the experimental work was compared and validated by means of computational simulation work.
  • Enhancing the electrical conductivity of carbon fibre thin-ply laminates
           with directly grown aligned carbon nanotubes
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): M. Russello, E.K. Diamanti, G. Catalanotti, F. Ohlsson, S.C. Hawkins, B.G. FalzonAbstractThe transverse electrical conductivity of thin-ply carbon fibre laminates, enhanced with carbon nanotubes (CNTs), was investigated experimentally. CNTs were directly synthesised on spread tow tapes of UTS50S carbon fibre through chemical vapour deposition (CVD). Unidirectional laminates were manufactured using both a thermosetting (epoxy) and a thermoplastic resin (polypropylene). A substantial increase in the electrical conductivity and a decrease in electrical anisotropy was observed for both the material systems investigated. Improvement in conductivity by a factor of 8 for the epoxy specimens, and 28 for the polypropylene specimens were reported.
  • Damage tolerance of an impacted composite laminate
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): N. Dubary, C. Bouvet, S. Rivallant, L. RatsifandrihanaAbstractComposites are known to be vulnerable to out-of-plane loading such as impact. Investigating the residual properties of the laminate as a function of damage detection is the main purpose of impact damage tolerance design in aeronautics. As a good alternative to experimental campaigns, numerical approaches would lead to saving of time. The model developed in Institut Clément Ader over the last years enables representation of behavior of composite laminates subjected to low velocity/low energy impact – including permanent indentation – and Compression After Impact. Damage such as permanent indentation, fiber failures, matrix cracks and delamination are taken into consideration at each step thanks to a discrete ply modelling. The work presented here deals with the use of this model to make a composite laminate design optimization according to impact damage tolerance design. A method to improve optimization by reducing computation time is also proposed, based on a “best candidates” selection.
  • Rapid guided wave inspection of complex stiffened composite structural
           components using non-contact air-coupled ultrasound
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Rabi Sankar Panda, Prabhu Rajagopal, Krishnan BalasubramaniamAbstractThis article demonstrates a rapid, fully non-contact inspection technique for a full-scale complex composite structural component using air-coupled ultrasonic guided waves. The presence of different features such as stiffeners, stringers and geometric variations in skin-stiffened structures makes the received guided wave signal cumbersome and difficult to interpret. Experiments, supported by three-dimensional finite element models, are used to demonstrate the physics of guided wave interaction with complex features and defect configurations. B-scans are used to detect geometric variations in skin, and also disbonds in the skin-stiffener interface. Correlation between the numerically simulated and experimentally obtained B-scans is established. Different regions in the B-scan images could be used to locate and identify the defects and geometric variations in the test sample. The size of the disbond can also be computed from the B-scan.
  • A supervised iterative approach to 3D microstructure reconstruction from
           acquired tomographic data of heterogeneous fibrous systems
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Ronald F. Agyei, Michael D. SangidThe recent ubiquitous utilization of short fiber reinforced composites (SFRCs) in applications that require complex shape conforming, light-weight materials with good strength properties, calls for in-depth studies to understand the underpinning physics behind SFRCs response to load and consequently damage. Since the accuracy of such studies is contingent on successful sub-volume characterization, the intricate sub-volume architecture of SFRCs requires conscientious methodology that addresses complex morphologies like fiber cross-overs, which is by no means a trivial endeavor. This paper proposes a novel framework that hinges on the synergy between robust 2D segmentation and 3D volume reconstruction techniques to faithfully reconstruct the fiber architecture of 3D X-ray tomograms of SFRCs. The implications of this framework not only include a platform that fully characterizes the complex sub-volume, but also provides a convenient means of incorporating tracking algorithms necessary for the in-situ characterization of the reconstructed fibers, if desired.Graphical abstractGraphical abstract for this article
  • Hygroscopic ageing of nonstandard size sandwich composites with
           vinylester-based composite faces and PVC foam core
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Anxin Ding, Jihui Wang, Aiqing Ni, Shuxin LiAbstractThis paper aims to assess the hygroscopic behaviour of nonstandard size sandwich composites constituted of thick Electronical-Chemical Resistance (ECR) glass fibre reinforced vinylester composite faces bonded to closed-cell Polyvinyl Chloride (PVC) foam core in the service environment as a reference and basis for materials selection. In order to exhibit the change of sandwich composites properties in realistic environment, the specimens fabricated by Vacuum Infusion Moulding Processing (VIMP) were immersed in two humid conditions: seawater with 30 °C (SWL) and purewater with 80 °C (PWH) for 1680 h. The moisture uptake and various mechanical properties of specimens, including the flatwise tension strength, flatwise compressive strength, in-plane shear strength, shear strength using short beam bending and edgewise compressive strength were tracked periodically. The results from water absorption measurement indicate that the specimens immersed in two humid conditions reach saturation levels after immersion of 1008 h, and non-Fickian and Fickian diffusion occur simultaneously. The characterization on mechanical properties was mainly placed on the variation of PVC foam core and faces-core interface properties, and corresponding results reveal that the moisture absorption has insignificant effects on the PVC foam core properties but appreciably affects the composite faces and face-core interface properties, especially for the specimens immersed in PWH.
  • Analysis of the hydro-mechanical behaviour of flax fibre-reinforced
           composites: Assessment of hygroscopic expansion and its impact on internal
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Abderrazak Chilali, Mustapha Assarar, Wajdi Zouari, Hocine Kebir, Rezak AyadAbstractThe present work aims at modelling the hydro-elastic behaviour of twill flax fabric-reinforced epoxy composites. These latter were manufactured using the vacuum infusion technique and aged into tap water until saturation. Their heterogeneity is taken into consideration by modelling the twill weave fabrics with two geometric paths: [0/90] and elliptical undulation. Moreover, the water diffusion coefficient and the hygroscopic expansion parameter of the flax fibre are estimated by an inverse approach exploiting the experimental results. In particular, the finite element simulations reveal high mechanical stress concentrations especially at the fibre-matrix interface caused by the differential swelling between the flax fabrics and the epoxy resin. This water absorption-induced internal stress is the main cause of damage initiation in the flax-epoxy composites, which leads to high variations of their mechanical properties and reduces their long-term sustainability.
  • Static behavior of grouped large headed stud-UHPC shear connectors in
           composite structures
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Jingquan Wang, Qizhi Xu, Yiming Yao, Jianan Qi, Hongliang XiuAbstractAccelerated bridge construction (ABC) utilizing precast systems offers many benefits such as faster onsite construction and lower traffic impacts. Ultra-high performance concrete (UHPC) becomes an innovative solution that facilitates some types of ABC. This paper proposes a novel steel-UHPC composite system and large studs with diameter of 30 mm. Push-out tests are conducted to investigate the shear behavior of large studs embedded in UHPC and compared with normal strength concrete (NSC). A total of 6 single stud and 18 grouped studs specimens are used to investigate the effects of casting method, precast deck strength, infilling material strength and transverse reinforcement in the shear pocket. Test results showed that grouped stud effect in the UHPC specimen was insignificant. Ultimate strength of grouped stud in precast UHPC deck was 10% higher than that of NSC precast slab while interfacial slip of UHPC specimen was 17% lower. Noting that grouped large studs better match with UHPC since no visible crack was observed at failure in UHPC slab while NSC slab displayed a number of cracks. Finally, load-slip relationship for large grouped studs embedded in UHPC was proposed based on experimental results and comparisons between the test results of strength and codes predictions were made.
  • Integrative hinge based on shape memory polymer composites: Material,
           design, properties and application
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Tianzhen Liu, Liwu Liu, Miao Yu, Qifeng Li, Chengjun Zeng, Xin Lan, Yanju Liu, Jinsong LengAbstractSelf-deployable structures based on shape memory polymer composites (SMPCs) have the capability of self-deploy, light weight and high load-bearing. This paper presents the detail of an integrative hinge fabricated by carbon fiber reinforced shape memory epoxy composites in the sequence of material selection, structure design and manufacture, material and structure experiments, and application. DMA experiments have been conducted to figure out the temperature sensitivity of SMP. The temperature dependent elastic modulus and strength of SMPC were determined by tensile experiments. Results from three point bending tests and shape memory recovery tests verify the variable stiffness of the integrate SMPC hinge under different temperatures and superior shape memory properties. Strain distribution during bending process are obtained from both digital image correlation (DIC) measurements and ABAQUS simulation, showing good consistency with each other. To compare the modal characteristics with traditional SMPC hinge, modal testing and computation have been designed with free boundary condition. It can be found that the integrative SMPC hinges have the characteristics of improved reliability and performance, and higher post-deployment stiffness and strength, when compared to traditional SMPC hinges. Finally, prospective applications of the self-deployable structure have also been illustrated.
  • Bending/tensile tests and simulations of the 2.5D woven T-shaped hooking
           composite structure
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Hongjian Zhang, Junhua Guo, Weidong Wen, Haitao Cui, Shu He, Ying XuAbstractThe bending strength and the tensile strength are the important mechanical properties of T-shaped hooking composite structures, which are one of the connection structures in aero-engine. In this paper, a kind of 2.5D woven T-shaped hooking composite structure, which consists of a groove structure and a T-shaped structure, was designed and used for bending test and tensile test, respectively. Experimental results showed that the initial damages both occur at the root-edge of web, and then the damages extend to the root-middle in bending test or extend perpendicular to the root-edge to the edge of the flange in tensile test. Then, a strength prediction method of progressive damage for 2.5D woven T-shaped hooking composite structure based on three-unit-cell model was proposed and used to describe the mechanical behaviors and damage processes of the connecting structure under bending/tensile loads, respectively. The comparisons between the simulation results and tests showed that the maximum error of the bending/tensile strengths is less than 15% and the damage modes between tests and simulations are similar. Therefore, the predicted strengths are accurate and the strength prediction method of progressive damage proposed in this paper is effective.
  • Effects of adhesive parameters on out-of-plane compression and compression
           fatigue response of adhesively bonded sandwiches with pyramidal core
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Zhi-jia Zhang, Qian-cheng Zhang, Xiao-bo Shi, Wei-jin Zhang, Feng JinAbstractEffects of key adhesive parameters such as curing temperature and the amount of adhesive on the out-of-plane compression and fatigue strength of sandwich panels with pyramidal core are experimentally investigated and compared with those of theoretical analysis. It is shown that two different curing temperatures lead to the different liquidity of surplus adhesive squeezed out and then the shapes of spew fillet. Sandwich panels with arc spew fillets have higher compression strength than those with rounded spew fillets. With the increase of the amount of adhesive, the out-of-plane compression strength of those sandwich panels clearly increases firstly and then gradually tends to the theoretical value. By analysis of the S-N fatigue curves of four types of sandwich specimens, the shape of spew fillet, the amount of adhesive and the loading ratios are identified as the key factors governing the compression fatigue properties of truss-cored sandwich structures.
  • On the solution of the dynamic stability of heterogeneous orthotropic
           visco-elastic cylindrical shells
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): A.H. SofiyevAbstractThe purpose of this study is to investigate the dynamic stability of heterogeneous orthotropic visco-elastic cylindrical shells (HTOVECSs) under an axial load. The hereditary theory is used for heterogeneous (HT) orthotropic cylindrical shells over the entire thickness. The behavior of HTOVECSs is described by integro-differential equations with heterogeneous elastic parameters. The method is proposed for calculating the critical time parameter (CTP) of HTOVECSs by using the linear visco-elasticity theory. Finally, the influences of heterogeneity, rheological parameter and shell characteristics on the critical time parameter of the orthotropic visco-elastic cylindrical shells (OVECSs) are discussed in detail.
  • A strain-based criterion for failure load prediction of steel/CFRP double
           strap joints
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): S.M.J. Razavi, M.R. Ayatollahi, H.R. Majidi, F. BertoAbstractOne of the most effective approaches to improve the strength of steel structures is using the carbon fiber reinforced polymer (CFRP) as externally-bonded sheets. In this paper, a strain-based failure criterion, namely the critical normal strain (CNS) is employed to predict the failure load of adhesively bonded double strap joints which are made of CFRP and steel plates. According to this approach, the adhesive joint fails when the normal strain along the adhesive mid-line attains a critical value at a critical distance. This work is based on a two-dimensional linear elastic finite element analysis. Failure load capacities are estimated theoretically for steel/CFRP double strap joints with different bonding lengths. The predicted values of failure loads are compared with the experimental data reported in literature. It is shown that a good consistency exists between the experimental failure loads and the theoretical predictions based on the new strain-based criterion.
  • Evaluation of microdamage initiation in Z-pinned laminates by means of
           automated RVE computations
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Gerrit Pierreux, Ling Wu, Danny Van Hemelrijck, Thierry J. MassartAbstractZ-pinning was originally designed to improve the delamination toughness and the impact resistance of composite laminates. However, there is extensive experimental evidence that this improvement is accompanied by a reduction of the in-plane properties. The main mechanisms responsible for this deterioration are the local change in fiber content, fiber distortion, and the inclusion of resin-rich regions near the Z-pin. The shape of these geometrical features strongly depends on the laminate stacking sequence and on pin parameters such as pin diameter, pin content, and initial pin inclination angle. Their shape complexity challenges analytical modelling approaches which are currently used to generate RVE geometries for simulations.A computational approach is presented to generate such geometrical models. Resin-rich regions are modelled by initially straight discretized lines which are gradually shaped by a set of geometrical operations mimicking pin insertion, pin rotation and fiber deflection. Fiber distortion is modelled in a post-processing stage in cross-sections accounting for the preservation of the amount of fibers. These models are then transformed into finite element mechanical models in order to investigate how local fiber volume fraction changes, fiber misalignment, or distortions in reinforcement due to pin rotation, affect the global stiffness and local stress concentrations.
  • An investigation of the mechanical behavior of three-dimensional low
           expansion lattice structures fabricated via laser printing
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): C. Mercer, J. Lee, D.S. BalintAbstractA feasibility study of the fabrication of a specific type of low expansion lattice structure via 3-D laser printing has been conducted. In addition, a detailed baseline understanding of the mechanical response of a specific low thermal expansion lattice geometry has been established. The printed Ti-6Al-4V structures exhibit robust mechanical behaviour and fail via initial buckling followed by strengthening and then fracturing of the struts. Finite element simulation can predict the mechanical behaviour of the printed structures with a good degree of accuracy until the onset of buckling, which is the first point of failure. An analytical model has also been constructed, and homogenization techniques have been implemented to determine the effective stiffness and strength of the lattice structure arranged periodically to be used in sandwich panels. The analytical studies of the lattice structure performance show that the low CTE lattices are suitable for lightweight applications. Additionally, analysis has been performed to optimise the design of a bi-material lattice structure and the optimised design was found to have better performance compared to the bulk material while maintaining a low coefficient of thermal expansion for most cases studied. The techniques used in this paper can serve as a foundation for future studies to optimise and improve such lattice structures.
  • Identification of failure modes of composite thin-ply laminates containing
           circular hole under tension by acoustic emission signals
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Chunfang Huang, Su Ju, Mingchang He, Qing Zheng, Yonglyu He, Jiayu Xiao, Jiangwei Zhang, Dazhi JiangAbstractComposite thin-ply laminates have been reported to exhibit superior performance in various loading conditions than standard-ply laminates due to positive size effects. However, the ultimate tensile strength of the thin-ply (0.125 mm) or standard-ply (0.125 mm) laminates with same size of the hole. Besides, fracture morphologies showed a transition from a combined mode of matrix crack, delamination and pull-out at 45° and −45° ply in the thick and standard-ply laminates to a quasi-brittle fracture in the thin-ply laminates. In order to explain the experimental phenomena, acoustic emission was used in this paper to identify and distinguish the failure modes of laminate specimens containing circular hole with different ply thickness, and finite element simulation was adopted to investigate the cause of lower tensile strength in the thin-ply specimen. Carbon fiber reinforced polymer matrix composite laminate specimens were prepared using prepregs with different ply thicknesses (0.02 mm, 0.055 mm and 0.125 mm). In tensile test, higher initial stress of damage, lower ultimate strength and quasi-brittle fracture morphology could be observed in the thin-ply laminate specimens with an open hole. The results of acoustic emission analysis demonstrated that the matrix damage and delamination were suppressed in the thin-ply laminates, and superior damage suppression and crack-propagating resistance in the thin-ply laminates lead to quasi-brittle fracture morphology. Besides the more homogeneous micro-structure and isotropic behavior of the thin-ply laminates leaded to higher initial damage stress compared to the laminates with thick plies. However, according to finite element analysis, the thin-ply laminates exhibited much stronger stress concentration after initial damage until ultimate failure of the specimens, leading to lower ultimate strength under tensile loading.
  • Vibration characteristics of a sandwich plate with viscoelastic periodic
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Meiping Sheng, Zhiwei Guo, Qi Qin, Yuanan HeAbstractThe vibration characteristics of a sandwich plate with viscoelastic periodic cores are examined analytically and experimentally, which extends the previous research of corresponding periodic sandwich beam structure. Closed-form solutions for forced response and band structure of periodic sandwich plate are theoretically derived, providing computational support on the attenuation analysis. In the theoretical model, a new admissible displacement function for sandwich plate is proposed. Although it is used in free boundary condition in this paper, it is also suitable for clamped, simply supported, slipping, and elastic boundary conditions. The formation of the band gap is carefully studied, showing that the overall band gap is proved to be the intersection of all the cross-stream modal band gaps, which is quite different from a corresponding periodic beam structure. The parametric analysis shows further that the overall band gap could disappear when length ratio, element width, or core thickness exceeds a cut-off value, which provides a guidance in the band-gap design. The attenuation in a sandwich plate with viscoelastic periodic cores is mainly dominated by Bragg scattering mechanism in the band gap and by energy dissipation out of the band gap. Owing to the combined effect of both mechanisms, the sandwich plate with viscoelastic periodic cores provides better attenuation performance than that with a uniform viscoelastic core. This research could possibly provide useful guidance for the researches and engineers on the design of plate-type damping structures.
  • A multi-scale modeling scheme for damage analysis of composite structures
           based on the High-Fidelity Generalized Method of Cells
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Junjie Ye, Chenchen Chu, Heng Cai, Yongkun Wang, Xiaojun Qiao, Zhi Zhai, Xuefeng ChenAbstractThis paper presents a description of a multi-scale method to investigate the failure behaviors and damage evolution of composite laminates reinforced with unidirectional fibers. The proposed approach is based on the microscopic mechanical theory and pre-processing function of the ANSYS/LS-DYNA software. At micro-scale, the High-Fidelity Generalized Method of Cells (HFGMC) is employed to establish the microscopic model, which can be used to acquire the microscopic stress distributions in the representative volume element (RVE). Moreover, a viscoplastic constitutive model is employed to describe the nonlinear behaviors of matrix materials. At macro-scale, each integration point in elements is employed to investigate the damage evolution for each lamina. In order to validate the proposed method, the numerical results of failure evolution path and stress-strain responses of the composite laminates are compared with experimental data. A good consistency between theoretical results and experimental data can be found. On this basis, the failure evolution path for each lamina is further investigated. The numerical results revealed that the crack firstly appeared in the 90° lamina. With the further increasing of external loading, the crack will accumulate along with the layer direction for −45° lamina, 45° lamina and 90° lamina.
  • A novel metal-composite joint and its structural performance
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Huaqing Tang, Longquan LiuAbstractA novel joining method between metallic and composite structures was developed to enhance the mechanical performance of metal-composite hybrid structures. According to this joining method, the metallic and composite components are adhesively bonded together and there are also some thin pins in the overlap region running through the joint plates. The pins are bonded together with the joined components as well. Comparatively tensile tests were conducted on the metal-composite joints so as to investigate the advantages of the proposed joining method. The load-displacement relationships, fracture modes and fatigue life were analyzed in accordance with the test results of the two different types of joints. The results show that the proposed joining method can improve ultimate failure load, failure displacement, energy absorption capacity and fatigue life significantly. Furthermore, the novel joining method decreases the suddenness of the failure of the joint and provides some plastically like behavior to the joint. Finite element models were developed to investigate the enhancement mechanism of the proposed method. Through the analysis of the failure process, it can be concluded that there are bridging force between the pins and the jointed components and the bridging force not only transfers load between the components together with the adhesive layer, also inhibits the adhesive layer from peeling.
  • Dynamic response of a functionally graded tube embedded in an elastic
           medium due to SH-Waves
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Hasan Faik Kara, Metin AydogduAbstractDynamic response of a cylindrical tube surrounded by an unbounded elastic medium due to plane harmonic SH-Waves is studied. A two-dimensional mathematical model is considered. Cylindrical coordinates are used for convenience. The surrounding medium is assumed to be homogeneous, isotropic and linear elastic. The tube is assumed to be made of linear elastic functionally graded materials (FGMs) such that shear modulus and shear wave velocity are assumed to change linearly from inner surface to outer surface. Material properties are constant along circumferential direction. It is assumed that the inner surface of the tube is traction-free and there is a welded contact between the tube and the surrounding medium. Governing equations are slightly different in the tube region and the unbounded region. Both of the governing equations are solved by applying Finite Fourier Transform in circumferential direction. The exact solution series are presented in terms of Fourier-Bessel series in the unbounded region and power series in the tube region. The presented numerical results show that when the incoming wave lengths decrease, shear stresses at the tube increase significantly. It was shown that for the shorter incoming wave lengths, tubes made of FGMs are subjected to smaller shear stresses compared to the tubes homogeneously made of outer surface material of the FG cases.
  • Flexural performance of FRP-plated RC beams using H-type end anchorage
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Yingwu Zhou, Xiaowei Wang, Lili Sui, Feng Xing, Yufei Wu, Cheng ChenAbstractThis paper investigates the performance of H-type end anchorage on the flexural strengthening of Fiber Reinforced Polymer (FRP) plated reinforced concrete (RC) beams. The H-type end anchorage (EA) consists of an anchorage section, a connection section and a deformation section. In the experimental study, the H-type EA was installed at the ends of FRP plate, and the FRP-plated RC beams were subjected to four-point bending load. The strengthening mechanism of H-type end anchorage mainly depends on the width of its deformation part, which further determines the overall axial stiffness of the end anchorage. The effect of H-type end anchorage on the flexural performance was evaluated in terms of critical loads, failure mode, deflection, ductility and strain behavior of various materials, all showing great improvement as compared to the FRP-plated RC beams without end anchorage. H-type end anchorage was found to be activated after certain thresholds of load was reached, and the elongation became excessive after its yielding. Finally, an analytical model was proposed and verified by the experimental results to estimate the ultimate load and failure mode of the EA-strengthened RC beams.
  • Short-term flexural behaviour of concrete filled pultruded GFRP cellular
           and tubular sections with pin-eye connections for modular retaining wall
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Wahid Ferdous, Ahmed D. Almutairi, Yuan Huang, Yu BaiAbstractA retaining wall system modularly assembled from pultruded glass fibre reinforced polymer (GFRP) sections filled with concrete is introduced in this paper. Two main components (i.e., plank and pile) of the modular system are investigated experimentally at different spans under four-point bending to understand different failure modes. The effect of concrete filling, infill concrete modulus, and section shape (round and square), section size (300–600 mm) and spacing (0–600 mm) are studied through validated finite element modelling and results are compared with the existing reinforced concrete solution. Results show that the concrete filling increases the bending stiffness and prevents premature local crushing, tendency of ovalisation and local buckling by providing lateral supports to GFRP walls. Depending on pile spacing, the square pile deflects 7–13% less than the round pile with equivalent cross-sectional area. It has been found that the existing concrete pile may be replaced by a similar size of concrete filled GFRP pile for comparable performance in terms of stiffness.
  • Higher-order beam theory for static and vibration analysis of composite
           thin-walled box beam
    • Abstract: Publication date: 15 December 2018Source: Composite Structures, Volume 206Author(s): Dongil Shin, Soomin Choi, Gang-Won Jang, Yoon Young KimAbstractA higher-order beam theory suitable for accurate analysis of composite thin-walled box beams is developed. Because anisotropic and laminate effects in composite beams produce deformation patterns that do not appear in isotropic beams, accurate analyses for composite beams require elaborately defined sectional shape functions that describe local cross-sectional deformations. Here, we present a new systematic method to define these functions and establish a one-dimensional finite element based on a higher-order beam theory for composite thin-walled box beams. The validity of the developed approach is checked by solving static and eigenvalue problems with composite thin-walled box beams, and by comparing the obtained numerical results with those obtained by ABAQUS shell elements.
  • Adaptive and Off-Line Techniques for Non-Linear Multiscale Analysis
    • Abstract: Publication date: Available online 20 August 2018Source: Composite StructuresAuthor(s): Stefano Zaghi, Xavier Martinez, Riccardo Rossi, Massimo PetraccaAbstractThis paper presents two procedures, based on the numerical multiscale theory, developed to predict the mechanical non-linear response of composite materials under monotonically increasing loads. Such procedures are designed with the objective of reducing the computational cost required in these types of analysis. Starting from virtual tests of the microscale, the solution of the macroscale structure via Classical First-Order Multiscale Method will be replaced by an interpolation of a discrete number of homogenized surfaces previously calculated. These surfaces describe the stress evolution of the microscale at fixed levels of an equivalent damage parameter (deq). The information required for these surfaces to conduct the analysis is stored in a Data Base using a json format. Of the two methods developed, the first one uses the pre-computed homogenized surface just to obtain the material non-linear threshold, and generates a Representative Volume Element (RVE) once the material point goes into the nonlinear range; the second method is completely off-line and is capable of describing the material linear and non-linear behavior just by using the discrete homogenized surfaces stored in the Data Base. After describing the two procedures developed, this manuscript provides two examples to validate the capabilities of the proposed methods.
  • Coupled thermal-mechanical damage model of laminated carbon fiber/resin
           composite subjected to lightning strike
    • Abstract: Publication date: Available online 19 August 2018Source: Composite StructuresAuthor(s): Qi Dong, Guoshun Wan, Lu Ping, Yunli Guo, Xiaosu Yi, Yuxi JiaAbstractThe degradation model of stiffness matrix containing thermal-mechanical coupling damage was constructed by the user-defined subroutine VUMAT on the basis of continuum damage mechanics (CDM) and phenomenological analysis method, then, it was introduced to the software ABAQUS/Explicit to simulate the damage caused by lightning induced effects of thermal ablation and expansion on carbon fiber reinforced polymer (CFRP) laminates. The results revealed the evolution of the coupling damage from the analysis of stress-strain state and damage variables involved. It can be concluded that the thermal-mechanical coupling model pushed the simulated in-plane damage much closer to the experimental results than thermal ablation model, and the good consistency of simulated in-depth damage and experimental results indicated that the lightning induced in-depth damage was mainly brought from the combined impacts of thermal ablation and expansion.
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