Abstract: Abstract The use of laminates allows an optimization of the material properties, these hybrid materials can unravel some problems in the industrial sector, particularly in aerospace, and advanced automotive industry. Fiber Metal Laminates (FMLs) can be produced both by laminating and by forming. Flat laminates are easier to produce by the lay-up process, for small and relatively complex shapes with low thickness there are significant challenges in the forming process even for small drawing ratios, In this investigation, a cylindrical GLARE cup was chosen, this shape with sharp curves and vertical geometrical walls, still face numerous difficulties in the forming procedure. Numerical simulations have been used and compared with the experimental results in the stamp forming to achieve good forming quality with higher depth. An extensive investigation of the effect of process variables has been done such as blank-holding force, and blank holder gap and the curing condition. Also, their roles in wrinkles formation, tearing and thinning, as well as formability have been performed. The results show a good agreement between the experiments and the numerical simulation and show clearly that the application of blank holder force and blank holder gap within specified limits has a positive effect on the quality of the formed cup and leads to higher depths. Understanding these parameters and the GLARE forming conduct and having a decent choice of these parameters can give the advantage to achieve smaller and more complex shapes with higher depth, especially for large scale manufacturing. Finally, this investigation can expand the modern application regions of the FMLs and GLARE parts. PubDate: 2019-11-21

Abstract: Abstract Compared with processing methods using conductive heating, microwave processing technology has many advantages such as its extremely short processing time and low energy consumption. However, the uneven temperature on the composite surface resulted from the uneven electromagnetic field distribution have become a big problem. Because the traditional model-based approach was difficult to establish the relationship between the composite temperature behaviors and microwave control strategies, existing methods mainly alleviated this problem by generating a relative movement between the microwave field and the object being heated, which cannot essentially achieve a uniform temperature distribution due to the uncertainty of the random compensation principle. In this paper, a data-driven method was proposed to solve this problem using an optimized convolutional neural network with extensive historical data. On this basis, the monitored uneven temperature distribution on the composite surface was accurately compensated in real time. Experimental results indicated that a reduction of ~53% in temperature difference was achieved compared with existing methods. PubDate: 2019-11-13

Abstract: Abstract This paper proposes a progressive damage model incorporating strain and heating rate effects for the prediction of composite specimen damage resulting from simulated lightning strike test conditions. A mature and robust customised failure model has been developed. The method used a scaling factor approach and non-linear degradation models from published works to modify the material moduli, strength and stiffness properties to reflect the effects of combined strain and thermal loading. Hashin/Puck failure criteria was used prior to progressive damage modelling of the material. Each component of the method was benchmarked against appropriate literature. A three stage modelling framework was demonstrated where an initial plasma model predicts specimen surface loads (electrical, thermal, pressure); a coupled thermal-electric model predicts specimen temperature resulting from the electrical load; and a third, dynamic, coupled temperature-displacement, explicit model predicts the material state due to the thermal load, the resulting thermal-expansion and the lightning plasma applied pressure loading. Unprotected specimen damage results were presented for two SAE lightning test Waveforms (B & A); with the results illustrating how thermal and mechanical damage behaviour varied with waveform duration and peak current. PubDate: 2019-11-11

Abstract: Abstract The present paper investigates the impact performance of woven-fabric carbon-fibre composites based upon both thermoplastic- and thermoset-matrix polymers under high-velocity impact loading by conducting gas-gun experiments at impact velocities of up to 100 m.s−1. The carbon-fibre reinforced-polymers (CFRPs) are impacted using soft- (i.e. gelatine) and hard- (i.e. aluminium-alloy) projectiles to simulate either a soft bird-strike or a hard foreign-body impact (e.g. runway debris), respectively, on typical composites employed in civil aircraft. The out-of-plane displacements of the impacted composite specimen are obtained by means of a three-dimensional Digital Image Correlation (DIC) system for the soft-projectile impact on the composites and the extent of damage is assessed both visually and by using portable C-scan equipment. The perforation resistance and energy absorbing capability of the composites are also studied by performing high-velocity impact experiments using the hard-projectile and the resulting extent and type of damage are identified. In addition, a Finite Element (FE) model is also developed to investigate the interaction between the projectile and the composite target. PubDate: 2019-11-01

Abstract: Abstract The effects of pore in C/SiC composites on thermal diffusivity and thermal radiation properties were investigated systematically. Pores were introduced into C/SiC by oxidizing carbon phase at 700 °C and damaged the thermal properties of C/SiC composites. Because of little changes in the pore shape and the pore orientation in C/SiC, thermal diffusivity of samples increased linearly with porosity. The pores within C/SiC absorbed and reflected the radiated heat, decreasing spectral emissivity. However, the temperature dependence of spectral emissivity didn’t change by the pore. With measurement temperature increasing, the pores weakened the thermal radiation property of samples gradually. A linear relation was suggested to quantify the negative effect of pores on the total emissivity. PubDate: 2019-10-25

Abstract: Abstract In order to predict the effective thermal conductivities of three-dimensional (3D) braided carbon/carbon (C/C) composites with randomly distributed void defects. Two-scale prediction model is developed based on the asymptotic homogenization method. Unit cell models both on fiber-scale and fiber bundle-scale are established according to the scanning electron microscopy observation of the material, and the randomly distributed void defects are considered. The effective thermal conductivities of fiber bundles with void defects are predicted firstly, then the effective thermal conductivities of the 3D braided C/C composites are predicted considering void defects in matrix pocket and interface by introducing the predicted thermal conductivities of fiber bundles. The predicted effective thermal conductivities agree well with the experimental results, demonstrating the validity of the two-scale prediction model. A parametric study is then conducted to analyze the effects of void volume fraction and interfacial thermal conductivity on the predictions of the developed model. The results show that the random distribution of void defects has a little effect on the effective thermal conductivities, while the void volume fraction has a significant effect on the effective thermal conductivities. The thermal conductivities decrease generally linearly with the increase of void volume fractions, and the effect of void volume fraction of matrix pocket is greater than that of fiber reinforcement. The effective thermal conductivities increase with the increase of interfacial thermal conductivity, and the effect of void volume fraction of interface becomes larger with the increase of interfacial thermal conductivity. A higher interfacial thermal conductivity have a greater effect on the effective thermal conductivities of the material than a smaller interfacial thermal conductivity. PubDate: 2019-09-13

Abstract: Abstract A novel device is adopted in order to experimentally investigate the effect of various loading rates on the pull-out response of a fastened composite joint configuration. The joint coupons comprise a composite plate made of the carbon/epoxy AS4/8552 material system and a centrally located titanium lockbolt. Tensile-type (pull) loading was applied to the specimens in a velocity range from quasi-static to 2.1 m/s. Both quasi-static and dynamic tests were conducted using the same specimen geometry and boundary conditions, which conform to international and industrial standards. The experimental work expands the limited literature and understanding of the mechanical response of composite pull-out joints under the action of dynamic loading. The main experimental observations revealed an increase of 15% regarding maximum load values when loading rate shifts from the static to the impact regime, while the failure patterns derived from static and dynamic tests were similar, although the latter presented a more intense damage zone. PubDate: 2019-08-27

Abstract: Abstract The strength of plain-woven SiC/SiC composites was predicted with the multi-scale method. Firstly, a three-dimensional unit cell was used to characterize the geometric structure of plain-woven SiC/SiC composites. Secondly, the yarns were seen as minicomposites, whose axial mechanical properties were obtained by the shear-lag model, and the fiber defect model was adopted to simulate the failure process of minicomposites. The strength of plain-woven SiC/SiC composites predicted with the multi-scale method is in good agreement with the experimental result. Besides, the effects of heat treatment and load-carrying capacity of broken fiber on the strength of plain-woven SiC/SiC composites were evaluated, and the effect of woven geometry structure was also evaluated. PubDate: 2019-08-27

Abstract: Abstract The purpose of this article is to investigate the effect of an initial pre-damage induced by a fatigue loading on the tensile dynamic behavior of Advanced Sheet Molding Compounds (A-SMC). Tension-tension fatigue preloading at a frequency of 30 Hz is performed at various applied stress levels prior to subject the A-SMC specimens to tensile tests at different strain rates, namely: 10−3 s−1 (quasi-static), 1 s−1 and 60 s−1. The developed experimental approach provided significant findings in terms of residual behavior and damage accumulation in relation to the applied pre-fatigue loading conditions. Indeed, it has been shown that the overall quasi-static and the dynamic responses are strongly affected by the level of fatigue number of cycles reached prior to applying the high strain loading. The effect of fatigue pre-damage is found also strongly strain-rate dependent. Experimental results showed that the damage threshold in terms of stress and strain increased with strain rate. However, for a given strain-rate the damage stress threshold depends on the number of cycles applied during the fatigue preloading. PubDate: 2019-08-10

Abstract: Abstract The surfaces of the carbon fiber resin matrix reinforced polymer (CFRP) are completely cleaned and partially cleaned by controlling the ultraviolet laser (UV) scanning speed. Residual resin and surface energy of laser cleaning samples are analyzed and correlated to the adhesive bonding tensile properties. The results show that the main damage form of CFRP bonding joints obtained by UV laser complete cleaning and partial cleaning are mixed failure, in which the interface failure and cohesion damage play an important role in the tensile properties of the two kinds of joints, respectively. The surface of the samples after UV laser partial cleaning has been proved to have obvious infrared absorption peaks. Residual resin on the surface of partial cleaning samples is beneficial to improve the tensile properties of bonded samples. The CFRP surface energy by UV laser partial cleaning is 83.35 mJ/m2, which is far higher than that of the original surface. Nevertheless, the CFRP surface energy after UV laser complete cleaning is 56.67 mJ/m2, which is lower than that of UV laser partial cleaning. To a certain extent, the magnitude of the surface energy reflects the bonding property of CFRP. Therefore, the strength of the CFRP adhesive joint after partial cleaning is stronger than that of CFRP joints after complete cleaning. PubDate: 2019-08-01

Abstract: Abstract Voids formed during liquid composite molding significantly degenerates mechanical performances of the final products, accurate prediction of the formation and size of void has significance for the parameter design of LCM. However, the 3D simulation method of void formation, in which the complex interconnecting of pores can be fully considered, has not been developed. In order to analyze the meso-scale-void formation process in full dimensionality, the mechanisms of dual-scale flow and void formation are analyzed firstly in this paper, then the mathematical models for the two-phase inter-tow and intra-tow flow are established based on the VOF theory. During numerical solving, the 3D geometry model is used and the momentum source of capillary force is updated in real-time to guarantee the simulation accuracy. The simulated formation process and size of meso-scale-void are compared with experimental results to verify the effectiveness and correctness of the developed method. PubDate: 2019-08-01

Abstract: Abstract In this paper, a novel numerical simulation framework using meso-scale finite element model is developed to predict the mechanical properties and damage mechanisms for one-layer biaxial braided composite tubes with gradient braided structures in axial direction, which involves braided reinforcements with an evolution of braiding angle. To bridge the relationships between the braiding procedure and geometric model, this paper develops an automatic algorithm that generates the geometric model with requiring braiding parameters as input parameters. The braided fabric model is generated by circularly arraying the yarn model, which is established by sweeping varying cross-sections along the centerline with the control of guidelines. The geometric model of matrix pockets is obtained by extracting the fabric model from the whole geometric model of composite tube. After that, a braiding yarn mesh in hexahedron format and co-node matrix mesh in tetrahedron format are generated from the assembled braided fabric and matrix pockets. The framework established in this paper is validated by comparison with the experimental results of the composite tubes with braiding angles from 36.6° to 49.6° subjected to quasi-static axial compression. PubDate: 2019-08-01

Abstract: Abstract This paper proposes a modified method to predict composite laminate’s delamination under out-of-plane impact, which takes the interface friction effect as physical mechanism to explain the phenomena of interface strength’s enhancement under transverse load. Firstly, bilinear model is chosen to describe the relationship between traction and separation. Secondly, a macromodel of composite laminate under out-of-plane impact is given to show how the interface strength is enhanced. Contact pair of adjacent layer and interface friction coefficient directly reflects the interface friction effect. Thirdly, criterion of delamination is modified based on the interface friction effect, which derives separation expressions of cohesive element under mixed mode fracture. Numerical example of different interface friction coefficients is given to check the modified method’s rigor and rationality, which is also validated by experiment. Compared with experiment results, the finite element simulation shows that the modified method possesses good accuracy in the prediction of composite laminate’s delamination under out-of-plane impact and definite meaning in the explanation for the phenomena of interface strength’s enhancement under transverse load instead of adjusting parameters of cohesive element subjectively and unreasonably. PubDate: 2019-07-04

Abstract: Abstract A composite material consisting of carbon fiber fabric and polyurethane resin was used to fabricate circular tubes by resin transfer molding. The composite tubes were tested under both axial static compression and axial impact. To establish delamination criterion for this composite material, short-beam tests and curved-beam tests were executed, and it was verified by step cantilever-beam tests. The short-beam and curved-beam tests indicate that the interlaminar shear and tensile strengths of the composite are around 54.0 MPa and 8.8 MPa, respectively. Also the established delamination criterion has nice prediction for the delamination of the step cantilever-beam test. In addition to the delamination criterion, the finite element analysis with progressive failure was applied and could predict agreeable values on the total absorbed energy and the specific energy absorption of the braided composite tube under both the static and dynamic tests. These indicate that the present analysis could catch the axial crushing behavior of the braided composite tubes. PubDate: 2019-06-25

Abstract: Abstract This paper presents an experimental study for the assessment of a three-dimensional Progressive Fatigue Damage Model (PFDM) with a carbon fiber/epoxy (AS4/3501–6) material system. Specimens with a central circular hole were selected to represent notched composite structures. Digital Image Correlation (DIC) was used to monitor the surface strain evolution throughout the fatigue lifetime. The PFDM model was implemented in the commercial finite element software ABAQUS using the user material (UMAT) utility. Residual stresses from the composite manufacturing cycle are included in the fatigue damage modeling. Results are presented that compare experimental and predicted strain distributions and fatigue lives. Comparisons between the experimental and simulated response highlight the value of the PFDM model while demonstrating its shortcomings. PubDate: 2019-06-22

Abstract: Abstract The microstructure morphologies have been characterized by high resolution laboratory X-ray computed tomography in Carbon Fiber Reinforced Carbon and Silicon Carbide (C/C-SiC) ceramic composites fabricated by Gaseous Silicon Infiltration (GSI) from C/C preforms of three different architectures: 3D stitched cloth fabric; 3D orthogonal woven fabric; and needled short-cut felt. Each composites’ microstructure was influenced by the structure of the C/C preform. By incorporating tomography with gravimetric analysis, the 3D distribution of the SiC was visualized, showing a connected SiC network in the needled short-cut felt, and more heterogeneous SiC formation on the surfaces of the fiber bundles in the stitched and woven fabrics. The needled short-cut felt provided the largest contact surface for the GSI reaction and generated ~56% volume fraction of SiC, which is almost twice and three times that achieved in the stitched and woven fabrics respectively. Differences in the open and closed pore distributions were also measured by mercury intrusion porosimetry and tomography. PubDate: 2019-06-19

Abstract: Abstract This study presents an integrated numerical and experimental investigation of a laminated aluminum composite structure. The laminated aluminum composite structure was created by attaching structural tape adhesive in between aluminum layers and curing it in an oven. Three point bending tests were conducted on samples with different span lengths and thicknesses and their effect on the flexural response was observed and discussed. Using realistic material fracture models, simulations were performed to capture the different failure modes that were observed experimentally (large plastic deformation, wrinkling, and delamination). Good agreement was observed between the simulations and experiments. The delamination mechanism in the simulations was also discussed in detail. The developed simulation methodology can be used as a robust tool to predict the performance of laminated aluminum composite structures with more complex geometries. PubDate: 2019-06-13

Abstract: Abstract The aim of this research is to design a telescopic hydraulic cylinder, normally used in industrial filed, made of different materials and in particular composite material instead of classical structural steel. Specifically it will refer to the application of this actuator on a dump truck and designated to the transport of soil material, starting from hard load conditions and from the minimum incline to guarantee the complete emptying of the dump truck, the geometry of the cylinder has been defined. The peculiarity of this research is about the materials employed for the design, and the future fulfilment of this component. The work deal with the custom of 4 different materials, or rather: 2 type of steel (structural: S235 JR and stainless AISI 304), aluminum alloy 7075-T6 (Ergal) and a composite material made of epoxy resin and carbon fibers. The elaboration of the new solutions presented, has been realized evaluating the barrel of the cylinder as a container in a pressure vessel with thin walled, whereas the rod as a beam prone to buckling. Is possible to observe how the study has been faced also with the aid of analysis about finite elements, as well as to verify the design of the component, also to prove others phenomena, as the instability for peak load. Moreover is possible to highlight that the adopted theory for the planning of composite barrel, despite load conditions are the same, they differs from the theory used for aluminum and steel because of his anisotropic behavior. Given the particular nature of the composite material, the arguments related with technology are set out, about technology production through filament winding and the assembly of the components of the telescopic cylinder. Thanks to the achieved results, is possible to observe how the use of the composite material, for the realization of that component, can be extremely favorable for the weight achieving a reduction of the 96% starting from 5537 N, reaching 196 N. PubDate: 2019-06-12

Abstract: Abstract A cohesive element able to connect and simulate crack growth between independently modeled finite element subdomains with non-matching meshes is proposed and validated. The approach is based on penalty constraints and has several advantages over conventional FE techniques in disconnecting two regions of a model during crack growth. The most important is the ability to release portion of the interface that are smaller than the local finite element length. Thus, the growth of delamination is not limited to advancing by releasing nodes of the FE model, which is a limitation common to the methods found in the literature. Furthermore, it is possible to vary the penalty parameter within the cohesive element, allowing to apply the damage model to a chosen fraction of the interface between the two meshes. A novel approach for modeling the crack growth in mixed mode I + II conditions has been developed. This formulation leads to a very efficient computational approach that is completely compatible with existing commercial software. In order to investigate the accuracy and to validate the proposed methodology, the growth of the delamination is simulated for the DCB, ENF and MMB tests and the results are compared with the experimental data. PubDate: 2019-06-11

Abstract: Abstract Injection-compression-compression (I-C-C) process was studied to prepare polypropylene/ short carbon fiber (PP/SCF) composites. The effects of I-C-C process on the conductive network, fiber distribution and electric conductivity were investigated. The distance between conductive particles of the blending system was reduced by two-stage compression, so that the conductive network was compacted. The forming of dense conductive network significantly improved the conductivity. Moreover, I-C-C can effectively interfere with the fiber flow direction to enhance the conductivity of the infiltrated surface. Combined with the microstructure and electrical conductivity, the applicable mold temperature and compression speed range of the I-C-C process for PP can be obtained. The results showed that the electrical conductivity of the I-C-C prepared PP/SCF was increased up to 5 orders of magnitude higher than that of ordinary injection molding. Conductivity of PP/ 10 wt% SCF conductivity reached 3.7S/m, PP /15 wt% SCF reached 33S/m, and PP/ 20% SCF reached 150S/m. PubDate: 2019-06-08