Authors:A. Alijani; M. Mastan Abadi; A. Darvizeh; M. Kh. Abadi Abstract: The purpose of the present study is to investigate the static behavior of cracked Euler–Bernoulli beams resting on an elastic foundation through implementing analytical, approximate and numerical approaches. Among common approximate and numerical approaches, Galerkin’s and the finite element methods, respectively, are selected to solve the governing equations. The crack-caused imperfection is simulated by two discrete spring models whose stiffness factors are determined in terms of the stress intensity factor and the geometric parameters. In the analytical solution, a Dirac’s delta function is used to define the singularity in the flexural stiffness and to derive an improved governing equation. In the Galerkin solution, two deflection functions corresponding to the right- and left-hand sides of the crack point are offered to satisfy the governing equation. In the finite element method by introducing a novel technique, a modified stiffness matrix whose components are enriched by material and geometric parameters of the crack is proposed. This study focuses on the effect of various parameters including the crack depth and position, boundary conditions, elastic foundation as well as the discrete spring models on the beam deflection through aforementioned theoretical approaches. Lastly, results from these three theoretical solutions are verified through comparison with each other and Abaqus software. PubDate: 2018-02-06 DOI: 10.1007/s00419-018-1347-0

Authors:Andrzej Chudzikiewicz; Jaroslaw Korzeb Abstract: This paper presents an example of low-floor trams simulation tests. The tram under study was unique because of using the system of independently rotating wheels in the bogie IRW (“Chudzikiewicz et al., in: The structural design of a modern, completely low-floor tram with independently rotating wheels (Report in Polish) NCBiR—DEMONSTRATOR+, Warsaw University of Technology Faculty of Transport—PESA Bydgoszcz, 2014”). In this paper, the dynamic behavior of the vehicle was examined, and the phenomenon of wheels and rails wear, during the rolling contact, was subjected to the identification. For this purpose, a dedicated computational model was built in MATLAB environment, taking into account the phenomenon of kinematic pair wear using Archard’s model. PubDate: 2018-02-06 DOI: 10.1007/s00419-017-1301-6

Authors:Wei Sun; Rong Liu; Yunfei Fan Abstract: Finding the best coating location with the fixed shape of the hard coating is an urgent need for the engineering application of the hard-coating damping. In this paper, a study on optimal placement of hard-coating damping treatment for vibration reduction in the cantilever plate was presented. Based on the energy method and the assumed mode method, the analytical model was derived for free vibration analysis of the thin plate partially covered with hard coating, and the modal loss factors of the coating structure were determined by the modified modal strain energy method. The damping optimization model of the hard-coating thin plate was described with the maximum modal loss factor of single order or multi-orders as the objective function and the coating position as the design variable. Moreover, a method named multiple population genetic algorithms was proposed to search for the optimal coating position. Finally, a cantilever titanium plate with a single side partially deposited with NiCrAlCoY+YSZ hard coating was taken as an example to carry out a case study. The correctness of the analytical results was verified by ANSYS software and experiment, and the rationality of the damping optimization results for the hard-coating plate was also verified by experiment. PubDate: 2018-02-05 DOI: 10.1007/s00419-018-1348-z

Authors:Kai Zhou; Jinpeng Su; Hongxing Hua Abstract: This paper investigates the free and forced vibration of moderately thick orthotropic plates under thermal environment and resting on elastic supports. Three kinds of elastic supports, namely non-homogeneous elastic foundations, point elastic supports and line elastic supports, are considered in the present study. The first-order shear deformation theory is employed to formulate the strain and kinetic energy functions of the structures, and then the stiffness and mass matrices can be obtained by applying the Hamilton’s principle. The modified Fourier method is adopted to solve the dynamic problems of moderately thick orthotropic plates with different combinations of temperature variations, elastic supports and boundary conditions. The accuracy and reliability of the proposed formulation are validated by comparing the obtained results with the finite element method results. Finally, the effects of some key parameters including temperature variation and stiffness values of the elastic supports on the modal and dynamic characteristics of the plates are analyzed in detail. In views of the versatility of the developed method, it offers an efficient tool for the structural analysis of moderately thick orthotropic plates under thermal environment and resting on elastic supports. PubDate: 2018-02-01 DOI: 10.1007/s00419-018-1346-1

Authors:M. R. Behnam; M. M. Khatibi; A. Malekjafarian Abstract: Frequency response functions (FRFs) can be estimated only from responses of structures without knowledge of input forces. Mode shapes identified from operational modal analysis (OMA) methods are unscaled, and the unscaled mode shapes provide unscaled FRFs. In this paper, mass change and mass–stiffness methods are employed to construct FRFs from the response-only measurements. A numerical case study of a cantilever beam is investigated using the finite element method. It is shown that the mass–stiffness change method provides more accurate results compared to the mass change method in the low-frequency range. A laboratory-scale steel beam is also tested using an OMA method and conventional hammer test. The experimental results show better accuracy of the identified FRFs in the low-frequency range when the mass–stiffness method is used. PubDate: 2018-01-31 DOI: 10.1007/s00419-018-1345-2

Authors:G. Lengyel Abstract: The paper investigates how the shape affects the Couplet–Heyman minimum thickness of the masonry pointed arch. The minimum thickness is such a structural thickness, at which a vault made of rigid voussoirs is stable for self-weight. It is expressed as a function of the pointed generator curve’s deviation from the semicircle. The arch is analysed in its undisplaced, geometrically perfect state. In the present study, perfect symmetry is assumed, and any disturbance in the symmetry is not considered. The joints between the voussoirs are placed in the radial direction. Two approaches are applied to derive the minimum thickness of the pointed arch, like Limit State Analysis (henceforth LSA) and Discrete Element Modelling (henceforth DEM). The application of the LSA leads to a nonlinear optimisation problem, which is solved by the so-called active set method. DEM technique is also applied, in which the model consists of discrete blocks each of which can move independently from each other. In DEM, sliding failure can freely develop during the loading process, which is neglected in the LSA. The results of the analyses show great correspondence, if sliding failure does not appear. PubDate: 2018-01-22 DOI: 10.1007/s00419-018-1341-6

Authors:Zuzana Murčinková; Pavol Novák; Vladimír Kompiš; Milan Žmindák Abstract: The paper presents the process of homogenization of the composite material properties obtained by method of continuous source functions developed for simulation both elasticity and heat conduction in composite material reinforced by finite-length regularly distributed, parallel, overlapping fibres. The interaction (fibre–fibre, fibre–matrix) of physical micro-fields influences the composite behaviour. Comparing with finite element method (FEM), the interaction can be simulated either by very fine FE mesh or the interaction is smoothed. The presented computational method is a mesh-reducing boundary meshless type method. The increase in computational efficiency is obtained by use of parallel MATLAB in presented computational models. The stiffness/conductivity is incrementally reduced starting with superconductive/rigid material properties of fibres and the fibre–matrix interface boundary conditions are satisfied by the iterative procedure. The computational examples presented in paper show the homogenized properties of finite-length fibre composites; the thermal and elasticity behaviour of the finite-length fibre composites; the similarities and differences in composite behaviour in thermal and elasticity problems; the control volume element for homogenization of composite materials reinforced by finite-length fibres with the large aspect ratio (length/diameter). The behaviour of the finite-length fibre composite will be shown in similar the heat conduction and elasticity problems. Moreover, the paper provides the possibilities and difficulties connected with present numerical models and suggested ways for further developments. PubDate: 2018-01-17 DOI: 10.1007/s00419-018-1342-5

Authors:Mahdi Zeidi; Chun IL Kim Abstract: A model for the deformation of an elastic solid reinforced by embedded fibers is presented in which elastic resistance of the fibers to bending is incorporated. Within the framework of strain-gradient elasticity, we formulated the equilibrium equations and necessary boundary conditions which describe the finite plane deformations of fiber-reinforced composite materials. The resulting nonlinear partial differential equations are numerically solved by employing the finite element method. A complete analytical solutions is also obtained within the limitation of superposed incremental deformations. PubDate: 2018-01-16 DOI: 10.1007/s00419-018-1344-3

Authors:Qingjun Hao; Wenjie Zhai; Zhaobo Chen Abstract: In this paper, free vibration of connected double-beam system under general boundary conditions is investigated by a modified Fourier–Ritz approach. The effects of the restrained stiffness of the springs and the elastic layer stiffness on modal properties are incorporated in the current framework. The displacement components can be expressed as Fourier cosine series plus auxiliary polynomial functions, which aim to eliminate the discontinuities of displacement and its derivatives at both ends and to enhance the convergence of the results effectively. Numerical examples were presented and discussed for several different geometric and material properties as well as distinct boundary conditions. The effectiveness and rapid convergence of the present method can be verified from the results. Numerous new results for connected double-beam system with arbitrary boundary conditions are presented. PubDate: 2018-01-04 DOI: 10.1007/s00419-017-1339-5

Authors:Andreas Lehn; Marcel Mahner; Bernhard Schweizer Abstract: The performance of air foil thrust bearings (AFTBs) is studied for aligned, distorted and misaligned operating conditions on the basis of a very detailed numerical model for the foil sandwich. The exact geometry of the bump foil is modeled by a Reissner–Mindlin-type shell theory. A penalty-type contact formulation including frictional effects is applied for the contact between top foil and bump foil as well as between bump foil and base plate. The minimal film thickness within the thrust bearing is used as a criterion for comparing different air foil thrust bearings with rigid thrust bearings. If the rotor disk and the base plate are perfectly parallel (aligned conditions), AFTBs are proved to have always a lower load capacity than (optimized) rigid thrust bearings due to unequal bump foil deformations and top foil sagging effects. This finding is in contradiction to previous works based on simplified foil models, which claimed AFTBs to be superior to rigid thrust bearings. Furthermore, for both operating conditions—thermally induced distortions of the rotor disk as well as misalignment—an individual pad of an AFTB is found to be unable to effectively compensate for the disturbance in the gap function. Consequently, a tailoring of the stiffness distribution in the AFTB is shown to be of limiting effect. Instead, the overall compliance of the pads in an AFTB is demonstrated to be the essential reason for the superior behavior of AFTBs to rigid thrust bearings under misaligned conditions. PubDate: 2018-01-04 DOI: 10.1007/s00419-017-1337-7

Authors:İsa Çömez Pages: 1993 - 2002 Abstract: In this study, frictional moving contact problem for a rigid cylindrical punch and an elastic layer is considered. The punch is subjected to concentrated normal and tangential force, and moves steadily with a constant subsonic velocity on the boundary. The problem is reduced to a singular integral equation of the second kind, in which the contact stress and the contact area are the unknowns, and it is treated using Fourier transforms and the boundary conditions for the problem. The numerical solution of the singular integral equation is obtained by using the Gauss–Jacobi integration formulas. Numerical results for the contact stress and the contact area are given. The results show that with increasing values of relative moving velocity, contact width between the moving punch and the layer increases, whereas contact stress decreases. PubDate: 2017-12-01 DOI: 10.1007/s00419-017-1306-1 Issue No:Vol. 87, No. 12 (2017)

Authors:Chang-Gon Jeong; Seong-Kyun Kim; Joo-Hee Lee; Jong-Woong Kim; In-Sung Luke Yeo Pages: 2003 - 2009 Abstract: Screw loosening, which is closely associated with the preload of an abutment screw, is one of the most frequent complications in clinical implantology. The aim of the present study was to investigate the preload prediction of a joint screw assembly between an implant and abutment based on a mechanical analysis. A mechanical formula was determined to relate preload, the dependent variable, to the tightening–loosening torque difference, the independent variable. To confirm the equation, 15 implant–abutment assemblies were prepared. These assemblies were divided into five groups based on tightening torques, and joint screw loosening torques were recorded. Preload values of the assemblies were calculated using a mechanical formula and compared with those previously obtained from direct measurements. In addition, the recommended tightening torque was deduced to prevent screw loosening using the linear relation between tightening torque and the tightening–loosening torque difference. Theoretically calculated preload values were similar to those directly estimated using devices to measure preload. Every predicted preload was insufficient in preventing screw loosening. However, the theoretical preload for prevention was clinically unavailable. These results indicate that prevention of screw loosening requires repeated tightening of the abutment screw. Moreover, this study suggests a useful tool to predict preload, which was practically applicable to the implant–abutment assembly, in dental implantology. PubDate: 2017-12-01 DOI: 10.1007/s00419-017-1307-0 Issue No:Vol. 87, No. 12 (2017)

Authors:Qianqian Sui; Changliang Lai; Hualin Fan Pages: 2011 - 2024 Abstract: To reveal free vibration modes and fundamental frequency of one-dimensional periodic IsoTruss tubular composite structures (ITTCSs), finite element modeling method and dynamic equivalent models were developed. ITTCS has two typical vibration modes: (a) shell-like modes and (b) beam-like modes. Short ITTCS and large inclinations of helical members easily induce shell-like vibration modes, while long ITTCS and small inclinations easily induce beam-like vibration modes. For shell-like vibration, the fundamental frequency is decided by the inclination, while the length has little influence. For beam-like vibration, the fundamental frequency depends on the column length and the inclination has slight influence. Dynamic continuum beam-like model and shell-like model were developed to predict the fundamental frequency of the IsoTruss structure. The predictions are consistent with the numerical simulations, and these models can be applied in engineering to instruct the dynamic design of the IsoTruss structure. PubDate: 2017-12-01 DOI: 10.1007/s00419-017-1308-z Issue No:Vol. 87, No. 12 (2017)

Authors:Roohollah Ghaedamini; Aazam Ghassemi; Amir Atrian Abstract: Residual stresses in composite constructions are created because of non-uniform contraction of layers during cooling from curing to ambient temperature. The aim of this study is to investigate the feasibility of incremental ring-core method to estimate non-uniform residual stresses in various laminates of polymer matrix composites. To carry out this test, glass/epoxy specimens were selected in two different types of symmetric cross-ply laminate \(\left( \left[ 0^{\circ }_{4}/90^{\circ }_{4}\right] _{S}\right) \) and symmetric quasi-isotropic laminate \(\left( \left[ 0^{\circ }_{2}/\pm 45^{\circ }/90^{\circ }_{2}\right] _{S}\right) \) . The samples were created using hand layup and vacuum bagging. By experimental tests, released strains measured during milling process and coefficient factors for every annular groove machining operations were obtained by finite element modeling. As well, residual stresses were calculated by classical lamination plate theory. For symmetric cross-ply, the maximum difference between experimental and theoretical results was about 16%, which was observed in the first and eighth layers. Symmetric quasi-isotropic specimen showed also good agreement between the results and the maximum measurement error of 8% was observed. For the mentioned two cases, summation of components of the residual stress in all directions is near to zero. The results of this study show that in the ring-core method, because of the nature and higher volume of material removal than other methods, values of residual stress released are higher and the results have a good consistency compared with the theoretical values. PubDate: 2017-12-29 DOI: 10.1007/s00419-017-1340-z

Authors:Kerimcan Celebi; Durmus Yarimpabuc; Naki Tutuncu Abstract: A novel approach is employed in the free vibration analysis of simply supported functionally graded beams. Modulus of elasticity, density of material, and Poisson’s ratio may change arbitrarily in the thickness direction. The equations of motion are derived using the plane elasticity theory. The governing differential equations have variable coefficients, which are functions of material properties. Analytical solutions of such equations are limited to specific material properties. Hence, numerical approaches must be adopted to solve the problem on hand. The complementary functions method will be infused into the analysis to convert the problem into an initial-value problem which can be solved accurately. Solutions thus obtained are compared to closed-form benchmark solutions available in the literature and finite element software solutions to validate the method presented. Subsequently, it is demonstrated that the method is efficiently applicable to material properties changing arbitrarily through the thickness with continuous derivatives. PubDate: 2017-12-21 DOI: 10.1007/s00419-017-1338-6

Authors:Marina Rakočević; Svetislav Popović Abstract: This paper presents the analysis of simply supported rectangular laminated composite plates loaded perpendicularly to the middle plane using a new computational method based on Reddy’s layerwise theory. The stress–strain analysis was based on the analytical solution of equations of the layerwise theory, where the plates with an antisymmetric layer arrangement were analysed. Each of the layers contains continuous fibres oriented in one of two mutually orthogonal directions. The results obtained by applying above-mentioned computational procedure have been compared with the results obtained using three different models of finite elements of the ANSYS software package. The quantified limits of the computational method in terms of the impact of plate thickness, the number of layers and the aspect ratio of the plate on the accuracy, convergence and stability of primary variables—components of displacement, and secondary variables—components of stress, have been analysed in the paper. PubDate: 2017-12-16 DOI: 10.1007/s00419-017-1334-x

Authors:Wenjun Yang; Taotao Hu; Xu Liang; Shengping Shen Abstract: Flexoelectricity becomes remarkable in nanoscale dielectrics where strong strain gradients are expected. The effect of flexoelectricity on elastic plane waves propagating in nanoscale layered phononic crystals is discussed in the current work. The fundamental governing equations and boundary conditions are derived from the virtual work principle. Detailed calculations are performed for nanoscale two-layered and three-layered phononic crystals using the transfer matrix method. Numerical results indicate that phononic crystals possess frequency pass bands and stop bands. For nanoscale layered phononic crystals, flexoelectricity increases the middle frequency regardless of the thickness ratio, whereas the flexoelectric effect on the bandwidth depends on the thickness ratio, which implies that there is an optimal thickness ratio to maximize the bandwidth. In addition, the middle frequency and bandwidth decrease with an increase in the unit cell thickness if the thickness ratio is fixed. Hence, considering the flexoelectric effect on band structures of nanoscale phononic crystals may provide guidance in manipulating elastic wave propagation and facilitate potential applications in phononic crystal devices. PubDate: 2017-12-12 DOI: 10.1007/s00419-017-1332-z

Authors:Lei Zhao; Zunyi Zhao; Lianyong Xu; Yongdian Han; Hongyang Jing Abstract: The interaction and combination of multiple embedded cracks would accelerate cracks growth and shortened the components life. In this study, the interaction of the multiple embedded cracks in a finite thickness plate subjected to remote tensile loading in the creep regime was investigated using comprehensive finite element calculations. In addition, the features of cracks and material properties (e.g., crack aspect ratios a / c, relative crack depth a / t, relative distance s / c and creep hardening exponent n) were considered. The results revealed that the creep interaction factor distribution was asymmetric along the crack front. In addition, the creep interaction factor increased as the crack depth and creep hardening exponent increased and gradually decreased as the position away from the each other. However, the crack shape changing from elliptical shape to circular shape had slight impact. Furthermore, based on the comprehensive analyses, an empirical formula to determine the multiple interaction level considering the crack configurations and the material properties was proposed for the embedded cracks operating at elevated temperatures. PubDate: 2017-12-12 DOI: 10.1007/s00419-017-1335-9

Authors:Francesco Foti; Luca Martinelli Abstract: Cables are widely used lightweight and efficient structural members affected by various nonlinearities. This paper is devoted to the development of a finite element approach to the study of the nonlinear dynamic behavior of cable structures under wind loading. Firstly, the formulation of a co-rotational beam-cable element is presented to account for cable geometrical nonlinearities within the context of an Updated Lagrangian approach. The Euler–Bernoulli kinematics is adopted in the co-rotated frame assuming small or moderate displacements and strains. Secondly, the formulation of an aerodynamic element, meant to be superimposed to the mechanical beam element, is developed to fully account for the nonlinearity of the aerodynamic forces. The wind interaction forces are computed within the framework of the quasi-steady theory. Appropriate procedures for applying the aforementioned elements in static and dynamic analyses are presented and applied to the study of the static configuration and the galloping vibrations of a suspended cable under steady and turbulent wind conditions. The results point out the importance of the first anti-symmetric in-plane mode on the galloping response of the iconic selected structure, and reveal the role of the mechanical and aerodynamic model by comparison with a different discretization based on cable finite elements. A mechanical model, such as the proposed co-rotational finite element formulation, which includes the description of torsional rotations is required to properly model the aerodynamic loads in dynamic galloping analyses under steady wind. The mechanical and aerodynamic assumptions, instead, play a less important role in the case of turbulent wind conditions, leading to an eminently buffeting response entailing a strong effect of the swing of the structure. PubDate: 2017-12-11 DOI: 10.1007/s00419-017-1333-y

Authors:Jiangen Lv; Houjun Kang Abstract: In this paper, the one-to-one interaction of a cable-stayed arch structure under the cable’s primary resonance is investigated. Based on the coupling condition at the arch tip, the partial differential equations governing the planar motion of the system are derived using the extended Hamiltonian principle, while with the application of the Galerkin method, these equations are transformed into a set of ordinary equations. Applying the method of multiple scales to these ordinary equations, the first approximated solutions and solvability condition are obtained. The one-to-one interaction between the cable and the arch is investigated under simultaneous internal and external resonances for an actual cable-stayed arch structure. Based on the shooting method and the pseudo-arclength algorithm, the dynamic solutions of the system are obtained, and a period-doubling route to chaos is analyzed. The effects of the cable’s initial tension, inclination angle, the arch’s rise-to-span ratio and intersection angle between the cable and the arch are explored, and the results show that the interaction response mainly depends on specific parameters. PubDate: 2017-12-11 DOI: 10.1007/s00419-017-1328-8