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On the basis of the experimental results in previous work, a multiscale numerical modeling strategy on the failure behaviour of three-dimensional orthogonal woven carbon/carbon composites under pin-loading was presented. In consideration of the complexity of internal woven architecture, the finite element analysis at micro-/meso-/macro-scale levels was performed to exhibit the effective material properties and mechanical behaviour. The geometric models were reconstructed via X-ray tomography technology to obtain feasible configurations based on actual microstructure, meanwhile the models considered the fibers random arrangement in the yarn and voids stochastic distribution in the matrix. The anisotropic composites damage evolution was characterized by Murakami-Ohno damage theory. Additionally, for a further exploration on the practical bearing failure mode, the macro-scale open-hole plate model was established using mesh superposition method to expose the damage mechanism of each component in composites at hole edge, and the numerical predictions agreed reasonably well with the experimental results.

During the formation of complex shapes, textile reinforcement is subjected to large local and global deformation, which affects the quality of the final composite product. This study investigated the deformation behaviors of 3D angle-interlock woven fabrics, which were used in their "dry state". Hence, both cyclic tensile tests and picture-frame type of shear tests were performed to compare the deformation processes. The results showed that the shear cyclic displacement condition produced a higher shape-preserving ability than its tensile counterpart. In addition, the negative Poisson’s ratio in the thickness direction was observed only when the tensile displacement was applied along the warp direction. A theoretical model was presented to predict the thickness variations of the woven fabrics and the results agreed well with the experiments.

An experimental approach of three-dimensional woven carbon/carbon composites arranged in various geometrical configuration is presented in this paper. Seven types of samples divided into three groups were tested under pin-loading to determine the effects of width-to-hole diameter ratio (W/D), edge distance -to- hole diameter ratio (E/D) and hole diameter-to- thickness ratio (D/t) on the failure mode. For an advanced understanding of failure propagation, damage mechanism was observed and assessed combining acoustic emission monitoring. The experimental results and observations indicated that net-tension failure and shearing-out failure switched to bearing failure with the increasing ratio of W/D and E/D, respectively. while D/t hardly affected the failure mode. Major features of the damage mechanisms included matrix crashing and cracking, fiber micro-buckling and bending, interface debonding and fiber breakage with different acoustic emission signal ranges.

Critical drawback of poor stiffness in traditional auxetic materials limits them to be applied where negative Poisson’s ratio behavior and excellent load-bearing capacity are simultaneously desired. In this work, a general prescription for designing auxetic lattice structures with high stiffness and controllable isotropic/anisotropic elastic properties is proposed. Based on it, we rationally design a class of novel auxetic lattice structures whose deformation is mainly governed by the stretching mechanisms and conducted an investigation on a tree-like re-entrant structure. A combination of theoretical predictions, numerical simulations and tensile test experiments have been carried out to gain a comprehensive understanding of the structural in-plane elastic mechanical properties along both the principal axes as well as in the off-axis directions. Besides, theoretical model for designing tree-like re-entrant structure with isotropic elastic properties is established and experimentally verified with specimens fabricated with CFRP composite. The results of this research has proven the tree-like re-entrant structure exhibits excellent effective Young’s modulus, shear modulus and obvious negative Poisson’s ratio effect along omni-direction. Investigation on the directional dependence of structural effective elastic properties has further indicated the proposed structure presents a great potential for designing auxetic material with controllable anisotropic elastic properties. In particular, the proposed structure is capable in achieving isotropic design with any negative Poisson’s ratio between −1 and 0. The design philosophy presented in this paper provides a general prescription for solving the challenge of poor stiffness in traditional auxetic materials and paves a new way for isotropic auxetic design.

In this paper, by use of test combined with numerical simulation, the out-of-plane loading-bearing failure process of CFRP and C/C joints were studied, while Hashin failure criterion was selected t...

In the process of studying the curing deformation behavior of fiber metal laminates (FMLs) subjected to thermal stress, there are some discrepancies between analytical models and experimental results for the room-temperature stable configuration. The main reason is the uncertainty of the parameters in the analytical calculation. In present paper, a parametric sensitivity analysis of the influence of Young’s modulus, Poisson’s ratio, thermal expansion coefficients, ply thickness, ply angle and temperature difference on the cured stable configuration is carried out to identify the most sensitive properties. Accurate characterization of these sensitive properties and precise control of manufacture process can reduce the discrepancies and obtain a more accurate prediction model. It is believed that the present study can be helpful of guiding the design and manufacture of the FMLs in the engineer application.

This work presents an in-situ assessment of damage occurring in the single-lap fiber metal laminate joints with various geometries under uniaxial tension and identify the crucial geometric role in the damage formation. The acoustic emission combined with digital image correlation is applied to record the damage events and strain field. The identification is made with the peak frequency, in which intervals of peak frequency containing [0–100 kHz], [100–200 kHz], [200–300 kHz] and [300–400 kHz] represent matrix/metal crack, delamination, fiber pull-out and breakage, respectively. The Hashin criterion, cohesive constitutive relation and ductile damage criterion are used to predict the damage evolution of fiber metal laminate. The combination of cumulative AE energy and simulation results reveals damage onset, evolution and severity. The incongruity of bearing capacities and stress situations caused by the distinction of geometric parameters result in the bearing damage, the brittle damage and the ductile shear damage in different structures.

In this paper, a novel porous polyetheretherketone-hydroxyapatite (P-PEEK-HA) composite is designed and fabricated by powder mixing-heat press-alkali cleaning method. FTIR and XRD are employed to determine the component and molecular structure of the P-PEEK-HA composite. The porous layer morphology is evaluated using mercury intrusion porosimetry . FTIR and XRD suggest that there are no new crystalline phase formations during the fabrication process and no change in the crystal structure of the PEEK and HA. Mercury intrusion porosimetry shows that the pore size range is mainly 250.64–16.68 μm, and macro-meso pores larger than 5 nm are also existed. And excitedly, the open porosity of P-PEEK-HA reaches 34.115 ± 1.953%, while its closed-cell porosity is only 0.368 ± 0.022%. The pores can provide connected reticular structure for body fluid transmission and bone cells ingrowth, and HA can improve bioactivity for osseointegration. This work provides valuable basic data for the orthopedic application of P-PEEK-HA composite material, showing its excellent potential in medical engineering.

This paper introduces a new methodology for generating three-dimensional (3D) negative Poisson’s ratio behavior with lattice representations of the rotating rigid mechanism as a starting point. Based on it, a class of new 3D auxetic lattice structures is proposed. The elastic properties of a representative 3D auxetic lattice structure, including the homogenized Young’s modulus and Poisson’s ratio along the three principal axes, are systematically investigated in a combination of analytical predictions, numerical simulations and experimental tests. Moreover, effects of the structural geometrical parameters and specimen size on the elastic properties as well as structural nonlinear mechanical responses along the principal axes are carefully discussed. Different from most traditional 3D auxetic materials that are only capable of achieving negative or positive Poisson's ratio, our results suggest that the homogenized Poisson’s ratio effect of the proposed 3D lattice structure along all principal axes can be tuned from positive to negative in a wide range. The excellent design flexibility would help to expand and hasten the adoption of the new 3D auxetic lattice structures in engineering applications.

This paper presents the non-local theory solution to a three-dimensional rectangular permeable crack in magneto-electro-elastic materials (MEEMs) using the generalized Almansi's theorem and the Schmidt method. The problems are formulated through Fourier transform as three pairs of dual integral equations, in which the unknown variables are the jumps of elastic displacement, electric potential and magnetic potential jumps across the crack surfaces. The displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials to solve the dual integral equations and the resulting equations are solved using the Schmidt method. Numerical examples are provided to show the effects of the geometric shape of rectangular crack and the lattice parameter on the stress, the electric displacement and the magnetic flux fields near the crack edges in magneto-electro-elastic materials. Unlike the classical solution, the present solutions exhibit no stress, electric displacement and magnetic flux singularities near the crack edges in magneto-electro-elastic materials.

Poly-ether-ether-ketone (PEEK) possesses excellent biocompatibility and similar elastic modulus as bones but yet suffers from poor osseointegration. In order to balance PEEK's mechanical and osseointegration properties, a novel surface porous PEEK (SP-PEEK) is successfully fabricated by fused deposition modelling three-dimensional printing (FDM 3DP) and characterized by mechanical and osteogenesis in vitro tests. Moreover, the effects of pore diameter and pore layer number on the mechanical behaviors of SP-PEEK are investigated by theoretical model and numerical simulation. Comparison among experimental, theoretical and simulation results show good agreement. As pore diameter decreases, the equivalent strength and modulus become more sensitive to the decrease of pore layer number. In addition, the SP-PEEK exhibits the mechanical properties within the range of human trabecular bone and cortical bone, and thus can be tailored to mimic human bone by adjusting the pore diameter and pore layer number, which is benefit to mitigate stress shielding. The effects of pore diameter on the cell proliferation and osteogenic differentiation of SP-PEEK are tested by the co-culture of osteoblast precursor cells (MC3T3-E1) and SP-PEEK round discs. Results showcase that porous surface improves the osteogenesis in vitro, and the SP-PEEK group that the pore diameter is 0.6 mm exhibits optimal-performance osteogenesis in vitro.

The ultimate damage patterns of bolted composite joints would change from bearing damage to shear damage due to different geometric parameters . However, it is still a challenging task to evaluate real-time damage progressive of hybrid (bolted/bonded) FML joints consisting of complex components in detail. Here, acoustic emission (AE) combined with a digital image correlation system (DIC), optical microscope and C-Scan technique is applied to describe the mechanical responses of hybrid FML joints under quasi-static uniaxial tension load with an emphasis on determining the geometric role of joint on the damage propagation . A k-means cluster algorithm as an unsupervised pattern recognition approach is used to classify each failure mode occurring in the joints to further establish the connection between experimental phenomena and underlying mechanisms. The damage modes including matrix cracking , debonding of adhesive layer , fiber breakage and metal fracture are identified by clusters of AE signals, distributions of strain field and damage morphology . The results clearly reveal the effect of varied geometric parameters on damage propagation of hybrid FML joints and provide a framework for analyzing the relationship between the failure modes in FML and related AE parameters.

Experiments and finite element simulation were used to investigate the influence of geometric parameters on failure response of a single-lap bolted joint. Single- and double-bolt joints in three-dimensional six-directional braided composites were tested. The failure modes and mechanisms of the joints were evaluated. To accurately predict bearing strength, a three-dimensional composite damage model was used, which included the Yamada–Sun failure criteria based on the characteristic curve method. The finite element method (FEM) was validated by experimental results. The geometric reference value and failure envelope for the single-lap bolted joint were obtained. The results showed that the carrying capacity of the single-lap bolted joint decreased and the failure mode also changed owing to the secondary bending. It can also be obtained that increased the number of bolt rows can effectively reduce the secondary bending of the plates and thus generated less severe net tensile stresses.

The dynamic behavior of a rectangular crack in a three-dimensional (3D) orthotropic elastic medium is investigated under a harmonic stress wave based on the non-local theory. The two-dimensional (2D) Fourier transform is applied, and the mixed-boundary value problems are converted into three pairs of dual integral equations with the unknown variables being the displacement jumps across the crack surfaces. The effects of the geometric shape of the rectangular crack, the circular frequency of the incident waves, and the lattice parameter of the orthotropic elastic medium on the dynamic stress field near the crack edges are analyzed. The present solution exhibits no stress singularity at the rectangular crack edges, and the dynamic stress field near the rectangular crack edges is finite.

The accurate prediction of the permeability is the key to optimizing the molding process of fiber reinforced composites, thus to improve the composite quality, and reduce the material and labor costs in the manufacturing process. In this paper, the permeability of 2.5D woven preform with shear deformation was studied by experiments and numerical simulations. The permeabilities of the samples under various shear angles were measured by the radial flow method. An RVE (representative volume element) model based on the fabric microstructure and shear deformation is developed to predict the permeability of preform and the simulation results are compared with experiments value to verify the effectiveness of this model. Using this model, the effect of the fiber volume fraction on the permeability of the 2.5D woven preform was determined. Based on the structural characteristics, experimental and simulation results of the 2.5D woven preform, an empirical equation for predicting its permeability under shear deformation was formulated. The prediction accuracy of the equation was evaluated, and the equation was used to determine the change of permeability with shear deformation for the 2.5D woven preform.

In the present work, an experimental investigation on the failure of 3D woven carbon/carbon all-composites mechanically fastened bolted joints with protruding-head and countersunk-head bolts has been implemented under out-of-plane loading in air at room temperature and up to 1100 °C for the first time. The load-displacement curves and main damage mechanisms for the required temperature points were determined and evaluated, respectively. It follows that, for room temperature, the global mechanical response was characterized by pseudoplastic, and the failure was dominated by the damage mechanisms including matrix cracking, interface debonding and threads fracture, especially, edge bending to breakage occurring for countersunk fastener. For 1100 °C, silicon carbide ceramic anti-oxidation coating was applied to prevent from oxidizing. Due to the relief of the thermal stresses, joints bearing capacity was enhanced by fiber/matrix interface performance improvement accompanying with a brittleness tendency of mechanical response, and the dominating failure mechanisms were carbon/carbon substrate oxidation caused by air entering through the cracks in SiC coating.

In this paper, the non-local theory solution of multiple cracks in a functionally graded piezoelectric medium (FGPM) under the permeable electric boundary condition have been investigated. Overcoming the mathematical difficulty, a one-dimensional non-local kernel is used instead of a two-dimensional one for the fracture problem to obtain stress and electric displacement fields near the crack tips. By using Fourier transform techniques, the present problem was reduced to the solution of dual integral equations, which unknown variable is jumps of displacement across the crack surface. The present solution exhibits no stress and electric displacement singularities at the crack tips when non-local was used to investigate the problem. The non-local solution yields a finite hoop stress at the crack tips, thus allows us to use the calculated maximum stress as a fracture criterion.

This paper investigates a functionally graded piezoelectric material (FGPM) containing two parallel cracks under harmonic anti-plane shear stress wave based on the non-local theory. The electric permeable boundary condition is considered. To overcome the mathematical difficulty, a one-dimensional non-local kernel is used instead of a two-dimensional one for the dynamic fracture problem to obtain the stress and the electric displacement fields near the crack tips. The problem is formulated through Fourier transform into two pairs of dual-integral equations, in which the unknown variables are jumps of displacements across the crack surfaces. Different from the classical solutions, that the present solution exhibits no stress and electric displacement singularities at the crack tips.

The low-velocity impact behavior of glass-fiber-reinforced aluminum alloy laminates (GLARE) is analyzed under single and multiple impacts of the same total energy. A new failure-judgment method is proposed by modifying previous failure criteria. This method is combined with a materials performance gradual degradation method and is employed by writing the LS-DYNA user subroutine for the impact simulation and testing of GLARE. The established finite-element model is proved reliable by comparing test results. Analyzing the simulated single and multiple impacts of the same total energy reveals that, GLARE sustains greatest internal damages under single impact. However, repeated impacts induce the largest deformation. If the impact frequency is maintained constant, the GLARE's damaged area widens as the initial impact energy increases. Keywords: Glass laminate aluminum reinforced epoxy, Multiple impact behavior, Finite element analysis, Impact test

It is significant to theoretically evaluate the mechanical properties of hybrid (bonded/bolted) GLARE joint, especially under the condition of multiple assembly uncertainties. This work develops a double-spring analytical model that predicts the deformation of hybrid joints under the quasi-static load to solve this critical problem in the fabrication process of hybrid joints. Besides the mechanical properties of bolt, the stiffness of adhesive layers is introduced in this novel model in which the factors such as geometrics, properties of adhesive layer, bolt-hole clearance, laminate properties, contact condition, relaxation of pre-torque and types of materials are discussed in detail. Meanwhile, a Monte Carlo simulation (MCS) and a variance-based method are used to calculate their global sensitivity indices that have the ability to quantify the relative importance of those assembly factors in load distribution between the bolt and adhesive layer, fracture displacement at the initial stage and other mechanical properties. It is found that bolt-hole clearance, geometrics of laminate and properties of adhesive layer are the top three sensitive factors, the qualities of which must be strictly controlled in the process of fabrication. This model is able to provide a powerful approach for the future design of hybrid joints to achieve higher reliability and load capacity.

The viscoelastic properties of bolted GLARE joints, which are rarely reported, also play a significant role in the mechanical performance, especially for long-term services. Glass fiber reinforced resin matrix composite layers of GLARE show temperature dependence and viscoelastic response in thermal environments. Thus, a novel viscoelastic model based on the spring-based method is proposed to predict the relaxation behavior of bolted GLARE joint in this work. The Maxwell–Wiechert model with n dashpots in parallel is introduced into this model, and the specific meaning of each parameter in the model is discussed in detail. This model is established to link the viscoelastic theory to the macroscale relaxation behavior of bolted GLARE joints, which matches well with the experimental results. It is observed that the long-term relaxation results of bolted GLARE joints under uniaxial tension deformation present obvious differences at different experimental temperatures illustrating that the relaxations of bolted GLARE joints have strong temperature dependence. Finally, the time-temperature superposition principle (TTSP) is incorporated into this model to predict the long-term relaxation effect on the bolted GLARE joints according to the relaxation experiments at different temperatures. This work provides a guideline for the design bolted GLARE joint used in the extreme environment for a long-term service.

Summary The dynamic behavior of two 3D rectangular permeable cracks in a transversely isotropic piezoelectric material is investigated under an incident harmonic stress wave by using the generalized Almansi's theorem and the Schmidt method. The problem is formulated through double Fourier transform into three pairs of dual integral equations with the displacement jumps across the crack surfaces as the unknown variables. To solve the dual integral equations, the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials. Finally, the relations among the dynamic stress field and the dynamic electric displacement filed near the crack edges are obtained, and the effects of the shape of the rectangular crack, the characteristics of the harmonic wave, and the distance between two rectangular cracks on the stress and the electric intensity factors in a piezoelectric composite material are analyzed. Copyright © 2015 John Wiley & Sons, Ltd.

A new method for fabricating glass fiber composite sandwich panel with pyramidal truss cores was developed based on the vacuum assisted resin transfer molding technology. The microstructure and organizations of fabricated sandwich panels were examined by the scanning electron microscope. The out-of-plane compressive tests of composite sandwich panels were performed throughout the temperature range from −60 °C to 125 °C. Then the effects of temperature on the compressive strength, compressive modulus and failure mechanism were investigated and analyzed. Our results indicated that cryogenic temperature resulted in the increasing of the compressive modulus and strength, while high temperature caused the degradation of the compressive modulus and strength. The effect of temperature on failure mode of composite sandwich panel was also observed. Analytical expressions were presented to predict the compressive modulus and strength of composite sandwich panels at different temperatures.

The non-local theory solution to a rectangular crack in a 3D infinite orthotropic elastic medium is investigated by using the generalized Almansi’s theorem and the Schmidt method in the present paper. The problem is formulated through the double Fourier transform into three pairs of dual integral equations, in which the unknown variables are the displacement jumps across the crack surfaces. For solving the dual integral equations, the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials. Numerical examples are provided to illustrate the effects of the geometric shape of the rectangular crack and the lattice parameter on the stress fields near the crack edges. Different from the classical solutions, the present solutions exhibit no stress singularity along the rectangular crack edges in an orthotropic elastic medium. Thus, this allows us to use the maximum stress as a fracture criterion.

In the present paper, the non-local theory solution for a 3D rectangular permeable crack in piezoelectric composite materials under a normal stress loading is investigated by means of the generalized Almansi’s theorem and the Schmidt method. The double Fourier transform are used to solve the mixed boundary value problem as three pairs of dual integral equations. To solve the dual integral equations, the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials. The stress field and the electric displacement field near the rectangular crack edges are obtained. Numerical results are provided to illustrate the effects of the geometric shape of rectangular crack and the lattice parameter on the stress field and the electric displacement field near the crack edges in piezoelectric composite materials. Different from the classical solutions, it is found that the present solutions exhibit no stress and electric displacement singularities near the crack edges in piezoelectric composite materials.

The dynamic stress intensity factors (DSIFs) of two 3D rectangular cracks in a transversely isotropic elastic material under an incident harmonic stress wave are investigated by generalized Almansi’s theorem and the Schmidt method in the present paper. Using 2D Fourier transform and defining the jumps of displacement components across the crack surface as the unknown functions, three pairs of dual integral equations are derived. To solve the dual integral equations, the jumps of the displacement components across the crack surfaces are expanded in a series of Jacobi polynomials. Numerical examples are provided to show the effects of the geometric shape of the rectangular crack, the characteristics of the harmonic wave and the distance between two rectangular cracks on the DSIFs of the transversely isotropic elastic material.

The non-local theory solution to a 3-D rectangular crack in an infinite transversely isotropic elastic material is proposed by means of the generalized Almansi’s theorem and the Schmidt method in the present paper. By using the Fourier transform and defining the jumps of displacement across the crack surface as the unknown variables, three pairs of dual integral equations are derived. To solve the dual integral equations, the jumps of displacement across the crack surface are expanded in a series of Jacobi polynomials. Numerical examples are provided to show the effects of the geometric shape of the rectangular crack and the lattice parameter of the material on the stress field near the crack edges. Unlike the classical solution, the present solution is no stress singularity along the rectangular crack edges, i.e. the stress field near the rectangular crack edges is finite. Therefore, we can use the maximum stress as a fracture criterion.

The solution of a plane rectangular crack in a 3-D infinite orthotropic elastic material is investigated by means of the generalized Almansi's theorem and the Schmidt method in the present paper. By using the 2-D Fourier transform and defining the jumps of displacement components across the crack surfaces as the unknown variables, three pairs of dual integral equations are derived. To solve the dual integral equations, the jumps of the displacement components across the crack surface are directly expanded in a series of Jacobi polynomials. Numerical examples are provided to show the effects of the geometric shape of the rectangular crack on the stress intensity factors in an orthotropic elastic material.

The non-local theory solution for a plane rectangular crack in a 3D infinite transversely isotropic elastic material is presented under an incident harmonic stress wave by using the generalized Almansi's theorem and the Schmidt method. In order to overcome the mathematical difficulties, a two-dimensional non-local kernel is used instead of a three-dimensional one for 3D dynamic problem to obtain the stress near the crack edges. With the help of the Fourier transform, the problem is formulated into three pairs of dual integral equations with the jumps of displacement across the crack surfaces as the unknown variables. To solve the dual integral equations, the jumps of displacement across the crack surface are directly expanded as a series of Jacobi polynomials. Numerical examples show how the stress is influenced by the geometric shape of the rectangular crack, the circular frequency of the incident waves and the lattice parameter of the material on the dynamic stress fields near the crack edges. Unlike the classical solutions, the present solution exhibits no stress singularity along the rectangular crack edges, i.e. the dynamic stress field near the rectangular crack edges is finite. Thus, this allows us to use the maximum stress as a fracture criterion.

This study deals with the modeling of the behavior of fiber-reinforced composite laminas under fatigue loading. On the basis of continuum damage mechanics, the non-linear cumulative damage model is developed and established on the mesoscale of the elementary layer. Three damage failures are taken into account: brittle behavior in the fiber direction, elastoplastic damage behavior under shear and transverse tension stress. Meanwhile, the couple effect of damage anisotropy between transverse and shear directions in-plane is considered. The failure criterion is presented and proved as an accurate approach to predict fatigue life of composite unidirectional lamina. The results of the fatigue damage model are obtained by a numerical simulation method, and the step value of cyclic iteration is discussed to acquire the predictive life range. Finally, the results of prediction agree well with the relative experimental data.

By using the generalized Almansi's theorem and the Schmidt method, the solution of two 3D rectangular cracks in an orthotropic elastic media is investigated. The problems are solved through 2D Fourier transform as three pairs of dual integral equations, in which the unknown variables are the displacement jumps across the crack surfaces. To solve the dual integral equations, the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials. The effects of the geometric shape of the rectangular crack and the distance between two rectangular cracks on the stress intensity factors (SIFs) in an orthotropic elastic media are concluded.

Negative Poisson's ratio is one of the distinctive property of Miura-ori which is widely used in the deployable structures. A wavy surface was presented by replacing the polylines with trigonometric curves to eliminate the creases in the Miura-ori, and the auxetic response was inherited from the Miura-ori. The negative Poisson's ratios of the wavy surface in two orthogonal directions were obtained by parametric numerical analysis. A model to predict the Poisson's ratio was developed based on the auxetic mechanism of the Miura-ori. Least square method was used to calculate the parameters in the prediction models. The results show that the auxeticity in wavy surface is more evident than the Miura-ori in some cases. The design concept provides a new approach to construct smooth surface by exploring the repositories of the origami and tessellations.

The solution to four three-dimensional rectangular cracks in magneto-electro-elastic material is proposed by using the generalized Almansi's theorem and the Schmidt method under limited-permeable boundary conditions. The problem is formulated through Fourier transform as three pairs of dual integral equations, in which the unknown variables are the displacement jumps across the crack surfaces. For solving the dual integral equations, the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials. Finally, the effects of the electric permittivity, the magnetic permeability of the air inside the crack, the geometric shape of the rectangular crack and the distance among four rectangular cracks on the stress intensity factors, the electric displacement intensity factors and the magnetic flux intensity factors in magneto-electro-elastic material are presented and the magneto-electro-elastic coupling effects are also discussed.

The Schmidt method is adopted to investigate the fracture problem of multiple parallel symmetric and permeable finite length mode-III cracks in a functionally graded piezoelectric/piezomagnetic material plane. This problem is formulated into dual integral equations, in which the unknown variables are the displacement jumps across the crack surfaces. In order to obtain the dual integral equations, the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials. The results show that the stress, the electric displacement, and the magnetic flux intensity factors of cracks depend on the crack length, the functionally graded parameter, and the distance among the multiple parallel cracks. The crack shielding effect is also obviously presented in a functionally graded piezoelectric/piezomagnetic material plane with multiple parallel symmetric mode-III cracks.

The deformation mechanism of unit cell wall is investigated by use of FEM, and the numerical simulation results show that the predominant deformations consist of shear deformation and compressive deformation. One new model based the shear deformation and the compressive deformation is put forward to investigate the longitudinal shear modulus of honeycomb cores. Owing to taking skin effect into consideration in our model, it is found that the equivalent shear modulus depends on not only the material properties and configuration parameters of cores, but also the material properties and configuration parameters of facesheets.

In this paper, in order to enhance the equivalent shear strength of the corrugated ribbon sandwich structures, one new optimal design concept is brought forward to design the corrugated ribbon sandwich structures subjected to biaxial shear loads. Based on the performance harmony concept, the equivalent shear properties have been investigated and given. Analytical results show that the equivalent shear properties of the corrugated ribbon sandwich structure depend on not only the lattice truss cores, but also the facesheets, the interface and the shear loads imposed on the facesheets.

Dynamic analysis is performed for a crack in a functionally graded materials layer for plane problem using shear stress. The material properties of the functionally graded materials layer vary randomly in the thickness direction, and the cracks are parallel to the materials faces. A pair of dynamic loadings applied on the elastic planes faces are treated as stationary stochastic processes of time. By dividing the functionally graded materials layer into several sub-layers, this problem is reduced to the analysis of laminated composites containing a crack, the material properties of each layer being random variables. A fundamental problem is constructed for the solution. Based on the use of Laplace and Fourier transforms, the boundary conditions are reduced to a set of singular integral equations, which can be solved by the Chebyshev polynomial expansions. The stress intensity factor history with its statistics is analytically derived. Numerical calculations are provided to show the effects of related parameters.

An attempt has been made here to evaluate the effect of thermal exposure on the mechanical behavior and failure mechanisms of carbon fiber composite sandwich panel with pyramidal truss core under axial compression. Analytical formulae for the collapse strength of composite sandwich panel after thermal exposure were derived. Axial compression tests of composite laminates and sandwich panels after thermal exposure were conducted at room temperature to assess the degradation caused by the thermal exposure. Experimental results showed that the failure of sandwich panel are not only temperature dependent, but are time dependent as well. The decrease in residual compressive strength is mainly attributed to the degradation of the matrix and the degradation of fiber–matrix interface, as well as the formation of cracks and pores when specimens are exposed to high temperature. The measured failure loads obtained in the experiments showed reasonable agreement with the analytical predictions.

The solution of a 3-D rectangular permeable crack in a piezoelectric/piezomagnetic composite material was investigated by using the generalized Almansi's theorem and the Schmidt method. The problem was formulated through Fourier transform into three pairs of dual integral equations, in which the unknown variables are the displacement jumps across the crack surfaces. To solve the dual integral equations, the displacement jumps across the crack surfaces were directly expanded as a series of Jacobi polynomials. Finally, the relations between the electric filed, the magnetic flux field and the stress field near the crack edges were obtained and the effects of the shape of the rectangular crack on the stress, the electric displacement and magnetic flux intensity factors in a piezoelectric/piezomagnetic composite material were analyzed.

In order to reduce the stress concentration and improve the failure strength of adhesively bonded joint structures, a smart adhesively bonded joint structure has been developed by integrating piezoelectric layers into the adherends. For better design guide, a combined theoretical model and multi-objective optimization approach is employed to optimize the smart joint in this study. Firstly, the first-order shear deformation theory is utilized to model and analyze the detailed peel and shear stresses distribution in the adhesive layer. Further, considering the characteristics of the stress distribution, the interface debonding failure criterion is used to set up the objective; optimization variables are considered as the stacking sequence, geometries and applied electric fields of the integrated piezoelectric layer. Thus, with the aid of the Mathematica software, the optimal smart adhesively bonded joint system can be determined. Finally, some detailed examples are analytically solved to show the considerab...