Structural response of all-composite pyramidal truss core sandwich columns in end compression

With the equivalent mechanical properties of composite materials, analytical formulae of critical load for an all-composite sandwich column with pyramidal truss core are derived. Four failure modes are considered: macro Euler buckling, macro shear buckling, face-sheet wrinkling and face-sheet crushing. Failure mechanism maps are constructed with the four competing failure modes, and the relationship between the failure mechanism maps and material mechanical properties is discussed. Selected experiments validate the analytical predictions, and reasonable agreement is obtained. Macro shear buckling is the main failure mode for the sandwich column specimens, which is attributed to the low stiffness of core. The final failure loads is related to the strength of the nodes between face-sheets and truss core, so the node strength is the key of improving the failure load. Given by numerical simulations, the failure loads and failure modes agree well with analytical predictions.     

碳纤维蜂窝夹层结构动特性分析

对碳纤维蜂窝夹层结构的动力学问题进行了深入分析。将碳纤维网格表面等效为正交异性薄板,铝蜂窝夹芯按蜂窝实际受力情况和尺寸大小等效为三维正交异性体,并考虑到为了防止失稳破坏而进行的蜂窝局部加密、碳纤维表板加厚及结构局部加强。所建模型经复杂结构有限元方法分析,结果和试验相吻合,表明等效模型是合理的,方法是正确的。     

Ballistic resistance of hybrid-cored sandwich plates: Numerical and experimental assessment

The impact responses and ballistic resistance of sandwich plates having three different types of hybrid cores are investigated. The hybrid cores include metallic pyramidal lattice trusses, metallic pyramidal lattice trusses with ceramic prism insertions, and metallic pyramidal lattice trusses with ceramic prism insertions and void-filling epoxy resin. Three-dimensional (3D) finite element (FE) simulations are carried out for each sandwich type impacted by a hemispherical projectile. Upon validating the FE simulation results with experimental measurements, the ballistic limit velocity, energy absorption and failure mechanisms for each type of the sandwich as well as the influence of key material, structural and topological parameters are investigated systematically. Sandwich plates having metallic pyramidal lattice core with ceramic insertions and epoxy resin filling void spaces are found to outperform the other two sandwich types. It is also demonstrated that the back face-sheet plays a more significant role than the front face-sheet in resisting ballistic impacts.     

A new analysis of nonlinear free vibration behavior of bi-functionally graded sandwich plates using the p-version of the finite element method

Geometrically nonlinear vibration of bi-functionally graded material (FGM) sandwich plates has been carried out by the p-version of the finite element method (FEM). The bi-FGM sandwich plate is made up of two face-sheet layers of two different FGM and one layer of homogeneous core. The nonlinear equations of motion of bi-FGM sandwich plates are establish using the harmonic balance method and solved iteratively by the linearized updated mode method. The effects of amplitude vibration, mechanical properties, geometrical parameters, thickness ratio of bi-FGM layers, and volume fraction exponent on the nonlinear vibration behavior of bi-FGM sandwich plates are plotted and investigated.     

Fundamental frequency and design of the CFCF composite sandwich plate

The design efficiency of sandwich panels is often associated with the value of fundamental frequency. This paper investigates the free vibrations of rectangular sandwich plates having two adjacent edges fully clamped and the remaining two edges free (CFCF). The vibration analysis is performed by applying Hamilton’s principle in conjunction with the first-order shear deformation theory. The analytical solution determining the fundamental frequency of the plate is obtained using the generalised Galerkin method and verified by comparison with the results of finite element modal analysis. The approach developed in the paper and equations obtained are applied to the design of sandwich plates having composite facings and orthotropic core. Design charts representing the effects of the thickness of the facings and core on the mass of composite sandwich panel for a given value of the fundamental frequency are obtained.     

四边固支铝基蜂窝夹层板弯曲自由振动分析

基于经典叠层板理论, 将铝基蜂窝芯层等效为一正交异性层, 等效弹性参数由修正后的Gibson公式得出, 对四边固支薄蜂窝夹层板弯曲振动的固有频率进行了理论推导, 研究了蜂窝夹层板厚度、 芯层板厚度对蜂窝夹层板固有频率的影响。同时利用有限元软件计算了相应参数下的固有频率。计算结果表明, 经典叠层板理论可以较准确的计算四边固支蜂窝夹层板的固有频率。      

High Velocity Impact Response of Composite Lattice Core Sandwich Structures

In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.     

Vibration and Buckling of Truss Core Sandwich Plates on An Elastic Foundation Subjected to Biaxial In-plane Loads

Truss-core sandwich plates are thin-walled structures comprising a truss core and two thin flat sheets. Since no direct analytical solution for the dynamic response of such structures exists, the complex three dimensional (3D) systems are idealized as equivalent 2D homogeneous continuous plates. The macroscopic effective bending and transverse shear stiffness are derived. Two representative core topologies are considered: pyramidal truss core and tetrahedral truss core. The first order shear deformation theory is used to study the flexural vibration of a simply supported sandwich plate. The buckling of the truss core plate on an elastic foundation subjected to biaxial in-plane compressive loads is also investigated. It's found that the lowest buckling loads and modes are dependent on the foundation stiffness as well as bending and transverse shear stiffness of the plate. The geometric parameters of a sandwich plate are optimized to obtain strongest buckling resistance per unit weight. To verify the accuracy of analytical solutions, 3D finite element (FE) models are established, and good agreement is observed between them. It's obvious that the homogenization procedure leads to great savings in computational effort.     

Thermo-mechanical load interactions in foam cored axi-symmetric sandwich circular plates – High-order and FE models

This work presents analytical and finite element analysis (FEA) results of the thermo-mechanical non-linear response of an axi-symmetric circular sandwich plates with a compliant foam core. The study investigates the load–thermal interaction response of a sandwich panel where the properties of the core are temperature dependent and degrade as the temperatures are raised. It presents briefly the governing equations for a sandwich plate based on the principles of the high-order sandwich panel theory (HSAPT) which incorporates the effects of the vertical flexibility of the core material as well as the effects of temperature independent/dependent mechanical properties of the foam core. The effects of the thermal degradation of core material on the thermo-mechanical non-linear response of a simply supported circular sandwich plate are studied through the analytical and FE models. The difficulties involved in non-linear geometrical FE modeling of sandwich panels with a compliant “soft” core with temperature-dependent mechanical properties are discussed. The HSAPT model predictions are compared very well with FE result. An important conclusion of the study is that the interaction between mechanical loads, temperature induced deformations, and degradation of the mechanical properties due to elevated temperatures, may seriously affect the structural integrity of foam cored sandwich plates.     

Axisymmetric parametric resonance of polar orthotropic sandwich annular plates

Parametric resonance of polar orthotropic sandwich annular plates with a viscoelastic core layer subjected to a periodic uniform radial stress is studied by the finite element method. The axisymmetric discrete layer annular element and Hamilton's principle are employed to derive the finite element equations of motion for a sandwich plate including the transverse shear effect. The viscoelastic material in the core layer is assumed to be incompressible, and the extensional and shear moduli are described by complex quantities. The regions of dynamic instability are determined by Bolotin's method. The effects of various parameters on the dynamic instability regions are investigated.     

Mechanical behaviors of carbon fiber composite sandwich columns with three dimensional honeycomb cores under in-plane compression

Mechanical properties and failure modes of carbon fiber composite egg and pyramidal honeycombs cores under in plane compression were studied in the present paper. An interlocking method was developed for both kinds of three-dimensional honeycombs. Euler or core shear macro-buckling, face wrinkling, face inter-cell buckling, core member crushing and face sheet crushing were considered and theoretical relationships for predicting the failure load associated with each mode were presented. Failure mechanism maps were constructed to predict the failure of these composite sandwich panels subjected to in-plane compression. The response of the sandwich panels under axial compression was measured up to failure. The measured peak loads obtained in the experiments showed a good agreement with the analytical predictions. The finite element method was used to investigate the Euler buckling of sandwich beams made with two different honeycomb cores and the comparisons between two kinds of honeycomb cores were conducted.     

波纹夹层板线性弯曲分析的无网格伽辽金法

提出了一种求解波纹夹层板结构线性弯曲问题的无网格模型。将波纹夹层板看成两侧平板和中间波纹板核的复合结构,用正交各向异性板等效近似波纹板核。先基于一阶剪切变形理论,由无网格伽辽金法建立各板的刚度方程,再通过位移协调条件将各板刚度方程叠加,以得到整体刚度方程。采用全转换法处理位移边界。算例表明：该文所提出的无网格模型分析波...     

Active constrained layer damping of geometrically nonlinear vibrations of smart laminated composite sandwich plates using 1–3 piezoelectric composites

This paper deals with the analysis of active constrained layer damping (ACLD) of geometrically nonlinear vibrations of sandwich plate with orthotropic laminated composite faces separated by a flexible core. The constraining layer of the ACLD treatment is composed of the vertically/obliquely reinforced 1?C3 piezoelectric composites. The Golla?CHughes?CMcTavish method has been implemented to model the constrained viscoelastic layer of the ACLD treatment in time domain. The first-order shear deformation theory and the Von Kármán type nonlinear strain displacement relations are used for analyzing this coupled electro-elastic problem. A three dimensional finite element model of smart laminated composite sandwich plate integrated with ACLD patches has been developed to investigate the performance of these patches for controlling the geometrically nonlinear vibrations of the plates. The numerical results indicate that the ACLD patches significantly improve the damping characteristics of the sandwich plates with laminated cross-ply and angle-ply facings for suppressing their geometrically nonlinear vibrations. Particular emphasis has been placed on investigating the effect of the variation of piezoelectric fiber orientation angle on the performance of the ACLD treatment.     

Mechanical Response of All-composite Pyramidal Lattice Truss Core Sandwich Structures

The mechanical performance of an all-composite pyramidal lattice truss core sandwich structure was investigated both theoretically and experimentally.Sandwich structures were fabricated with a hot compression molding method using carbon fiber reinforced composite T700/3234.The out-of-plane compression and shear tests were conducted.Experimental results showed that the all-composite pyramidal lattice truss core sandwich structures were more weight efficient than other metallic lattice truss core sandwich structures.Failure modes revealed that node rupture dominated the mechanical behavior of sandwich structures.     

Free vibration analysis of composite sandwich plates with different truss cores

The free vibration of composite truss core sandwich plates is investigated. The natural frequencies of the sandwich plate are calculated by using the classic laminated plate theory, the first-order shear deformation theory, Reddy's third-order shear deformation theory, and a Zig-Zag theory. The differences between the natural frequencies, obtained from the four theories, are compared. The influences of structural parameters on the natural frequencies and the ratios of natural frequency to equivalent density of the sandwich plates with pyramidal core, tetrahedral core, and 3D-Kagome core are studied with the aid of the Zig-Zag theory.     

基于响应面全局优化技术的蜂窝板材料性能参数修正

蜂窝夹层板结构广泛应用于航空航天行业中,建立准确的蜂窝夹芯板有限元模型是分析和优化航天器微振动的必要前提。基于蜂窝芯的力学等效参数模型,建立了蜂窝板的动力学有限元模型。使用正交数值实验设计筛选出对蜂窝板动力学性能影响最大的蜂窝芯等效材料参数,并利用基于响应面模型自适应采样技术的全局优化方法快速地完成了蜂窝芯关键材料参数的优化修正。修正后的蜂窝板有限元模型前六阶模态频率与实验结果的平均误差小于1%。     

碳纤维增强聚合物复合材料方形蜂窝夹层结构水下爆炸动态响应数值模拟

基于ABAQUS有限元仿真软件,建立了不同夹芯相对密度的碳纤维增强聚合物（Carbon Fiber Reinforced Polymer,CFRP）复合材料方形蜂窝夹层结构在水中爆炸冲击波载荷作用下的仿真模型,分析了结构的变形过程、夹芯的压缩特性及结构的失效及破坏情况。数值模拟结果表明,CFRP复合材料蜂窝夹芯压缩量在前面板速度降至与后面板相同时达到最大; CFRP复合材料蜂窝夹芯的最大压缩量随着初始压力的增大呈先缓慢增大后快速增大的趋势,其增大趋势在夹芯接近完全压缩时又趋于缓慢; CFRP复合材料夹层结构失效随夹芯相对密度和初始压力的变化呈现不同的模式,且其防护性能优于等重的层合结构。研究结果可以为复合材料夹层结构在水中冲击波载荷防护中的应用提供参考。      

Smart damping of geometrically nonlinear vibrations of functionally graded sandwich plates using 1–3 piezoelectric composites

Geometrically nonlinear dynamic analysis of smart functionally graded (FG) sandwich plates integrated with the patches of active constrained layer damping (ACLD) treatment has been carried out by the finite element method. The constraining layer of the ACLD treatment is considered to be made of vertically/obliquely reinforced 1–3 piezoelectric composite while the constrained layer is made of a viscoelastic material, which is modeled using the Golla–Hughes–McTavish method in the time domain. The top and bottom faces of the substrate sandwich plate are composed of the FG isotropic material whose mechanical properties are assumed to vary according to a standard power-law distribution in terms of the volume fractions of the constituents while the core layer may be either a soft honeycomb material or a hard ceramic material. Several FG sandwich plates with different core configurations are studied to evaluate the numerical results. The numerical results indicate that the ACLD patches significantly improve the damping characteristics of the FG sandwich plates for suppressing their geometrically nonlinear vibrations. Effects of metal- or ceramic-rich top and bottom surfaces, the variation of power-law index on the control authority of the ACLD patches have been investigated. Emphasis has also been placed on investigating the effect of the variation of piezoelectric fiber orientation angle on the performance of the ACLD patches.     

Free vibration analysis of composite sandwich plates based on Reddy's higher-order theory

Two new C⁰ assumed strain finite element formulations of Reddy's higher-order theory are used to determine the natural frequencies of isotropic, orthotropic, and layered anisotropic composite and sandwich plates. The material properties typical of glass fibre polyester resins for the skin and HEREX C70 PVC (polyvinyl chloride) foam materials for the core are used to show the parametric effects of plate aspect ratio, length-to-thickness ratio, degree of orthotropy, number of layers and lamination scheme on the natural frequencies. A consistent mass matrix is adopted in the present formulation. The results presented in this investigation could be useful for a better understanding of the behaviour of sandwich laminates under free vibration conditions and potentially beneficial for designers of sandwich structures.     

Analytic homogenization for torsion of orthotropic sandwich plates: Application to corrugated cardboard

This paper presents an analytic homogenization model for the torsion of orthotropic sandwich plates and its application to the torsion modelling of corrugated cardboards. It is very difficult to determine the torsion rigidity of these kinds of 3D structures even numerically because of the boundary condition effects. Inspired by the gridwork homogenization model of Timoshenko, we decompose the plate torsion into two beam torsions. The plate torsion curvature is separated into two beam torsion rates and the beam torsion rigidities in these two directions are introduced to describe the torsion behaviour of the orthotropic plates. We demonstrate that the plate torsion rigidity is equal to a quarter of the sum of the two beam torsion rigidities, which are easily calculated analytically or numerically. This torsion homogenization model can be used not only for corrugated cardboard packaging structures, but also for naval and aeronautic composite structures.