矩形橡胶复合材料层合板几何非线性分析

文中应用简单高阶剪切层合理论和大变形理论对各向异性纤维增强的矩形橡胶复合材料层合板进行了几何非线性分析。与线性一理论相比，本文作者进行的层合板大变形状态的几何非线性分析和所计算的层板应力分布，更准确性。     

冲击荷载作用下轴向运动层合板非线性动力学响应

研究轴向运动层合板在冲击荷载作用下的非线性动力学响应。基于单层材料本构关系及大变形理论,考虑几何非线性得到冲击荷载作用下的轴向运动层合板非线性动力学控制方程;通过Galerkin法对控制方程进行离散得到模态方程组,用Runge-Kutta法对模态方程组求解,得到冲击荷载作用下轴向运动层合板的动态响应。讨论了轴向速度、冲击波峰值和相位持续时间对轴向运动层合板动力学响应的影响。     

基于共旋三角形厚薄通用壳元的几何非线性分析

基于共旋列式方法发展了一种用于复合材料层合板结构几何非线性分析的简单高效的三结点三角形平板壳元。该壳元由具有面内转动自由度的广义协调膜元GT9与假设剪切应变场和假设单元转角场的广义协调厚薄通用板元TMT组合而成。为避免薄膜闭锁而采用单点积分计算与薄膜应变有关的项, 同时增加一个稳定化矩阵以消除单点积分导致的零能模式。基于层合板一阶剪切变形理论, 给出了考虑层合板具体铺层顺序的修正的横向剪切刚度, 使该壳元可用于中厚层合板结构的分析。由于共旋列式大转动小应变的假设, 共旋列式内核的几何线性的单元刚阵可仅计算一次而保存下来用于整个几何非线性求解的过程以提高计算效率。数值算例表明提出的壳元进行包括复合材料层合板结构的厚薄壳结构的几何非线性分析的精度高且效率高。     

气浮台-复合材料层合板多体系统的刚-柔耦合动力学研究

基于非线性应变和位移关系,忽略横向剪切变形,用绝对节点坐标法建立了大变形复合材料层合板几何非线性动力学模型。在此基础上,综合考虑层合板风阻和气浮台风阻的影响,建立了气浮台-复合材料层合板多体系统的刚-柔耦合动力学模型。为了真实反映物体之间的约束关系,将气浮台和层合板之间的约束表示为面与面的固定约束。在单轴气浮台动力学仿真实验平台上进行了带有角位移驱动的复合材料层合板大变形刚-柔耦合动力学实验,验证了理论模型的正确性。比较了传统的点固定约束与面固定约束的计算结果差异,阐明了面固定约束的合理性。此外,分析了层合板风阻和气浮台风阻对仿真结果的影响,说明了考虑层合板风阻的必要性。     

复合材料层合板非线性热屈曲分析

本文基于高阶变形理论和修正型Hahn-Tsai非线性本构模型,提出一种复合材料层合板非线性热屈曲分析方法.针对四边简支反对称角铺设复合材料层合板,导出了非线性热屈曲临界温度封闭解.数值结果表明:材料非线性能显著降低层合板临界温度.      

层合复合材料冲击损伤破坏过程研究(Ⅰ)——数值分析

基于连续损伤力学,对弹丸冲击复合材料多层板靶的变形-损伤过程给出了必要的基本方程,进行了三维有限元分析.将靶板处理为具有材料各向异性和结构非均匀性;冲击引起的微损伤是各向异性的,造成材料的非线性;冲击造成的局部大变形,构成几何非线性.宏观损伤(包括层内基体开裂、纤维断裂和层间分层)在有限元分析中用节点分裂法处理.钢质弹丸假设是线弹性的,不考虑它在冲击过程中的损伤.计算结果表明,采用本文中提出的方法,能较好地模拟复合材料层合板受弹丸冲击时的损伤、变形过程.     

复合材料层合板非线性屈曲分析

本文基于高阶变形理论和修正型Ｈａｈｎ－Ｔｓａｉ非线性本构模型，提出一种复合材料层合板非线性热屈曲分析方法。针对四边简支反对称角铺设复合材料层合板，导出了非线性热屈曲临界温度封闭解。数值结果表明：材料非线性能显著降低层合板临界温度。     

含分层损伤复合材料层合板非线性动力稳定性

采用Reddy 的板高阶剪切变形简化理论研究了含分层损伤复合材料层合板的非线性动力稳定性问题。建立了分层模型, 推导了考虑几何非线性和阻尼效应的Methieu 方程, 给出了该方程的解析解表达式; 研究了参数振动解的稳定性; 然后通过典型数例讨论了分层损伤对层合板固有频率、屈曲临界力以及动力稳定区域的影响; 研究了保守与非保守体系的外载荷的激励频率对层合板第一参数振动的振幅的影响, 以及线性、非线性阻尼对非保守体系的最大牵引深度的影响。由典型算例讨论可知, 随着复合材料层合板分层损伤的扩大, 其动力稳定性能逐渐减弱, 特别是损伤接近层合板的中面时, 分层损伤对其动力稳定性能的影响最大。      

基于灵敏度分析的复合材料层合板优化设计

工程结构中的复合材料层合板的几何参数往往具有随机性质.如何研究随机参数层合板的灵敏度,并对参数进行优化分析,这对正确估计结构设计的可靠性有着非常重要的意义.根据层合板的一阶剪切理论,采用样条有限元法,推导并建立了层合板的振动方程,刚度矩阵,质量矩阵,比例阻尼矩阵以及求解反对称层合板响应灵敏度的计算公式,在基于灵敏度分析的基础上,进行了复合材料层合板的基频分析和优化设计,并用网格法计算最佳铺层角.数值算例验证了算法的有效性.     

复合材料层合板多钉连接结构累积损伤过程可视化仿真模拟

建立了分析复合材料层合板多钉连接结构的三维有限元模型, 考虑了接触状态非线性和累积损伤过程非线性的影响, 运用ANSYS 中的APDL 编制程序实现了对复合材料层合板机械连接结构整个承载过程的可视化仿真模拟, 同时进行了T300/ Q Y9512 复合材料层合板多钉单剪拉伸试验。结果表明, 在一定几何尺寸下, 复合材料层合板多钉连接结构钉载分配的不均匀性在整个承载过程中并无明显改善。根据本文中提出的累积损伤模型对各孔位变形进行了计算, 计算结果与试验结果吻合较好。从累积损伤过程的仿真结果可以明显看出, 不同几何尺寸的多钉连接结构中各钉孔附近损伤的起始和发展过程具有明显的区别。优化设计结果表明, 不同钉孔处层合板厚度的改变对各钉钉载分配无明显影响, 但孔边法向和切向应力大小和分布均受到严重影响, 对整个多钉连接结构的损伤程度产生很大变化。      

Finite cover method for progressive failure with cohesive zone fracture in heterogeneous solids and structures

The finite cover method (FCM), which is a cover-based generalized finite element method, is extended for analyses of progressive failure processes involving cohesive zone fracture, starting from an interface debonding and evolving toward one of the constituents of heterogeneous solids and structures. Assuming that the constituents fail according to the maximum principal stress, we are able to represent the evolution of the resulting failure surfaces of discontinuity independent of mesh alignment owing to the distinctive features of the FCM. Also, interface elements with Lagrange multipliers are introduced to impose compatibility conditions on the material interface so that debonding is judged by the multipliers. Representative numerical examples demonstrate the capability of the proposed method in tracing the smooth transition of crack paths from interfacial to internal failure, and vice versa.     

Application of composites to impact energy absorption

The sleeve, conical simple composite elements and polymer foam filled composite conical element behaviour during failure are presented and discussed. The impact energy in these elements is absorbed in progressive fracture process. Possibilities of energy absorption panels – the great structures made from simple elements in a certain military and civilian field are demonstrated.     

复合材料随机渐进失效分析与声发射监测

结合随机渐进失效分析方法和声发射监测对复合材料单向拉伸试件进行损伤分析。结果表明: 随机渐进失效方法能很好地反映复合材料失效的随机性和渐进性特征。受载初期, 复合材料失效的随机性特征明显, 在整个试件内均有失效产生。随着载荷的增加, 损伤不断累积, "随机临界核"形成, 复合材料很快失效, 且一旦有失效产生, 纤维断裂数的增加与声发射事件数的累积具有很好的一致性。比较基体开裂和界面脱粘对复合材料拉伸性能的影响: 界面脱粘比基体开裂更容易导致复合材料拉伸性能的下降, 当不存在基体开裂和界面脱粘时, 纤维断裂呈现"集簇"特征, 复合材料断裂的脆性特征较为明显。      

Combination of biological mechanisms for a concept study of a fracture-tolerant bio-inspired ceramic composite material

The biological materials nacre and wood are renowned for their impressive combination of toughness and strength. The key mechanisms of these highly complex structures are crack deflection at weak interfaces, crack bridging, functional gradients and reinforcing elements. These principles were applied to a more fracture-tolerant model material which combined porous stiff ceramic layers, manufactured by freeze casting, infiltrated and bonded by a polymer phase reinforced with fabric layers. In the hybrid composites, crack deflection occurred at the ceramic–fabric interface and the intact fabric layers served as crack-bridging elements. Fabric-reinforced epoxy layers stabilized the fracture behaviour and delayed catastrophic failure of the material. The influence of the different components was analysed by varying the ceramic, fabric and interface properties. More ductile fabrics lead to larger strain to failure and more crack bridging but reduced the composite strength and stiffness after initial cracking. Higher elastic mismatch between the components improved crack deflection and bridging but resulted in deterred load transfer and a lower strength. The stiffness and strength of the ceramic layers influenced the elastic properties of the laminar composite and the initial crack resistance. Flaw tolerance was increased with polymer infiltration. We show with our hybrid ceramic–fabric composite as a bio-inspired concept study how fracture toughness, work of fracture and tolerance for cracking can be tailored when the contributing factors, i.e. the ceramic, the fabric and their interface, are modified.     

Dynamic behavior of delaminated plates considering progressive failure process

The paper is to study on dynamic response behavior of the delaminated composite plates considering progressive failure process. A formula of element stiffness and mass matrices for the composite laminates is deduced by using the first-order shear deformation theory combined with the selecting numerical integration scheme. A damping model is constituted by a generalized orthogonal damping model on basis of Adams' strain energy method. A virtual interface linear spring element is also employing for avoiding the overlap and penetration phenomenon between the upper and lower sublaminates at the delamination region. The failure analysis method for the delaminated plates under dynamic loading is established by a modified Newmark direct integral method in conjunction with Tsai's failure criterion and corresponding stiffness degradation scheme. By some numerical examples, the effects of frequency of dynamic load, delamination length and location, and reduction of structure stiffness during the progressive failure process upon dynamic behavior of the delaminated composite plates are discussed. The method and conclusions would be useful for composite structures designers.     

Combined analytical and numerical solution of 2D interface corner configurations between dissimilar piezoelectric materials

The failure assessment of smart composite structures requires efficient analytical and numerical techniques in order to tackle electrical and mechanical field concentrations. The present work is directed to the analysis of interface corner and crack configurations which occur in smart composite materials. It delivers a new technique to solve the corresponding piezoelectric boundary value problems. The purpose of the given paper is to describe exactly the asymptotic behaviour at piezoelectric interface corner configurations using the eigenfunction expansions on the one hand, and in the linking of these expansions to regular finite elements on the other. Specific singular eigenfunctions for homogeneous and interface crack configurations are discussed. For the considered cases, the classical crack modes (Mode I and Mode II) and a new Electric Mode are identified. The coupling of the full eigenfunction expansions to the finite elements surrounding the tip region is based on the principle of virtual work applied to the orthogonalised eigenfunctions. Finally, one gets an asymptotic stiffness matrix which does not depend on the distance to the tip. The coefficients of the eigenfunctions can be obtained efficiently from the generalised displacements of the global solution by means of the orthogonalised eigenfunctions. The technique allows to numerically bypass possible singular oscillatory terms in the weak sense, although they actually exist in the strong solution. The given approach is proven and verified in numerical test examples. Standard finite element methods encounter difficulties to give correct solutions at piezoelectric interface crack tips.     

强噪声激励下C/SiC复合材料壁板动态响应与失效分析

高超声速飞行器热防护系统和热结构包含多种形式的复合材料薄壁结构,对巡航或再入飞行中的强噪声环境十分敏感和易发生失效破坏,严重威胁着飞行器结构的完整性和可靠性。为考核复合材料薄壁结构的耐噪声性能,基于高声强行波管噪声试验系统,选取厚度为1~3 mm的C/SiC复合材料平板作为试验件,试验件四周采用螺栓进行固定安装。通过开展156~165 dB噪声激励动态响应试验,获得了不同量级噪声作用下的动态响应变化规律。针对厚度为1 mm的试验件开展了失效试验,在168 dB噪声作用下,试验件发生了迅速破坏,采用红外无损检测设备对失效后的C/SiC复合材料平板进行检测,采用SEM对断面形貌进行观察,揭示出强噪声激励下的失效模式,可为高温复合材料结构优化设计和耐噪声失效性能评估提供技术支撑。      

Carbon/Carbon – an inverse composite structure

Carbon/carbon composites are a type of material, which combines the refractory properties of carbon with the high strength and stiffness of carbon fibres. Although one could not expect a reinforcement by the combination of a carbon matrix with carbon fibres the fibre properties can be used. Additionally the material shows a pseudoplastic fracture behaviour in spite of its ceramic nature. Explanations for this inverse behaviour in comparison to other composite structures will be presented including mechanical viewpoints, interactions at the interface between fibre and matrix, their influence to the fracture characteristics and micromechanical behaviour as well as the interactions between modulus and microstructure. Furtheron examples for some industrial applications are described.     

Influence of Stress Singularities on Scaling of Fracture of Metal-Composite Hybrid Structures

It has been recently shown that the nominal structural strength of metal-composite structures depends on the structure size, and such dependence is strongly influenced by the stress singularities. Nevertheless, previous studies only focused on structures that exhibit very strong stress singularities, which are close to the crack-like stress singularity. In the actual engineering designs, due to the mismatch of material properties and complex structural geometries, many metalcomposite structures may contain stress singularities that are much weaker than the crack-like stress singularity. This paper presents a numerical study on the size dependence of scaling of fracture of metal-composite hybrid structures for a wide range of stress singularities. The numerical examples include a series of metalcomposite hybrid beams with a V-notch under three-point bending with different notch angles, which lead to various magnitudes of stress singularities. By assuming that the bimaterial interface is weaker than both metal and composite, we use a mixed-mode cohesive element model to simulate the fracture behavior of these hybrid beams. It is shown that the resulting size effect curves strongly depend on the magnitude of stress singularities. The simulation results agree well with a recently developed energetic-statistical scaling model.     

复合材料厚壁圆筒的损伤问题

基于连续介质损伤力学理论,引入表征材料内部微细缺陷的损伤变量,导出了三维复合材料厚壁圆筒的损伤模型,预测该结构内各处的损伤过程;针对不同损伤模式,推导出包含不同结合力和损伤变量的损伤扩展准则;利用三维有限元分析软件模拟计算出结构损伤破坏的全过程,分析了复合材料圆筒的损伤模式与破坏机理,以及能量变化关系。