含分层损伤复合材料层合板分层扩展研究

采用基于Ｍｉｎｄｌｉｎ－阶剪切理论的四节点板单元,分析了含椭圆分层合板分层扩展行为。利用虚裂纹闭合技术计算分层前缘处的总能量释放率,并采用总能量释放率准则作为扩展准则,结合自适应网格移动技术,并考虑了分层前缘闭合接角效应,对 合材料层合板的分层扩展行为进行了模拟分析。结果表明,初始分层形状对其扩展有方式有限大影响。     

微裂纹损伤对复合材料层板分层的影响

本文将双标量损伤模型推广,考虑层内及层间微裂纹损伤相互作用,建立了层合复合材料的多标量损伤本构关系,并将该本构关系应用于含贯穿分层层板的后屈曲分析,采用准三维有限元法研究了分层尖端场与极限损伤区演变的特点,结果表明：损伤导致裂尖区层间应力奇异性消失,引起层间应力重新分布;损伤区的发展方向取决于分层上下表面层的铺设角,能量释放率不能反映损伤和分层扩展特征,因而有必要建立基于损伤演化的分层扩展准则。     

应变软化对复合材料分层尖端场的影响

提出了适用于纤维增强复合材料应变软化分析的多标量连续损伤模型,并将其应用于含分层裂纹的复合材料层板的后屈曲损伤破坏有限元分析,研究了软化参数对损伤场和应力场的影响。计算结果表明:(1)应变软化使分层尖端的应力奇异性降低或消失。(2)应变软化参数影响极限损伤区的大小及其扩展速度,应力跌落使极限损伤加剧。(3)由于损伤的影响,裂尖的能量释放率受软化参数的影响出现波动,已难反映分层特征,可以根据损伤程度来判断分层的扩展。(4)分层上下表面的纤维方向影响损伤形式及其扩展方向。     

PTFE/Al含能复合材料的压缩行为研究

金属/氟聚合物含能复合材料是一类新型的高级含能材料.研究了室温下Al含量和应变率对PTFE/Al含能复合材料压缩性能和反应性能的影响,所加载的应变率为6×10-3s-1～8×103s-1.材料压缩性能的应变率效应明显:与静态加载相比,动态加载下材料模量和强度明显提高,但应变降低.材料的损伤过程主要包括塑性变形、开裂和反应3部分.随着Al含量的增加,材料准静态和动态压缩强度均呈先升后降的趋势,在Al含量为35%时达到最高值102.6 MPa和154 MPa;引发反应所需加载的应变率增加,但对应的应力值差别不明显,基本在165 MPa左右,材料引发后反应完全性降低.     

层合圆柱壳体表层局部分层屈曲及其扩展

应用能量法研究了对称铺层的闭合圆柱形层合壳体的表层局部分层屈曲问题;表层分层形式有三角形、椭圆和双纽线;分析了母层壳、子层壳的几何参数、物理参数同分层屈曲临界应变值之间的关系;给出了子层分层为椭圆的分层扩展的可能发生方向.     

Z-pins增强C/SiC复合材料层间I型断裂韧性

提出手工预缝纫方法将3K丝束的T300碳纤维引入预成型体,经过多次反复化学气相渗透工艺,在预成型体和缝线处同时渗透SiC基体,制备Z-pins增强平纹编织C/SiC陶瓷基复合材料。通过双悬臂梁对称弯曲试验测定了层间I型应变能释放率,分析了材料的裂纹扩展行为和Z-pins增强机理,建立了层间I型裂纹扩展预测模型。结果表明：Z-pins植入平纹编织C/SiC陶瓷基复合材料层压板能提高层间I型断裂韧性。Z-pins增强平纹编织C/SiC陶瓷基复合材料层压板I型层间增强机理主要是Z-pins桥连和Z-pins拔出。层间裂纹扩展预测模型的预测结果与试验结果吻合较好。     

含分层损伤复合材料层合板剩余压缩强度研究

准确预测含分层损伤层合板的剩余压缩强度,对复合材料具有十分重要 意义。本文基于层合板一阶剪切理论,建立了一种考虑复合材料多种损伤的含分层层合板刚度退化模型,通过数值算例分析了分层屈曲临界载荷与材料强度极限的关系以及刚度退化对含分层层合板前后屈曲行为的影响。     

纤维／基体界面裂纹扩展断裂能

本文通过研究纤维／基体界面裂纹断裂能,分析了几种界面脱粘断裂功的理论表达式;着重研究了单纤维拔出试验中界面残余压应力及界面摩擦对界面裂纹能量释放率的重要性．     

黏弹性界面断裂分析的增量“加料”有限元法

提出了一种适用于黏弹性界面裂纹问题的增量“加料” 有限元方法. 利用弹性界面裂纹尖端位移场的解答,通过对应原理和拉普拉斯逆变换近似方法,得到了黏弹性界面裂纹的尖端位移场. 用该位移场构造了黏弹性界面裂纹“加料” 单元和过渡单元位移模式,推导了增量“加料” 有限元方程,求解有限元方程可获得应力强度因子和应变能释放率等断裂参量. 建立了典型黏弹性界面裂纹平面问题“加料” 有限元模型,计算结果表明,对于弹性/黏弹性界面裂纹和黏弹性/黏弹性界面裂纹,该方法都能得到相当精确地断裂参量,并能很好地反映蠕变和松弛特性,可推广应用于黏弹性界面断裂问题的计算分析.      

含分层损伤复合材料层合板的压缩强度研究

给出了基于一阶剪切变形理论的含分层损伤层合板有限元分析模型,将含分层损伤层合板在压缩载荷作用下的强度破坏分析和屈曲破坏分析统一起来,先区分其破坏形式,然后再进行具体破坏分析.在屈曲特性分析中考虑了铺层强度破坏引起的刚度折减的影响.数值结果表明, 该文给出的方法和结论对含分层损伤复合材料层合板的设计更具参考价值.     

Effects of voids on postbuckling delamination growth in unidirectional composites

This work examines the effects of manufacturing induced voids on the postbuckling behavior of delaminated unidirectional composites. In the finite element model developed, a through-width delamination is introduced close to one surface of a flat panel, and a void is placed in the delamination plane ahead of each delamination front. The panel is subjected to compression in the fiber direction. The postbuckling delamination growth is studied by calculating the strain energy release rate (SERR) using the virtual crack closure technique. Local stress analyses of the region near the delamination front are also performed to further investigate the void effects. It is found that although the presence of void does not significantly alter the postbuckling transverse displacement of the delaminated panel, the induced stress perturbation by the void affects the SERR. The Mode II SERR as well as the total SERR increase depending on the size of the void and its distance from the delamination front. Since the Mode I SERR shows non-monotonic behavior with the applied load, the effects of voids are studied on its maximum value.     

改进的虚裂纹闭合技术及其在复合材料脱层分析中的应用

提出一种改进的虚裂纹闭合技术（ＶＣＣＴ）对轮胎带束（一咱复合材料结构）不同脱层长度下的应变能释放率进行了计算。将强度裂纹闭合的位移作了一种可变约束施加在变形后的裂纹尖端,约束反力作了裂纹尖端力计算,应变能释放率由裂纹尖端力和约束位移的乘积得到。该方法的优点是简便易行,在物理理解上直观,实施起来方便。本文就用该技术对带束脱层进行了断裂力学分析,给出数值结果,并对带束的脱层寿命进行了评价。     

Fracture mechanics analysis of delamination in a thermoelectric pn-junction sandwiched by an insulating layer

A fracture mechanics analysis is conducted for a delamination problem of a multilayered thermoelectric material (TEM) that consists of an n-type layer and a p-type layer sandwiched by an insulating layer. A time-varying energy release rate is presented when the n-type layer delaminates from the insulating layer. Effects of the temperature difference across the system and the applied electric current on the energy release rate are identified. The influence of the thickness ratio of the insulating layer to the thermoelectric (TE) layer is also examined. Based on the energy release rate criterion, the critical temperature difference for delamination propagation is obtained. Some useful conclusions are given.     

Numerical analysis of delamination growth for stiffened composite laminated plates

A study of postbuckling and delamination propagation behavior in delaminated stiffened composite plates was presented. A methodology was proposed for simulating the multi-failure responses, such as initial and postbuckling, delamination onset and propagation, etc. A finite element analysis was conducted on the basis of the Mindlin first order shear effect theory and the von-K6rm~n nonlinear deformation assumption. The total energy release rate used as the criteria of delamination growth was estimated with virtual crack closure technique (VCCT). A self-adaptive grid moving technology was adopted to model the delamination growth process. Moreover, the contact effect along delamination front was also considered during the numerical simulation process. By some numerical examples, the influence of distribution and location of stiffener, configuration and size of the delamination, boundary condition and contact effect upon the delamination growth behavior of the stiffened composite plates were investigated. The method and numerical conclusion provided should be of great value to engineers dealing with composite structures.     

Study on failure process of delaminated stiffened composite plates under compression

Failure behavior of the delaminated stiffened composite plates under compression is studied by the finite element method, based on a Global-Local variational model. A virtual crack closure technique and a self-adaptive grid moving scheme are proposed to predict the delamination growth process. The contact effect along the delamination front is considered. The numerical results show that the influences of the distribution and location of the stiffeners, the configuration and size of the delamination, the boundary condition and the contact upon the failure behavior of the plates are significant. The project supported by the National Natural Science Foundation of China (59975014)     

Validation of the Rayleigh–Ritz method for the postbuckling analysis of rectangular plates with application to delamination growth

Postbuckling solutions of laminated rectangular plates are obtained by the Rayleigh–Ritz method using von Karman’s nonlinear strain displacement relations and high-order polynomial expansions of the displacements. The potential energy function and the nonlinear algebraic equations governing the undetermined coefficients are obtained by Mathematica. Reasonably accurate solutions for the membrane forces, the bending and twisting moments and the pointwise energy-release rates generally require more undeterminated coefficients. Such refined postbuckling solutions show significant non-uniformity of the in-plane forces and strains and certain boundary effects characterized by concentration of the curvatures and the bending moment.     

模拟长纤维增强树脂层合板冲击损伤的数值方法

建立了一套模拟树脂层合板低速冲击下损伤过程的方法.该方法采用Mindlin板模型并考虑板的大变形,使用以前提出的一种修正的Newmark时间积分方案进行层板的动态分析,全面考虑了复合材料的脱层破坏、基体开裂和纤维断裂等破坏形式及其相互作用.还建立了一种适合于 Mindlin板的计算应变能释放率的方法;构造了一种连续的罚函数来动态加人弹簧约束以考虑脱层间的接触效应;证明了球板之间的冲击过程是刚性系统,应使用A（α）稳定的数值方法求解;实现了模拟过程中的自适应分析.使用所开发的软件NBHULI完成了长纤维增强碳/环氧复合材料层板在低速冲击下损伤过程的模拟,取得了一些重要的结果.     

The effects of shear on delamination in layered materials

The effect of transverse shear on delamination in layered, isotropic, linear-elastic materials has been determined. In contrast to the effects of an axial load or a bending moment on the energy-release rate for delamination, the effects of shear depend on the details of the deformation in the crack-tip region. It therefore does not appear to be possible to deduce rigorous expressions for the shear component of the energy-release rate based on steady-state energy arguments or on any type of modified beam theory. The expressions for the shear component of the energy-release rate presented in this work have been obtained using finite-element approaches. By combining these results with earlier expressions for the bending-moment and axial-force components of the energy-release rates, the framework for analyzing delamination in this type of geometry has been extended to the completely general case of any arbitrary loading. The relationship between the effects of shear and other fracture phenomena such as crack-tip rotations, elastic foundations and cohesive zones are discussed in the final sections of this paper.