复合材料分层断裂判据及扩展准则研究

针对现有层间开裂判据及扩展准则未考虑断裂模式耦合性的现状,本文提出了基于模式混合度的复合材料分层断裂判据及扩展准则。依此模型计算了蒙皮/凸缘复合材料加筋层合板结构的分层扩展行为。计算结果表明,所提出的开裂判据及扩展准则能够较好的预测蒙皮/凸缘复合材料加筋层合板结构的断裂力学行为,所得结果对确定含损伤复合材料加筋层合板结...     

复合材料结构的内部分层及其扩展

本文用接触观点分析了复合材料壳体结构的内部分层问题，建立了求解摩擦接触问题的有限元迭代格式，并采用释放率判据分析分层裂纹的扩展。分层裂纹前缘采用轴对称奇异单元，并了结构的大变形特性。计算表明，层间裂纹呈Ⅱ型扩展趋势。本文同时还分析了层间摩擦系数的影响，并指出分层将导致壳体结构承载能力显著下降。     

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。     

低成本基板倒装焊底充胶分层裂缝扩展研究

采用MIL-STD-883C热循环疲劳加载标准，通过电学检测方法测定了B型和D型两种倒装焊封装焊点寿命。并使用无损声学C-SAM高频超声显微镜技术观测这两种倒装焊封装在焊点有无断裂两种情况时芯片／底充胶界面的分层和扩展，计算得到分层裂缝扩展速率。在有限元模拟中采用粘塑性和时间相关模量描述了SnPb焊点和底充胶的力学行为。使用裂缝尖端附近小矩形路径J积分方法作为断裂力学参量得到不同情况下的界面分层裂缝顶端附近的能量释放率。然后由实验裂缝扩展速率和有限元模拟给出的能量释放率得到可作为倒装焊封装可靠性设计依据的Par—is半经验方程。     

含多个分层复合材料层合板后屈曲性态研究

基于Mindlin假定下的大变形板／壳理论，采用参考面单元和虚拟杆单元相结合的非线性有限元方法，建立了分析含多个穿透分层损伤层合板后屈曲行为的有限元计算模型，并给出了考虑接触后非线性屈曲方程的迭代算法，从而研究考虑层间接触效应的多分层层合板的后屈曲性态。文中着重讨论了分层的深度、数目和尺寸对含多分层合板后屈曲性态的影响。大量数值分析结果证明了该模型的有效性，并且得到了一些对层合板结构设计和对含分层损伤层合板评估有益的结论。     

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。     

含分层损伤的变角度纤维层合板后屈曲力学行为研究

变角度(Variable angle tow,简称VAT)纤维复合材料层合板的纤维方向能够连续变化.相较于传统的直线纤维层合板,此类层合板通过刚度变化,整体的屈曲性能可以得到很大的提升.本文利用ABAQUS自带的粘结单元(Cohesive Element)对预制圆形分层的变角度纤维复合材料层合板进行了后屈曲力学行为研究,得出载荷位移曲线,以及分层裂纹萌生和扩展的情况.然后本文分析了预制分层尺寸对板的刚度、前后屈曲阶段和裂纹萌生及扩展的影响.最后通过变角度纤维层合板和直线纤维层合板的后屈曲力学行为进行对比,深入探索了变角度复合材料层合板在抵抗分层裂纹萌生和扩展方面的优势.     

含脱层层合板的能量释放率各型分量分析

本文是文献［１］的继续。文献［１］利用可动边界变分问题，导出了层合板内部脱层前缘各点处的总能量释放的表达式。在此基础上，本文对文献［１］的分析模型作了进一步的完善，导出了层板理论分析下的能量释放率各型分量的表达式，并对圆形脱层进行了计算分析。     

考虑面内破坏过程的含分层损伤复合材料加筋层合板的动力响应

基于复合材料层合板一阶剪切理论，推导了复合材料层合板单元的刚度阵和质量阵列式；同时采用了Adams应交能法与Rayleigh阻尼模型相结合的方法，构造了相应的阻尼阵列式；为了防止在低阶模态中分层处出现的上、下子板不合理的嵌入现象，建立了含分层损伤复合材料加筋层合板动力分析的分层分析模型和虚拟界面联接模型。在上述模型和理论基础上，采用了Tsai提出的刚度退化准则和动力响应分析的精细积分法，对含分层损伤复合材料加筋层合板结构进行了动力响应和破坏分析。通过算例，分别讨论了外载频率、分层位置，以及破坏过程的刚度退化对含损伤复合材料加筋层合板动力响应特征的影响，得到了一些具有理论和工程价值的结论。     

低速冲击下纤维/金属层合板抗分层性能研究

本文采用内聚力模型，对纤维/金属层合板(FMLs)在低速冲击载荷作用下抗分层性能进行研究。内聚力模型对裂纹的模拟具有它独特的优势：一是该模型不需要预先假设初始缺陷；二是在计算过程中随着裂纹的扩展，该方法不需要重新对结构进行网格划分。借助该模型，本文对低速冲击载荷作用下，纤维层合板(FRP)分层进行了模拟，并验证了该模型计算的有效性。在此基础上，本文研究了低速冲击载荷作用下，不同金属含量的纤维/金属层合板抗分层性能，并与纤维层合板进行了比较。最后从能量的角度讨论了金属含量与铺层结构对FMLs低速冲击性能的影响。     

NUMERICAL ANALYSIS OF DELAMINATION GROWTH FORSTIFFENED 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)     

具有分层损伤的不同加筋形式复合材料层合板的后屈曲性态研究

基于板的一阶剪切理论和V on-K arm an大挠度理论,分别推导了复合材料层合板和层合梁的几何非线性有限元列式,提出了含嵌入分层的复合材料加筋层合板在受压缩载荷作用下的后屈曲有限元分析方法,对在板厚方向具有不同分层位置的加筋板结构进行了有限元数值分析,研究了不同的加筋方式及筋的分布对具有分层损伤的复合材料加筋层合板的后屈曲性态的影响,所得结果对确定在压缩载荷作用下含损伤复合材料加筋层合板的剩余承载能力具有参考价值。     

复杂载荷下复合材料对称层合板的椭圆形分层屈曲

应用Ｒａｙｌｅｉｇｈ－Ｒｉｔｚ法对含有单个椭圆形分层的复合材料对称层板在压剪载荷联合作用下的脱层屈曲问题进行了分析计算。给出相应于不同的椭圆长短半轴之比ａ／ｂ值下及不同椭回主轴的偏角时，脱层屈曲的临界应变值。此计算考虑了层板的拉伸剪切藕合刚度影响及子层本身弯曲－扭转耦合刚度，和拉伸－弯曲耦合刚度的影响，给出有工程参考价值的计算结果。     

含有分层损伤的复合材料加筋层合板的屈曲性态研究

基于Ｍｉｎｄｉｎ假定推导了考虑剪切的复合材料加筋层板的有限元列式,并在此基础上计算出筋间基板含嵌入分层以及筋与基板连接处含穿透分层的加筋层合板在受压缩载荷情况下的屈曲模式和临界力。本文所给出的有限元方法及结论对从事复合材料结构设计的工程人员具有参考价值。     

Dynamic stability analysis of composite plates including delaminations using a higher order theory and transformation matrix approach

A refined higher order shear deformation theory is used to investigate the dynamic instability associated with composite plates with delamination that are subject to dynamic compressive loads. Both transverse shear and rotary inertia effects are taken into account. The theory is capable of modeling the independent displacement field above and below the delamination. All stress free boundary conditions at free surfaces as well as delamination interfaces are satisfied by this theory. The procedure is implemented using the finite element method. Delamination is modeled through the multi-point constraint approach using the transformation matrix technique. For validation purposes, the natural frequencies and the critical buckling loads are computed and compared with three-dimensional NASTRAN results and available experimental data. The effect of delamination on the critical buckling load and the first two instability regions is investigated for various loading conditions and plate thickness. As expected, the natural frequencies and the critical buckling load of the plates with delaminations decrease with increase in delamination length. Increase in delamination length also causes instability regions to be shifted to lower parametric resonance frequencies. The effect of edge delamination on the static and dynamic stability as well as of delamination growth is investigated.     

Buckling-driven delamination in layered spherical shells

An analysis of buckling-driven delamination of a layer in a spherical, layered shell has been carried out. The effects of the substrate having a double curvature compared to previous studies of delamination on cylindrical substrates turn out to be non-trivial in the sense that additional to the effect of the shape of the substrate, a new non-dimensional geometrical parameter enters the conditions for steady-state delamination. It is shown that this additional geometrical parameter in most cases of practical relevance has insignificant influence on the fracture mechanical parameters involved for the problem. The consequence is that solutions need to be mapped as a function of one rather than two dimensionless parameters. Furthermore, the shape of the substrate has profound influence especially on initiation of delamination growth.     

受弯脱层层板后屈曲有限元分析

脱层是复合材料层板结构中主要的缺陷形式之一。当脱层层板受到压力载荷的作用会造成脱层的局部屈曲和扩展,从而使结构的强度和刚度大为降低。含脱层层板的弯曲问题包含了脱层的压缩问题,却比压缩问题更加复杂。本文对含穿透脱层层板在纯弯载荷作用下的后屈曲问题进行了基于一阶剪切层板理论的几何非线性有限元分析,运用虚裂纹闭合技术求解了纯弯载荷作用下的脱层尖端的能量释放率各型分量,并用脱层扩展判据求解了脱层起始扩展载荷。     

Buckling of delaminated bi-layer beam-columns

An improved analytical model is presented to analyze the delamination buckling of a bi-layer beam-column with a through-the-width delamination. Both the transverse shear deformation and local delamination tip deformations are taken into consideration, and two delaminated sub-layers as well as two substrates in the intact (un-delaminated) regions are modeled as individual Timoshenko beams. A deformable interface is introduced to establish the continuity condition between the two substrates in the intact regions. Consequently, a flexible joint is formed at the delamination tip, and it is different from the conventional rigid joint given in most of studies in the literature, in which the local delamination tip deformations are completely ignored. In contrast to the local delamination buckling in our previous study (Qiao et al., 2010), the present model accounts for the global deformations of the intact region in the delaminated composite beam-column, thus capable of capturing the buckling mode shape transitions from the global, to global–local coexistent, and to local buckling for asymmetric delamination as the interface delamination increases. Good agreement of the present analytical solutions with the full 2-D elastic finite element analysis demonstrates the local deformation effects around the delamination tip and verifies the accuracy of the present model. Parametric studies are conducted to investigate the effects of loading eccentricity, delaminated sub-layer thickness ratio, and interface compliance on the critical buckling load for the delaminated composite beam-column. Transitions of buckling modes from the global to local delamination buckling are also disclosed as the thickness of one sub-layer reduces from the thick sub-layer to a thin film. The developed delamination buckling solution facilitates the design analysis and optimization of laminated composite structures, and it can be used with confidence in buckling analysis of delaminated composite structures.