两类有脱层损伤层合圆柱壳的半解析法研究

为了研究层合壳脱层,本文首先建立了柱坐标系下Hamilton 正则方程的8 节点等参元列式;然后分别采用了"先分后合" 模型和"弱粘接" 模型对开口壳的脱层损伤进行了模拟;通过利用层间的力学关系建立了整个壳的求解方程;最后分别从粘接完好和脱层两类情况对开口壳进行研究,并计算脱层前缘裂纹扩展的能量释放率. 数值实例的分析结果表明环向脱层受外载荷影响大于轴向脱层外载荷影响,脱层深度对两类脱层模型影响较大.     

Compound Bifurcations in the Buckling of a Delaminated Composite Strut

An analysis of the buckling and post-buckling of a delaminated composite strut is presented using a simple 4 degree of freedom nonlinear Rayleigh–Ritz formulation. Bifurcation analysis indicates that instability occurs in general at an asymmetric point of bifurcation. Depending on the depth of delamination both thin-film and overall buckling can occur in the post-buckling range, the transition being seen at a point of secondary bifurcation. For certain combinations of parameters this becomes a stellar bifurcation, associated with a double eigenvalue, where there are three possible subsequent routes for the post-buckling. The method used is fast and reliable and can be readily extended to modelling a composite with several layers.     

On the Delamination of a Viscoelastic Composite Circular Plate

Delamination of a symmetric circular plate made of viscoelastic composite is studied. It is assumed that the plate has a penny-shaped crack whose edges have a minor axisymmetric imperfection. The lateral surface of the plate is clamped and is compressed by uniform radial normal forces through a rigid body. The studies are made using the exact geometrically nonlinear equations of the theory of viscoelasticity. The delamination criterion is assumed unrestrained growth of the initial imperfection. The Laplace transform and FEM are employed. In particular cases, the results are compared with those for elastic composites     

On Debonding and Delamination Effects in Adhesively Bonded Cracks on Fractal Type

The present paper studies the influence of adhesives on the behaviour of cracks in deformable bodies. Especially the delamination and debonding effects are studied. The adhesive material is assumed to introduce nonmonotone possibly multivalued laws which can be described via nonconvex superpotentials. Cracks of fractal geometry are considered. Approximating the fractal crack by a sequence of smooth surfaces or curves and combining this procedure with an algorithm based on the optimization of the potential and of the complementary energy for each approximation of the fractal crack, we get the solution of the problem. Numerical examples, using singular elements for the consideration of the crack singularity, illustrate the theory. This revised version was published online in August 2006 with corrections to the Cover Date.     

纤维金属板层分层尺寸的测量方法研究

导出了纤维金属胶接层板双面裂纹搭接剪切（ＤＣＬＳ）试样分层尺寸和柔度之间的线性关系式，提出了ＤＣＬＳ试样分层尺寸的柔度测量法，并与用光测法测得的分层尺寸进行了对比。结果表明，用柔度法测定ＤＣＬＳ试样的分层尺寸，不仅测量结果准确，而且简单易行，避免了光测法的诸多麻烦和精度低的缺点。     

复合材料Ⅰ型层间断裂韧性GIC和初始裂纹长度

从经典梁理论和弹性基础上的正交各向异性梁理论出发，分析了梁的弯曲剪切效应和弹性基础对用双悬臂梁试件测得的复合材料层合板Ⅰ型层间断裂韧性Ｇ＿（ＩＣ）的影响，发现当试件的初始裂纹长度较短时，剪切效应和弹性基础对Ｇ＿（ＩＣ）的影响是显著的，建议将初始裂纹长度取５０毫米。实验结果表明，初始裂纹长度由２０毫米增加到５０毫米时，测得的Ｇ＿（ＩＣ）值的离散系数降低２０％～４０％，数据趋于稳定，分散性减小。     

基于累积失效法的含损伤格栅加筋板非线性屈曲状态分析

分别采用基于Mindlin一阶剪切理论八节点层合板单元和三节点层合梁单元来模拟蒙皮和肋骨,用累积失效法研究了在压缩载荷作用下蒙皮内含分层损伤复合材料正交格栅加筋板的非线性屈曲性态,分析中考虑了加载过程中蒙皮和肋骨纤维断裂、基体损伤和纤维-基体剪切失效造成的刚度退化,并采用了非线性接触单元模型处理蒙皮分层上下子板间的接触效应。通过典型算例,讨论了蒙皮铺设方式、蒙皮分层的面积和深度、肋骨与蒙皮的刚度比,累积失效行为等因素对格栅加筋板非线性屈曲性态的影响。     

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.     

Postbuckling behaviors of open section composite struts with edge delamination using a layerwise theory

We investigate the mechanical stability of L-section and T-section composite struts with single edge delamination. We propose a solution procedure based on a layerwise theory and the first order shear deformation theory by taking into consideration of the von Karman geometrical nonlinearity. We derive the nonlinear equilibrium equations according to the minimum total potential energy principle, and solve them using Rayleigh–Ritz method and Newton–Raphson method. In modeling the delaminated L-section and T-section struts, we divide the structures into regions, and exert continuity conditions between different regions. The proposed model is capable of analyzing both local buckling of the base laminate and sublaminate as well as the global buckling of the whole structure. We present numerical results to provide an insight into effects of size of delamination on buckling mode and post-buckling behaviors of the struts. We perform the three-dimensional finite element analysis using the ABAQUS commercial software. The results show a very good agreement with those obtained by the analytical method. The results indicate that the presence of delaminations not only reduces the load-carrying capacity of open section struts remarkably, but also plays a pivotal role in the critical buckling load and buckling mode shape of the struts.     

含脱层损伤复合材料层合梁的冲击动力屈曲

针对含初始缺陷和脱层损伤的复合材料层合梁的轴向冲击动力屈曲问题进行了分析。基于Hamilton原理导出了考虑初始缺陷、轴向和横向惯性、横向剪切变形以及转动惯性影响时含脱层损伤复合材料梁的非线性动力屈曲控制方程;基于B-R准则,采用有限差分方法求解了受轴向冲击载荷作用下含脱层损伤复合材料梁的动力屈曲问题;讨论了冲击速度、初始几何缺陷、铺层角度以及脱层长度等因素对复合材料层合梁动力屈曲的影响。