Micro-punching process based on spallation delamination induced by laser driven-flyer

In this article, we proposed a micro-punching process for microstructure on films based on laser driven-flyer induced spallation delamination phenomenon at the interface between a film and its substrate. To validate such a micro-punching process, a series of experiments were carried out for fabrication of microstructures on Au films coated on K9 glass substrates and polyimide substrate. Results show that through such a punching process, the microstructure on Au films can be fabricated efficiently and the spatial resolution is able to reach micron level. Moreover, we found that this method was more suitable for films coated on soft substrates rather than that coated on brittle substrates due to the additional destruction of the brittle substrate. This micro-punching process has a wide range of potential application in microfluidic devices, biodevices and other MEMS devices.     

Nonlinear progressive damage model for composite laminates used for low-velocity impact

In order to effectively describe the progressively intralaminar and interlam- inar damage for composite laminates, a three dimensional progressive damage model for composite laminates to be used for low-velocity impact is presented. Being applied to three-dimensional （3D） solid elements and cohesive elements, the nonlinear damage model can be used to analyze the dynamic performance of composite structure and its failure be- havior. For the intralaminar damage, as a function of the energy release rate, the damage model in an exponential function can describe progressive development of the damage. For the interlaminar damage, the damage evolution is described by the framework of the continuum mechanics through cohesive elements. Coding the user subroutine VUMAT of the finite element software ABAQUS/Explicit, the model is applied to an example, i.e., carbon fiber reinforced epoxy composite laminates under low-velocity impact. It is shown that the prediction of damage and deformation agrees well with the experimental results.     

Modeling vibration behavior of delaminated composite laminates using meshfree method in Hamilton system

Free vibration analysis of composite laminates with delaminations is performed based on a three-dimensional semi-analytical model established by introducing the local radial point interpolation method (LRPIM) into a Hamilton system. The governing equation is derived with a transfer matrix technique and a spring layer model based on a local weak-form equivalent to the modified Hellinger-Reissner variational principle. Main superiority of the present model is that the scale of the governing equation involves only the so-called state variables at the top and bottom surfaces, and is insensitive to the thickness and the layer number of the composite laminates. Several numerical examples for analyzing the vibration frequencies and mode shapes of delaminated composite beams and plates are given to validate the model. The results are in good agreement with the pre-existing results.     

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.     

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．     

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.     

冲击作用下复合材料叠层板层间开裂演化模型

采用双线性特性破坏模型研究了复合材料叠层板层间开裂裂纹的演化, 通过引入弹性/剪切模量的损伤参数, 推导出损伤参数与应变之间的微分方程, 并得到裂纹耗散功率与损伤参数变化率之间的关系. 计算不同初始冲击速度下复合材料叠层板某界面上应变、应变率响应以及损伤参数的演化, 即可得到该界面发生层间开裂的情形及其对剪切模量的影响.通过检查界面各点处的损伤参数是否发生改变, 预测了冲击完成之后复合材料叠层板第1, 2层之间发生层间开裂区域的大小与位置; 该预测结果与实验数据及其他破坏准则计算结果基本相符. 计算结果表明, 在冲击过程中当界面上任意点处的剪应力超过剪切强度后, 该点附近的剪切模量开始发生衰减, 衰减大小随铁球初始冲击速度的增大而增大, 并从靠近冲击中心的位置逐渐向周围递减. 在四边简支边界条件下, 复合材料叠层板的层间开裂区域同样最先出现在界面中靠近冲击点的位置, 区域面积随初始冲击速度的增大不断扩大. 当初始冲击速度足够高时, 第1, 2层界面的两条对称轴上开始出现多个独立的开裂区域.      

基于粘结界面模型的三维裂纹扩展研究

根据界面断裂的特点,将粘结界面模型应用于有限元,采用非线性显式动力学算法,编写粘结-体积单元计算程序.其中体积和粘结单元分别采用四面体和三棱柱单元;粘结单元本构关系选择双线性内聚力-位移曲线,避免了界面完全断裂后发生穿透;以界面相对位移的形式定义线性损伤准则;以Benzeggagh-Kenane模式的扩展准则确定界面失效位移;以Turon模式的初始损伤准则确定界面启裂位移.该程序能够实现混合加载模式下材料界面断裂问题的三维数值模拟.用所编写的程序(CVFEM)分别对Ⅰ,Ⅱ,Ⅲ型裂纹扩展问题进行数值模拟,并且与Abaqus6.7计算结果进行对比.     

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。     

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。