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Entwicklung robuster Interface-Elemente für die Simulation von Delaminations-Prozessen in CFK-Laminaten

开发用于模拟 CFRP 层压板分层过程的稳健界面元件

基本信息

批准号：
181611900
负责人：
Professor Dr.-Ing. Werner Wagner
金额：
--
依托单位：
Institut für Baustatik (IfB)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2010
资助国家：
德国
起止时间：
2009-12-31 至 2013-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/181611900?language=en
关键词：
Entwicklung robuster Interface Elemente die

项目摘要

Delamination is a commonly observed failure mode in composite materials. Due to stiffness changes and the lack of reinforcement in thickness direction, delamination already occurs by low loads and can yield total structural collapse. For instance, interface elements are used to simulate thin resin layers between lamina, providing the opportunity for an adequate simulation of crack initiation and propagation. Typically, linear and exponential cohesive laws are used to simulate the softening behavior. The drawback of the cohesive zone model is the requirement of a correct reproduction of the stress distribution ahead of the crack tip. This means that very fine meshes, due to high stress gradients in the delamination process zone and the associated partial bonding in one element, are needed. Thus, the element size along the delamination part is defined by the interface elements and not as usual by the adjacent shell elements. The purpose of this research is to improve the robustness of discontinuous interface elements with different numerical techniques. In the application for research the results of the past work is summarized and later on providing prospective works are presented. In the research done so far, the interface element has been improved by a multi hybrid formulation from Hu-Washizu with bilinear and special developed shape functions for stresses and strains whereby the element size could be reduced by 50 percent. High order and adapted integrations schemes were investigated to describe the total stress distribution in one element. Finally the bilinear element kinematic has been enhanced to quadratic and serendipity shape functions to give a better approximation of the displacements within the delamination process zone. In the subsequent research an additional mixed IF-Formulation by Hellinger-Reissner (HR) will be developed and implemented into the element algorithm. Providing free shape functions for stresses, the mixed HR-Formulation offers a good approximation of the stress distribution ahead of the crack front and can advance the robustness. Further investigations in the field of enhanced kinematics shall soften the stiffness and avoid oscillation in the load-displacement curve. Beside the current nodal displacement degrees of freedom at each node, additive rotational degrees of freedom and additive virtual element degrees of freedom are to be implemented in the interface formulation. Afterwards, the additional degrees of freedom will be integrated in the developed hybrid interface. Finally, focusing on the improvement of robustness the cohesive law will be amplified. In the current state of work the exponential cohesive law is based on relative displacements. The contact formulation and the mixed mode problem, including a cohesive law depending on the interlaminar fracture toughness, are to be reviewed in collaboration with the DLR and the RWTH Aachen.

分层是复合材料中常见的失效模式。由于刚度变化和厚度方向缺乏加固，低载荷就已经发生分层，并可能导致结构整体倒塌。例如，界面单元用于模拟层板之间的薄树脂层，为充分模拟裂纹萌生和扩展提供了机会。通常，使用线性和指数内聚定律来模拟软化行为。内聚区模型的缺点是需要正确再现裂纹尖端之前的应力分布。这意味着，由于分层过程区域中的高应力梯度以及一个元件中的相关部分粘合，需要非常细的网格。因此，沿分层部分的单元尺寸由界面单元限定，而不是像通常那样由相邻壳单元限定。本研究的目的是通过不同的数值技术提高不连续界面单元的鲁棒性。在研究申请中，总结了过去的工作成果，然后提出了未来的工作。在迄今为止所做的研究中，界面单元已通过 Hu-Washizu 的多重混合公式进行了改进，该公式具有双线性和专门开发的应力和应变形函数，从而单元尺寸可以减小 50%。研究了高阶和适应性积分方案来描述一个单元中的总应力分布。最后，双线性单元运动学已增强为二次和意外形状函数，以更好地近似分层过程区域内的位移。在后续研究中，Hellinger-Reissner (HR) 将开发额外的混合 IF 公式并将其实施到元素算法中。混合 HR 公式为应力提供自由形状函数，可以很好地近似裂纹前沿之前的应力分布，并可以提高鲁棒性。增强运动学领域的进一步研究将软化刚度并避免载荷-位移曲线的振荡。除了每个节点当前的节点位移自由度之外，还将在界面公式中实现加性旋转自由度和加性虚拟单元自由度。之后，额外的自由度将被集成到开发的混合接口中。最后，着眼于鲁棒性的提高，内聚律将被放大。在当前的工作状态下，指数内聚定律基于相对位移。接触公式和混合模式问题，包括取决于层间断裂韧性的内聚定律，将与 DLR 和亚琛工业大学合作进行审查。