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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.

分层是复合材料中一种常见的破坏模式。由于刚度变化和厚度方向缺乏配筋，在低载荷下已经发生了分层，并可能导致结构整体倒塌。例如，界面元素被用来模拟薄层之间的树脂层，为充分模拟裂纹的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。粘聚区模型的缺点是需要正确地再现裂纹尖端前面的应力分布。这意味着需要非常精细的网格，这是由于分层过程区域中的高应力梯度以及与之相关的一个单元中的部分粘结。因此，沿分层部分的单元尺寸由界面单元定义，而不是通常由相邻的壳单元定义。本研究的目的是通过不同的数值方法来提高不连续界面单元的稳健性。在研究应用中，总结了以往工作的成果，并对后续工作进行了展望。在到目前为止所做的研究中，界面单元已经通过胡-瓦伊祖的多杂交公式进行了改进，该公式具有双线性和特殊开发的应力和应变的形函数，从而可以将单元尺寸减少50%。研究了描述单元总应力分布的高阶积分格式和适用的积分格式。最后，将双线性单元运动学增强为二次形函数和意外形函数，以更好地逼近脱层过程区域内的位移。在随后的研究中，Hellinger-Reissner(HR)将开发一个额外的混合IF公式，并将其应用到单元算法中。混合HR公式提供了应力的自由形状函数，可以很好地逼近裂纹前沿的应力分布，并可以提高鲁棒性。在增强运动学领域的进一步研究将软化刚度并避免载荷-位移曲线中的振荡。除了每个节点的当前节点位移自由度外，在界面公式中还将实现附加的转动自由度和附加的虚拟单元自由度。之后，额外的自由度将被集成到开发的混合界面中。最后，着眼于稳健性的提高，将内聚律放大。在目前的工作状态下，指数内聚力定律是基于相对位移的。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力定律，将与DLR和RWTH Aachen合作审查。