NCF--CAE: Simulation of Non-Crimp Fabrics based on Computational isogeometric shell elements, Analytical averaging and Experimental analysis

非卷曲织物(NCFs)是一种用于直(非卷曲)纤维复合材料的纺织增强结构。由于其经济的制造，NCFs在汽车和航空工业中已经变得非常突出。纤维与纤维层之间的复杂相互作用给NCFs的计算建模带来了巨大的挑战。就我们所知，目前还没有一个计算框架能够精确和高效地再现NCFs的复杂材料行为，该项目的主要目标是从精度和效率两个方面改进NCFs悬垂过程的计算技术。为此，提出了一种基于等几何无旋转壳体形式和不同本构模型的NCFS计算框架，并对该框架的精度进行了研究。所提出的材料模型考虑了NCFs所有重要的变形机制，如拉伸、弯曲和各向异性面内剪切响应、层内和层间滑移以及纤维体积分数的变化。到目前为止，所有这些特征还没有在一个框架中被捕捉到。所提出的计算壳公式将允许高效和稳健地模拟纺织品的行为，包括结构不稳定性的存在，如起皱和面内剪切不稳定性。为了建立计算框架，对NCFs的变形机理进行了详细的实验分析。获得的数据为材料模型的开发及其验证提供了基础。通过这项实验研究，验证和补充了NCFs性质对变形行为的影响，该项目的结果是一个经过验证的新的计算框架，与传统的有限元方法模拟NCFs悬垂相比，该框架具有更高的效率、精度和鲁棒性。此外，还全面了解了NCFs的所有变形机理。为了传播研究成果，新的有限元程序将在项目结束时在线发布，供免费下载。

Non-crimp fabrics (NCFs) are textile reinforcement structures for composites with straight (non-crimped) fibers. Due to their economical fabrication, NCFs have become prominent in the automotive and aeronautic industry. The complex interactions between the fibers and plies lead to significant challenges in the computational modeling of NCFs. To the best of our knowledge, there is no computational framework able to reproduce the complex material behavior of NCFs in a precise and numerically efficient way.The main objective of the project is to advance the computational technology for the simulation of draping processes of NCFs in terms of both accuracy and efficiency. To this end, a computational framework for NCFs based on an isogeometric rotation-free shell formulation and different constitutive models is developed and the accuracy of this framework is investigated. The proposed material models take into account all important deformation mechanisms of NCFs, such as stretching, bending and anisotropic in-plane shear response, intra-ply and inter-ply sliding, as well as the change in fiber volume fraction. So far, all these features have not been captured in a single framework.The proposed computational shell formulation will allow the efficient and robust simulation of textile behavior including the presence of structural instabilities such as wrinkling and in-plane shear instability. For the development of the computational framework, the deformation mechanisms of NCFs are studied by detailed experimental analysis. The acquired data provide a basis for development of material models and their validation. By this experimental study, the influences of the NCFs properties on the deformation behavior are identified and complemented.The result of the project is a validated new computational framework that has a better efficiency, accuracy, and robustness in comparison to classical finite element method approaches for the draping simulation of NCFs. Additionally, all deformation mechanisms of NCFs are comprehensively understood. In order to disseminate the research results, the new finite element routines will be posted online at the end of the project for free downloading.