Computational Engineering of Mixed-mode, In-plane Crack Propagation in Laminated Fiber Reinforced Composites

Integrated Computational Engineering (ICE) is a valuable and cost effective resource for ensuring structural integrity and damage tolerance of future aerospace vehicles that are made with laminated fiber reinforced composite laminates. Towards that end, the variational multiscale cohesive method (VMCM) reported by the authors in previous AIAA SDM conferences, 23–26 is extended further to address problems of mixed mode in-plane crack propagation in fiber reinforced laminates. A set of experimental results obtained using a single edge notch eccentric three point bend test is used for validating the VMCM predictions. Further the applicability of VMCM is demonstrated through simulation of mixed mode in-plane crack propagation for different specimen geometries and different loading conditions. I. Introduction A large number of tests, which can contribute to a substantial portion of the total design and manufacturing cost of an aerospace vehicle, are required to ensure the structural integrity and damage tolerance of vehicle structures. These costs can be reduced by developing validated and physics based computational models that can exploit the power of advanced simulation techniques and the increasing computational power of digital computers. High fidelity computational models can provide valuable information regarding the performance of a structure upto and including failure, provided the modeling is based on correct physics, and is validated using laboratory tests that are designed to be discriminatory. The field of integrated computational engineering (ICE), that encompasses this activity, and also includes, in the case of composites, the modeling of the manufacturing process 14 is a rapidly growing and indispensable field which will continue to provide new insights into the performance of advanced composite structures. The finite element method (FEM), is a key enabler of ICE. It has become the mainstay of problems involving any of the broad phenomena of material deformation - elasticity, plasticity and damage. However, its utility for problems of crack propagation has met with mixed success. The distinguishing characteristic of crack problems, in general, is the formation and propagation of sharp boundaries, which are not part of the original boundary value problem. This is not an obstacle, if the resulting crack path is known a priori, and the mesh is ensured to have elemental surfaces align along possible crack surfaces; but often in practice, neither conditions are feasible. For all but trivial crack propagation problems, the crack path is not known beforehand and has to be determined as part of the solution process, and in structural level problems adaptive mesh generation/realignment is prohibitively costly. The traditional Galerkin FEM implementation is not suitable for problems that encounter crack propagation and also involve strain localization, as it leads to mesh subjective schemes, and the related limitations have been well documented in the context of spurious mesh related length scales 1,4,9 and requirements of mesh alignment relative to the localization