Use of unsymmetric finite element method in impact analysis of composite laminates

The use of metric trial functions to represent the real stress field in what is called the unsymmetric finite element formulation proposed recently is an effective way to improve predictions from distorted finite elements. This approach works surprisingly well because the use of parametric functions for the test functions satisfies the continuity conditions while the use of metric (Cartesian) shape functions for the trial functions ensures that the stress representation during finite element computation can retrieve in a best-fit manner, the actual variation in stress in the metric space. However the formulation so far has only been applied to static problems in literature and a dynamic problem of composite structure has not been addressed. In this paper, the impact response in composite laminate subjected to transverse impact by a metallic impactor is investigated using three-dimensional layered twenty-noded hexahedral unsymmetric finite element formulation. Some example problems of graphite/epoxy laminate (plate as well as cylindrical shell) are considered and impact-induced response is analysed using the above formulation. The performance comparison of this unsymmetric element is made vis-à-vis conventional symmetric 8-noded and 20-noded hexahedral finite elements.