Three-Dimensional Finite Element Analysis of Composite Laminates Subjected to Transverse Impact

Abstract

An interest in the low velocity impact probkins has been revived with the advent of laminated composite materials and their increasing use in aerospace and other applications. The reason for this new activity is that despite certain advantages of these materials over more traditional materials, composites are known to be vulnerable to impact. Impacts may occur anywhere during manufacture, normal operations,or maintenance and may induce significant internal damage in the form of matrix cracking, delarnination or fibre breakage, that are undetectable by visual inspection and cause significant reductions in the strength and stability of the structure. In the present paper. a three-dimensional finite element and transient dynamic analysis of fibre-reinforced polymer matrix composite laminates (e.g. graphite/epoxy, glass/epoxy, etc.) subjected to transverse foreign object impact is performed. Layered version of eight-noded isoparametric brick element with incompatible modes is used to model the laminate. Transient dynamic equilibrium equation is integrated step-by-step with respect to time using Newmark direct time integration method. Non-linear contact law reported in literature is used to model the local contact behavior and the timevartiing contact force is calculated based on the relative displacement between impactor and laminate using Newton-Raphson method. Based on the finite element model, a versatile computer software was developed in C++ programming language using object- oriented approach. The software can be used to determine several results such as contact force history, displacement and velocity histories of impactor and the timevarying displacements, forces, strains and stresses throughout the laminate. Some example problems are considered to study the effects of impactor velocity and laminate boundary conditions on impact behavior of graphite/epoxy composite laminates, and results are presented for time-history of contact force and laminate central deflection.The transient dynamic strains and stresses inside the laminate were also calculated for few cases