Modeling the Behavior of Impact Induced Multiple Delaminations under Compressive Load

Abstract

A two-part study is presented focusing on post-impact behavior prediction of compression after impact (CAI) specimens. The first part is dedicated to the study of cohesive zone model (CZM) and mesh density parameters as well as to the evaluation of their influence on resulting simulation accuracy and computational costs. For that purpose, two different tests are replicated by numerical simulations: double cantilever beam (DCB) and end-notched flexure (ENF) tests. The parameters under investigation are: element edge length, cohesive stiffness and strength for mode I and mode II loading. By comparing analytical with numerical results from the parametric study, an adequate parameter set is found and finally applied to the CAI model. In the second part, a procedure for predicting the behavior of impacted carbon fiber reinforced plastics (CFRP) structures under uniaxial compressive loading is presented by the example of a CAI test simulation. For that purpose, a model is used to represent realistic impact damages with multiple delaminations of elliptical shape as well as varying sizes and orientations distributed throughout the laminate thickness. Non-self-similar delamination propagation in the resin-rich zone and sublaminate and global buckling phenomena are considered in a nonlinear simulation based on the finite element method (FEM). The sublaminate buckling modes are calculated in a preceding buckling analysis and applied simultaneously onto each sublaminate as initial geometrical imperfections. Peel and transversal shear tractions emerge as sublaminate and global buckling develops, leading to delamination propagation. The predicted behavior is in line with numerical and experimental findings reported in the literature. _____________