Development of a Finite Element Methodology for Modelling Mixed-Mode Delamination Growth

Abstract

A critical failure mechanism for composite skin-stiffened structures in compression is separation of the skin and stiffener, which can be considered analogous to interlaminar cracking. This paper presents the extension of a numerical approach developed previously for simulating the propagation of interlaminar cracks in composite structures. The degradation methodology was implemented in MSC.Marc, and involves modelling the structures with shell layers connected by user-defined multi-point constraints (MPCs). User subroutines were written that apply the Virtual Crack Closure Technique to determine the onset of crack growth, and modify the properties of the user-defined MPCs to simulate crack propagation. In previous work, this model was applied only to specimens with Mode I crack growth, and two methods were proposed for handling the release of failing MPCs. In this paper, the model and release methods are extended to handle propagation in any crack growth mode. Numerical results applying the developed methodology are then compared with experimental results of fracture mechanics characterisation tests for Mode II and Mixed Mode I-Mode II. Based on this comparison, the capability of the model to represent delamination growth in any composite structure is demonstrated. Future work will focus on the application of the degradation model for the design and analysis of larger and more complex structures.