Failure Mechanisms and Strength Reduction in Composite Laminates with Cut-outs—A 3-D Finite Element Numerical Autopsy

Abstract

Organic composite laminates exhibit a ‘size effect’ when perforated with cutouts, such as holes or notches: the strength of components with a larger cutout is smaller than predicted by the effective strength criterion (i.e. constant average stress across the ligament). A Finite Element simulation model is presented to predict the failure strength of composite laminates, for arbitrary cut-out shapes and sizes, ply stacking sequences, and mechanical loading conditions. The model performance is demonstrated on the prediction of the failure loads of carbon-epoxy tension specimens with a central circular cut-out, for two hole sizes and two stacking sequences \0°/45°/90°/−45°\_s and \90°/−45°/0°/45°\_s. Comparison with experimental results shows good qualitative and quantitative agreement.

The model is used to investigate the sequence of failure events inside the laminate: initiation and propagation of matrix shear damage and crazing in each ply, with the load transfer mechanisms inside the ply and towards adjacent plies; progressive fiber fracture and delamination between plies near the free edges.

The numerical model is further exploited to identify the physical (material and geometric) parameters responsible for the cut-out strength reduction.