Effects of ply-arrangement on compressive failure of layered structures

Abstract

Using detailed finite element models, compressive failure mechanisms of composite structures consisting of many laminae are analyzed. It is assumed that the structures contain interlaminar delamination and their failure mode to be characterized by either buckling or delamination growth. Our primary goal is to identify the effects of delamination and ply-arrangement on the multi-layered structures. Up to 32 laminae are distinctly modeled in this investigation. Our study considers two most basic geometry; one is flat panels under compressive load and the other is cylindrical shells subjected to external pressure. In both cases, the energy release rate and mixed-mode stress intensity factors are computed to quantify the crack driving force. The results are used to determine dominant failure initiation mode, structural buckling or delamination growth. Regardless of the structural type and total number of layers, a significant reduction in the load carrying capacity may occur when interlaminar delamination exists. In the flat panels, interlaminar delamination can generate unstable post-buckling behavior and lower the steady-state post-buckling load. However, delamination growth does not likely to occur during the pre-buckling stage. For the cylindrical shells, delamination growth may initiate prior to structural buckling. The location of delamination also plays an important role in defining the critical crack initiation load. When the delamination is located within 25% to 40% of shell thickness measured from the outer surface, the crack initiation load can be as low as half of the buckling load. In both types of structures, as the total number of plies increases, the layer effect diminishes. The overall deformation and failure behaviors of panels with large number of layers approach those of the infinite-layer model with homogenized material properties.