Dependence of damage modes on the ply-thickness of ultra-thin-ply composites

Transitions between damage modes have been observed in ultra-thin-ply laminates. Numerical methods can be effectively applied to the design and optimization of the microstructure of ultra-thin ply laminates. It is difficult to precisely predict transitions between complex damage modes of composites, such as fiber breakage, matrix cracking, shear failure and delamination. In this paper, a numerical model was developed to comprehensively consider in-plane damage and delamination. The initiation and in-plane propagation of damage was simulated using a material degradation model (MDM), which was implemented by a user subroutine USDFLD in ABAQUS. A cohesive interaction between the surfaces of adjacent layers was used to simulate delamination. The numerical predictions for the transitions between damage modes in cross-ply and Bouligand thin-ply laminates were verified by comparison with experimental results. The novelty of this study is discovering the dependence of damage modes on the ply-thickness under bending load and revealing the influence of damage competition mechanism on the bending properties of thin-ply composite. The research results could help develop a useful tool for improving microstructure design or elucidating the underlying mechanism for the mechanical behavior of thin-ply microstructures.