THE EFFECT OF PLY WAVINESS ON DAMAGE INITIATION AND GROWTH IN COMPOSITES UNDER FULLY REVERSED CYCLIC LOADING

Abstract

This paper presents results of an experimental investigation of composites with embedded ply waviness defects subjected to cyclic loads. The aim is to investigate the influence of ply waviness defects on the initiation, interaction, and evolution of fatigue damage mechanisms. The composite laminates with ply waviness are tested in a four-point bend sandwich beam configuration. Fully reversed fatigue testing until failure and interrupted fatigue testing were conducted, and the sequence of fatigue damage mechanisms was studied via digital image correlation analysis. Results showed that during fully reversed cyclic loads, shear strains localize at the ply waviness region, which amplifies the stresses in surrounding plies. The failure mechanisms near the defect include delamination, matrix cracking, and ply splitting. However, at small ply waviness amplitudes, failure did not initiate at the defect but at other sites in the laminate where the strength was locally reduced. In these laminates, failure mechanisms due to microstructural defects compete and dominate the fatigue failure mechanisms at regions of ply waviness defects.