Experimental Investigations of Carbon-Epoxy Composites with Ply Waviness Under Cyclic Bending

This article presents results from an experimental investigation of composite laminates manufactured with ply waviness defects and tested in a sandwich beam configuration. The sandwich beam specimens with composite facesheets are loaded under quasi-static and fully reversed cyclic loading in a four-point bend configuration. The manufacturing variability of the ply waviness defect characteristic features (misalignment angle, waviness length and amplitude, and ply thickness changes) was analyzed, and a correlation between the waviness features and failure response was established. High-resolution imaging and digital image correlation (DIC) analysis are used for monitoring the strain fields developing near the wavy ply region, and explanations of the failure mechanisms nucleating in the material are presented. Under quasi-static loading, the peak load associated with compression failure shows a strong correlation with the ply waviness misalignment angle and waviness length. Under fully reversed cyclic loading, the initiation, interaction, and evolution of failure mechanisms are significantly different compared to those observed in quasi-static loading conditions. Possible explanations on the sequence of fatigue damage events, informed by DIC analysis and optical microscopy are presented.