Fatigue behaviour and failure mechanism of the thin/thick-ply hybrid laminated composite bolted joints

Abstract

Thin-ply composites have attracted increasing attention from researchers due to their higher damage tolerance and delamination suppression. This paper presents a detailed investigation of the fatigue behaviour and damage mechanism of symmetrical thin/thick hybrid design laminate-titanium joints under tension-tension loading. Laminates with four different configurations, thick, thick-thin-thick, thin-thick-thin and thin, were designed. According to the quasi-static bearing limit of the thick-ply laminates joints, fatigue testing of each hybrid joint was carried out at two load levels for a certain number of cycles. The deformation and damage of the hybrid joint were characterized by scanning electron microscopy (SEM). With thick plies and the addition of a number of thin plies, the hybrid design laminates can significantly improve the fatigue performance. Stacking thin-ply on the outermost layers of the laminate is more meaningful for double-lap joints than the use of thin-ply joints in the middle. Under an identical number of cycles, the deformation around a hole in the thin-ply laminate is only approximately 50% of that of the thick ply. The damage is delayed, and the propagation of inter- and intralaminar cracks is suppressed in the thin-ply laminates, resulting in the best fatigue resistance and less delamination under the two fatigue loads.