Experimental investigation on bearing behavior and failure mechanism of double-lap thin-ply composite bolted joints

Thin-ply laminated composites have recently gained increasing attention in the aerospace engineering field, due to enhanced design possibilities and positive size effects with regard to decreasing ply thickness. In this paper, the mechanical behavior of thin-ply laminate and TC21 titanium alloy hybrid joints with double-lap bolted structure under quasi-static loading was studied experimentally. X-ray computed tomography (CT) scanning and SEM microcosmic imaging at special stages of the whole loading process were used to clarify the progression of bearing damage and fastening hole deformation characteristics of laminates. A more gradual damage and failure in bearing was observed in all specimens from the stress-displacement curves. The final failure of hybrid joints is a combined mode of bolt tensile cracking and hole bearing deformation. More importantly, the common delamination of standard-ply composite laminated plates in the bearing failure plane and tensile failure plane was suppressed in thin-ply laminates, resulting in higher bearing failure strength and more damage accumulation. Therefore, the novelty of this work contributes to detailed experimental observations of the bearing failure mechanisms, which provide valuable information for developing accurate mechanism-based failure models to be used in simulations.

Automated summary

Thin-ply laminated composites have gained attention in aerospace engineering due to enhanced design possibilities and positive size effects. This study experimentally investigated the mechanical behavior of thin-ply laminate and TC21 titanium alloy hybrid joints under quasi-static loading, revealing a more gradual bearing damage progression and a combination of bolt cracking and hole bearing deformation in the final failure of hybrid joints. The suppression of standard-ply composite laminated plates delamination in thin-ply laminates resulted in higher bearing failure strength and more damage accumulation.