Failure mechanism and load transfer efficiency attenuation effect of 3D braided double hole joint

Double-lap joints with multi-hole arrays represent critical assembly components in aerospace composite structures. Their failure behavior under load is governed by a complex interplay between the yarn architecture and the discrete hole pattern. This study investigates the mechanical response and failure mechanisms of 3D braided composite joints containing multiple open-holes. A combined experimental and computational approach was employed to elucidate how the inherent braided architecture and the geometric arrangement of holes jointly govern load transfer efficiency and failure mechanisms. High-fidelity finite element simulations revealed that failure predominantly initiates via bearing damage at the open-holes, followed by tear-out failure emanating from the hole peripheries. Crucially, cracks were observed to diffuse and interact along the open-hole fiber pathways, leading to a complex coupled response. The distance between open-holes was identified as a critical configuration modulating this interaction. Experimental validation confirmed that this interaction mechanism causes a 33% reduction in bearing strength and a 21% degradation in load transfer efficiency for double-hole joints compared to single-hole joints. The insights gained provide a foundational framework for the multiscale modeling of 3D braided multi-hole joints. Furthermore, the elucidated failure mechanisms offer essential theoretical guidance for the reliable design of such joints in advanced aerospace applications.