Mitigating stress concentration through defense hole system for improvement in bearing strength of composite bolted joint, Part 1: Numerical analysis

Abstract

The use of defense hole system allows the flow of the stresses to be redistributed by introducing auxiliary holes in the low stress area near the main hole. However, the question remains on the optimal configuration of the defense hole system for effective stress mitigation at the bolt-hole region and, hence, increasing the bearing capacity of particular composite bolted joints. This study presents the influence of defense hole system geometrical design on the stress reduction in a single-bolt, double-lap composite bolted joint. The nonlinear material behavior of the joint was simulated using ANSYS through a progressive failure model, considering the circumferential and radial stresses at bearing, shear-out, and net tension regions of the bolt-hole. It was found that the stress has been reduced between 2.3% and 6.1% for the narrow laminates over a range of E/ D ratios (1–5) with the benefits of the defense hole was clearly marked at DS = 2 D and DHD = 0.75 D. In contrast, for those of wider laminates, the stress reduction ranged from 1.9% to remarkably 18.6%.