The effect of imperfections on crack growth rates in cold worked and interference fit holes

Abstract

This work examines the effect of imperfections on fatigue crack growth (FCG) in lap joints (Hi-Lok fasteners). The Finite Element Method (FEM) is used to model the cold-working and interference fit processes. FE predictions are shown to be consistent with experimental and computational results in the literature. The Extended Finite Element Method (XFEM) is then used to simulate a Mode I through crack in a rectangular plate starting at the fastener hole subjected to cold-working and interference fit. Four constant load ratio fatigue cases are investigated: (i) no residual stress, no imperfection, (ii) no residual stress, imperfection, (iii) residual stress, no imperfection and (iv) residual stress, imperfection. XFEM predictions used with the Walker equation predict that the presence of an axial gouge within a hole may result in a significant decrease (23%) in the component fatigue life under constant amplitude cyclical loading. This decrease appears to be exacerbated if a residual compressive stress field due to cold-work and interference fit is present.

Keywords

• fatigue
• crack
• fastener
• cold work
• interference
• finite element