Effects of bolt shape and pitch difference on fatigue strength for bolted joint

Abstract

In this study, the effect of curvature radius of the thread bottom and the pitch difference between of M16 bolt and nut on fatigue strength for bolted joint is considered experimentally. The M16 bolt-nut specimens having the two kinds of thread bottom radii and the pitch differences are prepared. The S-N curves for bolted specimens with different thread shapes are obtained by the stress-controlled fatigue test (stress ratio R>0). The experimental results are compared and discussed in terms of stress analysis. The finite element method is used to make a simulation of the fatigue experiment and the mean stress and stress amplitude at each thread bottom of bolt are analyzed. It is found that the initiation and propagation of crack are changed by introducing the pitch difference of α=15μm, from the crack observation on the surface of the bolt specimens after the experiment. Furthermore, the fatigue limit can be substantially improved by increasing curvature radius of thread bottom and introducing the pitch difference.

Keywords

• bolted joint
• fatigue strength
• pitch difference
• curvature radius
• finite element method