A Study of Induction Hardening Hole Surfaces in Clearance Fit Joints to Improve Fatigue Strength

Abstract

The feasibility of using induction hardening to improve the fatigue strength of clearance fit clevis-type joints was investigated. Clearance fit joints are desired to facilitate machine assembly and disassembly in applications where accessibility and safety are a problem. The purpose of induction hardening the hole surface was to induce compressive residual stress near the hole to reduce the mean stress and to increase material strength. According to the Goodman criterion for steel, a greater stress range is possible with a reduced mean stress. The residual stress distribution produced near the hole was estimated by induction hardening rings and using a modification of the Sachs boring out method. The hole surfaces of a typical link were induction hardened and tension-tension fatigue tested. The load stress distribution was estimated using strain gages. It was determined that the fatigue strength of a clearance fit joint can be increased by at least 100 percent by induction dardening the hole surfaces.