Fatigue lives for induction hardened shafts with subsurface crack initiation

Abstract

Induction hardened shafts have been fatigue tested with a torsional load. The tests have been performed both with a torque spectrum and with constant amplitude with different torque ratios. In this report, only fatigue failures which have their origin in cracks beneath the hardened layer in the core material are considered. Measurement of the residual stresses and simulation of the hardening process have showed that the tensile residual stresses are high in the core material. Simulations of the hardening process have been performed with different parameters. Fatigue tests in strain control are performed on small specimens of the core material. Fatigue life assessments are performed on the induction hardened shafts. The high tensile residual stresses at the core are very detrimental to the fatigue life. The fatigue tests indicate that the hardening process parameters significantly influence the fatigue lives. The fatigue life assessments made with a critical plane model are in relatively good agreement with the test results. Most of the life for the shafts probably consists of crack initiation, and the crack propagation part of the life seems to be short at intermediate lives.