Numerical Simulation Study on Fatigue Life of Notched Specimens with Gradient Surface Strengthening Layer

Abstract

A modified Tanaka-Mura model is carried out to derive the equivalent stress amplitude at stress ratio R=-1 of complex fatigue stress and the effect of compress residual stress on fatigue life. Then, the fatigue of notched specimens with gradient surface strengthening layer were investigated by means of numerical simulation. The results indicate that the fatigue initiation life and the initiation site of notched specimen are related with the thickness of the strengthening layer, the surface-to-internal hardness ratio and the residual stress. There is a critical thickness. If the strengthening layer thickness is less than the critical value, fatigue crack is initiated at the interface of the matrix and the strengthening layer, otherwise at the surface of the notch root. The critical thickness value is increased with the increase of surface-to-internal hardness ratio. Residual compress stress has little effect on the fatigue initiation life, but the residual tensile stress decreases the fatigue initiation life obviously.

Keywords

• surface strengthening process
• fatigue life
• fatigue initiation
• stress concentration factor
• notch