Effects of Laser Peening Treatment on High Cycle Fatigue and Crack Propagation Behaviors in Austenitic Stainless Steel

Abstract

Laser peening without protective coating (LPwC) treatment is one of surface enhancement techniques using an impact wave of high pressure plasma induced by laser pulse irradiation. High compressive residual stress was induced by the LPwC treatment on the surface of low-carbon type austenitic stainless steel SUS316L. The affected depth reached about 1mm from the surface. High cycle fatigue tests with four-points rotating bending loading were carried out to confirm the effects of the LPwC treatment on fatigue strength and surface fatigue crack propagation behaviors. The fatigue strength was remarkably improved by the LPwC treatment over the whole regime of fatigue life up to 10 8 cycles. Specimens with a pre-crack from a small artificial hole due to fatigue loading were used for the quantitative study on the effect of the LPwC treatment. The fracture mechanics investigation on the pre-cracked specimens showed that the LPwC treatment restrained the further propagation of the pre-crack if the stress intensity factor range ∆K on the crack tip was less than 7.6 MPa√m. Surface cracks preferentially propagated into the depth direction as predicted through ∆K analysis on the crack by taking account of the compressive residual stresses due to the LPwC treatment.

The Effects of Laser Shock Peening on Microstructure and Properties of Metals and Alloys: A Review

“…The rotating bending fatigue strength of the degassing process AC4CH material also improved considerably in comparison with that of the non-peened material [28]. The fatigue strength of austenitc stainless steel was improved in the whole regime of fatigue life by the Lpwc treatment and its fatigue strength at 108 cycles increased 42% [27].…”

Quarter Century Development of Laser Peening without Coating

“…A miniaturized optical head with a diameter of 10 mm was developed with a fast-responding focusing function [6,7] that controls the focal point Regarding fatigue issues, LPwC has positive effects to improve mechanical properties of various materials including ceramics [8,9]. LPwC significantly enhanced the fatigue strength and prolonged the fatigue life of steels [10][11][12], aluminum alloys [13] titanium alloys [14,15], etc. Recently, Sakino et al confirmed the effect enhancing fatigue properties of HT780 (780 MPa grade high-strength steel) by low-energy LPwC with pulse energies down to 20 and 10 mJ [16].…”