FEM of residual stress and surface displacement of a single shot in high repetition laser shock peening on biodegradable magnesium implant

Abstract

Laser shock peening (LSP) is one of the prominent surface processing techniques to improve the mechanical characteristics by inducing compressive residual stress on the specimen surface. Generally, LSP is performed using high energy, low repetition pulsed laser. Recently, High repetition laser shock peening (HRLSP) on biodegradable magnesium alloys has been reported. Increased speed and reduced operating costs are the key highlights of HRLSP. This work is aimed towards understanding of the residual stress profile beneath the specimen surface, where a Finite element method (FEM) has been proposed to show the ability of a tightly focussed nanosecond laser pulse for peening magnesium. The depth of maximum compressive residual stress of 48 MPa at 28 mm beneath surface was the result of the simulation. Also the Von Misses stress was analytically found to be 31.5 MPa, which is similar to the value from FEM at 30 MPa. Furthermore, the plastic displacement of FEM at 4.02 µm compares reasonably well with the experimental result at 3.698 µm, thereby validating the Finite element model. If increase in CRS can be created by single shot of laser pulse, it can be concluded that the same can be done beneath the entire magnesium surface using appropriate scanning protocols.