THE INVESTIGATION OF WARM LASER SHOCK PEENING AS A POST PROCESSING TECHNIQUE TO IMPROVE JOINT STRENGTH OF LASER WELDED MATERIALS
This study is concerned with investigating the effects of warm laser shock peening (wLSP) on the enhancement of mechanical performance of laser welded joints. A 3-D finite element model is presented which predicts the surface indentation geometry and in-depth compressive residual stresses generated by wLSP. To define the LSP pressure on the surface of the material, a 1-D confined plasma model is implemented to predict plasma pressure generated by laser-coating interaction in an oil confinement regime. Residual stresses predicted by the finite element model for wLSP reveal higher magnitude and depth of compressive residual stresses than room temperature laser shock peening. A novel dual laser wLSP experimental setup is developed for simultaneous heating of the sample, to a prescribed temperature, and to perform wLSP. The heating laser power is tuned to achieve a predefined temperature in the material through predictive analysis with a 3-D transient laser heating model.
Laser welded joints of AA6061-T6 and TZM alloy in bead-on-plate (BOP) and overlap configurations, created by laser welding with a high power fiber laser, were post processed with wLSP. To evaluate the strength of the welded joints pre- and post-processing, tensile testing and tensile-shear testing were carried out. To understand the failure modes in tensile-shear testing of the samples, a 3-D finite element model of the welded joint was developed with weld regions’ material strength properties defined through microhardness testing. The stress concentration regions predicted by the finite element model clearly explain the failure regions in the experimental tensile testing analysis. The tensile tests and tensile-shear tests carried out on wLSP processed AA6061-T6 samples demonstrate an enhancement in the joint strength by about 20% and ductility improvement of about 33% over as-welded samples. The BOP welds of TZM alloy processed with wLSP demonstrated an enhancement in strength by about 30% and lap welds demonstrated an increase in joint strength by 22%.