Through-depth residual stress measurement of laser bent steel–titanium bimetal sheets

Abstract

Laser bending is one of the thermal forming processes which in each pass of it, the temperature of sample increases at heat-affected zone during irradiation time considerably and then it cools to near ambient temperature after passing the laser beam. Consequently, it can be predicted that the process can induce significant residual stress in the sample. In this article, laser bending process of the explosive welded steel–titanium bimetal sample was done and the through-thickness residual stress profile of it was investigated by the slitting method experimentally. The pulse-regularization approach was used to calculate the residual stress in the bimetal sample. Also, simulation of the laser bending process was performed and the numerical residual stress profile was compared with the experimental one. Furthermore, the effects of process parameters including laser power, scanning velocity and number of scanning passes on the bending angle of bimetal samples were investigated experimentally. Besides, the effect of laser bending process on the surface microhardness was studied. The results demonstrated that the laser bending process can create significant residual stress at the heat-affected zone of specimen. In the residual stress profile of bimetal sample, a discontinuity was seen at the interface of the materials, as was expected. There was a good agreement between experimental and numerical results. The maximum compressive and tensile residual stresses raised by increase laser power and number of scanning passes. Both of them reduced by magnifying scanning velocity. The laser bending process can increase the surface microhardness at the heat-affected zone which can be attributed to the reduction of grain size at the heat-affected zone.