RESIDUAL STRESSES IN TAILOR WELDED BLANKS DUE TO SPRINGBACK AFTER BENDING

Abstract

Residual Stress is a stress that remains inside of a component after the original cause of stresses has been removed. These stresses are locked-in stresses in the material that is free of external forces and thermal gradients. These stresses self-equilibrate within the crosssection of the material and can result in unexpected failure if not accounted for. A Tailor Weld Blank is a flat sheet made by joining different pieces of metal either of dissimilar materials or different size, shape and thicknesses. The presence of weld zone and different thickness combination results in generation of residual stress in the blank which affect the forming behavior of tailor-welded blanks significantly. A good knowledge of variation, nature and magnitude of the residual stresses and of its distribution within the component is of great importance for the accurate assessment and evaluation of fatigue life of the cold formed components. The present study is based on the experimental characterization and numerical analysis of residual stresses in the tailor welded blanks prepared by Nd-YAG laser welding of interstitial free steel with a thickness combination of 0.8mmX1.5mm, after springback a non-destructive cosα technique using a portable X-ray device (μ-X360 residual stress analyzer) is used to measure the residual stress in the tailor welded blanks experimentally. The longitudinally welded specimens of tailor welded blanks are tested on V-bending setup with three different punch profile radii i.e. 10mm, 12.5mm and 15mm and the residual stress is measured on inner and outer side of the tested samples. The effect of the punch profile radius on residual stress before and after springback is observed to be very significant in bending of tailor welded blanks. As the punch profile radius increases, it is observed that residual stress decreases for a given thickness combination. The residual stress predicted by simulations agreed well with the experimental results for all punch radii.