Quasi-static crushing behavior of stretch formed domes of laser welded tailored blanks

Abstract

In the present work, similar thickness laser welded blanks (LWBs) and dissimilar thickness laser welded tailored blanks (LWTBs) of extra deep drawing (EDD) steels were fabricated and these were stretch formed by a 50 mm diameter hemispherical punch under lubricated condition. All these stretch-formed domes were manufactured keeping a consistent combined geometry of hemispherical and conical sections. Subsequently, these domes were crushed quasi-statically and the modes of collapse, load-displacement response, mean crushing load and energy absorption were comprehensively investigated both experimentally and numerically to get insight into the effect of weld zone (WZ), thickness ratio, deformation speed, forming histories and material anisotropy. During all the crushing tests, three similar collapse modes were observed and these were identified as flattening of hemispherical section, inward dimpling of hemispherical section and lastly the flattening of conical section. However, an additional collapse mode consisting of two asymmetrical lobes across the WZ with a stationary plastic hinge was identified in case of stretch-formed domes of LWTBs. It was concluded that the mode of collapse was predominantly affected by the presence of thickness ratio. On the other hand, the mean crushing load and energy absorption capacity were enhanced due to the presence of WZ and the selection of thickness combination. The energy absorption effectiveness factor of LWBs and LWTBs were estimated to be 1.33 to 2.75 times higher than that of monolithic EDD steel. It was further suggested through numerical modeling that the incorporation of strain rate, material anisotropy and forming histories such as non-uniform thickness and strain distributions along with WZ properties improved the prediction of modes of collapse, load-displacement response and mean crushing load.