Mechanical property and failure prediction of resistance spot welded advanced high strength automotive steels

The safety of vehicles is to a large extent determined by the property of resistance spot welds (RSW) that assemble all steel components together. Advanced high strength steels (AHSS) are known to be more susceptible to weld metal failure than conventional mild steels. Structural notch, detrimental grain orientation and high residual stresses in RSW lead to undesired failure modes. Often AHSS suffers from degraded fracture strength and rather low toughness of RSW welds. This research project aims at • getting fundamental insight on the weld microstructure: effects of grain composition, orientation and distribution on the deformation and failure behavior of the welds under external loading; • unique measurement of residual stress state and deformation: in-situ mechanical testing at microscale in scanning electron microscopy and quantification of residual stress state by using a combination of digital image correlation and focused ion beam milling; • design of micromechanical descriptions: mechanical behavior around the weld during shear and cross-tension loading. In order to identify optimized process and alloying strategies, it is necessary to understand how the metallurgical properties affect the actual mechanical performance. The key aspect of this PhD project is to understand the relationship between the heterogeneous weld microstructure, local mechanical properties and the total energy to failure of resistance spot welds in AHSS and to predict the failure mode under different loading conditions. This knowledge will lead to a new strategy for optimizing the welding process settings with respect to the specific alloying of new advanced/ultra high strength automotive steels.

Project leader & first supervisor

Prof. Dr. Yutao Pei

PhD student

Ali Chabok

Second supervisor

Prof. Dr. Jeff Th. M. De Hosson