Failure characterization of laser welds under combined loading conditions

This paper proposes a new failure criterion for laser-welded regions under combined normal and shear loading conditions for the crash analysis of an auto-body. The failure criterion had been deduced from experimental results with nine different loading conditions including the normal loading and the pure-shear loading condition. The fixture jig set to mount a specimen was designed to obtain failure loads of laser welds under combined loading conditions with a constant shear to normal load ratio. To evaluate the pure-shear strength of laser welds fabricated using the same welding condition with a two-layered lap joint, a testing fixture and a specimen were designed with the aid of information from finite element analysis results. Using the testing fixtures proposed in this paper, failure tests of laser welds of CR340 1.2t steel sheet were carried out with the variation of nine different loading angles from 0° to 75° at the interval of 15° and from 75° to 90° at the interval of 5° to obtain failure loads and for identification of the failure characteristics at each loading angle. Based on the experimental data, a novel failure criterion was proposed for the description of failure behavior of laser welds. The failure criteria are divided into two regions of base metal failure and interfacial failure. The base metal failure region is expressed as a function of the normal and shear load, which is the so-called β-norm function, while the interfacial failure region is represented in a form of a modified power law function. The failure criterion proposed provides a fairly accurate description of the failure load obtained from the experiments under combined normal and shear loading conditions.

► The testing systems were newly designed in order to obtain the failure load.
► A transition region was observed where the failure mode of laser welds changes from base metal failure to interfacial failure.
► A new failure model was introduced to describe the failure behavior of laser welds.
► The stitch-type laser welds are safer than the O-type laser welds when the normalized failure curves are compared.