Fracture Criteria of Spot Welded Joint for Car Crash FE Analysis 2006-01-0534

It has been widely recognized that the accurate estimation of spot welded joint fracture are needed to improve the accuracy of car crash FE analyses. The criteria model must be developed to realize the consideration of spot welded joint fracture under various kinds of load conditions. Conventionally, only tensile shear test and cross-tensile test have been usually performed for estimation of the strength characteristic of spot-welded joints. However, the spot-welded strength under complex loads can not be adequately estimated by using the conventional test methods.

In this study, newly developed tests, “Inclined Cross Tensile Tests”, loading both shear and axial force on spot welded joint were conducted to understand fracture strength and build up its criteria. Especially, in the inclination of cross-tensile test, special attachment for the specimen to prevent bending deformation was developed. The influences of the parameters such as thickness of the plate, nugget size and combination of welded materials on the criteria were investigated. In the experiments, the tensile strength range of the material was from 270MPa to 590Ma, and the thickness of the plate was changed from 0.65mm to 2.0mm. Based on the result of experiments, the fracture criteria were established by estimating the strength of spot welded joint under the various kinds of load conditions.

In order to verify the developed criteria, the destruction test with hat-shaped parts spot-welded at eight points was carried out to simulate the deformation of floor side member and the floor panel of automotive body at collision. And the FE analyses with the fracture criteria model were also performed to confirm the accuracy. In comparison of the FE analyses with the experiments, the calculated results of the destruction loads and the destruction strokes were well coincident with those of the experiments. As the results, it was clarified that FE estimation with developed criteria for various load conditions was well coincident with those of the experiments and the developed criteria was feasible for an improved estimation method of the strength of spot welded parts.