Spotweld Failure Prediction using Solid Element Assemblies

One current methodology for spotweld modelling utilizes a tied contact to connect the weld elements to the components. In order for this contact to be robust and acceptably mesh independent, multiple solid elements are needed to represent a single weld. Several studies were conducted which concluded that a cluster of eight hex elements provides significantly improved performance over a single beam or hex element. However, ease of use is critical to the application of these spotwelds since thousands of welds can be present in a single full vehicle model. Therefore, a single output is generated for each weld assembly rather than on an element basis. The time step for these hex clusters is controlled by the smallest edge length so using multiple elements does not result in a time step penalty since the thickness of the weld is usually the smallest edge length. This paper will present the development of the eight hex cluster weld, followed by the validation process of these cluster spotwelds. Failure parameters for the resultant-based Mat 100 Damage-Failure model were derived by simulating coupon tests of single welds in shear and tension failure. These failure parameters were then used in a component test model with dozens of welds, several of which failed under the applied load. Finally, these parameters were applied to a full vehicle model using automatic sorting of the welds by the pre-processing software. At both the component and full vehicle level, good agreement was found between simulation and test results. The additional mass scaling and run time penalties of the cluster spotwelds were not significant. Furthermore, the effort needed to apply automatic methods to organize the welds is small enough to be practical in the production CAE environment.