Spot welding is the primary joining method used in automobiles. Spot-weld plays a major role to maintain vehicle structural integrity during impact tests. Robust spot weld failure definitions is critical for accurate predictions of structural performance in safety simulations.
Spot welds have a complex metallurgical structure, mainly consisting of fusion and heat affected zones. For accurate material property definitions in simulation models, huge number of inputs from test data is required. Multiple tests, using different spot weld joinery configurations, have to be conducted. In order to accurately represent the spot-weld behavior in CAE, detailed modeling is required using fine mesh. The current challenge in spot-weld failure assessment is developing a methodology having a better trade-off between prediction accuracy, testing efforts and computation time.
In view of the above, cohesive zone models have been found to be very effective and accurate. It uses the principles of continuum mechanics and linear elastic fracture mechanics, to predict peak stress and damage accurately. This approach requires less number of coupon tests when compared to the existing MAT-100 material models. In this study, a rate-dependent, elastic-ideally plastic mixed-mode material model MAT-240 is chosen to simulate the spot-weld failure. Tensile and shear coupon tests are conducted for few material-thickness combinations. Further, peel and angular tests are conducted to enhance correlation. Subsequently, spot-weld material database is developed for different joinery combinations. The spot weld failure model is successfully validated in sub-system and full vehicle level simulations. The methodology was able to predict the trend and identify the critical locations of spot-weld failure accurately.