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Originally published in the 72nd IIW Annual Assembly and International Conference, Bratislava, July 7-12, 2019
Spot weld plays a critical role in the integrity of automotive and fatigue durability of the body over the course of service. Numerical analysis is a common tool to model the behaviour of spot welds in automotive under both service and crash loading. However, the welding modeling strategy can significantly change the result of analysis and therefore the final engineering decision.
Authors observed that modelers typically define the spot welds as a mechanical tie between two plates and ignore the local effect from welding process that changes the material properties in weld nugget and the surrounding Heat Affected Zone (HAZ). However, spot welding leads to property evolution to higher strength and toughness and lower ductility in the weld nugget than parents metal’s property. This evolution is opposite in HAZ with lesser strength and toughness and higher ductility than parents metal’s property. This local effect at the weld region changes the stress-strain behaviour of the structure and it becomes more significant when dealing with fatigue life prediction because fatigue is a local phenomenon and the analysis of fatigue uses the local stress and strain for life calculation. Therefore the simulation of welding process needs to be part of the analysis for making a realistic decision.
On the other hand, welding modeling could take longer CPU time for a large number of welding involved in the automotive body such that it is not feasible to model every individual welding process. Here, authors compared two modeling scenarios where one defines the weld as mechanical tie vs. the other one that includes the modeling of welding process and evolution of material properties in the weld metal and HAZ. The main criteria for the comparison are the fatigue durability and crack evolution in the weld nuggets and the structure. We also proposed a methodology to avoid the repetitive weld modeling for every weld nuggets and using the result of characteristic welds to cover all welding locations in the structure.
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