engleski

Numerical analysis of spot welds in sheet metal structures exposed to mechanical shock and vibration loading

Occupant safety, weight reduction, fuel efficiency, and vehicle crashworthiness remain the most challenging design objectives of the modern automotive industry. Recent improvements in sheet metal joining processes and the use of advanced high strength steels have increased fuel efficiency and enhanced vehicle durability, as well as the integrity of the passenger compartment, simultaneously increasing weight reduction. Resistance spot welding is the most widely used metal joining process in the automotive industry intended for the joining light gauge overlapping metal sheets. Although resistance spot welding includes complex interaction between mechanical loading, heating generated by the electric current, and rapid microstructural transformations, compared to other joining processes, resistance spot welding is fast, easily automated, and does not require the additional filler material. Since the material heterogeneity and geometric discontinuity around the weld nugget circumference cause stress concentration, spot-welded components are prone to premature failure under fatigue and crash loading conditions. Hence, it is crucial to understand the welded region microstructure and the mechanical behavior of spot-welded joints to balance competing design objectives and thus enhance vehicle durability and crashworthiness. In recent times numerical analyses have had a major impact on design optimization and cost reduction of full-scale experiments during prototype testing. Moreover, various numerical methods have been proposed to evaluate the fatigue strength of spot welds under constant amplitude loading. Generally, the fatigue analysis of spot-welded joints is classified into stress-based and force-based approaches. In comparison with the stress-based method, the force-based approach offers a quick solution and an accurate fatigue life estimation. Therefore, one of the objectives of the conducted research was to evaluate the existing methods for the fatigue analysis of spot-welded structures under constant amplitude loading and to study the effect of geometric characteristics on the fatigue behavior of spot-welded specimens. However, vehicle components are seldom subjected to the constant amplitude cyclic loading, thus the method of random vibration fatigue life prediction for spot-welded structures is evaluated. Finally, quasi-static damage analysis of spot-welded specimens is performed to evaluate the coupled force-based damage initiation criterion, which captures the complex behavior of spot-welded joints under general loading conditions, yet greatly simplifying the analysis.

Spot weld ; Finite element method ; Fatigue ; Random excitation ; Damage

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