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Experience from several car projects shows that S-N curves for spot welds generated under load control in the high cycle fatigue regime might be very conservative when used in the low cycle fatigue regime. Therefore, force and displacement controlled low cycle fatigue tests were carried out on peel and shear loaded specimens. Both constant (CA) and variable amplitude (VA) load signals were used. Finally, a method for predicting fatigue life of spot welds with increased accuracy in the low cycle fatigue regime is proposed. The method is simple, fast and accurate and can be used together with linear finite element analysis (FEA) and existing fatigue packages.

The durability and the life of spot welded sheet metal structures are mainly controlled by the strength of the joints. Designers are aiming at reliable information, already in early design phase, that the weld spots will indeed perform satisfactorily throughout the required life cycles of a complex structure under the operational loading conditions. Consequently, a theoretical approach for the determination of the structural durability and the reliable design and optimization of spot welded components has been developed and extensively verified for serial components by theoretical analysis and tests. The method starts with Finite-Element-computations of the structures in the design stage and strength data obtained from component-like specimens; both are commonly available in the design phase, but are not sufficient for the determination of the structural integrity.