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In the present study, several welded beam and plate specimens are fabricated using an electrical resistance type spot welder and studied experimentally applying the frequency response function approach. The experimental data is used to guide the dynamic finite element modeling effort, and to determine the weld joint representation that most accurately characterizes the measured dynamic response. The results reveal the compliant nature of the spot welds at higher frequencies and in applications consisting of more complex geometrical structures and boundary conditions. This finding shows the inadequacy in the classical rigid element representation that is widely used in current dynamic modeling practices.

The changes of dynamic frequency response, commonly used to determine the dynamic characteristic of built-up structures, were studied over the entire fatigue failure process for tensile-shear spot-welded joints. The results of an experimental study showed that the natural frequency varies non-linearly with the fatigue damage fraction. This behavior was modeled using finite element analysis of a progressively growing crack, initiating at the joining surface, then progressing to the outside surface of the specimen, and finally extending from the spot weld nugget. The relationship between dynamic frequency response and crack propagation may be applied to study effect of aging (high mileage) in NVH quality.