Measurement of fatigue damage based on the natural frequency for spot-welded joints

According to the observation of fatigue fractography for the spot-welded joints, cracking behavior was modeled for specimens of different dimensions using 3D FEA of a progressively growing crack that began at the joining surface, progressed to the outside surface, and finally broke. The natural frequency ratio of experimental and modeled situations displayed identical nonlinear damage behavior for different dimensional specimens. Thus, a new damage variable was proposed to measure fatigue damage using natural frequency nonlinear behavior, and a nonlinear fatigue damage model was developed. The results showed that this model can successfully describe fatigue damage for spot-welded joints.