Study on ultrasonic evaluation of connection state and service performance of resistance projection welding joints

Fatigue failure of welded joints is a performance factor of structural parts under dynamic load, and the effective evaluation of its life is always the key to the service ability of structures. The fatigue failure process of welded joints is complicated because of the non-uniformity of microstructure and asymmetry of structure. This study utilized ultrasonic C-scan imaging for non-destructive testing of the internal connection states of resistance projection welding (RPW). The connection state of RPW before, during and after fatigue test and the characteristic change of ultrasonic detection image were compared. With the occurrence of fatigue failure behavior, the area representing the fusion connection region in the ultrasonic C-scan image changes. The area of the molten connection zone in the ultrasonic images can quantitatively evaluate the fatigue limit of stainless steel RPW joints, providing an effective method for assessing fatigue life in practical engineering applications.