Ultrasonic evaluation of spot welds by local immersion method

摘要

In order to apply an ultrasonic testing with a focused probe to the large spot welded structures and the corrosive materials, a local immersion method was proposed. The ultrasonic testing is based upon the multiple reflections in the thin plate,and the measurement is carried out through the thin film at the bottom in the small sized tank, which is mounted on the spot welds via couplant. In this study, appropriate thin films and their combination with couplant were examined for the precisemeasurement of weld size and quality of spot welds.It was clarified from the ultrasonic measurement of spot welds with various thin films and couplants that the local immersion method was available to the nondestructive evaluation of large spot welded structures and corrosive materials, as long as therubber and plastic films were used. These materials possess almost same acoustic impedance as water and the appropriate combination with couplant was plastic-oil which showed long film duration and good protection against the rust in the measurement. Ascanning pattern with each four scanning lines in two perpendicular directions was also proposed for the short measuring time, the precision of which is almost same with the fine scanning measurement.