Patent attributes
Even in measurement in which the measurement time is limited to a short time, soundness of a spot weld zone can be evaluated with high reliability without being influenced by a positional deviation between an ultrasonic probe and the spot weld zone and the coupling condition between an ultrasonic probe and a metal sheet. Specifically, ultrasonic waves propagating along the surface of a test object are transmitted in a plurality of directions from a plurality of wave sending positions outside the spot weld zone in metal sheets (1a, 1b), and ultrasonic waves propagating along the surface of the test object with propagation paths not including the spot weld zone and ultrasonic waves propagating along the surface of the test object with propagation paths including the spot weld zone are received at a plurality of wave receiving positions outside the spot weld zone to evaluate the soundness of the spot weld zone.
