Patent ID: 7861910

Claim:
A method of estimating a joined region of a joined object in which two joining members are joined together while being overlapped one on another by using a spot friction stir joining method, comprising: a reflected wave measuring step of introducing an ultrasonic wave into the joined object from a face of the joined object opposed to a plunging face thereof in which a joining tool was plunged upon the spot friction stir process, and taking in a reflected wave of the ultrasonic wave introduced into and reflected from the joined object; and an estimation step of estimating an ultrasonic wave incident position as a position over the joined region, provided that among reflected waves taken in by the reflected wave measuring step, an observed reflected wave reflected in a vicinity of a position corresponding to an interface between the two joining members satisfies a predetermined boundary condition, wherein in the estimation step, the ultrasonic wave incident position, in which an amplitude of the observed reflected wave is lower than a predetermined amplitude threshold value, is estimated as the position over the joined region.