Patent ID: 11137304

Abstract:
A system, probe and method accurately measure the strain or extension of a fastener that occurs as a nut on the fastener is tightened and the fastener is put under load. The measurement technique is based on measurement of the time for an ultrasonic wave generated on one end of the fastener to travel a round trip through the fastener. As the fastener is tightened, the applied stress causes an associated increase in length. This length can be determined from a measurement of the increase in transit time. In various embodiments, the disclosed device and method uses laser ultrasonic testing (LUT), in which a pulsed laser generates the ultrasonic wave and a type of laser vibrometer detects the wave when it returns to the position of generation following a combination of longitudinal and shear wave reflections, which result in a higher magnitude and more easily and precisely measurable reflected signal peak than a signal peak associated with a signal directly reflected against the opposite end of the fastener.