Metod för bestämning av axialkraften i ett gängat fästelement vid åtdragning över sträckgränsen

摘要

A method for determining the axial load in a threaded fastener when tightened above its yield point by using the variation in travel time ( DELTA t) for ultrasonic waves induced in the fastener to determine the axial load (N) in the fastener, both in the yield point and at the final pretension state of the fastener. The yield point of the fastener is detected by indicating a significant change in the growth of the momentary transferred torque per angle unit of rotation, and comparing the actual travel time ( DELTA t) for ultrasonic waves in the fastener to a pre-tightening determined relationship between the axial load (N), the rotation angle ( PHI ) and the ultrasonic wave travel time ( DELTA t) for the actual type of fastener.