APPARATUS AND METHOD OF INDIRECT MEASUREMENT OF BOLT OR SCREW PRE-STRESSING

摘要

The pre-stressing of a bolt or screw (3) is measured by determining ultrasonically the expansion of the bolt or screw caused by stressing. The change of length is determined in a computer (9) from the time difference for the pulse before and after tightening of the bolt or screw. This change of length is compared with a test bolt or screw subject to the same pre-stressing. An ultrasonic probe 4 5) or an electrodynamic probe may be used, the probe being connected via an ultrasonic unit (8) to the computer (9).