In situ Damage Quantification in Bolts

Transient stress waves have been used to quantify the extent of damage in cylindrical structures. In the present study, this technique is extended to the in situ quantification of damage in a bolt. Piezoelectric wafers were bonded to either end of two bolts, one of which was loaded in tension in a steel block. Both bolts were incrementally damaged by sawing a cut, to observe the changes in a stress wave which had traversed the bolts in the presence of increasing damage. A clear relationship between the extent of damage in the bolt and the attenuation of the stress wave was observed. Tension in the bolt did not affect this relationship, illustrating the in situ applicability of the technique. In a second set of experiments, bolts were subjected to conditions in which stress corrosion cracking would occur, whilst stress waves were excited in each bolt, to illustrate the ability of the method to detect a naturally occurring form of damage. It was found that the attenuation of a stress wave which had traversed the bolt was proportional to the extent of stress corrosion damage, measured by the residual strength. It is concluded that the technique is capable of detecting in situ damage in structural grades of fasteners.