Application of an ultrasonic technique to assess contact performance of bolted joints

Bolted joints are a widespread type of connection used in mechanical engineering, but their performance, in terms of contact area size and shape and pressure distribution, is not easy to verify due to the nature of closed contact, which makes it difficult to investigate them with most experimental techniques. This study proposes the application of an ultrasonic method (through immersion scans of the potential contact region between the members of a bolted joint) aimed at obtaining both graphical maps of contact conditions and, after a calibration process, actual contact pressure distributions. The analysis is carried out on a number of joints characterized by different values of plate thickness and applied load. Moreover, to evaluate the quantitative accuracy of the ultrasonic technique, the results have been compared to those of another experimental technique (pressure-sensitive film) and numerical findings obtained by a finite element model of the experimental setup.