Experimental Study of Bolted Joint Self-Loosening Under Transverse Load

Self-loosening of bolted joints is a problem regularly encountered in aeronautical structures and much research has been devoted to this phenomenon. Developing detailed analytical equations for the dynamic study of unscrewing is difficult, so it is easier to reveal it experimentally, in the static or the dynamic case. This paper focuses on the experimental study of the dynamic self-loosening of a bolted joint when it is subjected to vibrations, a major cause of the problem. The experiment used a bolted assembly moved by a shaker, which caused the tightened parts to slide and the bolt to loosen. A load washer showed the axial load variation and a high speed camera recorded the movements of the assembled parts. The results show the progress of rotation of the different parts, the unscrewing of the bolt and the loss of tension in the assembly. The method provides a means to explore the loosening process of various types of bolts, under realistic conditions of vibration.