Hess D.

Loosening of threaded fasteners remains a widespread cause of failure in assemblies and structures subjected to dynamic loads. This paper presents results of analyses on failure of threaded fasteners by vibration induced loosening due to dynamic shear loads. Experimental work reveals fastener loosening occurs as a result of complete or localized slip at the thread and head contact surfaces. Finite element model analysis illustrates four different loosening processes that are characterized by either complete or localized slip at the head and thread contacts. The model is found to be capable of adequately modeling factors that influence slip and predicting the different loosening processes. It is found that loosening can occur at relatively low shear loads due to the process of localized slip.