The dynamic loadability of bolt-nut joints is one of the most important indices in designing machinery or structures, and many studies have been carried out on the fatigue strength of the bolt-nut joints having standard specifications specified in ISO 898's. However, there are many other practical applications of bolt-nut assemblies in which the mechanical properties of nuts (or female threaded fasteners) are not in accordance with ISO standards. This paper deals with the fatigue strength of such types of bolt-nut joints. Nut height, nut property class and nut material are selected as variables, and their effects on the fatigue strength have been investigated both by fatigue testing and FEM analysis. The results show that all of the variables affect on the fatigue strength and/or failure mode, and hence, it is concluded that we should pay more attention on the nut specifications in the fatigue design of bolt-nut assemblies.
