Abstract:

ESDU 13008, which supersedes ESDU 85004, gives stress-endurance curves through the results extracted from the literature of some 80 constant amplitude fatigue tests on five different types of studs with machined threads torque-tightened into a steel block. For fatigue failures in the thread of the nut, the studs failed at the first loaded thread in the block; see ESDU 84037. The relative merits of the five designs are compared. In particular, the provision of a proper seating allows the initial tightening torque to give a beneficial pre-tension that relieves the load subsequently applied to the stud thread by the assembly of a component on it. A discussion of how stud design detail affects the load paths through an assembly, and hence the fatigue strength, is also included. Two worked examples show how the fatigue strength of a collar stud and a normal stud can be established in practical situations.