IHS ESDU Fatigue strength of external and internal steel screw threads under axial loading. (Standard forms not greater than 1.0 inch diameter.) 84037

ESDU 84037 provides the evaluated analysis of some 1500 fatigue tests, drawn from the literature, on externally threaded members loaded through the nut. The results are shown in two graphs of stress against endurance, one for cut threads and one for form-rolled threads. They show that, for five standard thread forms (UNF coarse and fine, BSF, BSW and ISO metric coarse) and over a range of diameters from 0.25 in (6.35 mm) to 1.0 in (25 mm), the method of manufacture dominates fatigue strength. Variations resulting from five methods of thread manufacture showed fatigue limits that varied by a factor of up to three. Variations resulting from thread form or size within any one method of manufacture were too small in relation to the scatter of results to be distinguished. For internally threaded components, an evaluated analysis of some 50 tests, drawn from the literature, is given. Such components rarely fail in fatigue, but the results show that, if a thin nut is required, the risk of fatigue is reduced by maximising material ductility.