Stress analysis of some nut-bolt connections with modifications to the external shape of the nut

Abstract

The effect on the stress levels in an axially loaded bolt has been investigated for the case where a nut which incorporated a circumferential groove in its outer surface was used. It was found from a three-dimensional photoelastic frozen stress study that the modified nut reduced the maximum stress in the bolt by 5 per cent. The addition of a bevel to the load bearing face of this nut further reduced the maximum stress to 74 per cent of its value in a standard connection. It has been established that these modifications reduce the maximum shear stress in the roots of the nut threads, and that the stress concentration associated with the groove was smaller than the maximum stress concentration in both the nut and bolt thread roots. The increase indicated by photoelastic analyses in the strength of the connection produced by these modifications, has also been substantiated by fatigue tests of steel connections, but these results are not reported in this paper.