Stress analysis of some nut-bolt connections with modifications to the nut thread form

Six photoelastic frozen stress models of ISO nut-bolt connections loaded in pure tension were studied. Four of these models had modifications to the threads at the load bearing end of the nut. These modifications included tapered truncation of the thread crests and taper of the whole thread form for a portion of the nut length. The maximum stress in the bolt always occurred within one pitch of the load bearing face of the nut. Truncating threads increased the maximum bolt stresses. Tapering the whole thread form reduced the maximum stress and produced a more uniform load distribution in the bolt. The conditions at the load bearing face of the nut were found to influence the load distribution in the bolt threads more than the stress concentrations in the bolt.