Effect of nut geometries on screw thread stress distribution: photoelastic results

The structural merits of lip-type nuts engaging with ordinary bolts are assessed experimentally by means of frozen-stress photoelasticity. Thread pitch, lip radial thickness, and lip length are selected as design variables and scanned for possible effect on the maximum stress within the connection. In this respect, the length of lip is shown to play a major role while the other parameters have no decided effect. It is found that a nut with a lip covering 60 percent of total height reduces the stress concentration in the screw by nearly 40 percent with respect to a standard nut of equal height and outside diameter. This improvement is achieved without producing higher stresses in the nut than in the screw.