Measurement of Stress Concentrations in Threaded Connections

Abstract

The strees-concentration factors in bolt and nut fastening under tension are obtained by the copper electroplating method of strain analysis. In the bolt-thread roots, high stress concentrations occur at two locations, one being at the termination of the threaded portion and the other at the root of the first thread engaged in the nut. The mutual interference of the stress concentrations is examined by varying the distance between the above two locations. Stress concentrations in the bolt-thread roots engaed in the nuts with various shapes are also measured, in which one group of the nuts is different in height and the other group is the stepped nuts with tapered lips. By using a nut of different material from that of the bolt, the effect of the material property of the nut on the peak stress in bolt-thread roots is investigated.