Abstract
The axial tension of the bolt in plastic region tightening is influenced by the yield point load of the threaded portion under combined loads of axial tension and thread torque induced by tightening, namely interaction curve for yield. However the traditional estimation method for the interaction curve of the threaded portion has some problems. Firstly, a new estimation method for the interaction curve of the threaded portion is proposed based on the flow theory. Secondly, a combined load testing machine is developed in order to apply the tensile and torsional combined load on the threaded portion of the bolt, and the interaction curves of the threaded portion are obtained experimentally. In conclusion, it is shown that the new method is superior to the traditional one considering only the local yield condition.
