Abstract
The yield clamping force of the bolt in plastic region tightening depends on the yield condition at the threaded portion under combined load consisted of axial tension and thread torque induced by tightening, namely the interaction curve for the yield. A new estimation method for the interaction curve at the threaded portion based on the flow theory, proposed in the previous report, is superior to the traditional one based on the local yield condition ;however the proposed method has a some estimation error in comparison with the experiment. Experimental results obtained for the combined load on cylindrical test-pieces show that the estimation error is caused by idealizing the thread portion as a smooth cylinder having stress area. For the exact estimation of the interaction curve, it is recommended to idealize the thread portion as a smooth cylinder of minor diameter of thread.
