Abstract
The experimental considerations are performed to clarify the fatigue behavior of the bolt tightened up to the plastic region in the joint. The T-flange joint is treated as an example of bolted joints. The experiments are executed as the co-operative investigation by six bolt makers and a laboratory of the university. Firstly tension tests, tightening experiments, and fatigue tests of the bolt-nut joint are done in order to examine the mechanical properties of the bolt. Secondly the fatigue tests of the T-flange joints are performed in the same loading condition and in the three different tightening conditions - (a) elastic region tightening, (b) elastic limit tightening, and (c) plastic region tightening. As a result, the failure probability is found to be least in case (c), and greatest in case (a). These results coincide with the estimation from the stress measurements for the bolt in the T-flange joint. On the other hand, the difference in the behavior of the preload loss during fatigue tests are not so remarkable between three tightening conditions. Finally it is concluded that the bolted joints in the plastic region tightening have the more safety against fatigue because of higher preload, i. e. lower load amplitude on the bolt.
