It is observed that T-bolt fracture of DT III fastener affects the safety of railway operations. The present study is aimed at finding solution to this critical issue of DT III T-bolt fracture. The paper is based on outcomes of field studies and analysis of relationship between bolt installation torque and stress. A refined DT III fastener model is established based on test data and nonlinear contact theory as per the actual size of each component. It is being observed that head-shank joint is a critical area during service. With respect to fatigue and stress, when the installation torque is less than 300 KN-mm, the bolt is prevented from yielding during installation. To a certain extent it also improves the fatigue life of bolt. From the frequency spectrum point of view, the vibration sensitive frequency band (1050-1100 Hz, 1230-1270 Hz) of bolt in service is very close to the main frequency of bolt vibration (1200 Hz). It may cause bolt fracture. In order to avoid resonance, the train operational speed should be strictly controlled between 115 km/h and 120 km/h.
Keywords: DT III fastener; bolt; fatigue analysis; installation torque; refined model.