Analysis of Tightening Torque in Fasteners

Generally to provide clamping, a bolt is preloaded by applying torque. The value of applied torque is normally calculated considering the proof strength of the bolt. The bolt is usually preloaded in tension to 75% of its proof strength. Sometimes this value of torque is not applicable in applications where the yield strength of internal threads is very less because it can cause stripping of internal threads and which leads to failure of joint. In this paper different cases are considered for fastening and the method to choose the correct torque is proposed. It also takes into consideration of length of engagement of thread and stripping of internal threads.