An Experimental Study of Tightening Effects on Threaded Fasteners with Enlarged Thread Fillet Radius
The uniform thread engagement of nut -bolt makes the stress distribution between the threads more uniform and
thus the nut-bolt assembly becomes more reliable. But due to the manufacturing variables the stresses in the nut and bolt
assembly during tightening and the load sharing of individual mating threads remain non-uniform in general.Studies have
confirmed that the threads of nut-bolt assembly experience stresses being geometrically distributed, initiating from
maximum at the first thread which is near to bearing surface and then reducing subsequently. A large fillet radius at the
thread root which is more than the standard is proposed and to realise the effects, undercutting is done within the thread root
profile of ISO standard M24 bolts so as to induce elasticity in threads and changing the stress distribution from geometric to
simple arithmetic. Four specimens with different undercuts are investigated experimentally for proving the effectiveness of
the proposed modifications. The effect of tightening torque is observed on one experimental set up. The results are compared
between the existing and corrected thread profiles and the corrected thread profile has given better results.
Keywords - Stress Distribution, Fillet Radius, Undercutting, Tightening Force.