Effects of thightening torque to the tensile strenghth of bolts and stress-strain relations

EFFECTS OF THIGHTENING TORQUE TO THETENSILE STRENGTH OF BOLTSAND STRESS-STRAIN RELATIONS( M.Sc. Thesis )Ziya Turgut ÖZMENGAZI UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYMarch 2005ABSTRACTBecause of the uncertainities about how much of the torque is lost dueto the friction between the bolt head and the grip material surface ,aiming to determine the risks result from giving preloads to the boltsexceeding the yielding point either consciously or not, M16 x 160, DIN931, 6.8 Grade bolts are torked using a torque wrench at various valuesproviding preloads over the yield point followed by tensile tests using aspecial apparatus. Ultimate tensile and yield strength values obtainedfrom torqued tensile tests are compared with the results obtained fromthe direct tensile tests and a proportional increase in yield strength isobserved according to the applied torque up to a certain value and thisphenomenon is tried to be explained with an elastoplastical approachobtained from Prandtl Reuss and von Mises criterions on the circularsection of the bolt .No decrease in ultimate tensile strenght was observed but increase inthe yield strenght caused a decrease in the deformation capacity of thebolt.Science Code : 914. 1. 073Key Words : Elastoplastical approachPage Number : 73Adviser : Prof. Dr. Mahmut ÖZBAY