Study of joining bolts under tensile loading

Abstract

In this modem era a lot of development has taken place in jointing technology but still the bolted joint is the most important jointing method. Bolted joints are mostly used in motor transport, aircraft and other machine tool industries. The effectiveness of a bolted joint is usually measured by its ability to maintain an adequate level of clamping force on the jointing surface. It has been found that friction condition between the bolt under head and the matting surface has greatly influenced the magnitude of the clamping force and wrenching torque. In the present study detail experimental investigation, regarding the behavior of jointing bolt under different lubricating condition as well as under external load was carried out. Further more, the relationship between the wrenching torque and the torque transmitted to the shank of the bolt was also established. It has been observed that the better the lubricating condition between the bolt under head and the mating surfaces, the better the torque transmitted to the shank of the bolt and hence better the pre load developed in the bolt body. It has also been seen that in all the cases, the maximum load carrying capacity of a tightened bolt, when external tensile load was applied, remained the same. Moreover with the application of external tensile load, up to the ultimate load, the shank torque reduces to the residual torque of the bolt material. In order to do the aforementioned experimental investigation a test rig and a 30 kn capacity of compressive type load cell were designed, fabricated and calibrated. During experiment, attention was particularly given to find out the pre-load developed, torque transmission and the effect of external tensile load on shank torque. Finally it has been concluded that friction conditions between two matting surfaces not have any effect on the maximum load carrying capacity of the bolt.