Mechanical Behavior of Bolted Joints Using Powered Torque Wrenches during the Tightening Process

Abstract

  Torque wrenches driven by hydraulic, pneumatic or electric power are commonly used to tighten large bolts. Bolt tightening operations based on the torque control method are generally performed by applying the target torque to the outer surface of the nut. However, torque can sometimes be applied to the bolt head, due to the geometric limitations of the joint. It has been reported that during the tightening process with powered wrenches, the bolt side tightening sometimes produces lower bolt preload compared to the nut side tightening. This is caused by contact between the bolt cylindrical body and bolt hole surface, which can occur during tightening operations, and this friction consumes a part of the tightening torque. This paper is intended to identify critical conditions for the bolt body contact and slip at the bolt head bearing surface in a mathematical form. The slip phenomenon may lead to shortage of bolt preload. An equation that relates torque with bolt preload, which takes into account the effect of bolt body contact, is given in a similar form to the ordinary bolt-nut tightening. This paper aims to substantiate the validity of the proposed equation by conducting tightening experiments using a pneumatic wrench.