A Numerical Investigation of Bolt Underhead Temperature Evolution During Tightening

The temperature rise that occurs due to frictional heating under the turning fastener head during the tightening process of bolted joints can have a significant effect on surface and thread wear and galling. The subject has received little attention in the scientific literature. In the present study, the spatial and temporal temperature rise in a bolt during the tightening process are numerically investigated for a variety of sliding and loading conditions using finite difference methods. The effect of tightening speed, angle of turn, and frictional energy input is numerically investigated. Tightening speeds were varied between 1 RPM and 3000 RPM and the angle of turn was varied between 15 and 720 degrees past free spinning; this range of turn simulates joint stiffness variation from very hard to very soft joints. Significant temperature rises of the bolt underhead were observed for higher tightening speeds and the potential for localized melting or near-melting temperatures was shown. In the case of lower tightening speeds, the temperature rise was not as dramatic, but temperature increases are then observed along the length of the shank, showing the possibility of contributing to thermally induced galling between the threads. Due to the temperature variations observed in most cases in the underhead and along the bolt shank, this study indicates that such thermal effects should be considered when modeling the wear of bolted joints, particularly in cases involving larger tightening speeds or softer joints.