Numerical Investigation of the Evolution of the Heat Partition Factor During Bolt Tightening

Abstract

The temperature rise that occurs due to frictional heating under a turning fastener head during the tightening process may result in changes in the mechanical and thermal properties of the bolt and workpiece and can lead to wear and even galling of the underhead and the threads of bolted joints. In order to properly model this temperature rise, it is important to properly account for the fraction of the interface frictional energy that is transmitted to the bolt head. This study focused on numerically investigating the frictional temperature rise that occurs underhead during the assembly of a bolted joint and the evolution of the average bolt heat partition factor as a function of time. Numerical simulations were conducted for tightening speeds varying between 1 and 1,000 rpm and for different bolt/workpiece material combinations. The bolt heat partition factor was shown to vary with time but did not depend on the assumed tightening speed. Constant values of the heat partition factor may be assumed at high speeds but not at lower tightening speeds. The initial value of the heat partition factor can be predicted using a theoretical equation, and a general form of a curve-fit equation is proposed to model the asymptotic decrease of this factor as a function of bolt and workpiece material properties.