A comparison of shrink-fit holding torque using probabilistic, micromechanical and experimental approaches

A shrink-fit is a semi-permanent assembly system that can resist the relative movement or transmit torque between two components through the creation of high radial pressures at the interface of its constituent parts. The traditional approach to determine the holding torque of a shrink-fit is based on Lame´ʹs equation to predict radial pressures at the interface of the components and knowledge of the coefficient of friction and length of contact. This paper examines the validity of this approach and a variant, which takes into account surface roughness conditions of the interfacing components, by comparing statistical distributions of the holding torque with those found experimentally for a sample of a particular shrink-fit configuration. The probabilistic results of a micromechanical approach are presented which show good comparison with experimental results, indicating that current design formulae are inadequately predicting holding torque. In addition, the phenomenon of increased holding torque with loading cycle number is observed experimentally, and areas where further work needs to be conducted in order to model the situation using frictional and plastic shakedown are outlined.