An Evaluation of Common Analysis Methods for Bolted Joints in Launch Vehicles

Abstract

Accurate calculation of bolt force in a bolted joint under external loads and temperature changes is a fundamental requirement in many industries. Approximate hand formulas, based on idealized mechanical models, are widely used. We evaluate the accuracy of several hand formulas by investigating the consistency of the underlying models and by comparing hand predictions to detailed nite element results. We exploit nite element predictions for the dierential thermal expansion problem to provide estimates of eective geometric quantities uncontaminated by the prying action introduced by external forces. We then use these accurately determined eective quantities to make hand predictions of bolt force in a ange joint under combined external loading and temperature changes. We compare these hand predictions to results from a second detailed nite element model of the ange joint. Finally, we use the ange joint model to gain insight into the joint softening that arises from gradual, nonlinear opening of the ange gap under external tension.