Joint Interface Contact Area Predictions Using Surface Strain Measurements

Abstract

Bolted joints are vital constituents of almost every small-to large-scale built-up structure. An especially important aspect of bolted joint modeling is the prediction of the contact area inside the interface of the joint based on the torque applied to the joint and surface characteristics. This is because the joint interface contact area effectively determines the stiffness of the joint as well as the dissipative qualities resulting from slip-stick friction interactions. This research introduces a novel method of estimating actual contact areas inside the interfaces of bolted joints by measuring the strains on the external surfaces induced by the tightening of a bolt. This method can determine contact areas without directly interfering with or altering the interface like existing methods. The experimental specimen used to demonstrate the technique consists of two flat plates with a carriage bolt on the top plate. A carriage bolt instead of a conventional bolt has been used to facilitate surface strain measurements, measured using the digital image correlation measurement technique. Contact areas inside the interface are measured using pressure-sensitive films, and the torque is measured using a digital torque wrench.