<title>Simulation of ultrasonic preload measurement on a bolt in an interference fit joint</title>

An instrument called the ultrasonic extensometer is used to measure tensile preload in bolts. Commercial ultrasonic extensometers are intended for bolts in a clearance fit joint and not the interference fit joint. This paper develops theory governing the ultrasonic preload measurements when a diametrical interference is present in the joint. The theoretical model accounts for a change in the joint temperature. The model accounts for two cases, one when the bolt is preloaded by turning the nut and the other when the bolt is loaded due to a direct pull on bolt. The paper provides an ultrasonic technique to estimate the interference pressure and diametrical interference without disassembling the joint. A special case of the model, when the diametrical interference is zero, provides a more precise theoretical model for the preload measurement on bolts under pure tensile preload. The theory is modeled in a computer program to provide the preload measurement characteristics. A numerical example computes preload characteristics of a sleeve bolt whose experimental characteristics have been previously published by the author. The experimental and theoretical characteristics show good agreement.