Finite Element Stress Analysis of Bolted Joint and an Estimation of Axial Bolt Force

Abstract

An estimation of actual axial bolt force ill bolted joints is difficult. In practice, supersonic transducers have been used to measure the axial bolt force. However, the method is complicated and the accuracy for measuring the axial bolt force of bolts with shorter clamping length and the smaller nominal diameter is worse. It is necessary to develop a simple method to estimate the axial bolt force more accurately in practice. The displacement at the bolt head is proportional to the axial bolt force. Thus, when the relationship between the displacement and the axial bolt force is obtained, the bolt force is estimated as an inverse problem by using the bolt head displacement measured by a laser displacement transducer. In order to obtain the relationship between the displacement at the bolt head and the axial bolt force, finite element calculations were carried out. The effects of the friction coefficient between the contact surfaces of the bolt head and the clamped parts and the thickness of the clamped parts (hollow cylinder) are examined on the bolt head displacement by the FEM. As a result, the relationship between tile displacement and the axial bolt force was found to be linear by the FEM calculations. Then, the measurements of the bolt head displacement were carried out and the axial bolt force was measured by strain gauges attached at the bolt shank. By using the measured displacement and the relationship between the displacement and axial bolt force, the axial bolt force was estimated. The estimated values of the axial bolt force were in fairly good agreements with those measured by the strain gauges. It can be concluded that the method is available for measuring the axial bolt forces in bolted joints accurately.