FEM Contact Stress Analysis at the Bearing Surfaces in Bolted Joints With Washer Under Tensile Loadings

High strength bolts with washers are utilized widely for high reliability. The usage of the high strength bolts enables higher bolt preload, thus the contact stress at the bearing surfaces increase. When a bolted joint is under external axial load W, the axial bolt force increases by Ft and the contact stress increases at the bearing surface. This may cause the plastic deformation and a decrease in the axial bolt force. Consequently, it is important to determine the initial axial bolt force (bolt preload) considering external load. In this paper, The characteristics of hollow cylindrical bolted joints with plain washers under external tensile loadings are analyzed using elasto-plastic FEM such as the contact stress distributions, plastic displacement (permanent set) at the bearing surfaces and the load factor Φ = (Ft/W). The effect of thickness of the plain washers on the contact stress distributions and the plastic displacements are clarified. It is found that the effect of the plain washer specified in JIS B 1256 is small on the contact stress distributions and the plastic displacements. Also, the effect of the external load on the changes in the contact stress distributions and the plastic displacements at the bearing surfaces using the values of load factor is observed to be small. The prediction for the reduction in axial bolt force was compared with the experiment. As a result, it was found that a higher bolt preload shows a small reduction in axial bolt force.