Development of a solid bolt/nut model utilized in 3D-FE structural analysis for bolted joints

This study aims to develop a solid bolt/nut model utilized in 3D-FE analysis for the strength design of mechanical structures with bolted joints to obtain the internal forces and the bending moment acting on the bolt/nut assembly. A solid bolt/nut model has an advantage to save the time for calculation drastically since it requires fewer numbers of elements and contact surfaces. On the other hand, the solid model has to have the same axial and flexural stiffnesses as the actual bolt/nut assembly to maintain the accuracy of the equilibrium of forces and displacement in the bolted joint and of the internal forces or stresses acting on the bolt/nut assembly calculated. This study depicts how to determine the design parameters for the solid model directly from the specifications of actual bolt/nut assemblies appropriately. To demonstrate the validity of the solid model developed, the stresses acting on the bolt/nut assembly in a cylinder cover bolted joint subjected to internal pressure are calculated by 3D-FE analysis using (a) fully modeled axi-symmetric bolt/nut assembly and (b) the solid bolt/nut model developed. The results obtained using the solid model proposed coincide accurately with the ones using the fully modeled axi-symmetric bolt/nut assembly model, and show good agreement with the measurement using the strain gauges put on the bolt shank as well. This clearly highlights the effectiveness and usefulness of the solid model developed.