Finite element modeling and analysis of structural joints using nuts and bolts

Abstract

The majority of the structural failures of mechanical structures and systems are found in joints rather than continuous material. Joints have historically consisted of assemblies involving nuts, bolts, screws, etc. and the design and analysis of these joints can be quite challenging. This work provides two baselines on the finite element modeling (PEM) methods and analysis of a nut and bolt joint. The first baseline involves a basic modeling method using linear calculation of 2D plates and bar elements, and the second baseline involves one of the more complex methods using non-linear calculation of 3D solids. The two methods are described for modeling of a joint for two test conditions, namely the double shear joint in tension with two different bolt sizes and two plate thicknesses. First, the simplified method of rigid elements and equivalent strength beam elements is considered. This technique lacks the simulation of bearing stresses, stress concentration at the bolt hole location, and bending stiffness of the bolt. The second method, uses 3D models that provides the actual nut and bolt surfaces, bearing stresses are introduced in the joint modeling. Classical hand calculations are carried out on the static tests and compared with the FEM results. Additionally, the effects of element mesh refinement on the nut and bolt contact surfaces, and types of contacts are analyzed for the 3D models. A parametric study is carried out on the stresses developed and stress concentration factors.