Abstract

In many applications in industrial field, bolted joints are often subjected to a combination of axial and bending loads, which cause stress concentrations in the thread root and in the transition from bolt shank to bolt head. The design of bolted joints is typically based on nominal stress, i.e. these local effects are not taken into account. However, in order to properly analyze the fatigue strength of a bolted joint, multi-axial stress state and support effects due to stress gradients cannot be neglected. Within numerical investigations, the evaluation of the local stress at the notch root requires a fine discretization of the finite element model in the notch area, which leads to a high amount of calculation time, especially in case of 3D simulations. To ensure that the results of the finite element analysis are not affected by size and shape function of the elements, the convergence behavior needs to be considered. The aim of the work is a study on the relationship between 1) mesh density and shape function used to model highly notched specimens and 2) the evaluated maximum stress and stress gradient on the surface. Numerous mesh configurations with different element sizes have been investigated in the notch area and compared with an extremely dense mesh. The convergence of maximal stress and stress gradient has been analyzed and discussed. The results show that the convergence rate for the maximum stress is much better than that for the stress gradient. However, in terms of computation time, it is usually not advantageous to increase the size of the finite element model of a bolted joint with a very dense mesh. Hence, a less dense mesh is proposed, which allows a good evaluation of the stress gradient, even if a deviation compared to the results from extremely dense mesh occurs.