A nonlinear finite element connector for the simulation of bolted assemblies

Fine scale computations of bolted assemblies are generally too costly and hardly tractable within an optimization process. Thus, finite elements (FE) connectors or user-elements are commonly used in FE commercial codes by engineers as substitutes for bolts. In this paper, a non-linear FE connector with its identification methodology is proposed to model the behaviour of a single-bolt joint. The connector model is based on design parameters (bolt prestress, friction coefficient, bolt characteristics...). The axial behaviour of the connector reflects the preload effect and the axial bolt stiffness. The tangential connector behaviour accounts for frictional phenomena that occur in the bolt's vicinity due to preload thanks to an elasto-plastic analogy for friction. Tangential and normal behaviours identification is performed on a generic elementary single bolt joint. The connector has been implemented in ABAQUS through a user-element subroutine. Comparisons of the quasistatic responses between full fine scale 3D computations and 3D simulations with connectors on various bolted assemblies are proposed. Results are in good agreement and a significant gain in terms of CPU time is obtained.