| In numerical modeling of structural components and systems challenges are introduced in the modeling of bolted connections among which bolt model, contact algorithm, and modeling of bolt pretension are most noticeable. Bolt modeling is found to be particularly challenging due to the complexities introduced by providing non-conforming mesh for the exact modeling of bolt assemblage, which may destroy the monotonic convergence in finite element algorithms. Thus, this study focuses on developing a general purpose semi-meshless cyclic plasticity-based coupled nonlinear finite element computer program that can predict the response of structural systems subjected to non-proportional static and cyclic loads.; In the meshless contact algorithm, contact or separation is modeled by locking or unlocking the contact pairs, respectively. The contact surfaces are attached to one another through finite pairs of contact nodes which are initially located in identical spatial coordinates (and are given the same DOFs). The incremental system equilibrium equation is solved for the incremental displacement, strain, and stress components from which the relative total displacement and traction of the contact pair in the normal direction are determined. In each iteration, contact pairs are checked to see if their contact status is changed. For those contact pairs assumed to be in contact or separated in the previous iteration, their normal traction and relative normal displacements are checked, respectively. If separation has occurred, for the next iteration they are assumed to be separated and they are assigned independent DOFs. On the other hand, in case of penetration, the contact pair is assumed to be locked and they are given the same DOFs for the next iteration. Also, for meshless bolt modeling, two innovative modeling approaches are introduced. One-dimensional bolt model, assumes that bolt behaves as a truss element with just axial stiffness while, the more sophisticated three-dimensional bolt model can model both axial and bending stiffness of the bolt. In both models, it is assumed that bolt head and bolt nut behave as rigid plates, which makes the formulation of the two models based on imposing certain constraint equations on nodes in contact with bolt head (or nut). (Abstract shortened by UMI.)... |
