Search

Flow drill screw (FDS) joining is a modern mechanical fastening technique for connecting metal parts in lightweight car structures. Finite element simulation of FDS joining probably is one of the biggest challenges for CAE engineers in automotive applications. This is mainly because finite element methods inevitably encounter utmost numerical difficulties associated with meshing issues in modeling the extensive plastic deformation and material failure taking place during the thread forming operation in the FDS driving process. This paper presents a FDS thread forming simulation using a new particle method based on authors’ recent work (Pan et al. in Comput Mech, 2019. 10.1007/s00466-019-01673-8). Different from other particle stabilization methods which are obtained by modification of the variational equation using either residual or non-residual stabilization terms, the present method introduces a novel velocity smoothing algorithm to achieve the stabilization effect. It is shown that the semi-discrete equation based on the smoothed velocity field is consistently fulfilling the conservation of linear and angular momentum. Since the new method does not require stabilization terms, it avoids the fundamental difficulty inherent in the stabilization stress computation, thus computationally more efficient. Finally, the stabilized formulation is supplemented with the adaptive anisotropic Lagrangian kernel and bond-based failure criterion to extend the application in severe deformation and material failure analysis. Three numerical benchmarks including one FDS thread forming simulation are utilized to demonstrate the effectiveness of the new approach.

Abstract: An efficient Galerkin meshfree formulation for three dimensional simulation of large deformation failure evolution in soils is presented. This formulation utilizes the stabilized conforming nodal integration, where for the purpose of stability and efficiency a Lagrangian smoothing strain at nodal point is constructed and thereafter the internal energy is evaluated nodally. This formulation ensures the linear exactness, efficiency and spatial stability in a unified manner and it makes the conventional Galerkin meshfree method affordable for three dimensional simulation. The three dimensional implementation of stabilized conforming nodal integration is discussed in details. To model the failure evolution in soil medium a coupled elasto-plastic damage model is used and an objective stress integration algorithm in combination of elasto-damage predictor and plastic corrector method is employed for stress update. Two typical numerical examples are shown to demonstrate the effectiveness of the present method for modeling large deformation soil failure.