Implementations of User Defined Shell Elements and Material Models to LS-DYNA and Their Application

Robustness, accuracy and good computational performance for large scale models are some of the salient requirements for general purpose finite element programs. A new one point quadrature shell element that meets these requirements has been previously developed in the works of Cardoso & Yoon (2005). In the theory, the finite element strain-displacement matrices are described in a convective coordinate system for the efficient implementation of a physical stabilization procedure. In order to increase the computational efficiency of the shell element, in this work the resultant-stress equations are formulated by reducing dimensionality to the shell's mid- surface. In order to improve the simulation accuracy of sheet metal forming simulation utilizing commercial software, the proposed one-point quadrature element and a typical fully integrated element have been implemented to LS-DYNA using the user element interface. In addition, a plane stress yield function (Yld2000-2d, Barlat et al. (2003)) and a new anisotropic model (Yld2004-18p, Barlat et al. (2005)) that accurately describe the anisotropic behavior of aluminum alloy sheets were also implemented to LS-DYNA user material option (UMAT). Several examples including sheet forming are presented to demonstrate the element's robustness and efficiency and to verify the interface.