A new hexahedral solid element for three-dimensional FEM simulation of sheet metal forming

A new 8-node hexahedral mixed element was developed to facilitate the analysis of large strain, nonlinear, sheet form operations with material having complex elastic-plastic constitutive behavior. A new approach was followed to maintain the desired simplicity of formulation while suppressing locking and hourglassing. Analysis of the deformation field showed that the hourglassing modes were mutually orthogonal and thus contributions to strain could be identified individually. With this result in mind, shear and volumetric locking were avoided by ignoring, respectively, the shear and dilatational strain terms attributable to hourglass modes, thus neglecting the work of deformation associated with them. By this simple and direct method, the new element has the simplest formulation among all mixed hexahedral elements that found in the literature. The new element preserves the 8 integration points of the linear hexahedral element and there is no enhanced strain term needed.; As with all solid elements developed for coarse mesh applications with large problems and nonlinear behavior, the work of deformation of an element is not evaluated precisely. More further, the only way to assess the trade-off between large element performance and fine-mesh convergence (a characteristic only of pure displacement elements, which are generally impractical for large nonlinear problems) is through numerical testing and comparison.; The new element has been tested using a variety of special problems as well as two large-scale forming processes. Five other elements were also tested and all the results compared. The overall performance of the new element is the best among the 6 tested elements, it does not suffer locking and implementation of constitutive equations is simple and rapid.