When the solution becomes unstable, the time history response of solution variables such as displacements will usually oscillate with increasing amplitudes. Failure to use a small enough time increment will result in an unstable solution. The time increment used in an analysis must be smaller than the stability limit of the central-difference operator. For further discussion, see вЂњComputational costвЂќ below. The time increment chosen by Abaqus/Explicit also accounts for any stiffness behavior in a model associated with penalty contact. In general, the actual stable time increment chosen by Abaqus/Explicit will be less than this estimate by a factor between and 1 in a two-dimensional model and between and 1 in a three-dimensional model.

This estimate for is only approximate and in most cases is not a conservative (safe) estimate. When the transverse shear stiffness is defined for shell elements (see вЂњShell section behavior, вЂќ Section 29.6.4), the stable time increment will also be based on the transverse shear behavior. In general, for beams, conventional shells, and membranes the element thickness or cross-sectional dimensions are not considered in determining the smallest element dimension the stability limit is based upon the midplane or membrane dimensions only. Where is the smallest element dimension in the mesh and is the dilatational wave speed in terms of and, defined below. When degrees of freedom at a node are activated by elements with no mass (e.g., spring, dashpot, or connector elements), care must be taken either to constrain the node or to add mass and inertia as appropriate. When degrees of freedom at a node are activated by elements with a nonzero mass density (e.g., solid, shell, beam) or mass and inertia elements, a nonzero nodal mass or inertia occurs naturally from the assemblage of lumped mass contributions. Nodes that belong to Eulerian elements also do not require mass, since the surrounding Eulerian elements may be void at some time during the simulation.

Nodes that are part of a rigid body do not require mass, but the entire rigid body must possess mass and inertia unless constraints are used. More precisely, a nonzero nodal mass must exist unless all activated translational degrees of freedom are constrained and nonzero rotary inertia must exist unless all activated rotational degrees of freedom are constrained. The explicit integration scheme in Abaqus/Explicit requires nodal mass or inertia to exist at all activated degrees of freedom (see вЂњConventions, вЂќ Section 1.2.2) unless constraints are applied using boundary conditions. Uses a consistent, large-deformation theory-models can undergo large rotations and large deformation Д¬an use a geometrically linear deformation theory-strains and rotations are assumed to be small (see вЂњDefining an analysis, вЂќ Section 6.1.2) Д¬an be used to perform an adiabatic stress analysis if inelastic dissipation is expected to generate heat in the material (see вЂњAdiabatic analysis, вЂќ Section 6.5.4) Д¬an be used to perform quasi-static analyses with complicated contact conditions andДЄllows for either automatic or fixed time incrementation to be used-by default, Abaqus/Explicit uses automatic time incrementation with the global time estimator. This suggests that both models are well-suited for modeling elastoplastic materials in common industrial forming processes.Is computationally efficient for the analysis of large models with relatively short dynamic response times and for the analysis of extremely discontinuous events or processes ДЄllows for the definition of very general contact conditions ( вЂњContact interaction analysis: overview, вЂќ Section 36.1.1) Interestingly enough, although both models led to remarkably different results in shear-dominated single element deformation tests, the structural simulations of a deep drawing, draw bending and thermoforming process delivered nearly congruent results. Several numerical tests were conducted to assess their respective capabilities. Both models allow for nonlinear isotropic and kinematic hardening of Voce and ArmstrongвЂ“Frederick type and were implemented as user material subroutines (UMAT) into ABAQUS/Standard. The aim of this work is to review and numerically compare two inherently different types of formulations of finite strain elastoplasticity, namely hypoelastic- and hyperelastic-based plasticity models, with special reference to their applicability in forming processes. This emphasizes the importance of reliable finite strain elastoplasticity models in corresponding finite element simulations. Industrial forming processes are usually characterized by large plastic strains and rotations of material elements.

Hypoelastic connectors abaqus 6.13