Mechanical maps initial stress and strain data by direct interpolation of individual components. Numerically, this is the simplest method but it is physically inconsistent, especially in nonlinear solid mechanics applications.
Tensor fields associated with solid mechanics applications – such as stress, strains, and plastic strains – are not independent of each other. The strains are related to the displacements through the compatibility equations and the stresses are related to strains through the constitutive equations. In addition, for plasticity, other equations like the flow rule also relate the plastic strain tensors to the stress tensors. Hence independent interpolation of these tensors will violate these equations which in turn will create a globally un-equilibrated state of stress in the mapped domain. So, using these mapped quantities in nonlinear solid mechanics applications is not recommended. However, irrespective of these limitations, if the user wants to use these mapped fields, it is strongly recommended that he uses a dummy load step in the solver with the imported initial stress/strain results and only apply new loads and/or boundary conditions if and only if the dummy load step converges and the resulting deformation is physically consistent with the problem. Generally, the analysis with the dummy load step will not converge with loads generated via incorrectly mapped stress/strain fields. Even with a chance convergence in the dummy load step, no guarantee can be given with respect to the correctness of the results.
Mechanical provides an option to view contours of Equivalent (von-Mises) stress/strain, as well as individual components (XX, YY, ZZ, XY, YZ and ZX) using Component property in Details pane of Imported Initial Stress/Strain. User can insert a Mapping Validation object under the Imported Load, perform Source Value validation, and set the Display In Parent property to to view overlapping contours of interpolated data with source data and compare the equivalent stress/strain from the interpolated data with the source data.
The equivalent stress and strain are calculated using the von Mises equation:
