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Explicit Solid Mechanics
Posted Mar 16, 2015, 7:12 a.m. EDT Studies & Solvers, Structural Mechanics Version 5.0 4 Replies
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I have a solid mechanics problem comprising a hyperelastic material (Mooney-Rivlin(2 params) that is placed under compression resulting in large deformation. The construction is such that contact takes place resulting in a change in compressive stiffness as load is applied.
To date I have had very limited success using an auxillary sweep load with Lagrangian contacts in 2d axisymmetric and as soon as I consider 3D the success in terms of convergence if further reduced.
I'm thinking that perhaps I need to consider using an explicit time-dependent solver (no previous experience), Runge-Kutta, but when I attempt to set this up I getting the following error "singular explicit time stepping matrix" ...obviously I have something not quite correct but I am unsure where to start looking. I have also set 'linear solver to lumped'.
CG
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The Time Explicit solver will not work here. One reason is that the mass matrix is singular for this family of problems, since all degrees of freedom (e.g. the auxiliary pressure in the hyperelastic material) do not give mass matrix contributions.
There are several possible causes for the problems in your original model. Some examples:
- A Mooney-Rivlin material is only conditionally stable. For some strain states, the material model itself is singular.
- The penalty factor may need adjustment
- The mesh may need refinement
Regards,
Henrik
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The Time Explicit solver will not work here. One reason is that the mass matrix is singular for this family of problems, since all degrees of freedom (e.g. the auxiliary pressure in the hyperelastic material) do not give mass matrix contributions.
Thank you for your reply.
When you say family of problems I'm not sure what you mean ...the use of hyperelastic materials?
Cheers CG
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This solver is mainly intended for some transient wave-type problems, see the documentation. We do not recommend the Time Explicit solver for any structural mechanics purpose, since there are many features which are not adapted to it.
As an example, Contact using the Augmented Lagrange method will not work either.
Regards,
Henrik
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CG