Material Problems

If you only have 2 minutes

Material errors come in two kinds: a plasticity solve that fails (usually an unphysical or inconsistent material parameter), and a viscoelastic material used in a static analysis (viscoelasticity is time-dependent and needs a time definition). Check that your material values are physical, and run viscoelastic materials in a time-dependent analysis.

Plasticity solve failed

• Error 90: the plasticity solve hit a non-positive shear modulus. The shear modulus is derived from Young's modulus and Poisson's ratio, so this means one of those inputs is unphysical. Use a positive Young's modulus and a Poisson's ratio between -1 and 0.5.
• Error 91: the plasticity return-mapping could not converge. The hardening is set up so the yield surface outruns the plastic correction, so no amount of plastic flow brings the stress back to it. This is almost always the material's hardening parameters, not the geometry, mesh, or load step:
  • alpha must be zero or positive. A negative alpha makes the yield stress grow without bound, the most common cause.
  • k0 and k_inf must be positive and sensibly ordered; watch for a unit slip (Pa instead of MPa).
  • As a first pass, set the kinematic-hardening terms c = 0 and b = 0 (pure isotropic hardening) to confirm the error clears, then reintroduce them one at a time.
  • Only if the parameters are genuinely correct, take smaller load steps.

Viscoelastic material needs a time definition

• Errors 94, 96, 99, 100: a viscoelastic material was used without a time definition. Viscoelasticity is time-dependent (creep and relaxation depend on how the load is applied over time), so it cannot run in a static analysis. Give the analysis a time definition, a time-scheduled boundary condition or required_timestamps, so it runs as a time-dependent analysis. For a purely static check, use an elastic material instead.

For the material parameters and their valid ranges, see Define Materials.