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Exceptionally slow convergence of user-defined material model
Posted 1 mar 2016, 07:35 GMT-5 Structural Mechanics Version 5.2 0 Replies
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I decided to try out the functionality of user-defined routines in COMSOL, and chose a simple starting point - "incompressible" neo-Hookean.
I am using the regular form (same one used in COMSOL, according to the documentation) with a split strain energy function into isochoric and volumetric parts.
As I understand it, the output that COMSOL requests from the material routine is simply the continuum tangent stiffness, obtained by differentiating the second PK-stresses with respect to Green-Lagrange strains. My problem is an extremely slow convergence (or none at all, sometimes), as compared to the built-in neo-Hookean model. I have checked the expression for the tangent stiffness, but can't find any errors.
I have two questions in regards to this:
1) Am I correct in understanding that COMSOL requests the material tangent stiffness matrix (in Voigt notation), obtained by differentiating second PK-stresses?
2) Have anyone here had similar convergence issues with your custom material routines?
Best regards,
Björn
Hello Björn Fallqvist
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