Contact problems, indentation of cylinder
I have some “sliding interface contact” issues with the attached models (~14mm indentation of a nearly incompressible cylindrical silicone gel with supported sides and central hole). I’ve tried different meshes/contact parameters but little success so far. The attached simple model runs okay but have not been able to recreate this with my more realistic model.
1) The model (e.g. HEX_MODEL_half_size4_4470el_v2.prv) does not run with the auto penalty option. FEBio shuts down with the error message: “The application has requested the Runtime to terminate it in an unusual way. Please contact the application’s support team for more information”
2) What type of contact would be best for this model?
3) Augmented Lagrange contact seems to “pulsate”. Does this mean the penalty factor is too low? Also sometimes there is a sudden shift of elements (only noticed this with Augmented Lagrange contact), where something suddenly gives and the elements slide along the indentor surface.
4) How do you recommend “tweaking” the various parameters? I’ve tried using a simple model to get the parameters to work but they don’t seem to translate well to say a model with a slightly finer mesh.
5) Does it matter whether a geometry feature style surfaces (labelled in blue) are chosen or mesh feature (faces, e.g. a specific selection of element faces) style surfaces (labelled in red) for contact? I would imaging the latter is best since you can select a specific region of the model so FEBio does not have to check all outer surface nodes for contact but only the ones composing the selected region.
6) Sometimes the contact does not work at all (see model HEX_MODEL_half_size8_720el_ref_7680el.prv) even though I think I’ve set it up okay.
7) So far none of my models have run to full depth (~14mm from initial). Can you see any obvious reasons related to my modelling approach why this would be?
8) I’ve tried modifying the load application curve, so that the initial gap is crossed quickly, then the contact is established slowly, then the speed increases and then decreases again towards the end where the high amount of deformation is hard to solve. Is this a sensible approach? e.g. equation 0.05+0.95*(sin(t*(0.5*pi))^2)
9) I’ve tried different mesh densities. The coarser model I’ve attached ran quite far (91%) before it failed so I thought I’d try a denser mesh however this took almost 14 hours and got stuck much sooner. Am I doing something wrong?
10) Do you think the near in-compressibility is an issue for the contact?
Just some general comments:
Preview
- Ctrl+R is a short cut for add rigid constraint, not Run
Postview
- Many display settings (contour, mesh-on etc. ) are not kept when updating
- Transparency is not computed correctly for multiple parts and meshes of underlying part are not visible through transparent part.
- The total displacement contour is incorrect the first time you apply it (looks like x-displacement). If I try say the real x-displacement and then go back it looks correct.
- Iso-surfaces are not cut by cutting planes
- I’ve tried simple models with tetrahedral elements. Apart from the fact that they might be naturally harder to get to work the contour plots of stress (e.g. 1st principal stress) are very asymmetric and unrealistic. Is this purely an issue of tetrahedral elements or are there some stress visualisation issues related to tetrahedrons (e.g. compare the simple models)?
Thanks a lot, kind regards,
Kevin Moerman
I have some “sliding interface contact” issues with the attached models (~14mm indentation of a nearly incompressible cylindrical silicone gel with supported sides and central hole). I’ve tried different meshes/contact parameters but little success so far. The attached simple model runs okay but have not been able to recreate this with my more realistic model.
1) The model (e.g. HEX_MODEL_half_size4_4470el_v2.prv) does not run with the auto penalty option. FEBio shuts down with the error message: “The application has requested the Runtime to terminate it in an unusual way. Please contact the application’s support team for more information”
2) What type of contact would be best for this model?
3) Augmented Lagrange contact seems to “pulsate”. Does this mean the penalty factor is too low? Also sometimes there is a sudden shift of elements (only noticed this with Augmented Lagrange contact), where something suddenly gives and the elements slide along the indentor surface.
4) How do you recommend “tweaking” the various parameters? I’ve tried using a simple model to get the parameters to work but they don’t seem to translate well to say a model with a slightly finer mesh.
5) Does it matter whether a geometry feature style surfaces (labelled in blue) are chosen or mesh feature (faces, e.g. a specific selection of element faces) style surfaces (labelled in red) for contact? I would imaging the latter is best since you can select a specific region of the model so FEBio does not have to check all outer surface nodes for contact but only the ones composing the selected region.
6) Sometimes the contact does not work at all (see model HEX_MODEL_half_size8_720el_ref_7680el.prv) even though I think I’ve set it up okay.
7) So far none of my models have run to full depth (~14mm from initial). Can you see any obvious reasons related to my modelling approach why this would be?
8) I’ve tried modifying the load application curve, so that the initial gap is crossed quickly, then the contact is established slowly, then the speed increases and then decreases again towards the end where the high amount of deformation is hard to solve. Is this a sensible approach? e.g. equation 0.05+0.95*(sin(t*(0.5*pi))^2)
9) I’ve tried different mesh densities. The coarser model I’ve attached ran quite far (91%) before it failed so I thought I’d try a denser mesh however this took almost 14 hours and got stuck much sooner. Am I doing something wrong?
10) Do you think the near in-compressibility is an issue for the contact?
Just some general comments:
Preview
- Ctrl+R is a short cut for add rigid constraint, not Run
Postview
- Many display settings (contour, mesh-on etc. ) are not kept when updating
- Transparency is not computed correctly for multiple parts and meshes of underlying part are not visible through transparent part.
- The total displacement contour is incorrect the first time you apply it (looks like x-displacement). If I try say the real x-displacement and then go back it looks correct.
- Iso-surfaces are not cut by cutting planes
- I’ve tried simple models with tetrahedral elements. Apart from the fact that they might be naturally harder to get to work the contour plots of stress (e.g. 1st principal stress) are very asymmetric and unrealistic. Is this purely an issue of tetrahedral elements or are there some stress visualisation issues related to tetrahedrons (e.g. compare the simple models)?
Thanks a lot, kind regards,
Kevin Moerman
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