# Contact pressure on hyperelastic material **URL:** \ **Category:** Uncategorized\ **Created:** [May 12, 2024, 10:29am UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265 "2024-05-12T10:29:41Z")\ **Posts on this page:** 15\ **Page:** 2
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 13, 2024, 9:04pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/21 "2024-05-13T21:04:53Z")
still checking, it’s running. ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 13, 2024, 9:05pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/22 "2024-05-13T21:05:38Z")
Ok. But I used MPa, so I was lucky!? what are the formulas for the correction? ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [May 13, 2024, 9:11pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/23 "2024-05-13T21:11:28Z")
Don Guido wrote this in hyperelastics.f ```auto do i=1,3 k=jcoef(i,abs(ityp)) if(k.eq.0) exit if(dabs(elcon(k,j,nmat)).lt.1.d-10) then elcon(k,j,nmat)=(0.1d0/um)**i write(*,*) & '*WARNING reading *HYPERELASTIC: default value was' write(*,*) ' used for compressibility coefficient &s' write(*,100) i,elcon(k,j,nmat) endif enddo ``` ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 13, 2024, 9:12pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/24 "2024-05-13T21:12:59Z")
I guess is this using Poisson’s ratio = 0.475 ![Captura de pantalla 2024-05-13 a las 23.10.57](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/4/474f789692e1fc4efc2d6e5a77149f991634cdc9.png) ![Captura de pantalla 2024-05-13 a las 23.11.14](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/5/507704eb0372c6e0bd0d2b854dc1dab494c1ca47.png) ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 13, 2024, 9:16pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/25 "2024-05-13T21:16:33Z")
a surprising formula… 🫥 ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 13, 2024, 9:19pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/26 "2024-05-13T21:19:03Z")
I’ll post some results tomorrow, still stuck in the larger model 🤦‍♂️ ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 14, 2024, 2:02pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/28 "2024-05-14T14:02:07Z")
Same mesh C3D20, no changes. Still fighting with mortar contact…Next test will be changing D’s. ![imagen](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/8/8ad467a52b585c68f440a7421907fc0679965823.png) ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 14, 2024, 6:44pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/29 "2024-05-14T18:44:00Z")
just noticed…the lower surface…contact CPRESS is smooth! ![imagen](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/a/ad34cffeeccea9883cba455b9741092810c9d493.png) ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 14, 2024, 7:11pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/30 "2024-05-14T19:11:33Z")
looks like is a limitation of the method, but can’t figure out why so different in both sides Theoretical background here [https://aaltodoc.aalto.fi/server/api/core/bitstreams/243fb840-e11e-40fc-b709-9fa7e4197602/content](https://aaltodoc.aalto.fi/server/api/core/bitstreams/243fb840-e11e-40fc-b709-9fa7e4197602/content) ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 14, 2024, 7:14pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/31 "2024-05-14T19:14:04Z")
I changed all D’s to 0.001 MPa^-1, no change in results. ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [May 14, 2024, 7:51pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/32 "2024-05-14T19:51:38Z")
> [@JuanP74](#): > > just noticed…the lower surface…contact CPRESS is smooth! mmmh. that could be a good clue.!. Have you noticed there is the same master in two contact pairs?. Surface 5 is master in Contact\_Pair-2 and Contact\_Pair-3. That doesn’t happen in the lower surface. ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 14, 2024, 8:23pm UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/33 "2024-05-14T20:23:57Z")
right in the lower surface the stops are tied, no general contact. Good point. ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 15, 2024, 6:16am UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/34 "2024-05-15T06:16:24Z")
that was it! I removed contact pair 3, and this is the result: ![imagen](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/2/287d5adfd178d0db81ddb0aff1e3590031a2d790.png) Many thanks to @Disla and all of you. ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [May 16, 2024, 6:42am UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/35 "2024-05-16T06:42:38Z")
Hi JuanP74, I’m glad it finally worked. Seems there can’t be the same master in two contact pair definitions. Regarding the default values I still consider there is some issue. In my opinion, it is nonsense that the user’s value is discarded for being too small but it’s replaced by another value that is even much smaller. I consider a check should be performed also to those new values (D2 and D3) to see if they also fulfill the minimum allowable value for compressibility. Additionally, when using [Pa] as main units, there is no correspondence with the same model in [Mpa]. I guess the source is the way D2 and D3 are built as powers of D1 which makes the solution unit dependent. ![imagen](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/2/23eebeba2adc03f1aababe2788e7ddca21c52090.jpeg) Should we report it? Regards ---
**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\ **Post date:** [May 16, 2024, 11:58am UTC](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265/36 "2024-05-16T11:58:43Z")
> [@Disla](#): > > when using [Pa] as main units, there is no correspondence with the same model in [Mpa]. > I guess the source is the way D2 and D3 are built as powers of D1 which makes the solution unit dependent. This is clearly a mistake. The other point is related to the calculation of minimum values that as you said is faulty. So yes, this has to be reported. [Previous page](https://calculix.discourse.group/t/contact-pressure-on-hyperelastic-material/2265.md?page=1)