BB Model for OptiStruct Nonlinear Static
I am in need of capturing the Mullins effect of a TPE material but OptiStruct does not have such a model and I need to create a user material MATUSR.
I was thinking BB model may give me what i need, maybe with some additional damage model too, but it seems the Fortran code for it is not widely available for me to convert for use in OptiStruct.
Has anyone any good reference for this material characterisation, either in OptiStruct format or in general for Abaqus UMAT?
However, the Fortran code for the BB model, which may potentially provide me with what I want, is not readily accessible for me to convert for use in OptiStruct, which I believe is a shame given how much work it takes to get it to work.
I was under the impression that OptiStruct does not support user material models. Do you know if that is not true?
OK. I just looked into this some more. OptiStruct does support user material models, but the interface function is:
subroutine usermaterial(idu, stress, strain, dstrain, stater, state, nstate, drot, props, nprops, ndi, nshear, ntens temp, dtemp, ieuid, kinc, dt, t_step, t_total, cdev, cbulk, userdata, ierr)
Which does not provide the deformation gradient. It is not possible to implement the the BB model (with or without Mullins damage) using this subroutine. I have asked Altair to fix this limitation. They have not yet done it.
Hi Jorgen, thanks for the reply!
In the next release of OptiStruct (2022.1) we have access to dfgrOld, dfgrNew in the user material subroutine, which provides deformation gradient. I guess this would give what is required? I have MATUSR for Neo-Hookean in this version which works, but the Fortran implementation for your BB model is more problematic as it is not as easy to find a resource for the implementation.
I see the PolymerFEM tools are already available in the Altair Partner Alliance, if you would like to test anything in OptiStruct for BB implementation then I'm happy to help.
Here is the latest MATUR in OpriStruct 2022.1, you will see dfgrOld and dfgrNew which should make it possible to implement BB, right?
If you can share any further information or if you want to reach out privately that would be great. I actually wonder if one of the other PolyUMod models (TN or BB-Mullins?) might be better but these are also no available to run with OptiStruct yet.