Use of VUMAT-UMAT interface code for hyperelastic UMAT

[whelana5]

I'm using a fortran code which acts as an interface between a VUMAT and UMAT, so that a UMAT can be used in a dynamic simulation. The interface code can be found here:

https://soilmodels.com/download/vumat_umatinterface-zip/,

where the VUMAT calls the UMAT and re-orders tensors into the required VUMAT format.

The VUMAT interface has been used successfully for a hypoplastic material, but I am getting a number of errors when trying to use it with a hyperelastic UMAT. The simulation is a simple uniaxial load, which runs successfully using an in-built hyperelastic material model (i.e. the simulation parameters are set correctly). It seems that Abaqus cannot calculate the deformation gradient for the first increment, and the job eventually fails due to 'Error: Floating point exception detected in increment 1'. If anyone has experience with this interface VUMAT, or experience on where the floating point error typically comes from in a dynamic simulation I would greatly appreciate it.

 

[IceBreakerSours]

I do not have an answer to the specific question you have. However, I am curious: Since the hyperelastic model is already supported, why do you need the VUMAT/UMAT interface? Are you trying to enhance the hyperelastic formulation somehow?

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[whelana5]

Thanks for your reply. Yes the hyperelastic umat includes a model for fatigue induced damage and permanent set, so the in built models are not suitable.

 

[IceBreakerSours]

Okay. Two more questions.

a) Why do you want to switch over to explicit assuming you already have a functioning UMAT?

b) Alternatively, why not just convert the UMAT to a VUMAT? It would make you better appreciate the formulation, the code, and its strengths/limitations which will definitely come in handy when you start running into problems - which you most definitely will. VUMAT is simpler than UMAT; there is no tangent to worry about and incompressibility is out of the picture as well.

If coding is something you wish to avoid spending time on, then find some help. Take an Abaqus class on subroutines or talk to a consultancy.

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