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Modelling rubber block in Abaqus

Modelling rubber block in Abaqus

Modelling rubber block in Abaqus

(OP)
Hi all,

I am trying to model a simple block of rubber by applying a boundary condition to the top and displacing by about 420% it's original length (with three appropriately placed symmetry boundary conditions). Clearly I am modelling this using a hypereleastic material model. The uniaxial data I have experimentally got extends for strains of 450% (with max stresses of 22.5 MPa) and it is suggested that a reduced-polynomial strain function is used to best fit the data. Is it best to go for higher (N=6) or lower (N=1), or anything in between as they all apparently fit the data (Oddly enough Ogden doesn't fit the data- should I be concerned?).

I am getting a hundreds of negative eigenvalue in the system matrix and "Excessive distortion at a total of __ integration points in solid (continuum) elements" warnings (How normal is this?). The model is reaching strains of about 300% as a far as I can see and then terminating. The stresses at the point of termination is usually between 0.25 MPa and 0.37 MPa, even though according to the uniaxial test data 300% strain corresponds to 12.5 MPa - is this expected?

Overall, can anyone help me out and/or make any recommendations?

Thanks
Gazo

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