Elastomer modelling under compression and shear

[Laspalas]

Hello all,

I would appreciate oppinions about this. I have basically an elastomer block. This block is precompressed (for instance in x direction) and then the static stiffness is evaluated in compression (additional displacement in x direction) or in shear (in xy plane). To simulate this I have adjusted an hyperelastic models with material test data (uniaxial, shear and volumentric). There predicted response in compressión is very good but the shear respones is underpredicted by a factor around 2 to 3.

I have tried different strain density functions with different combinations of test dada in the paramenters fitting. Even I have tryed a reverse engineering of the model parameters directly from the real component response, forgetting then the material characterisation. The response is always similar, I can not increase the stiffness in shear without changing also significantly the response in compression. I seams that the strain density functions are not able to catch the existing coupling between compression and shear. Simulations with different compresion preload levels give almost similar shear response when tests show a strong stiffening.

Any suggestion of how to improve shear behaviour prediction when precompression exists? Thanks.

[Jorgen]

Perhaps you have already tried this, but I recommend that you validate your model using forces and displacements instead of stresses and strains. Different FE programs may define engineering shear stress/strain different than you think.

-Jorgen

[Laspalas]

Hello Jorgen,

Thanks for your reply. Yes, the comparisons we have done are in terms of force-deflection response in quasiestatic simulations (with ABAQUS) taking care of the definition of the engineering shear strains used in the program.

Commenting with few collegues they also have found difficulties when the elastomer is under shear, that is the reason that encouraged me to post this problem here. I wonder if this is a quite common problem and if so I would appreciate ideas how are people facing it.

Best regards

[Jorgen]

No, I would not say that is common problem. In fact, I usually see very good agreement between shear and compression predictions.

If by any chance your material slightly porous. That could explain the difference...

-Jorgen