Hey all,
I'm attempting to model the compression of cylinders of different radius and heights made out of silicone elastomers (hyperelastic materials) using abaqus. I've preformed some compressive tests on samples of the silicone I'm interested in to acquire to stress strain data and fitted this to a hyperelastaic Ogden relationship in Abaqus.
Using a python script I have written I'm able to model the compression of many different cylinders with different heights/radius. However some of the response I cant seem to explain. For a cylinder of a constant radius the compressive force for different heights seems to follow a shallow parabola. Where the force will start high for small cylinder heights and will then decrease and increase again for larger cylinder heights.
I cant seem to think of a reason this would happen. Perhaps my stress, strain data isn't very good resulting in inaccurate results?
Attached should be an image of the data i have collected showing this issue.
Any help would with understanding the physics behind this would be greatly appreciated.
Check the mesh density and the element type, perhaps? Difficult to say anything without seeing the model.
I would agree, this seems to be some modelling issue at first glance. So you have a 0.1-0.5 um tall, but 100--600um radius part, that's like a very very thin disc. Do you have lot of skewed/high AR elements? How many across the thickness? Another typical problem with compressive test could be friction between the tool and the specimen.
Maybe determine the basic shape factor of the specimen. The material needs a place to expand/flow when being compressed and if there is insufficient free area to allow shape change, then questionable results are created. Since Abaqus remeshes during a non-linear hyperelastic solution, you don't encounter non-convergence issues with strain increasing per time step past internal limits as in some other solvers (ANSYS, RADIOSS...).
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