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Hencky's hyperelastic material model.


I am working on my master's thesis. I have to find best fitting hyperelastic material model for simple shear test.

My task is to find most proper material model which will fit my laboratory test data. I have conducted the "single lap test" on bricks, using polymer PS.

I started my theoretical research with Hencky's model but again I faced a problem. Everywhere in the literature there is one equation describing this approach. When I was checking the LUSAS software manual concerning hyperelasticity I found a different equation. Perhaps it is only so called "czech mistake" with wrong placing of brackets and the programme works fine. The difference is shown in attached photo. 

Any comment would be appreciated.





Most hyperelastic material models were initially designed under the assumption of incompressibility.  People have added pressure dependence to these models at a later stage and that has led to a large number of models for the pressure term.  I'm sure the people at Lusas have very good reasons for choosing the form that they have; probably to better match exprimental data provided by one of their customers.  Academic models are not necessarily accurate representations of reality.

-- Biswajit

After contacting the LUSAS support I got the answer that there is a typo in the logarithm power. The square should be outside the brackets.

Software is implemented with the proper equation, it is only the manual's problem.

Rest of differences appeared due to different bulk strain energy notation.  

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