dynamic problem of rubber in Finite Element analysis 2

[candychan]

Hi,

I am trying to do a FEA for dynamic stiffness of rubber.My model object is a bushing under a cyclic load with a specified frequency,and the material damp is been considered,but I couldn't get the hysteresis loop.why?

Thanks.

 

[ElastomerXpert]

To not get a hysteresis loop implies that either your equipment isn't sensitive enough to detect the energy loss, or you are somehow operating in low enough strain with a pretty resilient compound that you're in the limited linear region of the material. But it's still unusual to have that result. Good luck, let me know if you find the reason.

 

[candychan]

Thanks ElastomerXpert.

I have got the hysteresis loop by testing,but not with Finite Element Analysis in the computer.I did the simulation by ANSYS,and defined damp to extremely large,and strain is also not small,and the results are not linear with a very small circuitous curve.I couldn't explain it.Of course I will try other means,any new progress I would tell you.

Candy

 

[ElastomerXpert]

OK, now I understand better and knowing you got the hysteresis loop in actual data is reassuring about your test method & equipment. The lack of the FEA answer to match reality is simply a reflection of its inadequacy to properly model the complex responses of rubber. It takes very specialized FEA programs to do that, and even then many of them will only give decent results for low strains. I would say you need to find an expert in rubber FEA (which I am familiar with but not expert in)to help you with this. U of Akron library can probably do a literature search on FEA and come up with articles, then you contact the authors and see if one of them can help you or direct you to the right people. Good luck.

 

[robamiller]

can anyone point me to a source for material properties for rubber with a 50 shore A hardness? I'm looking to do an FEA.

 

[ElastomerXpert]

A rubber compounder could make you a dozen different 50 durometer compounds that would vary greatly in dynamic stiffness (easily +/- 30%) and damping (even more of a contrast) so unless you generate data on YOUR compound or one very closely related to it, you won't get very far with the FEA. Rubber is not like steel at all, hardness does not correlate closely with any other physical or dynamic properties, in fact does not correlate at all with some.

Same advice I gave earlier- you need to find people who can really help with the testing and the right FEA program once you have real data. Good luck.

R J Del Vecchio
Technical Consulting Services
(consultant in Applied Rubber Technology)