set viscoelastic constitutive bond for polymer analysis

[radiohead]

Hello everyone,

Have any of you ever run structural fem analysis on polymeric artefacts?
how did you behave when defining materials?
have you hypothesized a linear elastic bond or have you used an ad hoc?
what rupture criterion did you use?

Thank you all in advance:

 

[Vmax]

I have made several calculations on plastic components, considering the characteristics of this type of materials typically have non-linear and particularly complicated constituent bonds, so no linear elastic analysis.
other thing is to find the data relating to the constituent bond of the material in question, I have experience of variations of 50-60% for nominally identical polymers but of different producer, and of 15-20% for different batches of the same manufacturer.
As for the criteria of breakup, there is a broad literature but not a unique answer, there is a discussion on the forum in which I participated where some usable criteria are reviewed.
If then the calculation involves repeated stresses, the thing becomes even more complicated as rheological characters become extremely complex, and thermal factors play a decisive role, since these materials, among other things, exhibit a very strong sensitivity to temperature.
Good luck, you'll need it. . .

 

[radiohead]

Hi, vmax.
Thanks for the answer.

clearly these materials have a completely "anomalous" behaviour compared to materials found in classical elastic theory, so I agree with non-linear analysis.

Usually the data available on plastics are a diagram of creep test and relaxation performed at different constant temperatures.
how do I insert this information into the software? how does ansys set a nonlinear elastic bond?

As for the load cycles, I thought in the first instance not to consider them.
However, it is clear that for polymeric materials the load history is often an important and therefore not negligible aspect.

the effects of temperature at the moment are not a problem, as I am doing a constant temperature analysis.

I'm just looking for the discussion about breaking criteria, if you can link me something.

thanks again for the interest shown :biggrin: