Model for vinyl ester

[AaronH]

I am new to polymers, having previously worked with metals and composite laminates. The project I'm working on requires modeling of a nanocomposite with a vinyl ester matrix. At this time, I'm primarily concerned with learning about behavior of the polymer matrix by itself.

I've been familiarizing myself with the general behavior and structure of polymeric materials, as well as the fundamentals of plasticity theory. Could anyone point me in the direction of some resources that may be helpful in moving me toward the FEM aspect, or anything specific to vinyl ester or other thermosets that exhibit similar properties and behavior?

Thank you.
Aaron

[Jorgen]

Hi Aaron,

I have not seen any specific references specializing on vinyl ester. The mechanical behavior of this type of matrix material, however, is relatively well known.
Depending on the magnitudes of the applied loads and displacements, the ambient temperature, and the desired accuracy of your modeling, you might be able to use a linear elastic, or linear viscoelastic material representation. There are also a few select advanced models that can capture the behavior at larger strains, if the material can be exposed to finite deformations without failing.
Depending on the application, you might also want to consider developing a stress or strain-based failure condition in order to predict material breakdown and failure.

What product are you studying? The presence of nano-sized particles can cause significant stiffening but also stress concentrations and reduction in toughness.

[AaronH]

Thanks for the quick reply. In fact, the goal of my project is failure prediction. Therefore, part of my research is to determine what stress/strain measures, yield condition, etc, are acceptable for such a material. The material is carbon nanofiber in a polymer matrix, and we are experimenting with various volume fractions. As I mentioned before, I have worked mostly with metals, and have only limited experience with metal plasticity, so I am starting from the fundamentals.

In our application, we will likely experience large deformation and finite strains, and do not want to limit our model to a small strain assumption. Another group is working on a micromechanics-based material model, so at this point I just need to find a model that will provide a suitable approximation until a more detailed model is developed.

I noticed today that you have posted an article on stochastic failure modeling of polymers, which is also of interest to me. Though we've used a deterministic approach so far, the goal is to move to a stochastic approach soon.

Thanks again, and any recommendations would be greatly appreciated.

[Jorgen]

Interesting project :!:
As you have noticed, predicting failure of polymer composites is a difficult task.

I recently did a study (http://www.polymerfem.com/modules.php?name=Downloads&d_op=viewdownloaddetails&lid=35&ttitle=UHMWPE_failure_model1.pdf) comparing simple stress and strain-based failure conditions. This study showed that for UHMWPE the chain stretch failure conditions was more accurate than traditional stress or strain based failure models. I suspect that this failure model might be useful also for the material that you are studying. This approach can also be extended into stochastic failure modeling, which is probably going to be very important for a vinyl ester due to its relative brittleness.

For the constitutive modeling, I would try the Hybrid-Model (HM) until you have developed a new specialized micromechanical model. The HM is a good general purpose model that is likely to work rather well for your material.

I am curious, what applications do you have in mind for this material, and what volume fractions of carbon nanofibers do you use?

[AaronH]

Thanks. I've found a couple of your publications, but haven't had a chance to look over them yet.

Assuming we meet our objectives, the applications could range from aerospace to consumer products (as the cost of the carbon nanofibers continues to drop). We are still experimenting with varying volume fractions of nanofiber to determine the range in which we will achieve optimum results.