Compression experience

[flo]

Dear Dr. Bergstorm and fellow Experts:

I am a Student of Physics and would like to ask you a few questions concerning my Master Theses. The topic of my Master Theses is 'the Compression of Fibre Mats'. The major task is to describe both the relaxation and the stress-strain curve.

What I have learned so far is that the stress-strain curve has a non linear graph. For instance, for a small strain the curve shows a rather little stress whereas for larger strain the curve shows a sort of exponential behaviour ( just guessing here at the moment). To learn more about these issues I would like to ask if you could provide me further sources of information, especially mathematically based models. Furthermore, is there anyone out there who could tell me what the software 'ABAQUS' is good for? And of one can fit with experimental data using this programme.

I hope that my questions have not been too boring for you and would like to thank you for your answers.

Best regards

Florian Wolferseder

[sq]

Florian-

This seems like a very interesting problem. Though I'll defer to Dr. Bergstrom (the real 'expert' around here), I'd be very interested in knowing what kind of fiber mats you're talking about. Is this something like carbon fibre in an epoxy matrix, or some other composite? Or are you talking about some sort of fiber-filled cushion?

I have to ask what type of specimen you're testing, and in what kind of deformation mode. For example, is this a single fiber in tension to get its properties? Are you squeezing a section of this fiber mat between two platens? This could help us understand whether your results are based on geometric changes or because of material behavior. Certainly, rubber is known to stiffen with increasing strain. But, the kinds of results you're talking about could also be associated with a compressible foam model in compression (as the empty volume collapses).

[Jorgen]

Good topic for a thesis. I can think of two possible avenues for addressing that issue:

:arrow: Develop closed-form equations capturing the mechanisms of the fiber mats as they are compressed. This will likely involve the development of a representative volume element that contains fibers with a pre-specified distribution. The challenge here is to understand the behavior of the unit cell and then use that to predict the behavior of the complete fibre mat.

:arrow: A second approach is to develop a finite element representation of the small section of the fiber mats, and then use the computer to simulate the response and from that develop both an understanding of the mechanisms that controll the behavior and the equations that capture the observed response.

Both of these approaches are commonly used when studying composite materials and foams.

Best of luck,
Jorgen