## Coupon Testing and Numerical FEA correlation

## Coupon Testing and Numerical FEA correlation

(OP)

Hi all,

I have been presented by a set composite coupon testing (using ASTM standard) and need to validate that using numerically using FEA software (in my case, using MSC Nastran/Patran). What is the best parameter to compare with the coupon testing data and numerical FEA results?

For example, tensile testing we can correlate the Force and Displacement from the testing with the same FE numerical result. How about OHT (Open Hole Tension) Coupon Test? What is the best parameter to correlate between the testing and numerical FE result.

The same goes with VNS (V-Notched test), what is appropriate parameter to correlate with? I manage to build up and simulate the model as per testing but then stuck up on what is the numerical results should I look for?

Thanks.

I have been presented by a set composite coupon testing (using ASTM standard) and need to validate that using numerically using FEA software (in my case, using MSC Nastran/Patran). What is the best parameter to compare with the coupon testing data and numerical FEA results?

For example, tensile testing we can correlate the Force and Displacement from the testing with the same FE numerical result. How about OHT (Open Hole Tension) Coupon Test? What is the best parameter to correlate between the testing and numerical FE result.

The same goes with VNS (V-Notched test), what is appropriate parameter to correlate with? I manage to build up and simulate the model as per testing but then stuck up on what is the numerical results should I look for?

Thanks.

## RE: Coupon Testing and Numerical FEA correlation

## RE: Coupon Testing and Numerical FEA correlation

Correlating the load-deflection response and far field strains is rather simple. Correlating the notched strength of composites so an entirely different story (decades of research without a well accepted approach). In fact, that is why such a test exists for composites (notched strength can not be analytically determined because of pseudo-plasticity and the hole size effect). Conversely, you don't need a OHT test for ductile metals because the capability can determined analytically. This difference can easily confuse people.

Brian

www.espcomposites.com

## RE: Coupon Testing and Numerical FEA correlation

I have come across this literature which using fracture mechanics approach to capture in-plane fracture energy criterion. This fracture energy derived from numerical FEM using the strength from experimental OHT result. Then, it says that it validate the same energy level with numerical VNS test. I couldn't get exactly what they are trying to do here. Furthermore, they are using Abaqus in validating this coupon testing.

I believe it involves on non-linear FEM as mentioned by you guys here. Could you please shed some light on me here.

Thanks.

## RE: Coupon Testing and Numerical FEA correlation

## RE: Coupon Testing and Numerical FEA correlation

We are now developing new material database for newly formulation of fiber and matrix and need to validate the mechanical properties and strength obtained from the coupon testing. This mechanical and its strength properties will be then used in our complete model simulation.

## RE: Coupon Testing and Numerical FEA correlation

You seem to be looking at this from the wrong angle. The way it works is that the coupon tests (OHC, OHT, FHC, FHT, etc.) are used to develop the analysis methods. For composites, these apparent properties are the lowest level building block properties (for notched strength). You can't really go "lower" without introducing a lot error and guess work (so how can you validate the test?). Again, the confusion usually results from the understanding of metals, where Ftu, Fty, etc. are the lowest level useful properties for the same scenario. Once you better understand the mechanics of notched strength, you should be able to understand what I mean.

P.S. When I say "unsatisfactory" analytical results, what I mean is that the accuracy is not that much better than an estimate (if better at all). In theory, it *may* be possible to be more accurate, and you *might* have more confidence in the solution, but that is yet to be proven and accepted. But you are guaranteed to spend a lot of time trying to get there. That is what I consider to be "unsatisfactory" from an engineering perspective. From a research perspective, that changes a bit...since that is the point of research.

Brian

www.espcomposites.com

## RE: Coupon Testing and Numerical FEA correlation

My intention here are to numerically simulate again the coupon testing and see how the experimental test result goes well with it. I believe if I use the same composite mechanical properties obtained from the experimental (E1, E2, G12, v12), I should be able to obtain its corresponding strength values (Xt, Yt, S, OHT). I'm not sure whether linear static are good enough to represent those simulation. Please correct if my approach here are not feasible at all.

Thanks.

## RE: Coupon Testing and Numerical FEA correlation

## RE: Coupon Testing and Numerical FEA correlation

I think you are lacking a basic *practical* understanding of composite failure criteria (and their shortcomings), notch sensitivity and pseudo-plasticity, etc. This tends to occur because what is taught in academia is somewhat misleading. I suggest you reread the posts in this thread and also search through the forum regarding failure criteria. We have had a few discussions about it. Good luck.

Brian

www.espcomposites.com