Trace a must have tool. 1

[berkshire]

I just read this article on pages 28 and 29 of Composites world, this seems almost too good to be true.
B.E.

You are judged not by what you know, but by what you can do.

 

[SWComposites]

It is. Really only good for stiffness. Useless for strength.

 

[ESPcomposites]

This would be useful, if it can be independently verified and shown to truly be an invariant.

But this statement seems incorrect and/or misleading:

"The implications of these universal connections
 are far-reaching. One of the most important is that 
for testing. We no longer have to start from scratch
 with each new material and conduct thousands of
 hours of coupon tests to establish design allowables. If we have already tested and established the design allowables for one CFRP material, we can, in fact, derive the allowables data for all other CFRP materials, using simple mathematical calculations based on the ratio between the traces of the materials."

The thing is, getting the elastic properties for a material is not very expensive and does not require very much testing. Lamination theory, which is well accepted, can then be used to determine the elastic properties for all the layup variations (and also provides additional components that may be necessary for analysis). But more importantly, the testing that DOES require "thousands of hours of coupon tests" is for strength properties (NOT elastic properties). Trace has no application to strength, as SWComposites stated. So the quoted statement, which seems to be the top claim, seems to be null and void...and misleading. That also makes me wonder just how extensive the supporting test database is. Since there is no physical foundation (at least not stated), one would need quite a bit of test data to claim it is truly an invariant.

*EDIT: I ran some sample problems with classical lamination theory. The trace worked *somewhat* OK for a lot of layups (same material system), but it was not truly an invariant and was in error by up to 10% (probably more if I tried various material systems). The claimed ability to extend this other material systems, using properties from one material system, would be expected to have additional error. That claim seems especially questionable unless there was a significant test database to support it. So I am not sure what practical use this could have. Perhaps someone else could run some additional studies.

Brian

http://www.espcomposites.com