Bill,
I agree, I am waiting for Andy to get into this discussion as well. If he can rewrite some of the laws of physics for the CTS blanks maybe he can do it for all carbon fiber blanks. LOL

"Hooke's Law states that for any elastic material there is a very linear relationship between stress and strain throughout the elastic region. I understand that there are materials that when enough stress is applied will pass from elasticity into plasticity where a small increase in stress can result in a large increase in strain or there is a nonlinear relationship between stress and strain."

Agreed

"Carbon fiber has a very linear relationship between stress and strain all of the way to the yield point beyond which point is just breaks and does not become plastic. "

In order for the material to break, the deformation will become non-linear and irreversible. My main point is that you can't typically relate the linear elastic modulus to an ultimate property like the strength or breaking strain.

As far the strengths of the IM vs. the HM/UHM fibers, I was taking an average. If you take the highest of the IMs you see 900+...no HM or UHM will touch that. On the low end, the HMs run under 300 and the IMs are still above 600.

mark

Mark,
I think part of the problem is we are looking at different data. The lowest tensile strength that I have in any of the 50 prepregs that I have data for is 420(KSI). And here are several examples that conflict with your data.
Prepreg Modulus Tensile Strength
64-650/HS40 64(MSI) 640(KSI)
M50J 69(MSI) 597(KSI)
M55J 78.2(MSI) 583(KSI)

But maybe the more important point is that the blank manufacturers are not going to pick the prepregs that have low tensile strength. The lower tensile strength prepregs must be used in some applications other than for fishing rod blanks. For example, I was told a couple of years ago that the prepreg that was used for the Lamiglas Esprit series was a prepreg that is called G55-700 from Toho that has the highest combination of high modulus 57(MSI) and high tensile strength 750(KSI) of any of the prepregs that I have data for.

Another piece of this is the two blank manufacturers that I am most familiar with, Lamiglas and Rainshadow, are both now blending or mixing prepregs to get the combination of characteristics not just in the overall blanks but even in particular sections of the blanks that they want. I suspect that some other blank manufacturers may be doing this as well.
Plus the data that I have is several years old and it would not surprise me if there were prepregs available now that have a better combination of tensile strength and modulus than the ones that I have data for. I also think that both Lamiglas and Rainshadow have made some recent changes in their prepregs and while I do not know this I have to believe that one of reasons that they did this was to improve either the tensile strength or the modulus or both with newly available prepregs.



Edited 1 time(s). Last edit at 05/07/2006 09:50AM by Emory Harry.

Emory,

I don't see a conflict in the data. I have some of the Toho G55-700 fiber. It's pretty expensive stuff and I'm not sure they're even making it anymore. The data sheet has the modulus as 57 Msi and the strength as 670 Ksi...it was one of the highest strength of the high modulus fibers, and there are plenty of other HMs with a strength around 600.

[www.matweb.com]


So here's my point....take the upper end of the HM fibers and the highest IM is still 38% stronger. The key though....most all of the HM/UHM fibers have an elongation to break, including the G55 at 1.1% strain to break......that's half of the IMs. So the HM/UHM fibers are typically twice as brittle as the IMs.


Sorry to belabor the point of the modulus vs.the ultimate properties, but I wanted to get you to think about the modulus as independent of the strength or elongation to break. When we measure modulus it tends to be at very small strains... 0.1% or less, which is far from the breaking point. One other thing that's kind of interesting is that many materials will exhibit non-linear elastic behavior. So, the modulus taken at very small strains can be significantly higher than at larger strains above the linear region and up to the breaking point.

mark

Mark,
I agree that if the material has a higher modulus it will have a lower strain, or in the case of tension less elongation, until it reaches the tensile strength. A material will deform less for a given amount of stress if it has a higher modulus. That is what modulus of elasticity means, higher modulus means less strain for a given amount of stress. A rod blank will bend less for a given amount of force if it has a higher modulus. I do not think that there is any disagreement between us on that point.

As far as the non-linearity is concerned, I think there is a difference of opinion between us. Hooke's law dictates that for any elastic material, like carbon fiber, that there is a very linear relationship between stress and strain through out the elastic region. Yes, some materials become non-linear, they go from elasticity to plasticity, most metals do. Plasticity means that there is a non-linear relationship between stress and strain. However, carbon fiber is not one of these materials. The tensile strength and the yield point are virtually the same point so when enough stress is applied to exceed the tensile strength it just breaks, it does not become non-linear or become plastic.

Plasticity also means that the material when it goes from elasticity to plasticity does not completely return to its original form or dimensions. Have you ever seen a graphite rod with a permanent set in it that was the result of it becoming plastic? I have not. A graphite rod will not take a set when over stressed it will break because it does not become plastic.

I don't think that you have belabored the point. I have found this discussion to be interesting. However, I suspect that many others have not.