I put it to the experts here. What modulus of graphite is required to produce the IM6 rating for a blank? I always thought, mistakenly or not, that it had to be in the 33-38-43 mil modulus graphite range to be considered IM6 worthy. I know a lot more goes into producing a rods inherient action than just the modulus of graphite, epoxy, taper, the location of mulit-taper transition points.

Another pesky question regarding the mythicly magical IM6 rating.
I heard, mistakenly or not, that Lamiglass coined the term originally and the "IM" stood for intermediate modulus graphite, and the (6)
ment 600,000 tensil strength. so extrapolating further, does IM7
have a 700,000 tensil strength or did the marketing wizards on Wall Street just ba$tardize a technically ambigious term without corresponding merit, as they sought to put a label on the next generation of rods.

Starting with what modulus of graphite, would a rod brandishing the
moniker "HIGH MODULUS GRAPHITE" need to possess?

I feel as if I just asked a question on the show "MR.WIZARD"
Thanks for any input on this quandry.

The moniker IM6 is not a rating, it is a trade name for a graphite fiber produced, I believe, by the Hercules Fiber Company. Off the top of my head I believe the orginal modulus for that particular fiber was in the range of 39 million. I could look it up for you if you really need to know the exact numbers. I believe Loomis was the first company to use IM6 in the manufacturing of fishing rods some time around 1984 or so. There are other fibers in the same 39 million modulus range made by other companies and sold under other names.

During the time it made its first appearance in fishing rods, it was the highest modulus graphite fiber yet used in the fishing industry. However, it was not the highest modulus graphite fiber being manufacturered. Just the highest modulus fiber used in fishing rods, at that time.

So IM6 is not a rating, it is trade type fiber produced by a particular company. Some monikers are rod company trade names and not necessarily the same as the fiber used to make them. A GL3 is a rod type. So is LHS or T3. But IM6 is a fiber type.

The terms "high-modulus" or "intermediate modulus" are used in a variety of ways and really only mean something if you compare them in relative terms to other fibers of the same family.

I suppose anything which falls somewhere in the middle of the currently available graphite fibers could be called an intermediate modulus fiber and anything near the top might be called a high modulus fiber. But this is changing all the time and there are many, many more graphite fibers with various properties and modulus ratings which aren't used for fishing rods.

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I'm on my way out so I will leave you with this info in case you are interested.

IM6 is a Pan - 5 micron fiber (size) with a modulus rating of 39 million psi and a strain-rate of 590,000 psi.

The original graphite fiber used in fishing rods was something called, I think, Narmco 96 which was a Pan - 7 micron fiber of 33 or 34 million modulus and 650,000 psi (Again, this is from memory and may not be exact). Notice that in the early days that as the modulus went up the strain-rate came down. IM6 was one of the first fibers to begin reversing this trend to some extent. At least to the point where high modulus type fibers were suitable for use in fishing rod applications.

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I do not know the numbers. But I rember reading in Tom's magazine, I think in the interview with Gary Loomis, that the real property that set IM6 graphite apart from the earlier stuff was that it was not as brittle as earlier fibers. That property was more important than just the modulus.

I do know that the modulus numbers given for graphite are more of a rating than an actual number. The reason is that graphite fibers are so brittle that they are hard to test in tension. I believe the standard test is to spin a bunch of fibers into a thread of a certain cross section and then lift weights with it until it breaks. As the thread size goes down, the modulus goes up (because there is less chance for a defect). So then they interpolate back to the indvidual fiber size. (regression)

The other thing I think I know is that it really does not matter a lot. It is still up to the manafacturer to make a good rod, and you can make a good rod with low modulus fiber. And a bad one with high modulus. And the worst rod I ever bought was an "IM7". I do not think they changed the design for the stiffer fiber.

From what little I know, Orvis might be on the right track with their T3 rods. According to my chemist aquantainces the newest trend is to coat the individual graphite fibers with something to act as an intermediary to get them to bond to the matrix. That looks like what orvis shows in their adds. Our guys are busy growing polyproplene crystals on wood fibers. Probably they grow a crystal around the graphite fibers to make them load better and act less brittle.

I'm pretty sure that graphite is not brittle in the least. In fact it is less brittle than most other types of fibers. I don't think strength and brittleness are the same thing.

What Orvis is doing now is what most other rod companies have done much earlier. The new resin systems are made of thermoplastic resins instead of epoxy resins and when the fiber prepeg or cloth is heated the resin naturally flows all in and around the fiber. This is nothing new.

Not to get on Orvis in particular, but the advertising they are using on the T-3's is either sheer genius or pure hype. But it only glorifies the natural process that occurs when any graphite prepeg is heated. But Orvis does make it sound impressive though.

I asked a question about graphite and cold weather some time ago and got a lot of good information that could also ad to this post.
[www.rodbuilding.org]
Mark Schulte

Brittle may not be the best work to describe some of these graphites. None of them are what you could call brittle, but there is a strength issue with many of them when used in fishing rod construction. In the early days many of these rod failed due to graphite fibers that did not easily lend themselves to use in normal fishing conditions. Many other rods used inappropriate fibers but had to be overbuilt to the point where they really offered little if any advantage over rods made from lower modulus fibers.

Mark is pointing you to some interesting info on the effect of cold weather on graphite. While we think of just about everything getting more brittle and fragile in very cold temps, graphite is actually stronger at colder temps. If you need the numbers on that I should have it around here somewhere as well.

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I am going to defend my choice of the word brittle as related to graphite fibers. When you look at a stress-strain curve if the material takes a lot of