As you might have guessed, I'm not a very technical savvy guy. I don't have any idea what tensile strength means. But I think I have the basic understanding of the practical applications of the modulus counts on rods. The higher the mod, the lighter the rod. Less material (thinner walls) is required for the desired "strength". Thinner walls translate to more opportunity for breakage. So, I think I get it. What I don't get is how these things are rated. IM-6, SCIV, 85 million modulus. What do those things mean? Not to mention that some IM-6 rods have 33-million mod, and others do not. Why can't we all just get along and standardize the way we describe the rod? What I'm hoping for is that someone here can give me a chart that's at least a starting point.

Something like this

IM-6=SCII=33 million (of course I have no idea if that's correct)
IM-7=


The reason I ask is that I have a factory rod that is HM85. This is by far the lightest rod I own, but the rod is poorly built. Not having any idea how those numbers translate into other rod manufacturer rod specs makes it extremely difficult to find a blank like it.

First of all, a higher modulus material doesn't automatically mean you'll have a lighter rod or one with thinner walls. In fact, in order to keep the durability up, the manufacturers often drop to a smaller diameter/thicker walled design when using the higher modulus materials. Of course, this tends to negate some of the reason for using a more efficient material to begin with. In some cases, the higher modulus rods may weigh more and perform on a lower scale than rods made from lower modulus materials. You have to keep in mind that the design of the structure involved has much to do with how much a rod will weigh, how durable it will be, etc. It doesn't all fall on the material.

Generally, all fibers from a given manufacturer with a given trade designation, such as IM6, will feature the same modulus. I don't think you're going to find any IM6 rated at 33 million and another at 45 million (39 is about the rating for IM6 if I recall correctly).

A great deal of this goes back to advertising and marketing. How the material is used and in what quantity related to any scrim (glass or graphite) plus the diameter and wall thickness all add up to a finished rod "modulus" that may not be anything at all along the lines of the main material the rod is advertised as being comprised of. During the so called "modulus wars," many companies just wanted to be able to say that their rods were manufacturered from the latest and greatest material, the highest modulus fiber, and yet they didn't go into much detail on how it was used or if it really even gained you any particular advantage. But many fishermen just automatically assume that if a higher modulus fiber has been employed, the rod must be "better."

Technically you can build a lighter rod, per the same stiffness, with a higher modulus material. But this is not guaranteed - it all depends on how the material is used and the structure involved.

Don't expect this to clear up anytime soon. But in the meantime, you can make a pretty good comparative guess based factors such as ERN, weight, butt and tip diameters, etc. These factors will put a lot closer to duplicating that rod than any comparison of fiber modulus will.

..............

Sean,
A couple of additional comments in addition to Tom's explanation. Modulus of elasticity is the ratio of stress to strain. Stress is just the amount of force that is applied while strain is how much does the material deform or bend under that stress. It really is very simple. Tensile strength is also very simple. It is just the strength under tension. When a rod is bent the top of the rod is under tension. If you apply enough force to exceed the tensile strength the rod will break.

"Why can't we all just get along and standardize the way we describe the rod?"

My interest is mostly in flyrods, so my answer relates only to them. Because that is exactly the last thing the add writers for the rod companies want to happen. Make the copy sound technical, use terms that people have heard of but really can't define, pick the "hot" ideas to push like "fast" rods or "titanium" or, and I guess this dates me, "powermatrix" and go with it.

My take is that you can make either a good rod or a bad rod using any of the materials on the market. More important is the rod designed and constructed well and is it suitable for the specific type of fishing it is doing. I have a really sweet casting bamboo rod and have dumped some really bad casting "IM7" rods. I don't think there is a "magic" rod material out there yet. And all rods seem to be combinations of materials. High tensile strength fibers, glass or low strength scrim, resin, all in different ratios.

Just want to make a few minor clarifications and add a few other notes.

First, Sean, the modulus has nothing to do with strength. Basically it is a relative measure of the stiffness of a material. The units are not even important in themselves (as long as you use the same ones) so long as you understand that they're linear and a higher modulus means a stiffer material.

Basically what it boils down to is how much it will bend per given amount of force. Strength is how much total force can be applied before the material fails. Whether that be breaking, becoming permanently deformed, etc.

Second, Emory, very close: Stress is force per area.

Another and very easily overlooked aspect of composites is the resin. The fibers used to make the rod are suspended in a resin. And the choice of resin is just as important as the choice of fiber.

On top of that you have a great deal of factors such as orientation of the fibers, size of the fibers and any number of other things including resin content. When working with composites you want the least possible amount of resin you can use and still fully saturate the fibers. Any excess resin is just adding weight.

THE most important aspect, however -- as Tom and Bill eluded to -- is design. The key to proper design of a rod is understanding how to properly use the materials you have. Then the three factors which effect rod performance are taper, diameter and wall thickness.

Hope this didn't make things more complicated.

Mark

IM6 is about 36 million modulus, it is the trade name for the HERCULES fibre made by Hexcel (hercules name came from the military as it was initially developed for it).Tradenames are not regulated, so the callout to IM6 does not mean much, as the supplier doesn't have to be from hexcel (e.g. from torryo, etc.). Next, the stated modulus on the blank/rod does not necessarily add up to a whole lot either, because most everyone uses pre layup or scrim modulus. Whenever you add less efficient mat'ls (be it fibreglass, resin, etc.), this will lower the modulus of the mat'l. Basically, without it saying directly what modulus it is, you have no idea what mat'l is in it just because it says IM6. some state 43mil, some 36mil, and some even 33mil. Keep in mind this is almost always pre-resin because they can state a higher modulus that way, which is a good marketing ploy.

basically muddy waters, and what i would have to say, don't use the IM6 IM7, IM8 designation as a good indicator as performance, weight, etc.

I did read somewhere that the rod industry has a few conventions as far as IM6, IM7, and IM8, but you have to keep in mind that no one is forced to adhere to these. They were something like(don't quote me on it, but it was something like this):
Standard Graphite 33mil
IM6 Graphite 36-43mil
IM7 Graphite 44-53mil
IM8 Graphite 54-63mil

this is going to muddy the waters a wee bit, but yeah. this is one area that vagueness and blurred lines is the rule rather than the exception.

steve

Okay, so you guys weren't much help (sarcasm). Basically what I got from this little thread is that all of that means nothing. IM-6, 65 mil, SC42 or whatever a rod company wants to call it really means nothing.

It would sure be helpful it there was a database that gave more information. I've checked out the CCS data and it just doesn't have enough blanks listed.

Mark,
Yes I know that stress is force over area just as strain is deformation over area. I was just trying to keep the expanation simple. While we are at it modulus of elasticity is not stricky speaking the same as stiffness. Modulus of elasticity is stress divided by strain while stiffness is just stiffness. However, I will agree that for all practical purposes they can be used interchangeably and modulus of elasticity is often called modulus of ridgitity.

Steven,
You are right on that the modulus of elasticity numbers that are given by rod/blank manufacturers is for the graphite fiber itself and do not include the effects of the resin; scrim, which is usually fiber glass; the finish on the rod/blank; any mis-allignment of the fibers; etc. Typically the real modulus of elasticity of a blank will be less than half of the number given.
An interesting part of this issue is that adding weight has the same effect as lowering the modulus but without the benefit of increasing toughness, lower modulus means higher toughness (strain energy for Mark).
And adding weight is mainly what we as custom rod builders are doing by adding guides, thread, epoxy, epoxy, reel seats etc. So the effective modulus of elasticity of a finished rod is a small fraction of the number that is specified for the fibers and we as custom rod builders have a ver large impact with the weight of the components that we add.
I have a little different set of numbers from a data sheet from Cape Composites that distributes graphite prepreg than you have for IM6,IM7,IM8. Here are the number that I have.

Modulus of elasticity
IM6 40M, IM7 40M, IM8 44M.
Tensile strength
IM6 760KSI, IM7 780KSI, IM8 790KSI

Sean,

I think Mark hit the nail on the head in his last paragraph, concerning the craft/art of rod building. While you can most certainly revel in all the scientific aspects of what makes a particular rod act or react in the ways it does, and knowledge is a powerful thing, you really don't have to fully concern yourself with them in order to build a top notch rod.

For my projects, I try and match the rods length, weight, action and power for the purpose in which it is to be used, more than I concern myself with why the rod is a certian length, weight, action or power.

Just MY 2C!

Regards

When all the scientific stuff is fully understood here comes the words "titanium" and "helium". I wonder what words will be used to confuse me next! Maybe some one will invent an "invisible" blank and then I can market a rod no one can see! How do you price that one?

Gon Fishn

Price less!!