Just to simplify a couple of the terms although I think most people understand them already. Keep in mind that these are all intrinsic material properties, and the properties of the blank are more specific. The modulus is simply the stiffness of the material, the strain is the amount of stretch or elongation, and the strength is related to the breaking force. When you hear manufacturers refer to “high strain fibers” it's a relative thing...higher than what? These fibers all tend to be brittle with breaking strains around 2%, but an IM fiber might be less brittle than a high modulus fiber that breaks at a lesser elongation.

Andy correct me if I'm wrong, but I think the main point is that the IM fibers are not largely different. I and don't think that is to say that modulus is not important either, but only part of a bigger equation. And the combination of materials along with the design can overshadow even larger differences in fiber modulus than what is seen across the IM range.

For example, a customer comes into Andy's shop and wants a blank comparable to his which is built on IM7 fibers.

Question to customer: What scrim is in your IM7?

Customer: "I don't know".

Question: Would it surprise you to know that the IM-X uses and intermediate modulus fiber and gains it's performance improvement over other typical IM fiber based blank due to its carbon fiber scrim?

Even differences in the scrim weights and tightness of the weaves within glass scrims can make a big difference in performance, not to mention the resin and resin to fiber density along with the design elements (transitions in the tapers etc).

Emory, I agree with you, but again, if the focus is too much on modulus, people tend to miss some things. The IMX is a good example of that but conversely, I think you would agree that just given a blank based on HM fiber, there's no guarantee that it's going to out perform something built on a lesser modulus fiber….depends on how well it is done.

mark

Emory,
I saw nowhere in this string where anybody discounted the importance of modulus....especially me. I am simply stating that before someone starts spouting off about modulus and the IM fiber designations, and WHY they prefer a specific material over another, they darn well better know what they're talking about! They average consumer hasn't been given all the facts about the IM designations, and most of the time they don't bother to do the research, therefore they draw their own conculsions, about fiber types, which are 8 times out of 10 incorrect. You are one of the small percentage that understands modulus....but you're an engineer.
It's unfair to the average consumer to continue to let them continue to believe that IM7 is better than IM6 because it has a higher modulus. My original post had nothing to do with high modulus vs. low modulus materials, or whether graphite is the best material for rods. It has to do with educating the consumer so they know what they are getting. I answer at least half a dozen emails a week from folks who want to buy blanks but they won't buy an IM6....they want IM7. When you ask them why, they say they like a higher modulus blank...it's unfair that they don't understand that modulus is not the differnece between IM6 and IM7

By the way, gald to hear you came through your surgery well....


Andy

Mark,
If I wasn't a dyed in the wool heterosexual redneck, I'd kiss you right now! You got it dude!

You should be the one to write that article on this subject.


Andy Dear
Lamar MAnf.

Thanks Mike. I am still weak as a kitten but feeling a little better each day.
I have just been watching here for several days but today I could not keep my mouth shut on this discussion about modulus.

Mark,
If I wasn't a blue blooded heterosexual Texas redneck, I'd kiss you right now! You got it dude!

You should be the one to write that article on this subject.


Andy Dear
Lamar MAnf.

Mark,
I am sure that you know this but others may not. The strain or deformation of the material as a result of stress is only stretch or elongation if we are referring to tension. When a blank or rod is bent the top will be under tension, but the bottom will be under compression and for a variety of reasons including the fact that the fibers are not perfectly alligned there will also be some torsion and some sheer.

Also I would argue with you that stiffness and modulus of elasticity are close but not exactly the same things but maybe we can save that discussion for another day.

By the way, I am very happy to see you back adding your knowledge and expertise here.

Andy,
I thought that there was that implication in a couple of the posts including yours. Sorry if I read something into the posts that was not really there.

To an amature builder like myself when reading adds for fly blanks there is clearly a connection between ever increasing modulus and higher performance. So its only natural that builders would look for greater modulus as a way to upgrade their rods. That said let me make a very important point. I am building a DC sig3 rod. I bought it for two reasons...1 because it was on sale but more importantly ...2 because after searching this site and others I found nothing but glowing reports of the quality of Dans products... In the end I bought a DC blank based on reputation. I never once asked about modulus nore did I care.

BTW...The only thing I know for sure about IM is that IM Bob in Bridgeton, NJ.

Emory, thanks and good to see you back too. Thanks to Andy for the kind words...I think LOL

On the stiffness. Yes, I agree and that's why I'd make the distinction between the modulus as the intrinsic stiffness of the material, as opposed to the Stiffness of an object, which is a wholly different animal.... For example, compare an aluminum bar to aluminum foil....they have the same modulus since it's intrinsic to the material, which if the modulus of aluminum. But the stiffness of the bar vs the film is different by many orders of magnitude. So the distinction is that modulus can be described as the stiffness of the material used, but there is an additional shape factor (area moment) to be considered in the calculation of the specific object stiffness. This is also why you can have all different rod powers built off of the same modulus fibers simply by changing the shape factors...larger diameter, wall thichness, etc., will increase the Stiffness of the blank of a given modulus.

Also agree on the tension vs. compression vs. shear. I think the tensile modulus is tends to be discussed since that is often what is listed in the literature for many of these fibers. The modulus of a material can be measured in different modes such as tension, shear, or bending. For many materials the flex or bending modulus is close to equal (carbon fiber excepted) and it's easy to see how this is true since bending is just a combination of tension and compression. Shear is an all together different mode and the shear modulus is typically significantly lower than the tensile value. The relationship between the modulus in tension vs. shear is controlled by a factor called Poisson's ratio...named after a French guy Sime'on Poisson who was born back in 1781. So you can see some of this stuff has been around a while. lol In any case, you're right about the issues between tension and shear and aside from fiber alignment, the torsion from a rod built with guides on top become even more significant.

mark

Robert,

If all things were equal, then modulus alone would be a great indicator of increasing efficiency and all the related performance benefits that go along with it. But we're dealing with more than just a fiber - we have to deal with the structure as a whole.

Keep in mind the relationship between blank diameter and wall thickness. You could take the highest modulus fiber available, and in an attempt to build a very durable product, you might chose to build a blank with a fairly small diameter and pretty thick walls. And in doing so, you'd have to add back a bit of material to bring up the stiffness to where you were before with a larger diameter design. On the other hand, you could take a fiber with a lower modulus and chose a design that had a slightly larger diameter with thinner walls and get the same stiffness at less weight. So in this case, the rod with the lower modulus fiber might actually be the more efficient of the two. This is one more reason why modulus alone isn't a good indicator, or at least shouldn't be the sole indicator, of the performance attributes of a blank or rod.

In some cases, rod manufacturers that wanted to increase sales solely on the strength of how customers perceive "modulus" have actually taken a very high modulus fiber, coupled it with a small diameter, heavy walled design, and built a pretty tough blank. But they also ended up with a rod that was actually less efficient; heavier for the same stiffness, than its predessor made from a lower modulus fiber. But it sure looks good for them to be able to spout those higher modulus numbers and that's what the customer is going to focus on - that's what the manufacturer is counting on. I'm sure this is what you're referring to in your post above.

A fiber that is suitable for making rod blanks, that has a higher modulus and sufficient tensile strength, gives a blank designer the ability to make a more efficient rod. Whether or not that happens, however, depends on how the designer chooses to use it.

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

Thanks Tom. Perhaps we should view graphite blanks like we do sausage. You don't want to see what went into them or how they were made as long as they taste good... The sausage that is...Bob.

Tom,
You make a really good point that the design is as important as the material. It does seem to me though that there is less difference in the design of blanks now than was the case a number years ago. Maybe it is my imagination but it seems as if the blanks from different manufacturers are becoming more and more alike.
I guess you could make the same argument about the material as well.

Mark,
It has been so long since I had any use for or was exposed to Poisson's ratio that I had to go look it up and refresh my memory on just exactly what it was. Thanks

Robert,
Maybe you are right that would be the best approach. But I think that there are always going to be those that just are not going to be satisfied with that approach and will have to pick at the sausage and look closely at it to see what it is made of and how it is made.

Some very good points made Emory!

Thanks,

Raymond Adams
Eventually, all things merge, and a river runs through it..

Emory,

You got me wondering what would come up in a search. This link was on top and looked to have a nice decription of the relationships:

[silver.neep.wisc.edu]

One reason that there is less variation in the designs of various companies these days has to do with the fact that most of the leading blank designers now employ computer test models to provide an optimum ratio of diameter to wall thickness for the amount of toughness or durability the manufacturer wishes to obtain with any particular material. It's rare that you end up with many truly "bad" designs anymore in terms of not getting the most out of a particular material. At least in regard to the higher end blank makers that most custom rod builders buy from.

However, among many of the very large rod companies where truly huge quantities of rods are sold worldwide, designs which create toughness at the expense of performance are still the norm. They let the modulus numbers baffle and amaze the consumer all the while playing it safe with designs that are more likely to ensure fewer returns at the expense of weight and performance. Most of the well known blank manufacturers that most custom rod builders are familar with are much more likely to push more toward the performance end of things at the expense of having a "bulletproof" rod blank. Not that they're fragile - they're not. But they tend to use the materials to the best possible advantage while still maintaining some reasonable amount of toughness or resistance to normal fishing wear, tear and occasional abuse. Two different market niches - two different approaches.

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

In the interview I did with Press Powell a year or two back, he said to me " You know, I think we have nade about as good a rod as can possibly be made out of graphite. without going to a completely new materia, I don't know what else can really be done"

I agree with you 100% Emory ( that's twice this year we agreed on something...wow). The gap is becoming extremely narrow insofar as designs between manf. go.


Andy Dear
Lamar manf.

Mark,
Thank you. That is a great site and the explainations were excellent. I am going to have to go back over the explainations a couple of times though to let it soak in.

Andy/Tom/Mark,
I guess I would agree with Powell as far as the presently available graphite is concerned. I also do not see much point in graphite that has a higher modulus than is available now because of the strain energy or toughness issue. Higher modulus is just going to result in more fragile blanks because the strain energy goes down in direct proportion to the increase in modulus. The high modulus blanks that are available today are already too fragile in my judgement. If the tensile strength could be significantly increased though the strain energy would also go up along with the increase in tensile strength and then even higher modulus material could be used. I think that the bigger issue today is not really higher modulus material but rather material with higher tensile strength.

EMory,

I agree 100%

Andy

Even with higher tensile strengh, we still run into the problem of the structure itself. As we move to higher and higher modulus material, you need less and less of it to do the same job. Thus, you end up with a structure that is smaller, thinner and therefore more prone to damage from impact or crushing forces. This is what breaks rods. Most rods anyway.

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

Tom,
Yes, you are right if the modulus goes up with the tensile strength but I think that what is really needed is higher tensile strength relative to the modulus.
If for example we could double the tensile strength while leaving the modulus the same the stress and strain would double but the strain energy or toughness would go up by a factor of four which would result in a much more durable rod.
Graphite is a great material for rods but it is really not very tough or durable and that is to a large degree because it does not have a very high tensile strength. I would guess that on the order of 25% of all the graphite rods built are ultimataely broken while the breakage of glass rods is probably more like 5%.
Actually maybe someone has better estimates of those numbers.

Sure, but my point is that at some time and place, we reach a situation that no matter how strong the material is, the structure itself will be suspect. Blanks walls can only be so thin before they crush far too easily. Diameters can only be reduced so much before tips have no resistance to any pinching force. Rods have to do more than just cast lures and lines and fight fish - they have to withstand the normal wear, tear and abuse that fishing rods receive even in the hands of the best and most careful anglers. Part of any rod's "toughness" comes from the material, but a large part of it also comes from the structure involved.

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