Tommy,
Welcome to the rodbuilding.org. site. I have not seen you post before and as you request I will try not to be too mean to you.

Your post is very interesting but I think that I have a couple of difference of opinions with you.

First, I completely agree with you that the two most important properties of carbon fiber are the modulus of elasticity and the tensile strength and also that the biggest weakness in the carbon fiber that is available today for blank construction is the tensile strength or actually the strength in all four axis, tensile, compression, torsion and shear. I do not agree that the tensile strength decreases as the modulus increases. I know that the process by which the carbon fiber is made is somewhat of a trade off between modulus and specific strength but the data that I have suggests that the tensile strength does not vary a great deal for the carbon fibers that are being used by the blank manufacturers for blanks. The tensile strength of the standard modulus, intermediate modulus and high modulus that are being used by blank manufacturers are all in the range of 750 to 900 KSI. However, the strain energy or toughness does drop in direct proportion to the increase in modulus.

Second, I completely agree with your point about the resin, which has much higher strain for a given stress or is more plastic, so distributes the load over a large number of the carbon fibers. But I do not agree that the fibers fracture when stressed. I would argue that they do not fracture until the specific strength is exceeded and when this happens in a carbon fiber blank it is not a question of a few fibers fracturing, the failure is typically catastrophic. The rod breaks. This is partially due to my third point.

Third, I agree with you about the problem with carbon fiber and impact. The problem is a bigger problem with graphite than other materials, say fiberglas, because carbon fiber is relative soft compared to other materials and easily damaged by impact. But the problem with carbon fiber and other materials as well is the fact that the load on the fibers drops off at the 4th power from the surface layers to the inner layers. So if only the surface layer is damaged by impact the rod is significantly weakened and likely to break regardless of the material or the modulus or tensile strength of the material.

Fourth, I do not understand your point about surf rods versus other types of rods. If your point is that surf rods are subjected to higher stress and strain I would argue that is bogus. The typical surf rod is long and has a relatively slow action which means that the stress and strain is more uniformly distributed than with other types of rods that are shorter and have faster actions.

Tom,
You and I have talked about this and I know that you know as well as I do that some of the breakage problem of high modulus graphite rods can be offset with the design of the blank, but not all of it. Rod builders just have to realize that a high modulus blank is not going to be as tough as a lower modulus blank and treat them accordingly or not use high modulus blanks in applications where they are going to see tough use. At least until we have carbon fibers with higher tensile strength or specific strength.
You are right that some of the lack of toughness of high modulus material can be offset by reducing the diameter and increasing the wall thickness of the blank but not all of it. The outer layers of the material are contributing much more to the stiffness or the power of the blank than the inner fibers. Because the stiffness or power drops off at the 4th power from the surface layers to the inner layers and increasing the wall thickness only increases the stiffness or power roughly directly proportional to the wall thickness making a blank smaller in diameter but thicker walled very rapidly results in doing little but adding weight. It does also naturally increase the hoop strength but hoop strength is not the problem with carbon fiber rod breakage.

Good Evening one and all,
Natural carbon exists in four structures: amorphous (soot), which has little or no structure, Graphite which consists of sheets of carbon atoms arranged with six carbon atoms in planar hexagons (rings). The chemical bonds between the atoms in the rings are rather strong). The layers of carbon sheets are bonded to other carbon sheets with much weaker bonds, which allows the sheets to "slide" over one another. A third form is that of diamond in which six carbon atoms form interconnected hexagons which have very strong bonds and are in the shape of a lounge chair. As a result the diamond structure is very dense and has the bulk property of of high hardness. A fourth form of carbon which was discovered about twent years ago belongs to a class called fullerenes (named after Buckminster Fuller). Fullerenes exist as spheres (bucky balls), long tubes, anda variety of other structures. I think that graphite rods were developed prior to the discovery of fullerenes,hence I doubt that if those fibers are fullerenes.

Which of these forms are the ones found in "Graphite" fibers or "Carbon" fibers (which I think are one and the same) I am not sure. I find it hard to imagine that irregularities in the structure of the carbon fiber would make it more suitable for rod building, but I am only a chemist and not material properties engineer.

From what I have heard from Emory, the properties of the tapered tubular rod blank results not just from the material it is made from, but also from the taper and tubular structure and the material used to fuse it together. Just my two cents late at night.

Mike Blomme

Tom and Emory,
Perhaps my statement about Surf Rods and Fly rods complicated the issue too much. From my analysis in the creation of surf blanks, the stress that a long distance surf rod imparts on the blank can be severe. We spent tremendous time trying to understand this and weren't capable of fully understanding it without high end computer models such as FEA (Finite Element Analysis). Tom you are correct that the tubular structure, or tool as we call is exteremely important and can't be overlooked. The taper and consequent hoop strength has a lot to do with not only action, but strength and ultimately durability.

As for the tensile properties, typically any rod that has tensile in the 750 to 900 ksi range as you talk about Emory, is not used in surf blanks because of the their relatively low modulus. Typical carbon in this range is around 30 million modulus, which typically speaking equates to a heavy rod and slower response. For the most part high end surf blanks are extremely fast action, which complicates the "load case" making rod design a little bit of trick. And Emory you are correct about the resin system and how it works with the fiber, perhaps I didnt' elaborate about that enough, I was trying to leave my initial thoughts somewhat simple and to the point. I have seen cases where the external fibers have fractured and not resulted in catastrophic failure. Typically this issue stems from what we call a resin lean condition instead of simple overload, but ultimately the end result can be the same.

In summary, I enjoy the discussion about carbon vs graphite as I am constantly asked this. I can assure you of this. There is a big difference between graphite and carbon fiber, if used in particular application the differences will be noted in a big way. Do some searching around in the military or aeronautical fields and you will see what I mean.

Later,

Tommy

I don't think any rods are or have been made from true graphite. That term has been used very loosely over the years but nearly all the rods and blanks we've dealt with since 1974 that have been called graphite are actually, technically termed, carbon fiber.

Smaller diameter blanks with thicker walls are more durable, but you do not get as much stiffness for the weight as you would with a larger diameter, thinner walled design with the same material.

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

Tommy,
I completely agree that, all other things being equal, a lower modulus of elasticity blank will weigh more and not respond as rapidly because it will have a lower resonant frequency and therefore lower tip velocity. But maybe I am going to show my ignorance of surf fishing when I say that I am surprised that surf fishermen prefer very fast action blanks because a very fast action rod will not cast as far as a slower action rod assuming that the weight being cast loads the rods properly. I was under the impression that surf fishermen wanted to cast long distances.
It is a trade off, a faster action rod will have a somewhat higher resonant frequency but when casting the section of the rod that is not deflecting, much of the butt section with a fast action rod, is not storing any energy. During the first part of the cast we are storing energy up in the rod. On the latter part of the cast the rod then releases that stored energy and, all other things being equal, how much energy that we can store up in the rod determines how far the cast will be. But again energy is only being stored in the portion of the rod that is deflecting which is naturally less in a fast action rod versus a slower action rod.
Rods that are designed for distance casting competitions do not have fast actions. What am I overlooking about surf fishing?

By the way, if I understand your statement about hoop strength I do not agree. Hoop strength will make the rod more durable in terms of resisting torque and sheer but has very little to do with what is the larger problem of durability in a fishing rod which is tension and compression.

I envy you being able to model and use Finite Element Analysis. I looked into doing this about a year ago with a couple of ME friends but it takes a lot more computer power than I have because a rod blank is a surprisingly complex structure. Plus I would have to make a bunch of assumptions about things like percent of resin and scrim, angle of the fibers, wall thickness etc.



Edited 2 time(s). Last edit at 05/05/2006 09:57AM by Emory Harry.

Emory,
Good points, to which I will try to answer. Rod action to me (personal opinion, not fact) is a bit like a radio volume knob. You can turn your radio up to say a volume of 7 or 10, but my radio volume of 7 or 10 may not really be the same as yours depending on what type of radio you and I have. Rods actions and powers to me are a bit the same. To us Surf distance guys, we typically use faster action rods, (By conventional standards) because we are typically casting such heavy weights, coupled with technique and such we load the rod a tremendous amount. Agreed that all of this is essentially a spring and we have to load the rod like a spring for there to be any stored "potential" energy. All very true. I suspect that to someone from the outside our rods, would probably seem extremely stiff in the butt and mid section. In reality that is what we need to allow us to cast such loads and still have a tip that something smaller than a phone pole. I haven't been designing rods since the fish was invented or anything, but it seems that this "trend" is probably going to continue, from what I've seen. As for the hoop strength comment, the hoop strength is a product of diameter and wall thickness of the rod. To go with a fast taper or small diameter rod, you have to increase the wall to maintain your desired deflection, in return increasing the hoop strength. The reverse is true as well, the thinner the wall, typically the larger the diameter to maintain the hoop strength. The durability comes in as a matter of consequence. If you damage the rod, ie. drop it ding it, etc, then for a thin wall larger diameter rod, the overall damage site is a larger percentage of the overall part, as compared to a thicker wall part that is smaller diameter. All of this appears to be a matter of desired strength, target weight, desired diameter, and required fatigue/abuse strength. Not very simple at all, for sure.

Tom,
As for the graphite stuff. In the past, most everyone used glass or some other type of "scrim" for rod manufacture. Hence making the blank, not 100% of anything. The newer technology is to run without scrim, making the parts for the most part out of 100% Carbon or Graphite depending on the manufacturer. This is due in part to new processing techniques (development of the manufacturing techniques) and partly due to reduced inventory of various materials. The by product is a lighter, stronger part, typically speaking.

Tommy

Right, about 15 years ago some companies began employing graphite scrim, but only by moving it from perpindicular to some angle that it would accept. As you know, graphite (carbon fiber if you prefer) will not accept the type of sharp bend you'd find when rolling it perpindicular to something the size of most rod blank mandrels. Some companies now don't use any scriim at all - installing their main prepeg fiber at an angle that they feel gives them the required hoop strength yet still retains enough structure modulus ot do what they want it to do at an acceptable weight.

When I began designing surf rod blanks way back in the 1980's, everybody told me that fast action surf rods wouldn't work - particularly those for heavy casting weights. I disagreed. I remember the first very fast action surf rods I built and sent down to the Outer Banks - amid great resistance, they caught on and before long nearly everybody had switched to fast action rods in place of the old telephone pole heavers that were a fairly moderate to slow action. Many shops began buying the Seeker CSU115 and shortening from the tip and adding an extrension to the butt to try and mimic what I was doing. It was good, but not quite what I was making. Although we had used the same mandrel that the 115 was built on, we slid the entire pattern back by 4 inches, added one more outer wrap, and built a 5 inch overlap ferrule (I don't mind sharing that now). That design was the granddad of most of the Loomis, All Star, BreakAway, etc., designs that have come down the pike in the past 10 or 15 years. I still have the first one that we produced.

Prior to all of this, fast action surf rods had gotten a bit of a bum rap largely due to the old Fenwick Big SurfStick which possessed a tremendously fine and fast tip. It wouldn't carry a great deal of weight and was designed more for tournament casting than for fishing and casting heavy surf sinkers and chunks of bait. It was a good rod, but it failed miserably because guys insisted on trying to use it for things it was not designed for.

You can indeed load the mid and butt section on any fast action rod because the design is progressive - the more load you put on it the more it shifts to the mid and butt areas. You aren't casting just with the tip - it tends to flatten out and the flex takes place down much lower on the rod. Provided, of course, that you do use enough weight and casting input to load it the way it was designed to be loaded.


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

Tommy,
You have some interesting comments. I agree that hoop strength is determined by the diameter and wall thickness in addition of course to the material but hoop strength mainly strengthens the rod against sheer and torsion. Hoop strength will have some effect on the rods resistance to impact but not much because the outer most layers of material, those that would be damaged by impact, are the ones that carry the vast majority of the load. The load on the fibers drops off at the 4th power of diameter so if just the outer most layer is damaged the rod is significantly weakened. I would argue that resistance to damage from impact is more a function of the hardness and strength of the material particularly the surface layers rather than the hoop strength.
I am sure that you know that the longitudinal fibers, those that run straight up the blank, have almost no effect on hoop strength. Hoop strength comes from the fibers that in effect go essentially around the rod which is what in most blanks the scrim does. You say that you use no scrim and that your blanks are all carbon fiber. This can result in a lighter blank with a higher resonant frequency just like the carbon fiber scrim that has been used in the past but again there is a trade off. Because the glass that is used in most blanks for scrim has roughly 1/2 the tensile strength of carbon fiber but has roughly 4 times the strain energy or toughness this means that it will take more material using carbon fiber to get the same hoop strength as it will take if glass is used. It seems to me that this is not necessarily bad but because carbon fiber has roughly 2/3 the density of fiberglass it turns out to be about a wash in terms of hoop strength.
Let me ask you a question unless you consider it proprietary, are you using what has been called a filament wound process?

Emory,
I have done filament winding and created a weaving type machine to do this in and automated fashion. In theory, it would be the king of all rod layups, but the metering of the resin/hardener combination was not something I could control very accurately. In a game where 2% is the difference between good and bad, we just couldn't get that accuracy even with an automated application. Now, new technology has it where you can get tow fiber in a pre-preg fashion, so some of that may change, but all of our stuff is roll-wrapped, so we end up with some compromise of longitudinal and axial strength, due to the tapered nature.

Good question.

Tommy

Tommy,
Yes, I can understand how the resin content could be a problem with filament winding. I know that some of the golf club shaft manufacturers are using it but they they are more concerned with torque and less with weight.
I thought that all material had a tow count and that it was just an indication of the size of the fiber?
I understand the problem with longitudinal versus axial strength and the alignment of the fibers. But let me ask you a question about that. Because the effective modulus drops off so rapidly as a function of the angle of the fibers and the fibers in the surface layers being so much more important and with roll wrapping it being virtually impossible to keep the fibers aligned due to the taper of the mandrel why doesn't anyone tack the prepreg on the mandrel at an angle that will result in the fibers next to the mandrel being misaligned but the fibers on the surface of the blank being aligned properly?

Over my head....

Here's my definition of Graphite/Carbon Fibre.......The stuff now used to make blanks that is lighter,more sensitive and stiffer than any previous wood, reed, or Fibre glass. Glad to know there someone out there that knows this stuff.........just know that I have no space for it. LOL

Bill,

Tom has mentioned this a couple of times, so don't throw away your rods quite yet, because they're all based on carbon fiber. Technically speaking, Graphite is more useful as pencil "lead" or in lubrication. Anyone who tells you that they're switching up from graphite to carbon fiber is not using the terms correctly. Intermediate Modulus fibers; IM4, IM6, IM7, ect (Hexcel Fibers and comparable) are all "Carbon Fiber":

[www.hexcel.com]

Emory,

The tensile strength of the fibers can increase though the IM range, but will fall off significantly in the High Modulus (HM) and Ultra High Modulus (UHM) fibers. In addition, the strain to break will fall off significantly as well for fiber modulus above the IMs. So that means that not only are the HM and UHM fibers more brittle and not as strong, but that is compounded by lighter thinner walled blanks.

mark

Emory,
Tow fiber is a generic term we use to describe raw carbon that is generally speaking dry and requires wet layup. All fibers have a tow count, correct its just slang for a roll of "Tow Fibers" that have some tow count like 1k, 3k etc. What you are talking about is the layup angle that the pre-preg is applied. A good bit of this already goes into the design. The usual limitation is the width of carbon that can be obtained. Typically speaking we are limited to 12" or 24" so any reall dramatic angles can become a challenge to get everything to line up perfectly. Another element is the one that most forget. The human element. Laying these up to get repeatability with real elaborate layup angles, seems to complicate things and we don't end up with what we want.

Later,

Tommy

Mark,
The data that I have is somewhat different than the Hexel data sheet but in looking at the Hexel data I see your point. I know from having read about the process of making the carbon fiber that the tensile strength is supposed to drop as the modulus goes up. If I remember correctly it has to do with the increased temperature. The difference is not really dramatic though. It certainly does not drop like the strain energy does with increased modulus.
As far as strain to break is concerned, it seems to me that higher strain to break is just another way of saying lower modulus. If the tensile strength does not change then higher strain by definition of modulus of elasticity mens lower modulus.

Tommy,
I can see now how you are using the word Tow and your use of it makes sense.
I do not see why the width of the prepreg is a limitation because multiple flags could be used but I do see how misaligning the fibers on the mandrel so that the alignment would come out correctly in the surface layers could be a problem in manufacturing with personnel training and repeatability especially sense every blank would start off with a little different angle.. But because the effective modulus drops so quickly with the angle and the angle gets worse toward the tip which is exactly where you do not want it to that I would think that someone would be attempting to get the fibers aligned properly in the surface layers.

There are companies rolling prepeg so that the outer wraps put the fibers in at nearly perfect linear alignment. It's not that hard to do, but as mentioned even after you determine the initial angle they must be tacked at, you have to bank on somebody actually tacking them in the right place each time. Blank making still depends heavily on human hand labor.

The final sanding operation is going to remove about 1 to 1.5 mil thickness of the blank. So some of the very outermost fibers are compromised anyway. I know that some companies build to allow for this while some others do not. There are a lot of places in the design and lay-up process that could produce a little more efficient blank, but it's going to require more careful labor and at some point somebody has to pay for that.

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

...pretty overwhelming information in this thread.


"If you build it they will come".....do the fisherman want it and like it?

Emory,

I would characterize the differences between the strength of IM and HM/UHM fibers as significant, and the differences in the breaking strains as fairly dramatic. Generally speaking, the strength of the IMs ranges around 800 Msi and the UHMs around 500. The breaking strains of the IMs tend to be about 2.0 - 2.2% and the UHMs about 0.8 -1.0 %......so the difference in the brittleness of the fibers is a factor of 2X. That's why I was saying that the aside from the fibers being significantly more brittle in the high modulus blanks, the lighter, more fragile structures will compound the problem. Not to say that the HM blanks will be prone to failure, but you have to be more careful with them. And things like over straining (high sticking) would be a bigger concern than overloading. Often the manufactures will avoid using the HM materials in the tip sections altogether. So you see some multi-modulus designs with the HM materials employed in the butt sections.

"As far as strain to break is concerned, it seems to me that higher strain to break is just another way of saying lower modulus. If the tensile strength does not change then higher strain by definition of modulus of elasticity means lower modulus. "

Yes, that is true but mainly in this case of carbon fibers where the stress-strain response is very linear. It's often hard to generalize in that way though because the modulus is taken at very small strains and for many materials the stress-strain curves take on more complex shapes. So quite often the modulus, strength (peak stress) and strain to break, all act quite independently.

mark

Two Engineering Degrees
MBA
Forty Years Project Management Aerospace/Nuclear Power
10 Yr Charter Fishing/Rod Building/Chef

This Thread -

Read 100 percent with total interest
Understood 21.34 %
Agreed with 18.12 %
Objected To 4.72 %
Skeptical of 19.38 %
Wondering About 43.72 %
Figuring Out What To Order Next - ???
Waiting For Andy's Entrance To Matter -
Looking For Misspelled Words -
Flock Em All And The Pieces Will Not Get In Your Eyes!!

Thread Rating - This One Should Be In The Library or The Magazine!!

Glad to see the blanks gurus posts!! Verrry Interessting!

Fsh No Mo

Mark,
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. However, carbon fiber is not one of these materials. 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.

As far as the relationship between strength and modulus of elasticity is concerned, I have done some reading lately about the processes used to make carbon fiber and there does seem to be somewhat of a trade off between the tensile strength and the modulus of elasticity based I guess mainly on the processing temperature. But the processes must be improving because I have the data on about 50 different available carbon fiber prepregs and the relationship between the tensile strength and the modulus is all over the map. Here are some examples of prepregs that I know that some blank manufacturers are using. Obviously the blank manufacturers know what they are doing and select the best combination of prepreg properties for the particular blank they are making but as you can see high modulus does not necessarily mean low tensile strength.
Prepreg Modulus of Elasticity Tensile strength
IM6 40(MSI) 760(KSI)
IM7 40(MSI) 780(KSI)
IM9 42(MSI) 920(KSI)
T800H 42.7(MSI) 796(KSI)
T100G 42.7(MSI) 924(KSI)
G55-700 57(MSI) 700(KSI)

I would sure agree that toughness or strain energy goes down directly in proportion to an increase in modulus of elasticity because it is just the area under the stress/strain curve.






Edited 1 time(s). Last edit at 05/06/2006 11:04PM by Emory Harry.