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First off, I want to thank one of our readers for the email; it read something
like this: "I am new to fly fishing and do not understand what 'modulus' is.
Can you help me?"
Well sir, I am not new to fly fishing but I felt I could not properly answer the
question. (I did answer his email, I told him to please watch this column for the
answer.) This has been a fun task. I called several rod makers and told them
I was writing this and why and asked them, if they wished, to give me their
definition of what modulus is.
I did consider calling a few 'fly-shops' for their ideas, but felt that may lead
more to the problem than the solution. Here are, in no particular order,
the responses.
When you called and asked me to write about modulus in one or two paragraphs,
I wondered if it was possible? Modulus, for history buffs, was coined by Thomas
Young (cerca 1810), an English physician and physicist. He gave the word energy
its scientific import, and Young's modulus, a constant in mathematical equation
explaining elasticity was born. For design engineers, this meant that at low tensile
stresses, there is a linear or proportional relationship between stress and strain
(known as Hooke's Law) and the slope of the strait line is (you guessed it) modulus
of elasticity. In the 21st century, the above equations are critical for advanced
composites which utilize a combination of resins and fibers, customarily
carbon/graphite, kevlar, or fiberglass with an epoxy resin.
The fibers provide the high stiffness, while the surrounding polymer resin matrix
holds the structure together allowing infinite design capability. In general, carbon
composites are two thirds the weight of aluminum, and two and a half times as stiff.
All this means that graphite composites as we know them have a high tolerance
to bending. The higher the modulus, the higher its tolerance. Graphite is resistant
to fatigue, and can handle harsh temperature fluctuations. Perfect for the walk-in
fisherman--right? To you fishermen out there: a rod touting a higher modulus rating
will be stiffer or bend less than a rod with a lower modulus rating. Be careful though.
Remember that these composites have an infinite design capacity.
That means marketing has unlimited means with which to present modulus. Since there
are no industry standards that I am aware of, there is no way to compare apples to
apples, i.e. the modulus of say IM6 to one manufacturer will not be the same as
the modulus of IM6 used by another manufacturer.
Of greatest importance in my opinion, is the design of the mandrel used to manufacture
the blank and the quality assurance of the end product based on the composite being
used. Rather than talk modulus, I like to talk performance with my customers.
Under what conditions are you fishing? What are you fishing for? What are the
characteristics of your ideal rod in this given situation. Now I know what the
customer wants. Forget modulus, you don't need to be a physicist or a design
engineer. I can help them select the rod based on performance required. We
can discuss power relative to stiffness of the rod desired, the action which is
relative to the taper design. I use G.Loomis blanks, not because of my
knowledge of modulus. I use G.Loomis blanks because I like the overall
rod performance . . .power, accuracy in casting, weight, and sensitivity . . . look
at the tool required for the job. ~ Mike Mattox, D&E RODS
The full definition of modulus of elasticity is a straight forward engineering term
and, although lengthy, can be found in any engineering text and perhaps even the
Webster's unabridged. It relates to the measurement of stiffness to weight ratio
of any material. However, it is not independently related to the performance of
laminates. Percent of resin (epoxy) in the blend with fiber (graphite) implies the
fiber volume.
This feature (amount of graphite Vs/ resin in a laminate cross section), among other
things is far more important than fiber modulus. Advertised modulus ratings are only
a rating of the raw fiber. IM6 is merely a trade name for Hercules fiber of (not
especially high) modulus.
IM6 is about 36 million modulus. There are many other brands of fibers in this
range. However, most makers of high performance rods now employ the use
of fiber with higher modulus.
The modulus of a laminate (fiber plus bonding resin) is always less than the original
fiber (since it has been "diluted" by the resin component). This modulus "drop" is, more
or less, varying with the percent and especially the resin used. This feature far outweighs
fiber modulus alone. Our fiber, our resin type and percent mix is a recipe we prescribe
for our use. As you can understand, it is therefore very proprietary and closely guarded.
~ Trevor Bross, T&T Rods
In general terms it is a measure of stiffness. The less a material moves with an
applied load, the stiffer the material. The higher the modulus value, the "stiffer"
the material. ~ Kevin Thompson, Sage Rods
Modulus is the measurement of resistance to strain expressed as a ratio. In context
of fishing rod design, it describes the stiffness of the fiber used to construct the rod.
It does not by itself determine rod stiffness, weight or strength. High modulus
materials can be used to make soft rods, and conversely, low modulus material
can be designed into making stiff rods. Several other important measurements
of rod material to consider include fiber strength, elongation, compression rate,
resin content percentage and resin toughness, scrim type and weight. The goal
of many rod makers is to optimize these variables, achieve the desired action
(combined taper and stiffness), high strength at low weight and reasonable cost.
~ Steve Rajef, G. Loomis
Technically stated modulus of elasticity is the ratio of unit stress to unit strain
within the proportional limit of a material in tension or compression. Otherwise
known as Young's Modulus. Where unit stress is force per unit area, usually
expressed in pounds per square inch. It can be either tensile (pulling), compressive,
or shear stress. And unit strain is the amount by which a dimension of a body changes
when the body is subjected to a load. Divided by the original value of the dimension.
To an angler, modulus is stated as a value of the raw material (the carbon fibers only)
used in manufacture of a rod, and can best be described as a materials ability to resist
bending. Higher modulus rods that are manufactured correctly can produce lighter,
sensitive rods that quickly want to return to the straight unbent state. Lighter because
less material is needed to attain the same flexural strength of lower modulus graphite.
Lower modulus rods typically tend to be slower to return and slightly heavier since
more material is needed to attain the same level of flex (although I have cast some
low modulus rods that felt light and quick). Although many anglers have gone to the
higher modulus graphite, there are still other that like the feel and action of the lower
modulus rods as they tend to be a bit slower and facilitate slower casting strokes.
Although modulus has become a buzz word in the rod industry there are many
other issues that are just as important, and maybe more so, than the modulus of
the material. Tapers (distribution of the graphite along the length of the rod), wall
thickness, ferrules, scrim or no scrim, epoxy resins, manufacturing techniques,
and more need to be considered in order to come up with a good casting rod,
regardless of the modulus of elasticity. All the manufacturers continue to seek
out higher modulus fibers to use in rod manufacturing, but in doing so must also
seek out new resins and techniques to manufacture using these fibers. The search
goes on. ~ Jim Lapage, Orvis
- Modulus of elasticity - Bulk
- Modulus of elasticity - Compressive
- Modulus of elasticity - Flexural
- Modulus of elasticity - Tensile
Bulk Modulus: The stiffness or flexibility of rubber, resin, or other relatively
soft materials. Usually expressed in units of lb/in2".
Modulus of elasticity: The stiffness or resistance to deformation of high
performance materials when stressed in their elastic range. Expressed in units of lb/in2".
Also referred to as "Young's Modulus." ~ John Brazelton, Redington
I am neither an acknowledged nor professed expert in the field of graphite. I am
not an engineer, a materials mechanic or a chemist. But, I have been involved in
the fishing rod industry for almost 25 years as a private label rod maker. I have
been involved almost exclusively in the manufacture of fly rods for the past 10 years.
I have long questioned what modulus means. As I understand the term, it is simply
a designation of any material's capacity to withstand deflection, or bending without
breaking.
Most any material can be tested in this fashion, but we are talking about materials
used in the construction of rod blanks so we shouldn't muddy up an already cloudy
subject by talking about iron bars or copper wire or whatever. The less a material
will bend before it begins to fail, the higher the modulus. All materials used in rod
making can be measured and assigned a modulus rating. Cane has a modulus rating,
fiberglass has a modulus rating, and the various "generations" of graphite have their
modulus ratings.
Each new generation of graphite has had a higher modulus rating than the generations
that came before. This, to me says that if a blank builder trades material generation
for generation, his blanks are becoming stiffer and more brittle with each new generation.
This has obviously not been the case. So some adjustment for the newer materials has
to have been made. I believe that in most if not all cases, materials have been blended
to arrive at a functional blank. I haven't heard of anyone that advertises a 100% highest
modulus blank.
In experiments, I've achieved no significant reduction in weight or improvement of
performance in a blank by substituting high modulus graphite for standard graphite.
In fact, in some cases, higher modulus graphite does not perform as well. In cases
where a great deal of flex is a desirable characteristic, lower modulus graphite greatly
enhances the blank's performance and extends it's useful life. ~ Ray Bauer, Global
dorbeR Group
So now you know, right? ~ James Castwell
Addendum: There is more information on modulus on our
Bulletin Board too!
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