Ok-- This question was asked today and I was not sure how to answer it.
So I'm going to put it out for you to help me to understand it more clearly.

The question was--- what is meant by modulus in a rod ?And what is greater for stiffness?? Say like a 7' with a 45 million rating to a 7'6" 85 million modulus ??

I know one would automaticly think that the higher number would be greater or stiffer but then again sometimes it's the other way around.

With that said. Any help here would be appreciated and many thanks in advance. Or maybe a painted picture...

I also hope I worded it right and hope it's not confussing..


Thanks again <<< DON >>>

At the top of the board there is a button for Search - type modulus and read for a year.

Here is one of the best of the lot! Click on it and have a nice day.

Mr. Putter: This is my last act of defiance! Onward to the closet and the glue!

[www.rodbuilding.org]

Gon Fishn



Edited 1 time(s). Last edit at 01/25/2006 09:51PM by Bill Stevens.

Or, go to the online glossary on this site and find each of your answers right there.

.........

Bill, yer off to the races-deserting the ship and just to sniff glue... I'm appalled.

Putter
Williston, ND

Thank you ...Bill . A whole lot of reading going on here. I sure don't know why that I'm so quick with the post rather than the search..I guess I'll just put a sticky at the top of the screen to remind me. Or may be a mallet over my head. Well had better get a hot toddie and start reading .

Thanks again <<<< DON>>>>

More than you will ever need (or want) to know about modulus:
www.hexcel.com/NR/rdonlyres/230A6C2A-FDFA-4EC7-B048-E4EB28E3BC8C/0/PrepregTechnology2.pdf

Donald,
I looked and I do not think that you will find in any previous posts a discussion about modulus of elasticity and stiffness and how they relate which if I understand is your question. So let me try to give you an answer in terms that are as straight forward as I can.

Modulus of elasticity and stiffness are often said to be the same thing but they are not the same thing at all.
The modulus is a property of the material, graphite or glass, that a blank is made of. The primary reason that graphite, carbon fiber, is an excellent material for rod blanks is because it has a high modulus and low weight. Modulus of elasticity is the relationship between stress and strain. This sounds complicated but it is not. Stress is just how much force is applied in square inches and strain is just how much the material deforms in square inches in response to the applied force. For any elastic material, like graphite or glass, there is a very linear relationship between stress and strain or the applied force and deformation of the material.
It does get a little more complicated because the modulus numbers that are typically advertised for a blank are not for the blank at all but for some of the fibers that the blank is made of. There are other fibers in what is called scrim, that basically go around the blank to give it what is called hoop strength, and there is also resin in the blank. The fibers in the scrim and the resin have lower modulus than the modulus numbers advertised. So naturally the more of these lower modulus fibers and resin that are used the less effect the modulus has on the finished blank. Plus the modulus numbers that are advertised are usually tensile modulus or the modulus under tension. Basically the top of a rod being bent is under tension the bottom under compression and the cross section under torsion. The compression and torsion modulus are both significantly lower than the tension modulus. So modulus is very important but the Numbers that are typically advertised can be very misleading unless you know what context to put them in.
Is higher modulus always better than lower modulus? Not necessarily. There is a trade off between modulus of elasticity and what is called strain energy. You can think of strain energy as toughness. So the higher the modulus of the material the lower the toughness. So a rod that is constructed of a high modulus material will be lighter but it will not be as tough. You have to choose which characteristic is more important to you in a given rod.
Now to the heart of your question about modulus versus stiffness. Higher modulus does result in higher stiffness, all other things being equal and stiffness is a property or characteristic of the blank. But stiffness is not a number like modulus. Stiffness is a curve. As you apply more and more force to a blank or rod it gets stiffer and stiffer creating this curve. Any given point on the curve is the stiffness at that applied force.
I hope that this answers your question about modulus versus stiffness. If I have not been clear enough send me an e-mail and I will see if I can clear up any confusion.