Material Damping in Graphite Rods - What is Rayleigh Damping?

[VGB]

I had a play with a rod yesterday that I suspect has a lot in common with Pauls noodle. Originally, it looked like this:

http://www.flyforums.co.uk/members....003.jpg

A combination float/spin rod that was given to me in 1972 and was virtually uncastable. The only clue to its genesis was a sticker saying "foreign made". I took the 2nd and 4th sections from the top and did this with them:

http://www.flyforums.co.uk/members....039.jpg

Solid, presumably e-glass, the material damping is virtually non-existent. I could not damp it for the life of me and every cast was a wiggle cast.

Vince

[Merlin]

Thanks Vince

It would have been interesting to get some measured characteristics from this rod.

If anyone else has got one, welcome

Merlin

[VGB]

Sorry Merlin. I carried it around the world for 40 years and no-one wanted it before now

I converted it to a 2 piece fly rod last October

regards

Vince

[gordonjudd]

Solid, presumably e-glass, the material damping is virtually non-existent.

Vince,
Very nice work on your conversion. It may still be a club to cast, but it looks great.

I do not have Perkin's book with me, so maybe Merlin could look it up, but I think his data showed the material damping of a fiber-glass rod was greater than the zeta for graphite.

He also mentions that the after-bounce vibrations were much worse with heavy tipped glass rods, so your problem may have more to do with its effective mass than it does with its damping.

It would have been interesting to get some measured characteristics from this rod.

If you still have it, and can take a video of its clamped vibrations I could get a measured damping ratio for it. Better yet do that vibration test with several different tip loads and we can get the k and mo values for it as well.

Gordy

[Merlin]

Vince

I found some scientific references on transient conditions for non linear systems, the only problem is that the full text is not available (restricted).

Gordy

The values in Don phillips book are 0.025 to 0.030 for graphite and glass, and 0.025 to 0.060 for cane. Reference is made to the afterbounce of glass rods in the fifties, the rods having a slow heavy tip. Don Phillips mention this was not due to internal damping.

This is no more the case today, some light, pretty fast rods do show an after bounce problem.

Merlin

[VGB]

Gordy/Merlin

Thanks for the build compliment, it was my 1st attempt. I built it to cast a short way in an overhung dribble of a stream that does not have room for 7'6" to move. Every summer, the trout there have been giving me the fin, this year I am going to get them.

He also mentions that the after-bounce vibrations were much worse with heavy tipped glass rods, so your problem may have more to do with its effective mass than it does with its damping.

The values in Don phillips book are 0.025 to 0.030 for graphite and glass, and 0.025 to 0.060 for cane. Reference is made to the afterbounce of glass rods in the fifties, the rods having a slow heavy tip. Don Phillips mention this was not due to internal damping.

I suspect that the low k may have something to do with it as well. I need to stop jumping to conclusions.

Do you have the detail on how you conduct your tests, I would like to get as close to your set up as possible to reduce experimental error. I will also have a S-glass blank in my hands within the next couple of weeks, if you want some more data. The s-glass will only have a tip ring initially.

Vince

[VGB]

Merlin

I found some scientific references on transient conditions for non linear systems, the only problem is that the full text is not available (restricted).

Do you have a link, it's not impossible that I may be able to get an inside copy. No promises though.

Vince

[VGB]

Merlin

I bumped into this as part of my day job, it may help with your model of the caster:

http://www3.fbw.vu.nl/~JSmeets/2002/Relative_damping-HMS02.pdf

Gordy

This may be on the wrong thread but I have been looking at undercarriage locks. A viscous friction damper at low frequencies and high rayleigh mass stiffness functions can become locked in and function as a rigid connection. It occurred to me that this may be the cause of your rebound hump but I have not had an opportunity to follow it up.

Vince

[gordonjudd]

Do you have the detail on how you conduct your tests,

Vince,
I just rubber band a paper penny roll wrapper to the tip of the rod and put in a different number of pennies (2.5 g/penny) to vary the tip mass. You want to make sure the mass of the pennies does not move independently of the tip as they will if you suspend a bag with the pennies in it from a piece of string as is done to make deflection measurements.

I then clamp the cork grip on the rod to a solid piece of 2x4 with a couple of wood clamps. Set up a video camera to track the y tip positions as the rod vibrates for 8-10 cycles. I try to get around 15 sample points per cycle, but you could get by with less so the 50 fps rate from a normal PAL video should be adequate.

Digitizing all of those points is a pain, but should be fairly straightforward to do with a free-ware program such as tracker.

I have a Matlab program that will do a least squares damped cosine fit to those sample points that makes use of the FMINS routine in Matlab. If you can take the video and digitize the data I will be able to do the fitting for you.

A range of 5-6 tip masses from 0 to 30 grams should give a reasonable number of points to determine the k and mo of that rod.

Gordy

[Merlin]

Hi Vince

Thanks for your kind offer. I shall try to find it again, it is somewhere on Scirius database and was produced by a Belgium University (Louvain?)

Merlin

[VGB]

Gordy

I am not sure our pennies are the same size but I can use fly tying lead.

Merlin

I'll see if my son can get it, he has a tie to some of the publishing houses. I did do some work with a Belgian vibration outfit a few years ago that were University sponsored. We got them to do some engine mount analysis for us.

Vince