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 rdsphoto |
#41 | |||
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Posts: 337 08/13/2008 00:37 |
fishbum - What is the maximum stress that the bamboo can withstand then? Are you referring to shear strength of the joint?? Please explain. Furthermore please
define the neutral center of the flexed rod and how you quantify it - thanks!
Best Regards, Rob |
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 fishbum |
Stress | #42 | ||
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Posts: 178 08/13/2008 10:21 |
Rob:
A few short answers to your questions. We have already sorta hijacked Bob's thread by moving towards a technical discussion of beams.
What is the maximum stress that the bamboo can withstand then?
Fiber Stress at Proportional Limit is the maximum bending stress a material can sustain under static conditions and still exhibit no permanent set or distortion. (1)
Modulus of rupture is the ultimate bending strength of a material. It describes the load required to cause a beam to fail and can be thought of the ultimate resistance or strength that can be expected. (1)
Garry found that the maximum allowable working stress for bamboo is approximately 220,000 ounces per square inch, (2)
The 220,000 ounces per square inch figure is the proportional limit.
Both the Proportional Limit and the Modulus of Rupture are difficult to determine for bamboo because it is a natural material and varies in its characteristics.
Are you referring to shear strength of the joint?? Please explain.
I am not referring to the shear strength of the joint. I am talking about the stress in the bamboo. The stress in a bent beam is maximum at a point furthest from the neutral axis.
Furthermore please define the neutral center of the flexed rod and how you quantify it-
The "neutral center" or "neutral axis" coincides with the center of gravity of a beam In a fly rod with a regular polygon cross section the neutral axis is at the point where all the strips meet in the center of the rod. The neutral axis is not a quantity it is a place.
Ref:
(1) Bamboo in the Laboratory, Wolfram Schott (2) A Masters Guide to Building a Bamboo fly rod, Everett Garrison & Hoagy B. Carmichael
http://en.wikipedia.org/wiki/Bending http://en.wikipedia.org/wiki/Stress_(physics) http://physics.uwstout.edu/statStr/Strength
Hope this helps. I know it is brief. Any library will have many books in their engineering and technology section that covers this topic in more depth than any of us needs to make bamboo fly rods.
fishbum
Last Edited By: fishbum 08/13/2008 11:53.
Edited 2 times.
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gooseberryrods |
#43 | |||
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Posts: 544 08/13/2008 11:01 |
So if Garrison and Fishbum are correct, wouldn't it stand to reason that rods with an unequal number of strips would weaken or become soft over time? There
are those on this board who have been looking for anecdotal evidence of broken pentas, but is the real issue that these rods could be more prone to becoming
soft rather than breaking? Anyone have this experience with pentas?
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fishbum |
#44 | |||
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Posts: 179 08/13/2008 11:20 |
Sorry about the messed up font in my reply above. It all looked so good when I put it together. It looks like I am yelling and I am not. I tried to fix it but
it still looks like crap.
fishbum |
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David Dornblaser |
#45 | |||
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Posts: 147 08/13/2008 21:28 |
fishbum,
Interesting post, it does raise a question - are the stresses that would break a penta, hex, or, quad anywhere near normal fly fishing stresses? I have not heard of anyone having a problem with a quad/penta configured rod. If Bob Clay can make a hollow-built penta endure the powerful torque generated with a spey rod doing a spey cast, I am not going to worry about my 4 & 5 wts. I really have enjoyed my current penta and I look forward to the one Jerry Kustich is working on now. - David www.UpperMidwestFlyFishing.com - fly fishing in the Upper Midwest. Spring Creeks to Smallies to Steelhead. |
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fishbum |
#46 | |||
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Posts: 180 08/13/2008 23:35 |
David:
We should be designing our fly rods with some safety factor so the operating range is well below a level where failure will occur. It matters not what the rod geometry is if you exceed the maximum stress that your rod can withstand it is going to suffer damage. It don't matter how that level is exceeded whether by the tail gate of the truck, by trying to horse a big fish or the ceiling fan in the hotel room if you exceed that level you have a damaged rod. The narrower the operating range is the more likely it is you can damage your rod in normal use. I have listed some resources that the reader can use to examine the stresses in different structures. The behavior of a cantilever beam is well known to engineers. The analysis applies to buildings, bridges, fly rods and even the shift lever in the old hot rod. I encourage anybody to do the math and compute the stress for a beam of triangular, square, penta, and hex cross section of equal cross sectional area. You will find the exercise enlightening. There are two ways to design a fly rod. You can design empirically or you can design by engineering analysis. I prefer the engineering approach. Actually engineer the prototype then adjust to get what I am looking for. Enjoy your new rod when you receive it. fishbum |
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rdsphoto |
#47 | |||
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Posts: 338 08/14/2008 01:24 |
fishbum- Do you consider a flexed rod in motion and under the effect of the line while casing to be a static load? Wouldn't 220,000 lbs per sq inch be
relative to the section points volume of fibre?? and is there any test data supporting this quantitative summation??? - from my experiences it seems totally
irrelevant to the actual loads or stress values that a well designed bamboo fly rod performs under. I do agree with your comment that "Both the
Proportional Limit and the Modulus of Rupture are difficult to determine for bamboo because it is a natural material and varies in its characteristics"
especially considering the vast range of finishing techniques and their effect on the finished rod. Your statement that "The stress in a bent beam is
maximum at a point furthest from the neutral axis." is most interesting to me as well for although I do confess that my math skills are very basic, again
from my experience the difference between the corner and the flat of ANY qualitative casting rod is not differentiated enough to cause such effect. I am very
familiar with Wolfram and have had past correspondence with him (hope he chimes in) since he published all those salmon rod tapers and his first article... -
It is My belief that under load this neutral axis does not exist in the bent fly rod - not having a correlative effect anyway - besides the dead center is
usually glue is it not???. Also to your follow up post I must confess that I do not completely follow, as I would not care to fish a rod that was designed to
withstand the stresses of a tailgate or ceiling fan unless it was an 8 or 9 weight - seriously. "Actually engineer the prototype then adjust to get what I
am looking for." - This sounds like starting with a modified guess based on computer data only to then feel out the final result anyway - no? I'm all
trial and error myself so please do not get me wrong just could never really get the same connection through the computer regarding bamboo....
David Dornblazer - I have not had the pleasure of a Bob Clay rod but you should be quit happy with your Kustich he definitely seems to understand the design. gooseberryrods - Having only owned about a dozen or so Uslan penta's as well as building only a few more straight penta rods of my own, I really cannot say as it would require exclusive fishing with specific rods for too great a period of time in order to appropriately respond, but thus far have never noticed such a softening of the action on any of them. This is not to say I have not noticed any damage on any of them either just nothing like Garrison predicted. |
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czkid |
Dynamic vs. Static Loads | #48 | ||
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Posts: 3561 08/14/2008 07:52 Moderator |
Folks, as an ageing Aerospace Engineer (read Rocket Scientist), I must remind you that most of the work done on fly rod loading was calculated as a static load. Dynamic loads are FAR, FAR different and generally worse. Dynamic loading considers the object under discussion in what would be a more realistic situation, and takes into consideration things such as rate of load application, frequency of the the applied load, etc. etc. Dynamic calculations are exceedingly complex, even for homogeneous materials of known consistency... and when you get to playing with natural materials like bamboo you introduce a whole host of new variables into the equations. An example: The military learned many years ago that when you march troops across a bridge you instruct the troops to go to "route step" or a casual walk, not to be "in step" or coordinated. Why??? Because troops that are marching "in step" tend to set up harmonics that cause the bridge (a structure) to react. If that harmonic is at a critical frequency all sorts of nasty things can happen. The weight of the troops doesn't come anywhere near the limit loads of the bridge, but the dynamic loading can exceed all the limits. Given the loads involved, and the general situations accompanying fly fishing, I believe it's safe to say that the lighter the rod (i.e. 4wt vs. 6wt),
the better chance you have of breaking it in normal usage. My "gut" feel is that a symmetrical cross section will be easier to calculate dynamic
loadings for than a non-symmetrical cross section under real life situations.
Last Edited By: czkid 08/14/2008 09:15.
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fishbum |
#49 | |||
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Posts: 181 08/14/2008 08:31 |
Thank you Ralph.
Great example of a dynamic system and the challange of dealing with the many variables that go along with analysing a dynamic system. Rob I have pointed you to the tools to understand and to prove to yourself what these stresses are. Stress is as relevent to a fly rod as it is to a bridge or a building. Fly rod design is a bunch of trade-offs. You have to decide for yourself what to trade. In the penta vs hex debate there is a small gain in stiffness in the penta for a larger cost of higher stress. You decide if the price is what you want to pay. fishbum |
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David Dornblaser |
#50 | |||
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Posts: 148 08/14/2008 09:40 |
rdsphoto wrote:
rdsphoto - I am really happy with my current Kustich penta. The one that Jerry is working on is a new taper based on our conversations, he calls it the Dornblaser-4, probably to have someone to blame.  Happily, he is really pleased with it and it just needs to be finished. It is a crisp, true 4 2/2
7/9".
fishbum - I find your comments interesting, but in less my hypothetical world, I see a number of very good makers using the penta configuration and even more anglers, including me, enjoying their rods. I have not heard of a single penta rod failure or softening. I am going to be very happy to have two pentas in my small quiver, along with their cousins, a handful of hexes, and maybe someday, a single quad. I can understand why non-classic rods like pentas aren't for everyone, it is nice to have a surprising large number of options in our cane world. - David www.UpperMidwestFlyFishing.com - fly fishing in the Upper Midwest. Spring Creeks to Smallies to Steelhead. |
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fishbum |
#51 | |||
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Posts: 182 08/14/2008 09:47 |
David
Like I said, there are trade-offs. You have chosen the ones you like and that is fine. I hope you enjoy your new rod from Jerry. I am going fishing! fishbum |
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czkid |
Fishing vs. Figuring | #52 | ||
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Posts: 3562 08/14/2008 10:45 Moderator |
From the purely sensual aspect of fishing vs. figuring out how to correctly build a rod, I must say there is quite a difference between the three x-sections
characteristics.
I've got experience in many hex rods; quads by Edwards, Nunley, Mallucci, and others; and pentas by Wire, Uslan, and Beasley. And most fortunately, most of them were in the same length, line weight rating. Firstly, I'd have to say that I've enjoyed the vast majority of all of them regardless of x-section. They each have their pluses and minuses, and I would say that they all have their "applications". I do find the pentas a bit "stiff" for my tastes, although my Uslan has some decidedly parabolic aspects to it which I find enjoyable. The quads are my choice for the times that I really want accuracy and preciseness, but don't try them when you're tired... Of course we all know about hex x-section rods and the vastly different tapers associated with them, sort of your handy-dandy general purpose tool. For just plain fishing I'd have to go with a hex or a quad in most cases. If I were in a situation where I was limited to one or two rods and I needed to occasionally push a 5wt into 6-7wt territory I'd want a penta around. But that's what CZKid likes, not Rolf Jacobsen, nor Harry Boyd, or whomever else you'd care to throw into the equation. That's why I always tell people, when you're shopping for a rod... cast'm; and when you find the right rod... buy THAT rod, not a copy. Petri Heil Guys!!! |
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senior |
Pentas weakest Link ?/ Tangible Index Of Deflection Issue ? | #53 | ||
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Posts: 16 08/16/2008 15:47 |
I remember one major penta manufacturer as stating that their cane was harvested only from hilltop locations , where it was normal for the wind to blow in from
different directions every day,thus developing the power fibers in a uniform way. I.E. the fibers were both stretched and compressed equally in incremental
time and stress frames . Is this an engineering factor ,(or quality control ) rather than a marketing ploy ?
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