Resin

[gordonjudd]

I assume that’s a lower modulus rod than Tim is bending - out of interest how heavy is the weight?

Paul,
I think that in most cases stiffer high modulus materials will tend to have lower strain failure limits. Merlin probably has more up to date values but I think the strain limit for graphite rods is around 2% while it is around 6% for fiberglass rods.

The rod in that photo was a 6.5 foot 3 wt. It took a fork lift to break a 10 wt. rod.

Gordy

[Lasse Karlsson]

I assume that’s a lower modulus rod than Tim is bending - out of interest how heavy is the weight?

Many years ago in a car park in Idaho Falls, Tim showed me a rod that he could bend butt to tip.

Cheers, Paul

Tim loves bending his rods

Why do you think its a low modulus rod?



Cheers
Lasse

[Merlin]

I am surprised that (on a sample of one at least), Loomis only got an effective modulus value that that was 20% of the rated carbon fiber value while Scott appears to get much larger values of 60%.

Gordy

I checked the two piece Loomis blank (ca 1996) for which I have dimensions and some characteristics (stiffness, speed, mass, etc.), and what I got from the reverse engineering exercise is the following, assuming unidirectionnal fibers:
* there is boron in the butt (high density, stiffer material)
* the prepreg used for the tip contains about 55% fibers or slightly less.
There is not enough information to analyze each piece independently.

I do not have an example of a 20% to 25% relationship for composite modulus versus fibers modulus. That could only come from the use of equilibrated cloth instead of unidirectionnal fibers, I think.

Merlin

[Paul Arden]

Hi Lasse, for the reason Gordy posted above!

Cheers, Paul

[Lasse Karlsson]

Hi Lasse, for the reason Gordy posted above!

Cheers, Paul

Still don't understand it? Are you saying that a high modulus rod would not be able to achieve that shape without breaking?

Tim has plenty more clips of breaking different rods, so does Hardy and several others, its interesting to watch, as is Tims explanations on rod faliures..

Cheers
Lasse

[Merlin]

Rod shaft can break before maximum strain is achieved. Higher modulus fibers can break with a lower strain value, the critical strain can occur before the strain limit of fibers (from 1.4% to 1.9%). In suitable conditions, 1% strain can be detrimental.

In Tim's example with a little rod, there is no stiff fibers I guess, otherwise the rod would be too fast and stiff; so the actual limit for fibers should be in the upper range (e.g. 1.9%). From the video, it appears that the critical strain for the rod is around 1.4 %, the radius of curvature being less than a foot. This corresponds to some 1% of ovalization of the rod section which breaks. The rod does not seem to have a specific hoop reinforcement.

As long as I do not have the rod in hand, I cannot tell if the photo posted by Paul corresponds to an average rod. With adequate hoop strength, you can go pretty far in bending shape.

Merlin

[Paul Arden]

Still don't understand it? Are you saying that a high modulus rod would not be able to achieve that shape without breaking?

I’d be surprised. That’s why I was asking.

Cheers, Paul

[gordonjudd]

From the video, it appears that the critical strain for the rod is around 1.4 %

Merlin,
What is critical strain?

The scrim used for hoop strength is a big factor so it may be difficult to have an apples to apples comparison of the failure strain limit of different materials, but does fiberglass have a much higher critical strain limit than graphite fibers?

Does ovalization failure tend to produce a clean snap at the failure point (Tim's example of a bad break) vs the blow up of the break over a larger area that you get with a strain limit failure (Tim's example of a good break)?

so the actual limit for fibers should be in the upper range (e.g. 1.9%). From the video, it appears that the critical strain for the rod is around 1.4 %, the radius of curvature being less than a foot.

Assuming the outer diameter of the rod was .0037 m (a guess) and the radius of curvature at the failure point was .233 m (measured) I estimated the strain at the break point to be around 1.6%.


Thanks for sharing your expertise.

Gordy

[gordonjudd]

I do not have an example of a 20% to 25% relationship for composite modulus versus fibers modulus. That could only come from the use of equilibrated cloth instead of unidirectionnal fibers, I think.

Merlin,
When Haun (and I) backed into an effective modulus value we did not worry about composite values, but just compared the measured natural frequency (Haun) and the deflection for a given tip load to the calculated values expected for an ideal beam based on the rod dimensions.

The lower effective modulus values that Haun and I computed comes from assuming the ideal beam was made with a material that had a uniform modulus (the so called effective modulus value) and the same inside and outside dimensions along its length as the measured values for the rod. Then you can just vary the modulus used in the ideal beam calculation until you get a matching deflection value (in my case) or a matching natural frequency value (Haun's calculation).

This is different than the expected composite modulus value you are talking about based on the relative volume content of the graphite fibers vs the content of the resin (around 60%).

Gordy

[Merlin]

Gordy

1) Strain: The critical strain is the strain limit linked to ovalization (we studied that topic by the end of 2012), and glass can withstand larger ovalization than graphite. Your calculation only applies to small deflections, not to very large ones, where ovalization occurs.

2) Haun: If the cross check of frequency and deflection did not work, it comes from calculations or a wrong description of the taper. I measure loaded stiffness and loaded deflections to check that point, and it must work. I never met such a lack of agreement. If you still have the inputs (taper, deflection, frequencies, etc.), I can have a check with my files.

It would be wiser to discuss those points outside of the board, we are far from resin issues.

Merlin