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Mast/Strut Fiber Angles

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foam-n-fibre
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Re: Mast/Strut Fiber Angles

Postby foam-n-fibre » Fri Dec 15, 2017 3:51 am

I'm not talking about the weight of the carbon on the scale, I'm talking about the unit weight of the carbon. So 200g or 6 oz of carbon is 1 layer of 200g/m2 of cloth, regardless of the surface area you are covering. Sorry, I thought that was obvious from my description.

I'm with you Plummet, I've also hit a submerged mystery thing and it came away unscathed. How much you need also depends a lot on whether you have a wood core or foam core. But.... we're getting a bit off topic here..... :)

Peter

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Re: Mast/Strut Fiber Angles

Postby bacon2109 » Fri Dec 15, 2017 2:04 pm

You're right, the conversation took another direction.

as mentioned above, I put 5Kg test info, which gives a clue, in my opinion.
the twist of my mast, looks good and flexsion too.
And there is better.
But like a child reaching out is hand from a moving car.
he feels that it oscillates even if the surface is not big.
That may be why some manufacturers put a fin on the fuselage.
For me, doing a other mast, according to the test of 5Kg result of my mast.
I would change the orientation and number of layers for 0/45/60
and some angle layers;
-from top LE to button TE,
-from top TE to button LE,

I dropped the angle of 30 degrees, in my opinion not enough influence in the tensions.
Hoping that this next mast will be stiffer

and again using only UD and this time a topcoat for the look

Additional info, if it's not used ....
On the French site, some likes to have a little softness for their mast
maybe not for those who make speed, race, but in free ride and wave.
I saw notes on the behavior of amateur masts
I will refresh my memory

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Re: Mast/Strut Fiber Angles

Postby foam-n-fibre » Sat Dec 16, 2017 1:31 am

I'll be interested to hear the results of adding fibers at 60 degrees if you think that is the solution. But just to be clear, I'm a mechanical engineer and have a pretty good idea about the physics here, and I can't understand why an angle this sharp would be the solution. This is not exactly my field though, so I'm not going to say it definitely would not work, but I think I want to hear a bit more science behind it before I'm willing to try this. My thinking was that 45 degrees might be too steep on this kind of structure and that a shallower angle might make sense. I'll need some serious convincing to go with a steeper angle like 60 degrees.

Peter

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Re: Mast/Strut Fiber Angles

Postby tegirinenashi » Sat Dec 16, 2017 3:32 am

I interpret your message, that as mechanical engineer, you have pretty good idea what stress tensors are for flex and torsion tests. This is not a homework: I'm not mechanical engineer, but would like to get a feeling how tension forces are distributed (with some approximation to their relative magnitude and direction). It is the lack of intuition what tension forces are significant that prompted the earlier suggestion to divide the full angle into even parts -- this way it minimizes a chance that the force might be coming from a direction which is not covered.

P.S. While glancing into some literature I came across "stress trajectory" as a curve of equal force, and "load transmission path spiral" as one such trajectory for a twisted beam. It is the pitch of this spiral that is unknown (unless you suggest a better idea), hence the guesswork about the angles.

P.P.S. On an afterthought it seems almost self-evident that by combination of twisting and bending one may effectively control which direction the tension force is coming from. Therefore, the more fibre angle coverage you get, the better.
Last edited by tegirinenashi on Sat Dec 16, 2017 4:08 am, edited 1 time in total.

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Re: Mast/Strut Fiber Angles

Postby downunder » Sat Dec 16, 2017 3:56 am

I recon, initially, only 0 carbon is opposing torsion anyway. This is for the first torsion angles. 0/90 in a sense of 0 being the mast length.

Correct?

Only if there is carbon placed on extreme low angles, it would kick in initially. But does anyone build in such a way? So, we can simplify and say the 0 degree carbon is a low angle.

And this is why, initially, some masts are stiff, coz they have heaps of 0 (uni). But, passing a low degree in torsion will snap mast on the micro scale. After than, will snap big time. However, we are not passing this point when riding. For example, a concrete beam is stiff, but will snap big time in torsion - when you reach the torsion strength. Again, it feels stiff right?

Even if you build only with UNI, it will be stiff. It does not matter on which 15/30/45... angle you place your carbon coz you'll never ever reach this angles initially. But, they are important if and only if we pass low angles.

What it does matter for torsion, as you know, is a SPIRAL reinforcement in high angles (in torsion direction, it would be almost 90, lets say 89 initially, than 88...). But we can't wrap the mast in spiral motion. However, big sailing masts are wrapped this way. Even windsurfing masts are. This is where biax kicks in in HF mast.

So, if we have all degrees between 45 and 90 ( biax covering degrees from 0-45), than the mast would be super strong in torsion. That is 45 layers, each side. Plus UNI for bending.

D.

PS
Did not read the above post before posted. :)

PPS
I take back wraping a sailing mast in spiral according to this:
https://carbonsugar.com/construction/wh ... -breaking/

However, that's from 2007...

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Re: Mast/Strut Fiber Angles

Postby foam-n-fibre » Sat Dec 16, 2017 1:09 pm

That windsurf mast article I don't think it very scientific. It's just a guy taking a semi-educated guess. A windsurfing mast in torsion? Torsion is twisting. The sail is not rigidly bonded to the mast. Only friction can apply any torsion on a windsurfer mast. If you have a cylinder in torsion (twisting) then an angled wrap of carbon makes sense. But we are not dealing with a circle, and wrapping around what is much closer to a flat plate with fibers bending super tight at the leading and trailing edge means that they are not really connected well for carrying load around that corner.

Twist a long flat plate and the greatest amount of stretch needed to do that is along a X from corner to corner. That's where fibers should work best for twisting (torsion). But was can't lay all of our fibers just along that area.

Peter

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Re: Mast/Strut Fiber Angles

Postby downunder » Sat Dec 16, 2017 2:07 pm

I did not say WS mast is under torsion! :) but, have a look how they are made in recent years.

Nope, the angled and spiral reinforcement is used in ie concrete anchorages. Which might not be cylindrical. Also used in concrete elsewhere. Nothing new in civil engineering.

That is what I've said: "Only if there is carbon placed on extreme low angles, it would kick in initially. But does anyone build in such a way?" ;)

But, if mast is built with foam, foam just as concrete, has min tensile strength. Plummet built his mast with bamboo, if remember well, and this will be stiffer than Paulownia I've used. So it is not only carbon but the core as well, me thinks.

Hence, the carbon Plummet used (or anyone else) is not the only variable on the mast twist test. This is why I'm skeptical on the twist results.

D.

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Re: Mast/Strut Fiber Angles

Postby plummet » Sat Dec 16, 2017 8:59 pm

foam-n-fibre wrote:
Sat Dec 16, 2017 1:31 am
I'll be interested to hear the results of adding fibers at 60 degrees if you think that is the solution. But just to be clear, I'm a mechanical engineer and have a pretty good idea about the physics here, and I can't understand why an angle this sharp would be the solution. This is not exactly my field though, so I'm not going to say it definitely would not work, but I think I want to hear a bit more science behind it before I'm willing to try this. My thinking was that 45 degrees might be too steep on this kind of structure and that a shallower angle might make sense. I'll need some serious convincing to go with a steeper angle like 60 degrees.

Peter

If running biaxle layers with fibres at 90 deg to each other you make an argument for a 30/60 placement. 30/60 would be better than layers at 0/90. The layers at 90 are doing almost nothing. They are a waste of weight and carbon. 30/90 will give you some torsional on one axis and good torsion on the other axis.

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Re: Mast/Strut Fiber Angles

Postby bohme » Sun Dec 17, 2017 1:07 pm

For stiffness, 0° fibre angle is best for bending and +-45° is best for torsion.
You can use +-15° angels (for example) that gives you the same spar bending and torsional stiffness. It does not have the same strength, but this is probably not important.
Angling +-45 biax (-30+60) is not ideal.
There are cheap/free 'classical lamination theory' software available, but you might want to read a book about it first.

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Re: Mast/Strut Fiber Angles

Postby downunder » Sun Dec 17, 2017 2:59 pm

Plummet,

looks like you did not measure torsion per suggested test:

viewtopic.php?f=196&t=2382637&p=985406& ... on#p985406

5kg test 30 cm from the mast centre on LE side is 14mm for my mast.

I'll add pic's tmrw.

I think 14mm in torsion is very good result with only 4 layers of carbon each side. I don't know how much carbon stringers added in torsion strength: viewtopic.php?f=199&t=2394338&p=960005& ... st#p960005

The only way to know would be to build another one with no carbon stringers.

If remember well, my layup was all 200g/m:
- big squares carbon 0/90
- 2x biax 45/45
- uni 0

More important is the max mast thickness which is 14.5 mm all the way. 930mm long.

Happy with the result tho, just 1.5mm more in torsion than Sword Taaroa!


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