Is the early wood the weak link to cause set?

[BoltBows]

This is beyond interesting. Thank you all who put effort into this!

Indeed one has got to wonder about what would happen with one continues ring on the back. Would it make significant difference?

I always figured a tree that bends in the wind takes most tension and compression on the, let's say- 'flat ringed' side. The 'edge grain' is more in the center so would have to take less punishment. A flat sawn board therefore be stronger in both compression and tension. Does that make any sense at all?

Jaap

[Allyn T]

So I'm wondering if this is where tillering comes into play. If the samples are uniform thickness and width that would be like a badly tillered bow, most of the bend taking place in the middle. If they had a straight width taper wouldn't they take less set? So maybe this is a good test of just the materials but doesn't show how soon set would start to show on a bow

[PatM]

It will still manifest the same way.  Whether you are isolating a smaller section or spreading it over a larger section you're still pushing the material to the same degree.

[Digital Caveman]

Each point along the limb has a different amount of force acting on it, so it needs to be shaped to bend to it's maximum stress at that point.  I believe these tests are telling us what the maximum strain is. 

[avcase]

Please post some pics and maybe links for the bits you are using when you have it all in hand.

Mark

Yes, I will do this as soon as I have something working.

I’m still waiting on the arrival of the strain gauges in the mail. Latest date is this Wednesday, so I probably won’t have any meaningful test data until this coming weekend.

Do a search on YouTube for “Curious Scientist Strain Gauge”, and he has a multi-part series with the same basic hardware that I am using.  I spent some time over the weekend playing with the Arduino microcontroller and it is pretty amazing what you can do with these. I bought one of the larger kits for about $60 because I often volunteer for extra-curricular activities at the schools that focus on introducing engineering to middle school and high school students.  The strain gauges are about $10 for a pack of 10.

[PatM]

Each point along the limb has a different amount of force acting on it, so it needs to be shaped to bend to it's maximum stress at that point.  I believe these tests are telling us what the maximum strain is.

 Sure but that's when you don't want it to break.  This test is supposed to break it.

[willie]

So I'm wondering if this is where tillering comes into play. If the samples are uniform thickness and width that would be like a badly tillered bow, most of the bend taking place in the middle.
you  are correct Allyn.

If they had a straight width taper wouldn't they take less set?
yes

So maybe this is a good test of just the materials but doesn't show how soon set would start to show on a bow

It should work for an entire bow if the area directly under the load is typical of the whole sample. There is a similar 4 point bend test, (the test Alan is doing is called a 3 point, I believe), where the sample has the load applied at two evenly spaced points. It tests the entire sample and averages the value better. Each test has it's specific formula to calculate MOE . The 3 point test is generally considered adequate for clear wood, and is simpler.

[Allyn T]

Thank you for clearing that up willie, you answered my question perfectly

[avcase]

I may switch to a 4-point bend test. I don’t expect a significant difference, but it does have the advantage of providing an unobstructed space in the middle of the test sample for the strain gauge.

3 point bending is like bending the test sample over your knee. 4 point bending is similar to gripping the ends of the test sample in each hand and bending it in half.  The formulas are a little different, but the methods for calculating the material properties are basically the same.

What i like about this is that we are getting some good measurements of the behavior and limits of bow materials without the additional uncertainties that come with specific bow designs or tillering.  In the future, it would be interesting to build on this and look at heat treating, laminating effects, and use of pre-stressing in laminates. 

Alan

[Tuomo]

Anything new here...?

Great topic, so hopefully the story continues!

[Selfbowman]

That’s what the was wondering. I think someone got real busy . I did. 😁😁😁

[willie]

Another future project will be to integrate a linear string pot encoder to the draw-weight machine that we use at our flight shoots. This can be used to generate real-time force-draw curves on a bow.  With a little coding, I can have it calculate total stored energy and other useful stats in just a few seconds. I have wanted this for a long time.  I am a happy nerd. Haha!

I think I heard him say it uses the Arduino       https://www.youtube.com/watch?v=teMO9oCl4YE

[HH~]

I would think just making a bow out of say good mulberry vs Good Hedge would get you a much faster bow by dropping lots of limb mass.

I like a heavy Hedge bow (mass weight). I do know that 13-14" risered 66" Super Pyramid is a zinger for a flat 40@28" bow. Flipped and with maybe 1/4" tips.  Has short working limb but it'll flat punch a 600grn arrow out of it.


HH~