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Poisson Effect Versus Neutral Plane - A Theory

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marvin:
One of the things I love about primitive archery is that it is both simple and complex. You don't need to know anything about the science or technical aspects to make a good bow and have fun. Yet if you want you can jump into the deep end of the pool and explore the amazing physics behind what is going on with a bow and how different design elements effect it's behavior.

You can have it both ways. Pick your pleasure :)

duffontap:

--- Quote from: bobnewboy on June 13, 2007, 11:06:24 am ---ACS-type section of <whisper>fibreglass limbs
//Bob

--- End quote ---

Bob,

I was thinking about an article I read in which fiberglass bows were forced into a hollow 'C' section.  Such bows had far superior performance.  I had thought for a which about hollowing-out a 'C' section bow to see what it acted like but it's too much work.  Is that what you're talking about?


Tom,
Where else have you been talking about this?  The PP site didn't have much.
               J. D. Duff

DCM:
JD the thread at stickbow is probably the longest I've seen.

duffontap:
Thanks a lot.

    J. D.

tom sawyer:
JD, yes the ACS limb cross-section is C-shaped.  Supposedly it made the limb stiffer, sort of like an I-beam.  I don't know whether the concave side was the back, or vice-versa.

I did find my copy of Archery the Technical Side.

A quote from page 34:  "If a bow having a symmetrical cross-sectoin is all made from either heart or sap-wood, the elongation along the back of the bow will in general equal the compression along the belly.  In such a bow there is a thin section located midway between the belly and back which is the neutral plane of bending."

This corroborates my position on where the neutral plane resides in a selfbow.

And page 38:  "Lay out the shape of the cross-section on a heavy cardboard, using any convenient enlarged scale.  Cut this cardboard section out with a pair of sheaars.  Draw a line from the belly to the back which divides the section into two equal parts.  Punch a small pin through the cardboard section on this line as such a position that the sectin will remain in balance on the pin for any position.  After a number of trials you will find a point where the cardboard section may be rotated on the pin to any position, and at which, it will be in balance.  This point is known as the center of gravity and is on the line corresponding to the plane of neutral bending."

This corroborates my position that the neutral plane is indeed a line at the center of gravity, meaning same amount of wood on either side of the line.

Interestingly, they are saying here that the neutral plane is a striaght line even when the cross-section is assymmetrical.  So my idea that the neutral plane is curved, and is trying to straighten out, might not be correct.

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