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Poisson Effect Versus Neutral Plane - A Theory
tom sawyer:
A summary of where I'm at with this:
1) The Poisson effect causes some stress in the bow limb that results in a strain that pushes the edgs of the limb upwards.
2) Assymmetry of limb cross section causes other types of stresses that cause limb wood to strain to get to a point of least stress, which is nearest the neutral plane. This movement can actually counter-act the Poisson Effect if the particular symmetry forces wood to move in the direction opposite this effect.
3) Assymmetry of cross-section can also be caused by assymmetrical material combinations, as in backed bows. This moves the neutral plane to somewhere other than geometrical center (centroid). The wood in the limb still strains in order to find the least stressful point.
4) Forced reflex glueups of backed bows with assymmetrical cross-sections, are about as complicated as it gets when it comes to trying to understand all the stresses in the limbs.
Thank goodness you don't have to udnerstand it to use it. But I do think those who would champion a particualr cross-section, have a lot more to consider than meets the eye.
tom sawyer:
Update.
Some guys on another site wrestled me down and twisted me arm behind my back until I admitted that wood can have slightly different MOEs in tension versus compression. So I now have to admit that the NP may not always be at the geometrical center of the bow. I did get them to agree that the strength values have nothing to do with NP though, that the poundage is coming from the stiffness aspect which is represented by MOE.
Hillbilly:
Uhhhg. Me put little stick on string attached to big stick. Me pull back, me let go. Little stick fly away. This good. Me happy. Uhhhg.
Lennie, not make me think more. Makes head hurt. Uhhhg. ;D
DanaM:
So easy a caveman can do it ;D
SimonUK:
So we sort of agree that a V or D shaped belly might have a slight advantage over a rectangular one. There are plenty of D shaped designs aren't there? It's just a question of how pronounced the D should be. Any ideas Tom?
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