Aussie, 1st of all I wanted to publicly thank you for converting the mass formula to an excel spreadsheet for me many years ago.
As for a bend test, I was never able to convert a bend test to usable information that I could apply to making a bow. I think if you could lay out the method for doing this, if it is not too complicated it would be a huge step in making higher performing bows. I came out with several tests that were useful in comparing wood but I was never able to directly apply it to a design. Hopefully you can send us in the right direction here.
Most welcome Badger, a pleasure and an honour to help out.
Laying out the method can be easy to understand, but it isn't necessarily something I can cover thoroughly in a short space. Fortunately though a few years ago I did lay out the method, from plank of wood to engineered bow here:
https://ozbow.net/phpBB3/viewtopic.php?f=34&t=5450 it might take a while to read through but I tried hard to make it accessible.
the answer to your question is yes,, no graph or formula needed, just make the two bows and see for yourself,, its that easy
BradSmith, if by this you mean that it's easy to show that a short bow will be inherently more stressed than a longer one, then no that isn't a fair demonstration of the hypothesis. All you will demonstrate is that a more stressed bow takes more set than a less stressed bow. The reason is without common metrics and methodology, there's no way to control for the amount of experienced stress in the bending bow. By this I don't mean that the stress is uncontrollable, but that you can't be sure that the stress in the two bows is the same.
An aluminium rod and a dowel feel cold and tepid, respectively, when you pick them up in your workshop. But the reality is that if you measured them scientifically, they would actually be the same temperature. Observational studies are not always reliable reflections of physical phenomena.
The amount of plastic deformation (permanent set) a piece of wood (a bow) takes is dependent on the maximum amount of stress the wood is subject to during bending. More working stress = more set. Less working stress = less set. This is completely independent of draw length, draw weight or bow length.
We've all made short bows that took little set and long bows that took more. It has less to do with the length than it does with the stress as a proportion of the elastic limit of that piece of wood. The shorter bow with less set experienced a smaller proportion of its potential stress, and the longer one with more set was caused to endure a larger proportion of its potential stress.
On the weekend I'll bring together a few different theoretical bows with dimensions and if people wish they can make their own according to the dimensions. I'll do a short Mollegabet, a medium pyramid bow, and a longer D bow.
