This is another bow building related question. In building all wood archery bows the topic will often come up about comparing tension strenths to cmpression strenghts.
We will often use one material for a backing ( tension) and another material for a belly on a bow ( compresion). Finding a best match through trial and error has been an onging process for decades now with seemingly no end in site.
It would be helpful to know when the wood bends how much of the bend is due to compression and how much is due to the back stretching or tension.
Intuitively it would seem to me that if I know the precise starting length of a test piece and then measure the length of the same test piece when wrapped around a radius that the compression side or inside of the radius will get smaller if it is compressing and the outside radius of the test piece will get larger. Simply measuring how much smaller and larger each piece gets respectively should give me a fairly accurate overview of what is happening in tension and compression and allow me to make fair comparissons to various matches of different woods.
Am I omitting something or should this be as simple and straightforward as it appears to be?
If you have big bucks, a system like this would be ideal.
But my first thought would be affix strain gages to the device under test. They’re pretty cheap, and data acquisition systems are very affordable nowadays. The biggest cost is often the signal conditioner. (Personally, I would just build the signal conditioners.)
That system would be the dream come true test device. It does everything we would like to know about. I was trying to find something like that online but didn’t find it. I wonder if any owners of this system would be willing to do an analysis on a working bow? It might be worth a bunch of guys pooling some funds and paying for a test. We could lean a ton from this.
I’m not sure if it’s the same system in the link, but the structural analysis lab (a floor below my lab) has an optical strain system. From what I’ve heard, you apply a special paint to the device under test, point the camera at it, and the software automatically measures compression and tension on the surface.
We hire summer students every year. They are required to do a project and write a report. It doesn’t have to be defense-related; last year one of the students did failure analysis on an alternator bracket in a race car. Perhaps next year, one of the students could do a project on… stress and strain of a bow.
I would be happy to ship off some bows for testing if you you could arrange this. That would be fantastic. It is very difficut to identify where the wood is working as far as compression and tension go. We are always looking for ways to better match up woods that have properties that will compliment one another.