This thing has gone on a crazy tangent and I know I share culpability. These ideas were never as evolved to the point of actually coalescing into a bow. I had to go back and read my own OP…….. I was thinking about making an experimental composite and was wondering if anybody had access to a testing lab where usable data could be obtained to compare with manufactured composites.
I can tell you what inspired me to consider alternatives to the current offerings, specifically the belly lam. Unfortunately I do not have any figures to share, guys like me count with our fingers and toes. But I have done some bend tests with both Gordon's and homemade. I clamp a 1.5" X 17" X .050" piece to my bench and start bending. I do stop incrementally to do a visual inspection with magnification and also check it on a surface plate, but I only have feelers down to .001".
Initially I had a pulley system with a scale attached to the unclamped end, but abandoned that right away because I was able to bend the sample way past the capabilities of my very primitive test set up. The first time I did this, I would unclamp the sample and do the visual and flatness inspection every 20deg or so. That was a Pia unclamping and re-clamping Now I just bent them to about 120deg before I start checking.
The first detectable sign of failure, which is consistent for all samples I have tested, is the surface epoxy will start to fret. It always happens first, on the tension side. The next stage is an increase in the fretting that causes distortion I can can measure (>.001). The next stage is where my tests shortcoming really shows. I can’t say that one or the other happens first, but it appears the the epoxy under compression does not start to distort before the lamination is fracturing on the tension side. Considering how far I had to bend the sample before it was obviously outside its elastic range and I could cause any discernible damage, I concluded that what we are using is likely severe overkill for its intended purpose. And that epoxy is stronger in resisting compressive forces than tensile ones. So the main problem I am having is reconciling you guys telling me it won’t work on paper, with how I am interpreting my crude test data. This created some curiosity, but the curiosity does not stem from a desire for speed or to create something or unique. In the case of the carbon lam, I am curious if I can make a decent version. Not planning on becoming the competition, but seeing how they are unavailable in a retail setting, I could not buy and try one if I wanted to. The other lam, I basing my curiosity on my bend test.…. I still have not see any evidence that the version I am thinking of making, is certain to fail or underperform.
I am definetly going to make both these experimental composites.
I’ve got nothing to loose and I will certainly report any success or failure.
The failure part will be easy. The success, if any will be a hard sell without real world numbers. I will try not to overextend the offer I received for testing.
Rich, now that you have thrown down the gauntlet, I’m just going to capitulate from the get go. I will never build a faster bow than you and so I don’t intend to try.
Topic: Question for any Engineers or Materials Scientists out there (Read 15124 times)
