Just found that video. All the tests went like expected with the exception of end grain maple.
Just found that video. All the tests went like expected with the exception of end grain maple.
IMO all that really shows is the flakiness/imprecision of his test.
The axial and bending tests are basically the same in terms of applied load at the glue joint, which may have something to do with why glue makers don't (and don't need to) specify performance in bending. Bending creates an axial stress distribution with compression at the top and tension at the bottom of the sample. The samples in the bending test all failed in tension, i.e. they failed by pulling apart along the bottom edge instead of, say, buckling at the top. This means that any difference in performance between the "axial" and "bending" tests reflects test-to-test variation rather than some deeper phenomenon.
Would have been better if they used ASTM test coupons that are specifically designed to test this sort of thing... it also would have been good to have data from a larger sample size. We had 3 large instrons at a previous employer, and broke hundreds of carbonfibre/fibreglass/kevlar/other composite layups of every resin and cloth we could get. The coupon shape and size matters a lot, as does having 10 or so test pieces for each material/method so you can average out process errors.
It's good that he actually used a proper tensile tester though!
None of the maple tests went as expected because he actually used maple with the wrong orientation. He was apparently unaware of the difference between end grain and long grain. He used cutoffs from the end of a board so the grain was running in the short direction. Pitiful test.
No, the maple samples all have the grain going crosswise and he does not even notice it. He calls joints end grain to end grain which are not that at all. They break where he does not expect it because he thinks the grain is the same direction as the pine samples.
Was anything unexpected in the actual tests that were done (regardless of his commentary I mean)? It seems to me that the failure for end grain to end grain was in the adhesive or cohesive bond (expected), and in the long grain to long grain the failure was in the wood. Yes, No?
Yes, I was concerned with the relief cuts he made on the lap joint pieces. By cutting the corners with a saw, and none too precisely, he created a stress point in the wood. His clamping method leaves a bit to be desired as well. I also saw the test piece of maple for the bending test was cut the wrong way.
Lee Schierer
USNA '71
Go Navy!
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This appears to be a video by an undergrad engineering student with a poor understanding of anisotropic materials, adhesives, and how to design an adhesive properties experiment.
Now that he has finished this informative test, maybe he should do one that proves that oak is stronger than Styrofoam.
I had made this video for a school project, I didn’t notice how much I’d overlooked! I’m quite green when it comes to proper woodworking, thanks for the expertise
I made an updated version with your comments in mind, I hope it does a more effective job:
https://www.youtube.com/watch?v=cGdhEQW3JdA
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Last edited by Tristan Fogt; 01-27-2018 at 11:38 AM.