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I think this is a wonderful thread and have been following it with great interest. But, I wonder if you are testing for the correct characteristics. It seems to me that the majority of testing is placing the emphasis on shear strength and, in my opinion, that is not the most important characteristic for an epoxy used on a knife. I say this because scales are not held on with glue alone, there are always pins or screws which would have to be overcome before the shear strength of the glue would start to be much of an issue. This is why we say that the glue is not a structural component of the handle, it is there to seal out moisture (you can see that sentiment in a lot of threads). So, while i think the shear strength test is important and informative, i would suggest another test more suited to the type of force a knife handle might be subjected to.
One test might be to glue some handle sized wood to a piece of steel at least 12" long. Then, slam the side opposite the wood down on a flat hard surface and see if the wood can be made to pop off.
Another test would be to glue steel to both sides of a piece of wood. The steel would have eyes welded on it so that the test piece could be secured to a stand and the weight could be attached to the opposite side (or hydraulic force could be applied with a jack) in order to see how much force is necessary to pull the steel off the wood.
In either of these tests and also in the shear testing you are doing, the results might be even more meaningful if you cleaned the bead of glue off the perimeter of the wood/steel bond. Knife handles don't have large beads of re-inforcing glue on them and that could be a significant factor.
Whether you do these tests or not I look forward to seeing more of your results ...
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