Originally Posted by
roger.alli
A good discussion Oli.
My impression of your result of the 5 min epoxy test, is that the resin only failed over approximately 50% of the tested area. Surely the resin that remains under the bit of hardwood that split off, is still intact, and didn't fail at all. It was the hardwood natural fibre cellulose bonds that failed in this ½ of the glued area, so should not the bond strength be closer to twice what you calculated??.
My point is, that while your tests might be interesting as to comparing a group of similar epoxies, I feel it to be unfair to compare say Hysol to Cyno, or clear silicone to PVA. All these adhesives are exceptionally good at their specialized tasks, but will all perform quite differently when asked to attach a servo mount to a piece of hardwood.
In my humble opinion, correct selection and proper application, is far more important than the overall strength of the cured glue.
Roger
Thanks Roger.
The bond sheared pretty clean in fact. The hard wood block you see on the picture was pulled out by 3 of the dots I made with the Dremel that were deeper than the other ones. the block is not bonded to the bracket any more. From what I can observe, I think that the failure on this one was representative enough. However if I have enough spare time, I will do this test again.
You are right, glues are very specialized. However it is interesting to know the glue jont resistance anyway. Even if it is unfair to compare CA with Hysol on a certain matter, one would still choose CA over Hysol on given application because of the ability to set instantly with activator. So knowing the strength of a CA glue joint is still relevant.
Also the purpose of this comparative study is to educate newer modelers and demonstrate the difference betweeen types of glue. I have seen more than once people using CA on servo brackets. Even on Chinese ARF kits...
And frankly, while I can guess what silicon compound will do on the stress test, I am still extremely curious to see the result for real.
Correct selection and application is important, but glue joint strength is equally important. The bond will be only as strong as the weakest link, as always...