Subject: Information (epoxy tension strength)
Date: Fri, 17 Jan 2003
I'm a PhD student and I will need to do some tension tests with small wood specimens. I'm writing to you due to the fact that I want to ask if you have any experience in this kind of work. The standards codes says that for tension tests, the piece shall be glued to steel plates. The gluing process shall be capable of ensuring the specified position of the test piece during test. A suitable adhesive for fixing the steel plates to the timber test piece is a two-part epoxy. Can you tell me about your experience on this field?
Any experience that we have in this area is informal. I can say that due to our experience with epoxies, it should be fine for gluing wood to steel as long as proper surface prep is used. This means a clean, dry, scuffed surface is best. Sanding the steel to white or near-white condition with 120 grit or coarser sandpaper. Sanding the wood sample as well. The epoxy will be stronger than the wood.
I'm not sure exactly what type of tension test that you are going to be performing, but if you glue a piece of wood to steel and then pull it with enough force, it will almost always break right behind the glue joint. The glue will not fail, but the wood fibers right behind the glue will break from localized fiber weakness due to damage from the act of cutting the wood. Priming the wood with CPES will help to strengthen the glue joint as it puts epoxy "anchors" deeper into the wood than what the plain epoxy glue can do.
Hope this is helpful,