> ... I like the thin
> strip method, clamped at one end with a weight on the other end; the only
> problem I forsee is that the stresses are increased at the clamp, so most
> of the failures would occur there rather than in the unsupported span. I
> may combine all these ideas and do a 3-point test with 3"x12" or
> 6"x12" samples.

It may be so flexible that it does NOT break at the clamp, too! I guess that would be technically a failure in the testing method, but what a paradox -- something that failed becuse it did not break.

Actually, these laminates can be VERY strong, and using a 12 x 12 panel (144 square inches) seems excessive if you are just trying to measure a force on a single square inch. If the thing held merely 100 pounds per square inch, you would need a pressure of over 7 tons per square foot. I suspect some of these composite laminates could hold 10 times that, or more. You are not really going to apply all that force over an entire square foot, so why make the panels so big?

> One more question: the issue of glass/epoxy application methods has been
> brought up many times before but: I would assume a rough-sanding with
> 80-grit, no fill-coat, a good squeege (or bubble roller) job to ensure
> that the cloth is as close to the wood as possible, and fill coats on what
> would be the outside surface before the epoxy completely sets. Any other
> considerations?

Yeah. Do some with fill coats. Those should tend to toughen the wood. Remember that you are putting a layer of 'fiberglass reinforced plastic' over the wood. The plastic has some strength, and the glass fibers reinforce it. Well, with the wood, the resin soaks in, and the wood fibers reinforce that plastic, too. The epoxy resin holds those fibers tighter than the natural resins in the wood (we know that from the wood splitting near a glue joint, and not the glue)

Also, try polyester and vinylester resins. I saw a quart of polyester for about $8 (a gallon was $15) and a quart of 3M vinylester for $23 today. These came with the hardeners for that price. This seems like not-too-expensive additions to your tests.

Vinylester is supposed to be really good stuff. It may test out better than epoxy. Polyester has been good for many years. It may surprise you in your tests. Considering the difference in price, if you are testing for greatest strength at lowest cost you may find that 1/4 inch lauan and polyester are a good combination. Or, you may not That's what the tests are for, right?

hope these suggestions are of use.

Paul G. Jacobson