Im doing a science fair progect that involves testing the diffrences in strength, bond to foam, and weight between epoxy/eps and traditional. This involves getting big, 12x8 sheets of foam, cutting them into smaller chunks (mabie like 3x2) and then glassing, then cutting them down into sample sizes. I want to do a 2x1 on each side, so how much resin (poly and epoxy) and cloth would I need to glass this? And if anyone had any suggestions for how to do these tests i’d appreciate it.
how about this… get two pieces of foam 1 inch thick. glass both sides, one using poly one epoxy. cut into strips 1 inch wide and 12 inches long. some of these pieces get more layers of glass. so you end up with pieces: single 4 oz glass both sides, single one side, double the other, double 4 oz both sides, etc. have duplicates or even better triplicates. place each piece on blocks with a 10" span in the midldle. pile bricks on until they break. count bricks, compare glassing schedules. the book Essential Surfing has a good description of how a board breaks.
This is how I’d do it: rectangular strips of whatever thickness, 18" long by 3" wide. Glass 'em a little larger, then saw cut to trim the excess so you’d have a more or less uniform section to work with. Get a sensitive scale and weigh the foam beforehand, weight the glass, then weigh the lammed section to assess how much resin is there to establish the resin/glass ratio. Maybe two or more different bits of the same combination, just different resin ratios between them, would show something interesting.
Different glass weights would be used in my experiment, but with the same glass on top as on the bottom. Varying the location of the neutral axis by putting more glass on one side would probably be pointless, and needlessly complicate the analysis, besides introducing the possibility of having a test specimen that really isn’t what you intended it to be. I’d be looking at ultimate strength as the key investigative item.
Testing would be by supporting each end on a 1" dowel, 1" from the end, and slowly increasing the load at the center till failure occurs. Suggest a bucket which you slowly fill with water, the bail (handle) of the bucket being a 1/2 inch diameter dowel or bit of pipe. Don’t want to point load the test specimen. Some notes about failure mode, and preliminary indications of failure.
A basic text in Mechanics of Materials (that’s what it’s called in engineering school) will show you the physics that you’re investigating.