Laminating and Testing

Update: I've "tested" the new laminates in a very scientific manner: by beating the crap out of them.  I placed them on a bucket and dropped an iron brick on them from 6 feet up, and whacked them with the claw end of a hammer. The carbon/Kevlar sample, in addition to being lightest, is definitely stronger. Damaged areas are much smaller than on the glass samples. The biggest problem is delamination. After several impacts, there are small damage areas and large areas of undamaged laminate that's simply not attached to the foam any more. I suspect the precoating with resin/micro is the problem and will no longer do this.

Older tests:

I've made some interesting discoveries about carbon versus fiberglass. The first set of test panels I constructed from a 12"x12" piece of Airex/Herex foam with carbon, Kevlar, or fiberglass vacuum-bagged. "Precoated" means that a mixture of resin and microballoons or glass spheres was applied in a thin layer to the foam before applying the cloth. This is recommended by the manufacturer for better peel strength and to prevent the foam from soaking up resin and starving the cloth.

What's interesting here is that the carbon/Kevlar samples, despite being made of a lighter fabric, are not lighter when laminated. Even more interesting is that the "precoated" sample is the heaviest, when precoating is supposed to prevent resin from being absorbed into the foam and therefore make the panel lighter.

These samples were then sliced into strips, which were suspended from the joists in the garage, and loaded with weights until failure. In the second test, samples were clamped to the supports, which ended up bending one of my clamps, but this should test both sides of the laminate. For the third test, samples were sliced in half, to approx. 1/2" width, and clamped with a clamp that has rubber feet. I haven't repeated the second and third tests enough to get good results, so I'm only showing the results from the first test here.

Sample 1 had a block of 1/8" plywood between the strap and the sample, while the others didn't, so it's not a valid comparison. I will have to do more tests to get accurate numbers. None of the samples were fastened to the supports so the bottom layer was bent but relatively untested. The carbon isn't a whole lot stronger than the fiberglass, but it is far stiffer. The fiberglass samples would bend at least an inch before snapping, while the carbon samples would bend no more than 1/4" before breaking.

I still haven't figured out a good method of impact testing, but at least this gives a measure of the relative static strengths of the materials.

I have made two new sets of samples. These seem to have a more reasonable spread of relative weights. All samples in the first set are precoated with a resin/micro mixture, and the 18 oz is a bidirectional fabric instead of cloth.

In the third group, the 12 oz fabric is also a bidirectional. Samples 1 and 3 are precoated, and sample 2 is not. I also weighed the cloth and foam before laminating so I would have an idea of how much resin is being absorbed and therefore what my fiber to resin ratio is. Here I've switched to metric to keep myself on guard.

The "resin" column is calculated by subtracting the fabric and foam weights from the total finished laminate weight. What's interesting here is that, once again, precoating the foam increases the weight of the final laminate. Also interesting is that without precoat, the fiber to resin ratio appears to be 3:1. The laminates were vacuum-bagged at 25" Hg but do not appear to be "dry" or resin starved at all.

Also interesting is that, based on the surface area of the F9RX being approximately 1150 square feet, the difference between carbon and fiberglass is only about 160 pounds (not counting the extra layers of laminate in some places).  This doesn't count the weight of CMMs, beams, daggerboard, rig, or even the additional reinforcements specified in the plans. Since the final displacement is going to be somewhere around 4000 pounds, building the exterior skin from carbon changes the displacement very little. I will probably use carbon for reinforcements (especially unidirectionals) and for areas which require stiffness, like the daggerboard, keel, and cockpit floor, and use 18oz bidirectional for hulls.

This laminate of 18oz glass + 5pcf foam + 12 oz glass is about the same weight per square foot as a light 1/4" plywood (such as mahogany, fir plywood is much heavier). It has slightly lower puncture resistance, but is much stiffer and probably has the same strength.