We had some free time over the long Labor Day weekend and decided to do a few test panels involving PVC skins and a composite sandwich construction. We decided that we’d try an sandwich that used a double PVC skin on what might be a deck side of a composite sandwich wakesurf board. Sailboards occassionally use a double sandwich for extreme conditions. Typically, those boards have a double PVC skin top and bottom. We opted to only lay up a test panel for a double PVC sandwich on the deck side. The test panels then are composed of an EPS core, a single 3mm Divinycell H80 bottom skin and then a single PVC skin on test sample 1 and a double PVC set of skins on test sample 2. We thought we’d walk you through the process so you can see how we document the construction and subsequenting testing. Sometimes the test panels don’t prove anything and sometimes they prove that the concept is just junk!
We like to test, to validate, one way or another and it does give us LOTS of emperical evidence that we can review later. The first thing we do is weigh all of the individual components going into the test panel. The actual weights don’t matter much, but relative increases as a percentage are quite useful! Now we convert our scale to grams, so that we can weigh the small incremental changes. You’ll note in the picture that we mark all of the components for ready identification and so we don’t mix them up.
We do that marking and weighing routine with each component, although we combine like components so that we can get an aggregate number.
Plus we record it all on a sturdy piece of cardboard! Actually we use the cardboard in the “lab” because we do slop epoxy on our notes and the wind almost always blows the paper away when we need it. Once we are all done, we transcribe the data into computer spreadsheets for use later.
We also tested one more concept in this test panel. It’s a layer of Kevlar under the double PVC skin. Now, Kevlar is great at impact resistance, but does suck up a bit of extra resin when laid up by hand. Here is a picture of the reinforcement fabric being weighed, but we didn’t reset the scale, so please ignore that reading of zero.
It’s impossible for us to accurately weight the amount of resin applied as it’s being done, so once the entire unit is laid up. The last number in each column is the total assembled weight. It does point out a few things. One is that we may have gotten a little sloppy with the resin application in sample number 2 and also the Kevlar seems to soak up resin when laminated by hand. We’ll have to go back and check the resin uptake on the Kevlar and see if we can resolve that or if it was just us getting sloppy.
That’s the test process we go through and mostly we just proved that we need to do it again! We’ll test the final test panels to see if there is any significant increase in compressive strength with this type of composite sandwich. This is a significantly different test panel than the honeycomb carbon wakesurf test panel.
Thanks so much for following along and we hope everyone had a great Labor Day weekend!
2 comments
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