6-10ft strapless airs are common in kiteboarding so sufficient impact toughness at a mimum weight was the design criteria My first round of tests tests were not terribly rigorous, build it, ensure Vf is reasonable, weigh it Jump on it, to see if it breaks dents or delaminates then compare to others.
Jumped from a height where the pain in my heels felt worse than a familiar flat landing after getting punted off a wave.
Tested sandwhich vs non sandwhich
wood veneer vs non wood veneer.
corecell vs dinycell
1lb vs 2-3lb cores
and different cloth orientations
Really weeds out some materials and build methods for what I wanted.
After testing multiple panels for impact toughness.
I found the following (much of this is probably familiar to most of you)
corecell absorbs significantly less resin than D-cell the resultant structure is therefore lighter
multiple lighter plies oriented at 0/90, 45/45 perfoms considerably better in impact than thick plies running in fewer direction
carbon performs poorly in impact. carbon is brittle, the resultant structure that will survive a comparable impact was heavier than a comparable E glass or S glass panel and unwelcomingly stiff
wood veneer (I tested birch) adds a lot of toughness but does so at bit of a weight penalty compared to other methods. heavy.
sandwhich structure was considerably better in impact than non sandwhich and considerably lighter than if core weight is increased to obtain similar HIGH IMPACT TOUGHNESS… (volume and required toughneess can easily change this conclusion depending on your application)
Spectra is a cool fabric. You can hit 4oz of it it with a hammer as hard as you can not pierce the composite. a metal tipped arrow fired from 15 yards will blow through it though. the tensile strength is off the charts, yet it is quite flexible. The flexibility did not have sufficient stiffness to protect the core and it dented easily (on it’s own) . compression buckling and delams between plies are also a concern…however this material has potential for high toughness applications.Especially when mixed with a stiffer composite on the 0/45/45 where it will not drastically affect the board stiffness.
My crude testing was not of sufficient resolution to determine the differnce between D cell and corecell toughness, E glass S glass toughness . or different resins. A controlled weight drop and compression buckling rig needs to be done before pursuing combinations of spectra and other materials.
Given I’m going ot build a board and not a test lab, I settled on
1 x 6 oz s glass @ 0/90
1 x 6 oz s glass @ 45/45
1/8" corecell voids filled with dry micro
1x 6 oz s glass @ 45/45
1lb EPS voids filled with dry micro
1 x 6 oz s glass @ 45/45
1/8" corecell voids filled with dry micro
1 x 6 oz s-glass @ 0/90
The resin I chose was system 3 general purpose. It has an abnormally high % elongation compared with other epoxies and tensile strength and modulous that are not out of line with the others. So in theory should be tougher than most under high deformations…It’s also cheap and readily available. My plan is to vac with perf ply and breather to obtain a high Vf then dry micro and paint to make back some weight gained with the extra glass so UV capability or colour is not a concern.
