Can you please explain to me which mehanical property quantifies a resin "stiffness" in the final laminate.
I have laid up some kiteboards in the past with both west system and resin research project 21 "2000" resin.
I am just finishing a board with resin research composite pro 2070
I think I may have chosen the wrong resin.
Exacty what is the difference with this particular resin other that the fact that my board seems to flex like a wet noodle (really it's not that bad but it seems waaay too soft even though the laminate schedule is the same as in the past).
Is it true that I should have gone with the 2050 resin? Will this board break more easily or just have very soft flex?
Will post-cure noticably improve the stiffness of my new board?
There are many opinions about what stiffness a board should have. We publish modulus numbers and some engineers use these to engineer their products. Having said that there are so many variables in composites that numbers never tell the whole story. Therefore there is always a bit of trial and error involved in designing a new product. You’ve found the 2070 to be a bit too flexible. We have customers who love 2070 and have designed whole systems around that product. Each system, which includes product application, materials, methodology, cure schedules, etc., will have it’s own unique outcome. Educated guess is where everyone starts and tweaking from there will allow you to get what you want.
To answer the pointed questions … will it break easier? It might but it might not. Depends on how all the parts in the composite application are working in conjunction with each other. I was making sailboards years ago and we were attempting to make the boards as stiff as possible to stop the buckling we were getting on the bottom of the board. We laminated a board with double 6 oz.carbon thinking that this would be the solution. I broke it within one hour. Tried unidirectional S-Glass on one. Broke it first day. Couldn’t figure out why these strategies didn’t work when everything I read led me to believe they should. Turns out making the laminate very stiff caused all the force to be taken by the skin.
We found that the entire composite needed to share the load. We then made boards with double bias … never broke one because the double bias fabric shared the load with the other components better than anything else we tried. In your case with a more flexible skin it may be fine or it could break because some aspect will fail because of the flexibility. I can’t really say because again there are too many variables. My suggestion is to ride it, see how it goes in the long run and begin to think about where to go next. We make resins in a sliding scale … we’re the only ones who do. The reason we do is for exactly this purpose. So builders can dial in the products to make the best they can make.
Hi Greg, thanks for your reply. I can see how this type of flexibility could be very beneficial. I am actually using biaxial laminate in my kiteboards because I wanted more longitudinal flex and less torsional flex.
I think I will keep this board for my wife - she's about 80 pounds lighter than me and will probably appreciate the higher flex.
What about combining stiffer resin with this product? For example - If I hot coat my very flexible 2070 laminate with kwick kick, do I have to worry about the hotcoat failing or cracking due to it's less flexible nature?