thank you for sharing your knowledge!
No original thinking on my part. It’s mostly just a regurgitation of info others have shared with us.
Thanks for the reply, really appreciate it. That’s some really nice work there mate, I would like to have a play with some texalium!
I am using Kwik Kick resin; the peel ply feels quite thick, like a 4 oz cloth maybe, I will see if I can track down some thinner stuff. Some really great advice for my next attempt. The problem I had was where the resin was tacky, I was really difficult to lay in without it creasing up, I’m going to try rolling it out next time on a piece of pvc pipe.
I never say i am a pro builder. I ever show with numbers what happen un other post. No problem with vacbag. I do it and calculate it for industrial parts. But i still say that it’s not necessary with light glass laminate over foam that are use in water and mostly experiment buckling stress. Happy you find coil secret.
I don’t see the point of using innegra in this way. Why not just use a thicker woven glass fiber and get some strength out of it.
All the best
Think of the skin like a beam. The top of the beam takes load, and the bottom of the beam takes load, but you can drill a whole lot of holes in the center, and not weaken the beam. The greater separation between the top and bottom of the beam makes the beam stronger.
So, if you think of your lamination the same way. Two layers of fiberglass gain strength the farther apart they are. So if you can separate them without adding weight…
So you want to use the lightest separator. Innegra is lighter than fiberglass. Also less prone to shattering.
So then you might ask, isn’t this thicker fiberglass skin going to be stiffer than a thin skin, and make my board ride like crap?
The answer is yes, it will be stiffer, and ride like crap. So what are you going to do about that? Well you have a couple of options. One is take out the stringer. Another is use something more elastic than fiberglass, so you add strength, but keep the flex.
Resin Research Kwick Kick is good for thick fill coats and pro glassers doing fast laminations. Try the RR 2020 high impact with a slower hardener for vac-bagging. Flows out great and wets out any cloth much faster-easier. I put my Innegra under cork. No drama easy-peasy.
Yes right for sandwich composits in pure flex stress, only flexural momentum. But surfboards are at least Stress in simple flex, by a “cut forces”, so you must care of “cut” stress that’s max in the neutral axis. With steel or other isotropic materials no problem but with light soft foam can be a problem well known by funboards builder wich of t’en use some kind of foam strenghners for Waves boards, and denser foam than for slalom.
With elastic material you don’t had strengh you had toughness. It’s not the samething. Is it better for our use ? YES, but you need to do something agaisnt buckling because what reduce buckling is stiffness…
A surfboard skin buckles when the wrinkle in the skin overcomes the skins ability to flex. I mean that a wrinkle in a rigid skin will fracture, while a wrinkle in a flexible skin will recover. An example is a wrinkle forced into a sheet of window glass will shatter the glass, while a wrinkle in cotton fabric will have no damage, and can be ironed out.
A less elastic skin like a fiberglass surfboard deck will be damaged by buckling forces before a more elastic skin would be. If you flex a glassed board, it will snap before an unglassed blank. I’m not talking about which one would take more force to snap, just which one would could recover from a greater amount of deflection.
So a flexible skin can recover from greater deflection than a rigid skin.
Now add another member to limit deflection, like carbon rails, and the entire construction will outperform.
Everysurfer, I agree with your point about innegra but if you compress it with a vac bag you reduce the separation dimension.
All the best
Sure, you reduce the separation. But no matter whether compressed or not, innegra is stronger and lighter than epoxy alone. Just about any fiber is better than epoxy alone. You will always have a better strength to weight ratio by compressing out in needed epoxy.
Someone earlier mentioned bagging creating pinholes. Unless really badly done, that just isn’t possible. The first thing that gets removed is any air that would make pinholes. It’s a vacuum!
What you say about elasticity is right for tensil stress and in some case for flexural stress for really flexible material (but there are other problems here like fatigue).
That’s not right for compressive strengh because flexible material even with realive low slenderness ratio buckle. According to euler formula Fc=pi²EI/l² so Force of buckling is only dependent of stiffness of material and shape of part (quadartic moment and lenght). Thats why you can stretch and elastic but he can’t take compression. Same principle for fiber reinforcement that can’t take compress forces because they have such a low I/l ratio that they buckle, that’s resin the key for those kind of forces.
For a sandwich panel that experiment simple flexural stress (from shear forces=perpendiculaire to flexural neutral axis= lip of wave), max Fc is in skin the farthest point of neutral axis and the nearest point of impact, that’s why you find so much people that experiment crease of their carbon rail boards.
Sorry but as you can see here (http://www.plastic-products.com/spec1.htm)
nylon 6/6 : flexural modulus 410000 psi, flexural strengh 17000 psi, density 1.14
and here (http://resinresearch.net/id8.html)
epoxy RR2000 : flexural modulus 480000 psi, flexural strengh 14800 psi, density 1.1 to 1.2
Not really big difference ! except nylon is a thermoplastique resin that can take lot of elongation in is plastic deformation range producing a ductile break (that’s way it is call a plastic) while epoxy wich is a thermoset resin produce a fragile break.
yeahbut. Yeah, but… innegra is plastic and no where near the strength of glass fiber reinforcement. If you are going to compress it and eliminate the thickness benefit, why not just use another layer of fiberglass. Ounce for ounce fiber is stronger. (but maybe not tougher. Lemat, true?)
all the best
I know that cutting fiberglass is way easier than cutting innegra. It’s not even close. In fact, I think it’s easier to cut B-stage innegra if it has a fiberglass cap over it than without.
That’s a pretty big exception! Comparing the flexural strength of cured epoxy vs. A fabric of woven nylon 6,6 is just silly. Are you suggesting putting a piece of cloth in a three point bend test? And then claiming failure when the cloth bends?
That last statement is nonsensical. The flex failure load of a block of nylon 6,6 has nothing to do with the bursting strength of a surfboard skin.
What property of strength do you mean? Glass shatters on impact. Plastic usually doesn’t.
Toughness, the resistance to abrasion might be a factor. That’s why plastics are hard to sand. They are too tough.
Tensil strength isn’t that important, because I’ve never seen a board torn in two.
About the only thing that fiberglass does best is look good, and polishes up nice… Kind of like my women…
Everysurfer some of your comments seems to show that you don’t really know how to mechanicaly calculate parts…
So you are right for all. World is so silly to spend so much time money and energy to find better materials whereas they have it under their eyes for so long time: polyamide 6/6. Near 90% of composits parts are made with fiberglass whereas they should be make with nylon, furthermore a cheaper material ? Be serious ! nylon fiber for composit is mostly sold as peel ply and as finishing surfacing veil to produce a resin rich coat, abraded and chemically resistant. Proprietary of nylon, Dupont de Nemours, worked to develop it for a composit use, it’s polyamide aromatic (aramide) called kevlar. But if you find how to make a nylon epoxy composit that outperform glass epoxy “mechanicaly” go for it show it, wright scientific paper, you can compet for physic noble price ! I will be pleased to accredit your work (it’s the practice) for free, my first place at national mechanical teacher contest give me some credit.
Greg, insert resiliant material (like plastics) between fragile ones give some energy dispersion advantage that increase fatigue resistance but with a noticeable lost of stiffness quickly after first limit elastic stress. Mostly because of poor adhesion of plastics with resin. So you have ductile failure material instead a fragile one. Search know look at stiff nanoparticule to stiffen toughen rubber epoxy. Adding rubber liquid phase in epoxy increase elasticity so it toughen resin (plastification) but reduce stiffness and strengh. Silice nano particule seems to noticeably increase this stiffness without loose of toughness.