The vast majority of surfboards break because the bottom skin stretches (tension) to a point past recovery.
The deck skin DOES delaminate aka buckles aka failure as a result of the previous.
This is one of the primary reasons I use Warp glass with 65% of the strands running the Warp vs. Weft aka fill.
Flexural modulus of the resin choice is critical when considering the above criteria which is a common occurence with surfboards.
Epoxies stick to considerably more substrates than do polyesters.
The epoxy bond is SUPERIOR in a molecular sense, no contest… look at the linkage comparisons of epoxy, vinylester, and polyester resins. Polyester is last.
Physics don’t lie.
Happy St. Patty’s Day… Whiskey is God’s form of birth control.
Wow, really? Glass is so strong in tension, I would think that buckling from axial compression would happen on the opposite side, well before the glass would break in tension?
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Epoxies stick to considerably more substrates than do polyesters.
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Yeah but I doubt the two layers of 4oz would seperate from each other, or at least this wouldn’t be the first thing to go!
I reckon it would be the glass delaminating from the core (because of compression buckling) - which is from the core actually failing itself just below the surface. The glass would have a thin layer of foam left stuck to it.
So as long as the polyester’s bond with the foam is stronger than the foam itself…
Just thinking through things using my own logic, I may be totally off!
I’m totally open to being convinced otherwise, as I haven’t really put a lot of thought into this
Just some informations from the mechanical teacher i am who work sometimes for composit industrial parts:
Stength in composits come from reinforcement so reinforcement need to be aligned with stress. Stress isn’t only in one direction so good orientation of reinforcement is a complicate key of composits optimization. Crimp of fiber create shear stress in laminate wich reduce life of composit structure.
Normaly resin just keep reinforcement in place, it’s a glue : it’s transmit stress resisting shear. Better is shear fatigue resistance better is glue, epoxy is far better than polyester for shear fatigue resistance, that’s why only epoxy (and sometimes polyimides, bismaleimides or polystyrylpiridines for temp properties) is use in High performance composits.
A composit structure fail because it too undergoes deformation. First glue break, composit loses more en more rigidity then reinforcement break. It can be more or less rapid, depends of stress intensity.
Normaly in a sandwich structure ( thin skin/ core /thin skin), core should only transmit stress from each skin to other. But light PU (less than 80 Kg/m3) or EPS aren’t stuctural foam core because of low shear strengh. Stringer give more structural strengh to core.
Standard PU/PE or EPS/epoxy surfboards, with light laminates, aren’t effective sandwich structure: skin aren’t strong enough. That’s why foam and stringer have an important role and that’s way for sandwich skin surfboards (stiff skin) foam account for almost nothing…
