mixing kevlar with glass matt and rovings in a lamination.

Gee...with enough laminates of Glass you will able to make your structure bulletproof.

Exotic fabrics are best for structures that must be light and strong...not a keel, skeg

No Square corners with glass fibers, big radius. You flange should be much bigger.

Commonly available eglass, Sglass fibers. Knitted structural fabrics.

As you can see..sglass is rare.

lightweight Tri ax eglass fabric should workable with your shapes

http://www.fiberglasssupply.com/pdf/reinforcement/KnittedFabrics.pdf

 

Viking ,S glass will pretty much match the elongation of epoxy. I have S glass at 665,000 psi , tensile strength, 332,000 compressive strength. 5.4 elongation capability, stiffness 12.6 . E glass tensile strength is 500,000 psi. Rick

 

There are all sorts of places to find info, i just rechecked where i had looked it up which was page 345 of Gerrs "The nature of boats" under "strengths of boatbuilding materials" He shows 170000 psi tensile for graphite,168,000 for spectra, 150,000 for titanium, 128,000 for S glass, 90,000 for kevlar, 15,000 for E glass. I will look elsewhere.

Steve.

 

It's commonly accepted that S glass is 30% (or more) stronger and 15%-20% stiffer than E glass, plus it can produce structures that are about 20% lighter, as a result of good laminate engineering. It also costs about 3 times as much and isn't as commonly available.

S Glass offers six enhanced properties, critical for demanding applications: strength (30%-40% higher than E-Glass), impact resistance (higher elongation and toughness than E-Glass), stiffness (20% higher than E-Glass), temperature resistance (392 F - 200 C higher than E-Glass), fatigue (longer life for highly fatigued parts), and radar transparency. When compared to aramid or carbon fiber, the S-Glass family may deliver better cost effectiveness, but working (designing laminates) with these "unique" fabrics should be done professionally, if you want to take advantage of what they offer.

 

Well -- the largest glass/resin supplier here in Halifax doesn't stock it and my fiberglass man has never worked with it so not much chance I'll work with it. That is unless the supplier phones me back tomorrow with the discovery they found a few yards left over from a military order. Then the great experiment begins with 4 to 6 layers of 1 sq. foot of laminate .

 

S glass can be found online, we just bought some 9 oz uni a couple of weeks ago for some rudder builds from Fiberglass supply. We used to buy our uni from Orcon corp 25 or so years ago but they dont seem to be around anymore, we used to build hulls with orcon uni but recently ive only used it for rudders and keels where you dont use so much that the extra cost is an issue.Your fiberglass guy will not have any problem, it handles the same as E glass.

Steve.

 

Thayercraft carrys it as well. Rick

 

A hull laminate firmly fixed and bounded by frames and stiffeners and subjected to a uniformly loaded pressure of water on the outside (wet side) would behave in a manner as illustrated by Lloyds.

The outer laminate when pushed by the water pressure would be under compression, the inner skin (dry side or bilge side) would be in tension. However, in the part where it is firmly fixed/supported by the frame, the stresses are reversed because the frame is resisting the forces and tends to move the opposite way. The laminate then is subjected to both compression and tension depending on the location.

The greatest stress in the laminate will occur at the base of the stiffener and at the neutral axis of the laminate. This stress is a vertical shear, similar to the action of a scissor when cutting a cloth (or Kevlar) and can sometimes reach high proportions. Since Kevlar is good in shear, let us decide where to place the Kevlar.

Naturally, the best place is under the base of the stiffener but where? We cannot place it on the wet side as it wicks water when the outermost protective barrier is breached. Locating it in the bilge side would also not be the best solution as most of the time it is wet. The best place then would be in the middle or the neutral axis, where it receives the greatest shear, plus it is hard to breach.

But it becomes complicated when you are combining different materials with different modulus. Refer to the tables posted by SamSam. Kevlar is comparable to S glass and just slightly better than E glass. Carbon is high modulus and brittle. At high impact strength, the carbon will shatter, leaving only the Kevlar to resist the impact. Again this is a general assumption but let us deal with that later. When combining materials, it is best to have different materials that will bend in the same rate as the other so it fails at the same time, one reinforcing the other.

This is analogous to combining resin and fiber. Choose the resin that will elongate in almost the same rate as the fiber. Attached is the spreadsheet that shows the relationship of fiber and resin elongation. The vertical dotted red line shows the elongation that will yield the highest tensile strength of the laminate. The rule of mixture formula will confirm that materials that have the same strain will yield the highest tensile strength.

Since we have chosen to locate the Kevlar in the middle portion, a better solution would be to substitute Kevlar with foam. Care must be taken to ensure that the foam will satisfy the shear requirement of the sandwich laminate and the modulus of the foam would more or less the same as the laminate. The face of the sandwich will then carry most of the stress of the panel as it moves away from the neutral axis. Carbon is good for facing as its high strength will absorb the impact and redistribute the load along the surface. Better is VE resin and E glass and cheaper too, or high elongation epoxy and E glass with E glass at around 4% elongation. That leaves us with no use for the Kevlar then. So as Tunnels said, “Leave it on a roll and carry it with you in the boat.”

 

Amen (so be it) to that Brother ---