Kevlar properties

[HELModels]

I just made a kevlar rod about 16 gauge in thickness and it is very flexible/whippy. The kevlar was scrap that I found and I know very little about strength of materials and such, but I wonder if kevlar is supposed to be so flexible when mixed with epoxy resin? The resin was West with 105 hardener.

I cut into a section of the finished product to see if epoxy penetrated thoroughly and it appears to.

[DaveSawers]

Kevlar is flexible. If you want stiffness, use carbon. If you want the ultimate in stiffness, strength and durability, use a combination of kevlar and carbon.

[Ollie]

Kevlar is very tough. It is strong in tension but will not carry much of a load in compression. Unlike the graphite form of carbon whose molecules form flat sheets, Kevlar has molecules that are shaped more like corkscrews. When graphite molecules are loaded edge wise they are very stiff and very strong but they break suddenly under extreme load instead of deflecting much. The shape of kevlar molecules allow them to deform and absorb energy without breaking. Kevlar in epoxy is so tough that it just fuzzes up when you try to sand it. A kevlar shell fuselage will fail by the failure of the epoxy but the kevlar fabric remains intact. It is often possible to straighten out such a fuselage and soak the kevlar where the epoxy has failed with thin CA to effect a structural repair.

[Robbie d]

thats why kevlar thread is used to tie the tyres on formula 1 cars to the chassis, it has enormous tensile strength. The best mix i've seen so far is a hybrid weave cloth, carbon and kevlar, looks like a tartan pattern.