Figured I was not the only one thinking about this. I'm just going to throw this out and see what you all think. So I'm thinking the laminate we put on the belly side is not optimal. We use a laminate that was obviously designed to placed on the bow's back. It's reinforced with unidirectional fibers that have one purpose. So why do we use the same laminate on the belly? Why not use a laminate designed to resist the compressive forces. I have been planning on doing some experimenting with epoxy and hollow glass microspheres. 3M makes some with 27,000psi crush strength. The epoxy I will use is 26,000psi. The density of the microspheres is 0.6 g/cc, the epoxy is 1.1 g/cc. Big potential for weight savings for no loss in strength. Plus I have been reading documents on testing of various composites and the addition of hollow glass microspheres has been shown to increase the modulus of resistance, so the theoretical laminate should be able to absorb and release more energy. I still need to do a bit more research to confirm and would like to see MOResistance specs for epoxy. I am still debating whether or not to add a .002 biaxial layer of glass for a bit more structural integrity and if the addition of more elastic epoxy is necessary, also the percentage of HGM to use in the matrix. I'd like to hear anybody's ideas, just remember I'm trying to move this idea forward, not stalling out or going backwards.
Flem,
What is the best way to make a composite for best compression strength? Maybe another example might help. A solid Steel column has very high compression strength, right? Now picture making an equivalent steel column out of many spaghetti-like strands of thin steel wire and put a compressive load on it. Even though an equivalent cross-section of wire is just as strong in compression as the solid column, it won’t support much weight at all because all the little strands buckle under load. But then take some super strong thread and tightly bind this bundle together so that it can’t buckle so easily, and put a compressive load on it. It will behave totally different. It will be able withstand a very high compressive load and will act more like the solid steel column. For composites, the epoxy is what is tightly binding these little thin columns together and preventing them from buckling.
Now add micro balloons to this bundle. What do you think will happen? In the example of the thin steel wires bound together, it will be like mixing marbles between the wires before they are bound together. This creates little voids and misalignments of the wires, which does two things. First, there will be fewer wires to resist the compression that can fit in the same space. Second, it can cause little misalignments and kinks in the wire bundle, which makes the bundle more susceptible to buckling under compression.
27,000 psi crush strength in not even close to the compression strength of a composite with unidirectional fibers reinforcing it. Unidirectional Glass or carbon composite materials have a typical compression strength of around 150,000-160,000 psi.
The strength of the epoxy is not a major factor. The elastic modulus of the epoxy is relatively low, so it just goes along for the ride when compressed or pulled in tension. In the example of the steel column, it is more like binding together the steel spaghetti column in a matrix of rubber.
Alan
Topic: Question for any Engineers or Materials Scientists out there (Read 15104 times)
