Quote: stiffer? a quick google search shows fiberglass' elastic modulus is 17.2 GPA, steel is 200GPA, so steel is 11.6x stiffer. to get the same effective stiffness, for a same length & width beam segment, the fiberglass spring will need to be approx 2.25x thicker (taller) to have the same spring rate as a comparable steel spring the way the equations work out.
I can't dispute your numbers, they sound correct, but two points, he might have meant comparable weights regrading stiffness, and a "leaf" is not a solid member, but sliding members, where a composite spring is obviously solid.
true, guess I'm a stickler for details I guess....there are 2 components to a part's "stiffness"--material properties and geometry. fact is, from a material property stand point, steel is MUCH stiffer. but a part can be stiffer with changes to the geometry to give more cross section.
but even looking at just a steel main leaf, which is what, 5/16" thick? the thinnest part of a fiberglass leaf would need to be approx 11/16" thick to get a comparable stiffness....
didn't bother looking at densities, steel is 7.85g/cm^3...a quick google search shows fiberglass as 2.5g/cm^3 or less (depending on glass to resin ratios), so you could have 3-4 times the volume of fiberglass in your part before it weighed more than the steel part.
so yes, stiffness per weight can be much better for fiberglass, if the space allows for the geometry differences.
Last edited by patrick; 02/15/1209:31 AM.
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