While a piece of steel is obviosuyly much stronger than a piece of wood of the same dimensions, if we stipulate equal *weights* rather than equal dimensions, the piece of wood may be stronger. The "specific strength" (or "strength to weight ratio) of some woods like balsa are greater than most steels.
That means that the applications of wood overlap the applications of steel somewhat. Some places where you need a little steel you can use a lot of wood and the result will be equally strong and weigh about
I'd take your post more seriously if you didn't make absurd generalizations like "steel is very stiff and wood is very flexible." From that alone it's obvious you understand nothing about materials.
I'd take your post more seriously if you didn't make absurd generalizations like "steel is very stiff and wood is very flexible." From that alone it's obvious you understand nothing about materials.
Alright then. Woods have a Young's modulus (along the grain) of around 3-12 GPa. Typical construction steels have a modulus of around 200 GPa. Therefore a steel beam will be stiffer than a wooden beam of identical dimensions. However, I do realize that *some* wooden objects will be siffer than *some* steel objects. For example an oak beam with a 10x10" cross section will be stiffer than a steel bar of the same length with a 0.25 x 0.25 inch cross section.
You probably already know all this, but for what it's worth, Gary Klein's realization that you can build a stiff frame out of anything if you just increase the diameter enough is completely apropos for wooden bike frame design. The problem, as the Renovo guys have found, is that you need like 5" diameter tubes to get even acceptable stiffness, since stiffness rises as the third power of diameter for tubes. But at those diameters, for a competitive weight, the walls have to be like sub-millimeter in thickness, making for an incredibly delicate bike. (Even old top-end aluminum Cannondales were notorious for having holes punched right through the downtube when the bike merely fell over in a garage and landed on some heavy steel thing.) So Renovo's going down the route of making egg-crate-like tubing with huge amounts of milling to form internal honeycomb structures. Most everyone else in the wood/bamboo bike frame world has shrugged and accepted a more flexible frame as the cost of aesthetics, but in some cases like triathlon bikes it's okay to have a flexible frame as long as it's aerodynamic. Of course, making a wood frame and then wrapping it with a layer of something with a really high young's modulus gets you a great frame... but then it's really a composite frame that uses wood rather than foam as its form, so that hardly counts.
I certainly remember when Klein's bikes came out; he was a few years ahead of me at MIT. I don't know if the larger tubing idea was actually his; he was part of a group of students working on an aluminum frame. The relationship of diameter to stiffness had neen known for centuries; I think Euler originally worked out that the bending stiffness of a beam is proporitional to the moment of inertia of its cross section. I expect a lot of engineers realized the potential of aluminum. What stands out about Kle
Actually, Gary Klein's 'realization' is just simple engineering, apropos and employed by Renovo, Cannondale, Cervelo, Boeing and any other manufacturer who employs engineers and wants a torsionally stiff tubular section. The 'Renovo guys' have (actually calculated) and tested that they can easily equal the stiffness of a Cervelo S2 or Scott Elite carbon frame using a 2.5 diameter downtube (the Scott is 2.07).
Your assertions about Renovo's frames are authoritative sounding, but altogether wrong. Sorry, Re
"There are things that are so serious that you can only joke about them"
- Heisenberg
Here's a curious fact about wood. (Score:2)
While a piece of steel is obviosuyly much stronger than a piece of wood of the same dimensions, if we stipulate equal *weights* rather than equal dimensions, the piece of wood may be stronger. The "specific strength" (or "strength to weight ratio) of some woods like balsa are greater than most steels.
That means that the applications of wood overlap the applications of steel somewhat. Some places where you need a little steel you can use a lot of wood and the result will be equally strong and weigh about
absurd generalizations (Score:2)
I'd take your post more seriously if you didn't make absurd generalizations like "steel is very stiff and wood is very flexible." From that alone it's obvious you understand nothing about materials.
Re: (Score:3)
I'd take your post more seriously if you didn't make absurd generalizations like "steel is very stiff and wood is very flexible." From that alone it's obvious you understand nothing about materials.
Alright then. Woods have a Young's modulus (along the grain) of around 3-12 GPa. Typical construction steels have a modulus of around 200 GPa. Therefore a steel beam will be stiffer than a wooden beam of identical dimensions. However, I do realize that *some* wooden objects will be siffer than *some* steel objects. For example an oak beam with a 10x10" cross section will be stiffer than a steel bar of the same length with a 0.25 x 0.25 inch cross section.
There, is that pedantic enough for you? Or do I
Re:absurd generalizations (Score:2)
You probably already know all this, but for what it's worth, Gary Klein's realization that you can build a stiff frame out of anything if you just increase the diameter enough is completely apropos for wooden bike frame design. The problem, as the Renovo guys have found, is that you need like 5" diameter tubes to get even acceptable stiffness, since stiffness rises as the third power of diameter for tubes. But at those diameters, for a competitive weight, the walls have to be like sub-millimeter in thickness, making for an incredibly delicate bike. (Even old top-end aluminum Cannondales were notorious for having holes punched right through the downtube when the bike merely fell over in a garage and landed on some heavy steel thing.) So Renovo's going down the route of making egg-crate-like tubing with huge amounts of milling to form internal honeycomb structures. Most everyone else in the wood/bamboo bike frame world has shrugged and accepted a more flexible frame as the cost of aesthetics, but in some cases like triathlon bikes it's okay to have a flexible frame as long as it's aerodynamic.
Of course, making a wood frame and then wrapping it with a layer of something with a really high young's modulus gets you a great frame... but then it's really a composite frame that uses wood rather than foam as its form, so that hardly counts.
Re: (Score:2)
I certainly remember when Klein's bikes came out; he was a few years ahead of me at MIT. I don't know if the larger tubing idea was actually his; he was part of a group of students working on an aluminum frame. The relationship of diameter to stiffness had neen known for centuries; I think Euler originally worked out that the bending stiffness of a beam is proporitional to the moment of inertia of its cross section. I expect a lot of engineers realized the potential of aluminum. What stands out about Kle
Re: (Score:1)