Originally Posted by
grolby
Au contraire, mon freire. You get a stress riser (i.e. a crack), whether by trauma or fatigue, and that crack grows until it is a break. Breaking by bending or snapping is VERY rare.
The point is that breaking isn't the only mode of failure. Well, it is in aluminum, but that's the point: steel bends. Aluminum just fails catastrophically.
Originally Posted by
grolby
No, it's not unreasonable. The OP is asking about aluminum frames cracking, and the vast majority of cracks come from fatigue failure. Impact (for example, if you're riding a frame that gets a lot of abuse, like a mountain bike) can definitely accelerate the process, or finish off a weakened spot, but you basically never get an abrupt failure that isn't from fatigue except in the case of a major crash.
Again, this is an an unsupportable assertion. Everything that follows is, therefor, nonsense.
Originally Posted by
grolby
Baloney. You have no way of knowing that this is true. Crack a few aluminum frames before you start talking about how much worse you would have been hurt by it. Check out CDR's explanation upthread. Break a chainstay or seattube and you're probably going to be okay, no matter what you're riding. Break a top tube, you've got a scary situation. Break a downtube or headtube, and you're in for a world of hurt, no matter what you're riding. Frames broken in a particular place all behave in the same way, no matter what they're made from.
Try riding an aluminum frame and/or fork into something hard enough to cause it to fail. Try the same thing with steel. Steel will bend long before it snaps. Aluminum just snaps. On the two occasions I mentioned, that phenomenon made a big difference to my face.
Originally Posted by
grolby
Actually, I do - experience, a rudimentary understanding of how the universe functions, and sheer common sense. Impact accelerates the process, but it's extremely difficult to take a brand-new frame and break it by smacking it into something in the course of normal riding. With accumulated wear and tear, all those sweet jumps will eventually do the job, but again, that's because of the continual process of pushing the material too far, weakening it and eventually starting micro-cracks that propagate into full-blown cracks.
I bolded the key bits again. I'm not going to get into an argument about the definition of "extremely difficult", but I've done it twice and I'd be willing to bet that someone, somewhere, is doing the same thing right now.