Alluminum Frames? What's all the fuss?
Posted April 09, 2005 - 04:01 PM
However, none of us would complain about less weight. If, at the end of the day, the next bike is 10 pounds lighter, I guess alluminum would be nice. If I had it my way, a lighter steel frame would be better, but I guess the current fad won't allow that.
Posted April 09, 2005 - 04:19 PM
Posted April 09, 2005 - 05:14 PM
The disadvantage of aluminum is that it has no fatigue limit, which means that if it goes through enough stress cycles, no matter how small the stress, it will eventually break. At low stress it takes a lot of cycles and at high stress, just a few. Steel has a fatigue limit. As long as the stress is below about half the ultimate strength it will never break no matter how many stress cycles it sees.
So when you are designing parts out of aluminum, they either need to be replaced at regular intervals (if we know the stresses, we can predict when the part will fail) or they need to be over-designed. With bikes, we don't want to replace wheels, swingarms and frames every few months, so the parts are made to keep the stresses low enough that the parts will last for a very large number of stress cycles. As a result, the parts loose some of their weight advantage over steel and they end up feeling stiffer because of the lower working stress. On the other hand, most people will accept the fact that a piston needs to be replaced at regular intervals. They go through hundreds of stress cycles per second, so they will reach their fatigue limit relatively quickly. The fatigue life of aluminum is one factor that goes into determining the recommended replacement interval for a piston.
Posted April 09, 2005 - 05:15 PM
Posted April 09, 2005 - 05:24 PM
Posted April 10, 2005 - 05:11 AM
Is the plane eventually going to break, or will it be retired after a certain number of hours???
Posted April 10, 2005 - 06:01 AM
Go fly and don't worry. Plane manufactures design parts with modern CAD systems and use FEA to predict the life of aluminum (all) parts. They then assign a life cycle to them and during regular service that part must be replaced wether it is showing wear or not. The part may look like new with no signs of wear but they are require to replace it. Now if you are flying on something really old before the invention of modern computers or something made in some off breed country you might want to take a parachute as your carry on luggage!
Posted April 10, 2005 - 09:57 AM
-If the Aluminum frames are so great, why is Honda's "new fangled" 450X heavier than a 2005 WR450?
-I don't like the cluttered "fat frame" look of Honda's frames (new Suzuki RM-Z450, etc.).
-I read in Dirt Bike mag recently, that Honda had major issues with their aluminum frames thus Yam and Suzuki have been trying (for years) to avoid such pitfalls in their designs -- must not be an easy task.
-Don't recall seeing complaints from KTM or Yam owners of broken frames here or on KTMtalk.