How can aluminum bars flex without cracking?

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#1
I'm confused. In mountain bikes aluminum frames don't flex like steel frames thus giving a harsh ride. Aluminum also doesn't absorb punishment like cromoly for BMX frames. Yet aluminum handlebars exist that flex? Seems like they would eventually break or that steel would be the better choice since its springy. How can this be? I thought aluminum tended to crack and become brittle when flexed too many times?
 
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#2
I suppose any piece of metal could be engineered to Flex with different alloy's, wall thickness and other treatments. Some amount of flex is necessary to any critical component to prevent failure at a given point. If a component is too ridgid, usually another part will suffer, ie; knees, wrists, elbows etc.
 

jeffd

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#3
Ever crush a beer can in your hand? Did it crumble or bend? :)

-jeffd
 

jmics19067

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#4
I suppose any piece of metal could be engineered to Flex with different alloy's, wall thickness and other treatments.
;)

1 thing to consider is that steel bars has the cross bar welded straight across the middle section and aluminum bars have a pivot point on the ends of the crossbar slightly higher than where they are fixed to the handlebars. This would allow some flex. Of course the big handlebars with no cross bar have more flex yet.

All materials will fail with repeated stress cycles it is only a question of when,with overloading,crash damage, wear and the useful life of the rest of the bike being exceeded being more common.

If never crashed aluminum bars would probably fatigue faster than steel but since the steel bars are easier to bend and more likely to be bent back into shape they will fail faster than the aluminum. I say probably only because aluminum tends to have weaker fatigue properties than steel but it would take a good engineer with the proper numbers of cycle loading ,wide sprectrum cumulative fatigue and the physical properties of the different handlebars to truthfully answer that.
 
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#5
Sounds like different types of aluminum flex more than others, i.e. 6061? I think bars are 20__ something type aluminum.
 

MikeT

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#6
Steel, Aluminum, they all will flex until they yield then they crack. Think of a aluminum wire. If you push on it, it will flex and bend back to its original shape unless you bend it too far and it yields. You know that a metal has yielded when you bend it and it does not bend back. This isn't bad because obviously all handle bars have bends in them. If you continue to bend them they will stretch and crack. I'm pretty sure steel will bend a little more but since there are many different types of steel and aluminum the engineers choose the best blend for the job.