iab

I heard crabon assplodes too. Good to know it has company.

3alarmer 

.
...I must be the only person on teh Beikforums who has broken an (old French) handlebar, while enroute on the bicycle it sat on. I was going pretty slow, and it sort of ripped, not too far from the stem. It made an impression on me. Not something I'm anxious to repeat. I like to think it's my massive guads, and all the force I was putting down into the pedals. But it was probably just timing and usage.

iab

I snapped a steel crank. Like you, I blame my massive guads.

But I am sure as **** I'm not going to preemptively replace cranks.

old's'cool

Sorry, the only accurate details in your post are yes, Aluminium is how the British and other nationalities refer to what is called Aluminum in the US, and yes, there is a thing called work hardening, but it is not what you described.
Work hardening is the process of making a metal harder (not stiffer) through plastic deformation. An aluminum (inium) framed bike will not get stiffer through use. But, if it starts to feel softer, it is ready to be melted down.
Flexing without plastic deformation does not cause work hardening, but it tends to cause what is called cumulative damage, especially in a material like aluminum (inium) that has no fatigue limit. Cumulative damage eventually leads to crack initiation and propagation, which eventually results in failure, if flexing persists.

oneclick 

I don't ride ally-framed bikes, but from a material properties viewpoint this is difficult to understand; perhaps the op would explain in mechanical terms what he means by "harsh".

Johno59

I'm not strong enough to bend bars thru pedaling hard but it should be mentioned what happens to old suspect bars when you hit a nasty pothole. All of a sudden the jolt turns you into King Kong and any weakness in the metal will reveal itself. I had some favorite 'World Champion' bars that I'd buffed down and slavishly polished - very much admired.. Hit a nasty pothole and snap. The brakes still worked of course and I managed to steer using the stem, away from the 60 mph traffic and the left hand brake lever and into the comparative safety of a grassy ditch.

Gary12000 

Thanks for the education, either I mis-remembered or was given bad info.

so do I understand you correctly that use of an aluminum frame can lead to a crack and ultimately failure?

Gary12000 

my terminology was wrong I've been corrected by a previous post, however in the context of my post by Harsh I was meaning the frames become more stiff, who knows maybe stiff is an incorrect term also.

steelbikeguy

I can't answer that directly, but I've worked in aviation, and the aluminum aircraft structures are usually rated for a fixed number of operating hours. They might be torn apart at that time and inspected closely for cracks and such. Sometimes key elements will be replaced, such as wing spars or skins, to permit additional use.
I would assume that aluminum bike structures, i.e. frames, handlebars, etc., would have similar limitations. Unfortunately, we don't know what the design lifetime of these parts are.

Steve in Peoria

icemilkcoffee 

Are thin-walled (T6 type alloy) aluminum bars more susceptible to corrosion and castastrophic failure or less? I love the thin-walled bars for the weight savings.

oneclick 

T6 (as commonly found in aluminium spec such as 6061-T6) is a reference to the tempering process, not the alloy.

Aluminium alloys do vary widely in corrosion resistance.

oneclick 

It might be; in engineering use it has a specific meaning and value for various materials. I am unaware of any measured change in this value with time (other than initial heat-treatment etcetera) for aluminium alloys.

Trakhak

I spent the first 30-plus years of my cycling life riding high-end steel racing frames and the last fifteen or so on high-end aluminum racing frames. Over my last 50-ish years of riding, racing, and working in bike shops, I heard any number of bicycling myths, including the aluminum-frames-become-stiffer-over-time one, the myth that steel racing bike frames become soft and should be retired after a season or two of hard use, the myth that tubular (sew-up) tires should be aged for at least one season before use, etc.

The majority of bikes sold by U.S. bike stores have featured aluminum frames since about the mid-1990s. I've been reading posts on the Bike Forums site since 2005, and I've never read a single report of an aluminum frame becoming perceptibly stiffer over time.

The reason that aluminum frames came to dominate bike store sales, by the way, is that manufacturers prefer to replace as few frames as possible under warranty---and they have found that increasing the wall thickness of an aluminum tube greatly increases the likelihood that the frame will never fail in normal use. Thicker aluminum tubes don't weight much more than thinner tubes, so those frames are still reasonably light.

steelbikeguy

why does my mind immediately dredge this up?



I'm guessing that Schwinn never had to pay warranty on a Varsity frame... if they did, there was probably a story about how it had been used to carry bags of concrete or some such thing.

Steve in Peoria
(yeah, that Varsity weighed somewhere between 38 and 41 pounds!)

old's'cool

So as not to beat a dead horse, short answer, it depends (since this has been adequately answered in more detail, above).
For sure no metal structure I can imagine will get stiffer with use, and if it starts getting softer that means it's failing, i.e. cracks are occurring in critical locations.

noglider 

When I was building a bike I was going to race on the track, my friends convinced me to use a steel handlebar. I think they imagined me as being much stronger than I really am. I followed their advice, so I suppose steel isn't a bad choice. And I have handled the handlebar that comes on a Schwinn Varsity. That is a very heavy handlebar indeed.