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Old 07-28-05, 08:17 PM   #1
FarHorizon
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How tolerant is aluminum to stress?

I got a MTB style shifter/brake lever with an aluminum bar clamp (22.2mm?). I pried the gap apart until I could fit it over a moustache bar (24mm OD). I know that aluminum doesn't bend happily. I also know that aluminum is prone to stress cracking and catastrophic failure.

My question is "How safe is this?" The extra 8% stretch that the clamp had to do hasn't visibly caused any cracking or other stress. Provided that the clamp is inspected before each ride, should it be reasonably sound, or is undetected stress cracking likely?

I like the ergonomics of the adaptation, but don't want to risk my life if the darned thing breaks unexpectedly (particularly under heavy braking). Opinions? Thanks.
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Old 07-28-05, 08:37 PM   #2
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What you should be watching for is repeated stress, which the tension stress you placed on it is not. It will not likely crack from this instance, particularly if you have not found cracks or lines in the finish. To be certain, snug the clamp where you want it and use it hard. If you can stress it beyond that of pperation and it survives, it will work. If it is opened or compressed again, as it would be for removal, it will likely crack however.
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Old 07-29-05, 02:44 PM   #3
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Thanks, mtbikerinpa! That's what I'd hoped to hear. I'll try it as is and monitor it closely. Should I find cracking or other signs of problems, I'll retire it immediately. I appreciate your prompt reply.
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Old 07-29-05, 06:38 PM   #4
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every material has a certain amount of elasticity, that means it can streach without loosing its strength charcteristics. but i dunno dude, its just a shifter i think. first find out the type of material it is. then find its young modulus,then ull know how much it can strech before it explodes. alumium just gives up the ghost, no warning, so be careful.
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Old 07-29-05, 06:43 PM   #5
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Originally Posted by toomyus
every material has a certain amount of elasticity, that means it can streach without loosing its strength charcteristics. but i dunno dude, its just a shifter i think. first find out the type of material it is. then find its young modulus,
Isn't youngs modulus about stiffness? Viagra is too,but that's another story.
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Old 07-29-05, 06:52 PM   #6
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Originally Posted by sydney
Isn't youngs modulus about stiffness? Viagra is too,but that's another story.

Stiffness involves youngs modulus, but the two aren't exactly the same. Young's modulus, E, is the slope of the Stress/Strain curve of a material in it's elastic (linear) portion.

The real issue with aluminum, as mtbikerinpa pointed out, is it's rather "low" fatigue curve. A low maximum stress over a few cycles can possibly be enough to cause failure.
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Old 07-29-05, 06:53 PM   #7
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youngs modulus is stiffness. Yield strenght is how much it can take before it breaks
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Old 07-29-05, 07:01 PM   #8
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I just raided my bookshelf to refresh my memory, and in axial members, k(stiffness) = AE/L, where A is the cross sectional area, E is the young's modulus, and L is the length of the member. It may have a greater relationship with viagra than you had thought...
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Old 07-29-05, 07:19 PM   #9
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all there is is stress and strain pretty much cos ur putting a load< force> on a part. when u test metal, u pull it apart, when u see the graph, u first see how much it streched before it totally lost its structural integrity< meaning, u changed its compositon> then after that point it will be kinda crappy and a max force applied will tear it apart. now, i figured ur put something big, on something small, which is in a sence placing a force on it, so u have a few variable, one is youngs modulus , which says how elastic the metal is and how much it streches and can still be nice and strong still , and the other is axial stress and ur placing huge force on the piece from the inside. its complex stuff, but fun at the same time. basically ive no clue, u need to know loads of info, im just an engineer, u need a bike expert that had done the same thing . id say its bad news .so expect it to fatigue on u when u least expect it.
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Old 07-29-05, 07:25 PM   #10
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the correct way to spell:
Because
You
Your
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Old 07-29-05, 07:25 PM   #11
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.... basically ive no clue,
OK.....
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Old 07-29-05, 07:34 PM   #12
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lol, dude, uve given me no specs on the al part. i cant whip it out of my behind and go tensile test it. im no bike engineer. i do turbo chargers and stuff. so frick, give me small break. i said it will break, thats my answer. but i hope it doesnt
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Old 07-29-05, 08:20 PM   #13
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Thanks for the replies, folks, but I think mtbikerinpa hit it on the head. This part won't be repeatedly stressed (flexed). It is now in place and hasn't broken. That being the case, it'll probably survive for a long time or until it is flexed again (removed?), when it'll break. It is past its tensile strength part of the curve and is now ready to crack, but until it has a chance to move again, it isn't likely to.

I'll ride it awhile and report back.
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Old 07-30-05, 10:49 AM   #14
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Originally Posted by phantomcow2
the correct way to spell:


Your
Nope, it's "you're". I this case "U R" is actually closer to correct than "your".
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Old 07-30-05, 11:52 AM   #15
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lol
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Old 07-30-05, 03:53 PM   #16
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ya that could be true it material, even though being slightly streched can still be in its elasticity tolerances. so it which caseits cool. but likei said, thepart was too small for the bars in the first part so you would figure it would be anono. anyways, id do the same and test it and stuff. alumium just goes, but its cool cos its not like its the handle bar or anything that will snap. oh and Al934, thanks so much for ur tips on spelling. gosh, i dont know how id live with out ur advice . i mean this forum is so formal and stuff.
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Old 07-31-05, 08:54 PM   #17
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Quote:
Originally Posted by toomyus
ya that could be true it material, even though being slightly streched can still be in its elasticity tolerances. so it which caseits cool. but likei said, thepart was too small for the bars in the first part so you would figure it would be anono. anyways, id do the same and test it and stuff. alumium just goes, but its cool cos its not like its the handle bar or anything that will snap. oh and Al934, thanks so much for ur tips on spelling. gosh, i dont know how id live with out ur advice . i mean this forum is so formal and stuff.
Take another look, I wasn't criticizing your post. I just thought it was funny that the guy who did criticize your spelling got it wrong. People who live in a glass house should not throw stones..... or something like that.

Peace bro.

Last edited by Al1943; 07-31-05 at 09:01 PM.
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Old 08-01-05, 08:00 PM   #18
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Actually...you will be putting stress on it....everytime you apply the brakes/shift. You are putting a tiny amount of stress on it every time you do so. You ride on rough terrain? You ever do a panic stop? It will fail on you sooner or later. And of course are they top notch shifters or lower end? A better grade of Al vs. a cheaper one. If you just commute, you probably will be good for some time, but if you huck and chuck in the woods/mountains/wherever, your going to be up the creek w/o a paddle sooner than you'll think. I'm an aircraft mechanic like a collegue on here and have been for a long time. Things I thought would never fail (crack, break, etc) on a plane have done so, things I thought would fail in a blink went on til the life was up. It's a risk we all take when pedalling as anything could fail for no apparent reason but knowingly stretching something to make it fit is taking a risk that could have some nasty results.
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Old 08-02-05, 05:22 PM   #19
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Quote:
Originally Posted by bison33
Actually...knowingly stretching something to make it fit is taking a risk that could have some nasty results.
Agreed. I'm open to alternatives. Does anyone make MTB type integrated shifters/levers that will fit a road bar diameter?
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Old 08-02-05, 05:30 PM   #20
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i was thinking bout this. what ur doing is putting force on the bar. kinda like over squeezing a coke can. so its ur bar thats will fail. god im so stupid sometimes, i should have seen that comming. so it will be ur bar that will fail if it get one hit, it will buckle pretty much
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Old 08-02-05, 06:27 PM   #21
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Most steels have an endurance limit below which fatigue does not occur. Aluminum, however, does not have an endurance limit. Therefore, it's simply a matter of time before catastrophic failure occurs in you aluminum part.Most steels have an endurance limit below which fatigue does not occur. Aluminum, however, does not have an endurance limit. Therefore, it's simply a matter of time before catastrophic failure occurs in you aluminum part.
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Old 08-02-05, 08:33 PM   #22
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Quote:
Originally Posted by Al1943
People who live in a glass house should not throw stones..... or something like that.

Peace bro.
No it's "People who live in a glass houses shouldn't throw nude parties"
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Old 08-02-05, 11:51 PM   #23
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If the operational fatigue life were a concern, it would be a concern to all clamped brake levers. I have yet to see a brake/shift lever crack off a bar. If it passes the ultimate strength test, the operational fatigue is almost nil in comparison.
I fail to see where the post about the bar failure is coming from unless he means the clamp was formed over the bar and kinked it. The place handlebars fail(1-2 seasons of competition is reccomended changeout) is the stem clamp. Not the lever clamp. If the levers are propperly tightened, not excessively, the stress on the bar is only concentrated in the middle. The hand force of the brake application is almost miniscule next to the force of body weight on the stem. Would there be a possible crack at the brake lever? Maybe, but certainly long after the bar is changed out for stem area cracks.
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Old 08-03-05, 06:29 PM   #24
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thats eh, all true i suppose mountainbiker in pa. thats called a bending moment, and there is the most bending moment at the stem cos ur cranking on the bars as u ride which are far away from the stem, hence leverage, law of the lever and all that great stuff. the focal point at hand , is that this guy shoved a brake clamp which is too small, on a bar thats too big. so before u begin, there is more stress than its meant to deal with on the clamp. basically alumium is oversized cos its weaker than steel, so to make it strong they build it out the ways. so a clamp thats prob to tight, will not work good on a bar liek that and a bar thats to big wont like a clamop thats too smal, kinda obvious isnt it.anyways, its fricken trivial, its a lil over board at this point. peace yall and keep on crankin thoes pedals
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Old 08-04-05, 07:23 PM   #25
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Wow, I had to put tommyus's posts through my word-processor and do a search->replace based upon phantomcow's substitution table before I could even understand it..

What he's getting at in this last post is the concept of a stress-riser. This occurs in an area with high-torque due to a long moment-arm adjacent to an area of little movement (the clamped in part). This highly stressed area combined with any surface notches will lead to a propagation of cracks and eventual failure. To spread out the stress-riser, you want a tapered joint, like a fillet-brazed joint on steel frames. This is done by making the stem-clamp thinner towards the outside and by adding a sleeve on the bar in the center.

In this particular case, due to different wall-thicknesses, the bar will most likely fail before the clamp. What I would do is gently slide that bar out and lightly sand off any scratches and surface imperfections, then polish it.

Also the brake-lever clamp is not the same situation as the stem-clamp because the brake-lever clamp doesn't fix the bar in place, thus no stress-risers.

Last edited by DannoXYZ; 08-04-05 at 07:29 PM.
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