How Serious is a Crack In An Aluminum Frame
06-16-06, 07:35 PM
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Originally Posted by Scooper
My problems with aluminum as a frame material are the very low elongation property of aluminum compared to steel or titanium, and the fact that most aluminum alloys don't have an endurance limit.
Elongation is the property of the metal that determines how far it can be bent before it breaks (brittleness), while lack of an endurance limit means that even a minuscule load, if applied enough times, will eventually result in a fatigue failure, often without any warning. Sudden, catastrophic frame failure can ruin your day.
Steel frames, OTOH, have higher elongation percentages and do have endurance limits, so failures are predictable instead of sudden or catastrophic. Because steel has endurance limits, repetitive small loads that aren't big enough to deform the material permanently (bend it) can be imposed on steel frames over periods of many years without failure, and if failure does occur it invariably does so with some advanced indication that it is about to fail (fatigue cracks, etc.).
For me, carrying a few extra ounces of weight in a steel frame is cheap insurance. New high strength stainless steel alloys like Reynolds 953 make possible thinner walled (lighter) steel frames that compare favorably with titanium and carbon fiber composite frames in terms of weight without compromising strength or durability, and without the low elongation (brittleness) of carbon fiber.
Just my opinion; I could be wrong.
Elongation is the property of the metal that determines how far it can be bent before it breaks (brittleness), while lack of an endurance limit means that even a minuscule load, if applied enough times, will eventually result in a fatigue failure, often without any warning. Sudden, catastrophic frame failure can ruin your day.
Steel frames, OTOH, have higher elongation percentages and do have endurance limits, so failures are predictable instead of sudden or catastrophic. Because steel has endurance limits, repetitive small loads that aren't big enough to deform the material permanently (bend it) can be imposed on steel frames over periods of many years without failure, and if failure does occur it invariably does so with some advanced indication that it is about to fail (fatigue cracks, etc.).
For me, carrying a few extra ounces of weight in a steel frame is cheap insurance. New high strength stainless steel alloys like Reynolds 953 make possible thinner walled (lighter) steel frames that compare favorably with titanium and carbon fiber composite frames in terms of weight without compromising strength or durability, and without the low elongation (brittleness) of carbon fiber.
Just my opinion; I could be wrong.
.ed rader
06-16-06, 07:37 PM
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Originally Posted by Brian Ratliff
All metal, and aluminum especially, has this nasty habit of propogating cracks over time until the structure breaks. The most vulnerable part of the bike frame is at the welds. The crack will not stop at the welds, it will, rather, reroute itself to follow the weld line. Eventually, the weld will fail.
Keep away from a cracked aluminum frame. If the frame has a crack, IT WILL FAIL IN TIME. This is not opinion; this is fact.
PS. I just looked at the picture. It is junk. The crack will simply propogate around the weld until the frame fails.
Keep away from a cracked aluminum frame. If the frame has a crack, IT WILL FAIL IN TIME. This is not opinion; this is fact.
PS. I just looked at the picture. It is junk. The crack will simply propogate around the weld until the frame fails.
?is there a shortage of aluminum frames?
now if it were copper or gold i could understand these days
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06-16-06, 07:40 PM
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Originally Posted by urbanknight
One thing I like about aluminum for MTB is that the protection from rust since my bikes tend to get dirty and muddy on rides. Aside from that, they're economic and light. I still prefer steel, though, especially on road bikes. The ride is smoother and the frame lasts longer.
ed rader
06-16-06, 07:44 PM
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I had some aluminum aerobars suddenly snap on me a few years ago. My triceps were the color of a Tahitian sunset for a couple weeks from hitting the top of my drop bars, but I was able to stay upright and not lose any skin. They were cheap aeros on a used bike, so I have no clue of their origin, but it was certainly a case of metal fatigue. Then again, now I ride a 16-year-old aluminum C'dale, and it is as solid as could be and I have done some very bad things to that bike. Bar hopping on bikes tends to cause that. It is certainly in much better shape than I am.
However, if I ever saw any cracks forming in that frame i would be afraid to go near it. Steel bends, aluminum breaks.
j
However, if I ever saw any cracks forming in that frame i would be afraid to go near it. Steel bends, aluminum breaks.
j
06-16-06, 08:01 PM
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Originally Posted by erader
a good aluminum bike with carbon fork can be very smooth, and much lighter than any steel bike.
ed rader
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06-16-06, 08:31 PM
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It's clear that the recommendation is to stay away from this frame. For personal reasons, I am still interested in it. What about welding the crack? Does anyone have any experience welding such a crack? I have access to an individual who is an experienced aluminum welder. The cost to me would be nominal. Has anyone tried to repair such a crack and then experienced failure?
I really do appreciate all the feedback. Please let me know if you've tried to repair such a problem.
I really do appreciate all the feedback. Please let me know if you've tried to repair such a problem.
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06-16-06, 08:55 PM
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TIG welding is iffy at best. I used to work in a welding shop and even the old timers would curse aluminum welds. When you safety is involved I would stay away. I don't think the frame would ever have real integrity. Nor would it have its original strength. But they are your teeth, you can do with them as you choose.
j
j
06-16-06, 08:58 PM
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How serious? Deadly.
Tube replacement MIGHT be possible, depends how it's built. Check with a local builder.
Sounds like you absolutely MUST have this bike.
Tube replacement MIGHT be possible, depends how it's built. Check with a local builder.
Sounds like you absolutely MUST have this bike.
06-16-06, 09:52 PM
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Originally Posted by TRaffic Jammer
How serious? Deadly.
Tube replacement MIGHT be possible, depends how it's built. Check with a local builder.
Sounds like you absolutely MUST have this bike.
Tube replacement MIGHT be possible, depends how it's built. Check with a local builder.
Sounds like you absolutely MUST have this bike.
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06-17-06, 12:05 AM
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Originally Posted by spider-man
An aluminum frame with a crack in it may be quite light, but it will not be smooth on the road for very long.
06-17-06, 07:48 AM
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Originally Posted by Mothra
Basically the repair CAN be done with welding since that's how the factory originaly built these bikes to begin with. However, unless you follow all the procedures to get the highest-quality welds, you won't have as strong as an original frame. You gotta do all the steps possible, like flushing and filing the tubes wtih argon to prevent contamination from the back side of the weld. Annealing/stress-relieving the joint afterwards to reduce the concentration of stresses in the HAZ, etc. This level of welding requires quite a bit of equipment and experience, might not be cost-effective compared to buying a frame that's not broken to begin with...
The welder I'm working with outlined the same process you did. But the responses here, which I greatly appreciate, are making me think twice about investing in something that has such failure potential.
By the way, being a Godzilla fan, I like your handle.
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06-17-06, 11:19 AM
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AL frames have a limited lifespan whereas steel does not. I would not buy any AL bike that has a crack in it. There's not much else to say about this. It's like buying a cracked carbon frame but worse.
06-17-06, 12:34 PM
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I'm glad i read this thread, my commuter bike has a crack along the left side bottom bracket weld, it makes noise when i pedal hard, like a faint click. I thought it was a loose bottom bracket. I'm getting a surly 1 x 1 probably tuesday and will ride my fixed till it's built up. Thanks again for the info..........
07-07-06, 05:58 AM
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Being the owner of a very well used and abused '92 Cannondale (or Crack-n-Fail as one of the earlier posters called it. Funny stuff) SM-700 mountain bike frame, I am concerned that my frame might have some sort of hidden damage waiting to rear it's ugly head when I'm riding it. I am fairly light (135 lbs), but the frame saw it's share of hard off road use. (translated: I crashed it a lot when riding trails in my more youthful days) Is there any way, other than stripping it down and doing some high speed NDI (Non-Destrutive Inspection) that I'm sure will cost a pretty penny, to check the frame for cracks? When I pedal out of the saddle up hills with a lot of force I can hear the rear brake rubbing the rim with every pedal stroke. Is this just normal frame flex tightening the brake cable? This thread has got me wondering. Maybe I'll go over the frame this weekend. I've been wanting to build up a steel framed commuter so maybe this is just the angle I need to convince myself to take the plunge...
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07-07-06, 06:50 AM
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Originally Posted by operator
AL frames have a limited lifespan whereas steel does not. I would not buy any AL bike that has a crack in it. There's not much else to say about this. It's like buying a cracked carbon frame but worse.
07-07-06, 07:27 AM
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Originally Posted by Phantoj
Steel frames have a limited lifespan, as well. But I wouldn't buy a cracked frame of any material. You can get a new frame for less than $100, and good used frames are also cheap.
A cracked steel frame can be repaired by replacing the tube or fitting. The cost may be prohibitive but it can be done. Cracked Al should be discarded.
07-07-06, 07:32 AM
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Originally Posted by Phantoj
Steel frames have a limited lifespan, as well. But I wouldn't buy a cracked frame of any material. You can get a new frame for less than $100, and good used frames are also cheap.
Buying a complete bike with a cracked frame might be a good deal if the price were low enough for the components you strip off of it. But buying a cracked frame is like buying your neighbors garbage.
