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Titanium Frames
Greetings all.
I read the other Titanium thread with much interest and then started to ask a few questions of people who I thought would know how good a "Ti" frame would be. I was told by one person that Titanium frames have a propensity to crack due to metal fatigue. This was supposed to be from the lack of give in the very rigid frame. He also said that pro riders don't really care if the frame cracks because they can just chuck it away and get another. Anyone had any experiences with this, or know of anyone who has had this problem? Thanks in advance. Andrew |
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#2
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Titanium Frames
"Around Australia Recumbent Style" wrote in message ... Greetings all. I read the other Titanium thread with much interest and then started to ask a few questions of people who I thought would know how good a "Ti" frame would be. I was told by one person that Titanium frames have a propensity to crack due to metal fatigue. This was supposed to be from the lack of give in the very rigid frame. He also said that pro riders don't really care if the frame cracks because they can just chuck it away and get another. Anyone had any experiences with this, or know of anyone who has had this problem? Thanks in advance. Andrew My el cheapo radioactive chinese Ti mountain bike frame has been going fine for about two years now. (Ab)Used several times a week for long rides in the bush. My two ti road bikes are going well too. http://www.geo.net.au/~mart/personal/martys_bikes.htm Marty |
#3
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Titanium Frames
Around Australia Recumbent Style:
I was told by one person that Titanium frames have a propensity to crack due to metal fatigue. This was supposed to be from the lack of give in the very rigid frame. This is nonsense. Look up the fatigue strength of titanium versus aluminium, and see that the former has the advantage. A frame that is well made will be durable regardless of the metal used. A frame made of titanium will have a longer fatigue life over an _equivalent_ aluminum frame. However, for a reasonably sized Al frame (ie not stupid light), you're likely looking at a life of hundreds of thousands of cycles, if not in the millions, the point being that extending fatigue life beyond this is most likely not a significant consideration. Many, if not most, aluminium frames last hundreds of thousands of kms, lifetimes for many riders. He also said that pro riders don't really care if the frame cracks because they can just chuck it away and get another. Maybe so, but this has nothing to do with what material the frames are made of, but more of the money involved in sponsorships. Enter this person in a tall stories contest; he might serve a useful purpose there. |
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Titanium Frames
"Jose Rizal" wrote in message nk.net... Around Australia Recumbent Style: This is nonsense. Look up the fatigue strength of titanium versus aluminium, and see that the former has the advantage. Actually, that's only one part or a very complex problem. But put simply, neither Aluminium or Titanium has a fatigue limit. That is, one day after X number of cycles, the material WILL break. Steel has a fatigue limit. But this all is irrelevant, since it's the design of the frame (wall thickness, design, joining etc) that is the biggest factor in how long a frame of any metrial will last, and that frame's characteristics. The material it's made out of is just one part of the design. Cheers Gemma |
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Titanium Frames
Gemma Kernich:
"Jose Rizal" wrote in message nk.net... Around Australia Recumbent Style: This is nonsense. Look up the fatigue strength of titanium versus aluminium, and see that the former has the advantage. Actually, that's only one part or a very complex problem. But put simply, neither Aluminium or Titanium has a fatigue limit. That is, one day after X number of cycles, the material WILL break. Steel has a fatigue limit. Nope, both titanium and steel have fatigue limits, Al does not. But this all is irrelevant, since it's the design of the frame (wall thickness, design, joining etc) that is the biggest factor in how long a frame of any metrial will last, and that frame's characteristics. The material it's made out of is just one part of the design. Fatigue limit (or lack of) is not irrelevant, since in good designs it is what defines the frame tube sizes for each material, such that either the fatigue limit is not reached in steel and Ti frames, or the fatigue life of the Al frame is of reasonable length. Since there isn't much of a variance in most frame designs, the triangle front and rear being the most common, it's not a complex thing to do to design frame tubes of sufficient gauge using different metals to allow for durability. |
#6
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Titanium Frames
"Jose Rizal" wrote in message nk.net... Gemma Kernich: "Jose Rizal" wrote in message nk.net... Around Australia Recumbent Style: This is nonsense. Look up the fatigue strength of titanium versus aluminium, and see that the former has the advantage. Actually, that's only one part or a very complex problem. But put simply, neither Aluminium or Titanium has a fatigue limit. That is, one day after X number of cycles, the material WILL break. Steel has a fatigue limit. Nope, both titanium and steel have fatigue limits, Al does not. But this all is irrelevant, since it's the design of the frame (wall thickness, design, joining etc) that is the biggest factor in how long a frame of any metrial will last, and that frame's characteristics. The material it's made out of is just one part of the design. Fatigue limit (or lack of) is not irrelevant, since in good designs it is what defines the frame tube sizes for each material, such that either the fatigue limit is not reached in steel and Ti frames, or the fatigue life of the Al frame is of reasonable length. Since there isn't much of a variance in most frame designs, the triangle front and rear being the most common, it's not a complex thing to do to design frame tubes of sufficient gauge using different metals to allow for durability. So why do we see so many cracked Aluminium frames? Marty |
#7
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Titanium Frames
"Marty Wallace" wrote in message om.au... "Jose Rizal" wrote in message nk.net... Gemma Kernich: "Jose Rizal" wrote in message nk.net... Around Australia Recumbent Style: This is nonsense. Look up the fatigue strength of titanium versus aluminium, and see that the former has the advantage. Actually, that's only one part or a very complex problem. But put simply, neither Aluminium or Titanium has a fatigue limit. That is, one day after X number of cycles, the material WILL break. Steel has a fatigue limit. Nope, both titanium and steel have fatigue limits, Al does not. But this all is irrelevant, since it's the design of the frame (wall thickness, design, joining etc) that is the biggest factor in how long a frame of any metrial will last, and that frame's characteristics. The material it's made out of is just one part of the design. Fatigue limit (or lack of) is not irrelevant, since in good designs it is what defines the frame tube sizes for each material, such that either the fatigue limit is not reached in steel and Ti frames, or the fatigue life of the Al frame is of reasonable length. Since there isn't much of a variance in most frame designs, the triangle front and rear being the most common, it's not a complex thing to do to design frame tubes of sufficient gauge using different metals to allow for durability. So why do we see so many cracked Aluminium frames? Because of exactly what Jose said (sort of) - as frames _aren't_ necessarily designed for durability!! I have seen quite a few broken frames in my time...., cracked seat tubes, down tubes, stays... still waiting for a fork to fail! Look around at all the expensive frames that only have a one-year warranty - it's engineering for other things, lightness and the marketing value mainly I'd say. And apologies to Jose, I did get the fatigue limit arse-about, now I remember why I didn't do mech eng It's Al and Magnesium I was thinking of (anyone own a Merida Mag? Cheers Gemma |
#8
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Titanium Frames
The issue of fatigue is an interesting one. I think all materials fo
bike frame manufacture could crack under fatigue type loading But let's examine the loading required to initiate fatigue. First of al materials have elastic and plastic deformation zones The elastic zone is where the material can be loaded (to say 10kN) the unloaded, without a change a change in any dimension If you go past the elastic limit of the material it will deform and i will not return to it's original dimensions or shape. This is a goo property of say Al & Fe, because we can sometimes detect parts ar fatiguing before they break The other component that can dramatically assist fatigue is a stres concentrator. If you a nick or a scratch in the material at the righ place that fatigue wants occur, it will hasten the process 10 fold powin - |
#9
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Titanium Frames
Marty Wallace:
"Jose Rizal" wrote in message Since there isn't much of a variance in most frame designs, the triangle front and rear being the most common, it's not a complex thing to do to design frame tubes of sufficient gauge using different metals to allow for durability. So why do we see so many cracked Aluminium frames? Several things: poor welding techniques (cheap), inadequate post-welding heat treatment (cheap), undersized frame tube thickness (for that stupid-light feel). I also believe (but haven't got empirical evidence of) that Al alloys like the 7000 series are more prone to stress-corrosion fractures once their usually anodized surfaces are breached by scratches and the like. You can glean a hint of this when manufacturers like Race Face warn on stress corrosion and taking off anodization on their cranks, and looking at the properties of the higher series aluminium alloys. HOWEVER, how much more likely stress corrosion is to happen in these alloys once the anodizing is breached is anybody's guess, or if it is really much of a concern at all. |
#10
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Titanium Frames
powinc:
The issue of fatigue is an interesting one. I think all materials for bike frame manufacture could crack under fatigue type loading. But let's examine the loading required to initiate fatigue. First of all materials have elastic and plastic deformation zones. The elastic zone is where the material can be loaded (to say 10kN) then unloaded, without a change a change in any dimension. If you go past the elastic limit of the material it will deform and it will not return to it's original dimensions or shape. This is a good property of say Al & Fe, because we can sometimes detect parts are fatiguing before they break! What you mention has to do with tensile strength and modulus of elasticity, and while it has some bearing on fatigue, it's a different mechanism. Al can be cyclic loaded within the elastic zone and yet its fatigue life is still shortened because it does not have a fatigue limit. You won't see any permanent deformations and yet it will still fail after a certain number of loads. Steel and Ti can also be cyclic loaded within their elastic zones but if their fatigue limits are reached, they will fail eventually. |
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