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

"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

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.

"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

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.

"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

"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

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


-

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.

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.