Titanium Frames

Around Australia Recumbent Style

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

Marty Wallace

"Around Australia Recumbent Style" <andrewandjoanne@hotmail.com> wrote in
message news:zaKkc.6750$TT.506@news-server.bigpond.net.au...
> 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

Jose Rizal

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.

Gemma Kernich

"Jose Rizal" <_@_._> wrote in message
news:mkQkc.1061$a47.688@newsread3.news.atl.earthlink.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

Jose Rizal

Gemma Kernich:

>
> "Jose Rizal" <_@_._> wrote in message
> news:mkQkc.1061$a47.688@newsread3.news.atl.earthlink.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.

Marty Wallace

"Jose Rizal" <_@_._> wrote in message
news:3U%kc.2364$8S1.440@newsread2.news.atl.earthlink.net...
> Gemma Kernich:
>
> >
> > "Jose Rizal" <_@_._> wrote in message
> > news:mkQkc.1061$a47.688@newsread3.news.atl.earthlink.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

Gemma Kernich

"Marty Wallace" <mart@geo.net.au> wrote in message
news:4094bef3$0$27645$61ce578d@news.syd.swiftdsl.com.au...
>
> "Jose Rizal" <_@_._> wrote in message
> news:3U%kc.2364$8S1.440@newsread2.news.atl.earthlink.net...
> > Gemma Kernich:
> >
> > >
> > > "Jose Rizal" <_@_._> wrote in message
> > > news:mkQkc.1061$a47.688@newsread3.news.atl.earthlink.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

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!

The other component that can dramatically assist fatigue is a stress
concentrator. If you a nick or a scratch in the material at the right
place that fatigue wants occur, it will hasten the process 10 fold.

powinc



--

Jose Rizal

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.

Jose Rizal

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.

Jose Rizal

Gemma Kernich:
> now I remember why I didn't do mech eng

It's all good though!

Gemma Kernich

"Jose Rizal" <_@_._> wrote in message
news:0H9lc.1821$a47.1650@newsread3.news.atl.earthlink.net...
> Gemma Kernich:
> > now I remember why I didn't do mech eng
>
> It's all good though!
>
I went down the civil eng path. I also remember the "Engineering Materials"
subjects were always after lunch on a cheap beer Wednesday or something like
that... *grin*
Gemma

Richard Sherratt

On Mon, 3 May 2004 10:57:47 +0930, "Gemma Kernich" <gemm@holon.net>
wrote:

>
>"Jose Rizal" <_@_._> wrote in message
>news:0H9lc.1821$a47.1650@newsread3.news.atl.earthlink.net...
>> Gemma Kernich:
>> > now I remember why I didn't do mech eng
>>
>> It's all good though!
>>
>I went down the civil eng path. I also remember the "Engineering Materials"
>subjects were always after lunch on a cheap beer Wednesday or something like
>that... *grin*

Well I *did* do mech eng (and civil, electrical, etc.) and I can't
remember the details of most of this stuff. It was a long time ago and
I went straight into the software development after uni. But I'm
enjoying reading the posts, so thank you to the experts.

PS, There's an interesting article on carbon fibre by Raoul Luescher
in the Q & A section of May June 2004 Bicycling Australia. Raoul has
posted here in the past.

--
Regards.
Richard.

Around Australia Recumbent Style

Thank You everyone for your input, most of which went straight over my head
at the same altitude as the Space Shuttle, but I think I get the engineering
drift.

Nice bikes Marty. I think I might have to try those Chinese Ti frames after
all.

Regards and safe travels,

Andrew

"Around Australia Recumbent Style" <andrewandjoanne@hotmail.com> wrote in
message news:zaKkc.6750$TT.506@news-server.bigpond.net.au...
> 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
>
>