titanium frame cracked

The titanium frame on one of my bikes has cracked around the pedal crank. It
has the look of a typical fatigue crack. It runs around half the forward
down tube, and penetrates into the crank case itself. The welding is not
affected - seems it is stronger than the original metal. Luckily the
manufacturer is fixing it for free. But I am quite surprised as I thought
titanium frames were fairly fatigue proof.

Ric must be edykated coz e writed:

The titanium frame on one of my bikes has cracked around the pedal crank. It
has the look of a typical fatigue crack. It runs around half the forward
down tube, and penetrates into the crank case itself. The welding is not
affected - seems it is stronger than the original metal. Luckily the
manufacturer is fixing it for free. But I am quite surprised as I thought
titanium frames were fairly fatigue proof.

Stress fractures can be introduced during welding, that do not show up until
the frame is under load.

--
Ian

http://www.catrike.co.uk

Ric wrote:

The titanium frame on one of my bikes has cracked around the pedal crank. It
has the look of a typical fatigue crack. It runs around half the forward
down tube, and penetrates into the crank case itself. The welding is not
affected - seems it is stronger than the original metal. Luckily the
manufacturer is fixing it for free. But I am quite surprised as I thought
titanium frames were fairly fatigue proof.

Titanium has a fatigue limit but it's rather low so not very useful
(i.e. you'd need a 15lb frame to guarantee it wouldn't crack over an
infinite lifetime). Like steel though, crappy building can introduce
weaknesses that override any inherent qualities of the tubes themselves.
In a recent fatigue test I read, two of the frames that *didn't* break
- and there weren't many - were aluminium. Despite its total lack of a
safe fatigue limit, a well designed and built alu frame will outlast a
poorly designed and built steel frame. Quality control and design in
bikes is very poor, and there seems to be little accumulated knowledge
so manufacturers keep reinventing the wheel (almost literally).

"Zog The Undeniable" wrote in message
...
Ric wrote:

The titanium frame on one of my bikes has cracked around the pedal
crank. It
has the look of a typical fatigue crack.

What make/model out of interest?


--
Mark (MSA)

Bike shop assistant...
"We couldn't repair your brakes, so we made your horn louder"!

Here you go...this is good fun for debunking the myth that steel lasts
forever! http://www.sheldonbrown.com/rinard/E...tigue_test.htm

From: Zog The Undeniable

Here you go...this is good fun for debunking the myth that steel lasts
forever! http://www.sheldonbrown.com/rinard/E...tigue_test.htm


It's just amazing what you can find if you spend enough time digging through
all the info Sheldon has there. I'll still live with my lugged steel British
racing green Masi though. Goes well with the matching Triumph Sprint.
Bill C