In article <
[email protected]>,
"Mike Jacoubowsky" <
[email protected]> wrote:
> >> bikes.
> >>
> >> Oh, darn. All those failing aluminum stems... ****. That's quite a
> >> few thousand dollars of inventory I'm going to have to dump. And
> >> the failed Belleri handlebars. ****. That's going to be many
> >> thousands of dollars more of inventory I can't trust.
> >
> > Like this tem owned by a friend, who discovered this condition the
> > day after a 104 mile ride we undertook on hilly road including
> > gravel and rough pavement?
> >
> > http://www2.bitstream.net/~timmcn/stemphotos/stem_right.png
> >
> > How would a CF stem have fared with cracking like this?
>
> It doesn't matter whether a carbon fiber stem would have survived
> with a crack like that; the relevant question is whether it would
> have developed that crack.
Nope. Stuff breaks. The world is not optimal. How does a material
deal with those facts? Does it fail catastrophically or gradually? The
photographs show a gradual failure.
> >> Oh, darn. All those steel frames that buckled under impact,
> >> causing the front wheel to make contact with the downtube and
> >> throwing the rider violently. ****. We can't use steel for frames
> >> anymore.
> >>
> >> Oh, darn. All those titanium frames that had sheared downtubes,
> >> due to cracks beginning at the downtube cable guides. ****.
> >>
> >> Oh, wait, nevermind. It wasn't the material that was the issue, it
> >> was how it was used. Incredibly dangerous failure modes, yet
> >> nobody was calling for manufacturers to stop using aluminum, steel
> >> or titanium for bike parts.
> >
> > As hyperbole goes, this doesn't work very well. The failure mode
> > for these materials is rarely catastrophic unlike CF and is thus
> > not "incredibly" dangerous.
>
> That's the part of this discussion I find so incredible. Catastrophic
> failure modes have been around for as long as manufacturing. Carbon
> fiber didn't invent them. Carbon fiber didn't cause them. Flawed
> designs & manufacturing did. Back in the day, we saw a lot of
> "catastrophic" failures. People have either forgotten about that, or
> else, because those failures were on "tried & true" technology,
> materials that had been around for some time, they were, for some
> reason, tolerated. Why?
Previous materials with widespread use have not had the catastrophic
failure issues prevalent in CF composites. When CF fails, it tends to
fail right now, boom. Other materials have not shown that tendency.
The exception has been failed welds, particularly in titanium and
aluminum. That is less about materials properties than about faulty
manufacturing processes.
Let's defined catastrophic failure: the component breaks into two or
more discrete pieces nearly instantaneously. This is typical of brittle
materials (glass, for example) and not typical of metallic materials
commonly used in bicycles
> There is obviously something appealing about taking on the latest
> technology and putting it down.
New materials have different properties that might be beneficial and
different properties that might be detrimental. We have seen the
"latest technology" repeatedly prove to be unsuitable for the
applications for which it was marketed. There is legitimate question
about the suitability of CF composites for use in bicycles. The issues
raised here are those mirrored in the materials literature and mirrored
in the published statements of manufacturers that use this material-
including Trek and Calfee.
> It becomes a fun game, apparently, to see someone post a picture of a
> failed frame on the Internet and, without ANY corroboration of the
> JRA (Just Riding Along) story, extrapolate wildly from it.
I have, along with others, tried very hard to avoid extrapolating about
that specific frame because we don't have enough information about the
crash or the condition of the frame before the crash.
> The smartest person I know in the "warranty" department (which I put
> in quotes because most of what he deals with isn't actually a
> "warranty"), when presented a failure that might be questionable,
> always ask one simple question. "What do you think *really*
> happened?" It gets you to thinking a bit outside the oral or written
> history actually presented. And sometimes you get a customer with a
> "JRA" and you ask him (almost always a "him" by the way) "What do you
> think really happened" and, hold down the fort, they will actually
> tell you. Bizarre yet true. They come in claiming it's a JRA, but you
> ask for details and yikes, it's something entirely different.
Yup. And since not JRA is normal use of bicycles, that raises
significant concerns about the toughness and damage resistance of the
materials used in critical components of bicycles. There are some that
can easily get you severely injured, disabled or killed if they fail
catastrophically.
> > The problem with steel frame in your example was the impact- a CF
> > frame would have shattered rather than bending. The problem with
> > the titanium frames didn't result in the downtube just snapping.
>
> You're making an assumption that is rarely correct. Modern carbon
> frames & forks will, I will claim, generally "survive" a head-on
> impact more readily than the steel frames of yesteryear. They will
> not survive as readily an impact from the side. These claims come
> from observations over many years, many product lines, many
> customers, many impacts.
Please define "survive."
> And the titanium frame that you didn't think resulted in a downtube
> snapping? Think again. I was there. Time between first hearing
> something and failure was about 3 miles. We obviously aborted the
> ride after hearing a strange noise and running it down (a very small
> tear on the downtube), and decided to ride back to where he'd parked
> his car, 6 relatively-flat miles away. After three miles the tube had
> torn through and I had to go get my car. The failure was definitely
> catastrophic, although since we were keeping an eye on it there was
> no injury, no crash. If we hadn't figured out what the noise was
> coming from, it could have been otherwise.
The rider had advanced warning and had a non-catastrophic failure.
Catastrophic does not mean that the tube broke. Catastrophic failure is
nearly instantaneous.
> If we want to get personal, I did the carbon bike into car gig
> myself. 16mph into the side of a Mustang some kid backed out of his
> driveway onto the road. My teeth fared much worse than my bike.
Unfortunately your carbon frame is not readily inspectable for damage.
I hope that is in in fact undamaged.
