This is an excellent point, that repetitive impulse loading stresses frames beyond the elastic range.
Ken Freeman Ann Arbor, MI
-----Original Message----- From: classicrendezvous-bounces@bikelist.org [mailto:classicrendezvous-bounces@bikelist.org] On Behalf Of Hughethornton@aol.com Sent: Friday, August 05, 2005 7:51 AM To: classicrendezvous@bikelist.org Subject: Re: [CR]Soft frames? Hard Frames?
The fact is that aluminum, when subjected to cyclical loads, will eventually fracture. The number of cycles it will withstand depends on the magnitude of the stress. A well designed aluminum frame will last a long time, but will eventually expire.
Steel on the other hand will last indefinitely provided the stresses are below a certain level. If the stresses exceed that level then, as with aluminum, the life is dependent on the magnitude of the stress.
Hence a steel frame can, in theory, be designed to last forever, crashes and corrosion permitting. In practice of course it will be ridden over the occasional pothole, momentarily sending the stresses way up -- enough of those and any realistic frame is going to break.
Hugh Thornton Cheshire, England
In a message dated 05/08/05 09:15:57 GMT Daylight Time, stevem@mail.nonlintec.com writes:
> The comment about early aluminum frames is a good one, and illustrates
> another point I might have made. The diamond bicycle frame has been
> optimized, if only by trial and error, over its 100+ years of existence.
> In the early 80s, welded aluminum frames were pretty new; in fact,
> widespread use of aluminum, generally, had existed only about 30 years.
> It's no great surprise that it took a while to get the design criteria
> and fabrication processes right, and that early frames might have had
> problems.
>
> Steve Maas
> Dublin, Ireland
>
>
> Mazzeo, Daniel wrote:
> > Guys,
> > I would chime in that I have seen aluminum frames as the exception to
> > the "does not reach the stress limits in frame use" rule. All of the
> > folks I knew who had '80s Trek Aluminum frames suffered fatigue failure
> > in the 20-25,000 mile range with the failure usually occurring at the
> > bottom bracket. This suggests to me that the frame design and use did
> > not keep the material from reaching its limits due to repeated flexure.
> > Steel, having a considerably higher modulus of elasticity does not
> > exhibit this problem when used with standard size tubing. I have also
> > noticed that the newer Cannondales use a larger diameter tubeset to
> > overcome this lower property of aluminum.
> > Has anybody checked Young's modulus for titanium recently??? Is there
> > any published data for carbon fiber???
> > Dan Mazzeo