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.
The real problem in dealing with things like fatigue is not so much the fundamental characteristics of the materials. It's what happens to those characteristics when you do traumatic things to them: bending, forming, welding, brazing, and so on. These change the materials' characteristics locally (i.e., at the site of welding or whatever) and create a possibility of cracking. I'm not going to be more specific, since this is getting quite a bit outside of my area of knowledge.
This is a good reason to stay away from the highly hyped, new technologies at the outset. Give them time to mature.
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
> --------------------------
> Sent from my BlackBerry Wireless Handheld
>
>
> -----Original Message-----
> From: classicrendezvous-bounces@bikelist.org
> <classicrendezvous-bounces@bikelist.org>
> To: Mark Stonich <mark@bikesmithdesign.com>;
> classicrendezvous@bikelist.org <classicrendezvous@bikelist.org>
> Sent: Wed Aug 03 20:39:49 2005
> Subject: Re: [CR]Soft frames? Hard Frames?
>
> Well that makes sense since I'm aware that all types of steel tubes have
> the same stiffness.
>
> I wonder if the argument I heard was one of those at the theoretical
> limit cases where there is a theoretical but for all practical purposes
> non-existent effect.
>
> Similar to a steel frame flexing and absorbing energy. From what I
> understand, upon flexing some energy is lost to heat, but for steel,
> aluminum, and titanium the amount is so insignificant that it just
> doesn't matter.
> -------------- Original message --------------
>
>
>>At 8/3/2005 10:20 PM +0000, you wrote:
>>
>>>If anything, as engineering friends have explained to me, frames
>>>work harden and in theory that would make them stiffer and at the
>>>same time closer to a failure.
>>
>>A couple of hundred years of materials testing has shown that steel
>>has the same modulous of elasticity (Young's Modulous) no matter how
>>hard it is. Work hardening, heat treating or annealing have no
>>effect on stiffness.
>
> Now for the arguments that frames which are well designed will not
> fatigue for a substantial time, I think that lack of overheating must
> also be factored in. My guess is that reduces the elastic range of the
> tube and in many cases brings the fatigue life into the range for which
> many riders may experience a failure.
> Mike "not an engineer" Kone in Boulder CO
>
>>
>>Mark Stonich;
>>Minneapolis Minnesota
>>http://mnhpva.org
>>http://bikesmithdesign.com
>>
>>
>>
>>
>>
>>
>>
>>_______________________________________________
>
>
> _______________________________________________
> _______________________________________________
>
> .