Re: Anodized planes ?

Date:         27 Aug 99 03:08:16 
From:         drela@mit.edu (Mark Drela)
Organization: Massachvsetts Institvte of Technology
References:   1
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In article <airliners.1999.870@ohare.Chicago.COM>, JF Mezei <jfmezei.spamnot@videotron.ca> writes:
> Bicycles and airplanes use a lot of similar technologies. Both need to
> be strong and light.
>
> One example is bicycle wheel rims. Most are high tech aluminium (and
> some now carbon-fibre).
>
> For rims and other parts, anodisation is often used. It not only
> provides a very long lasting and clean finish, but, i am told, also
> strengthens the aluminium. (is that true ?).

No.   This is done purely for marketing.

The hard anodization on bike wheel rims actually weakens them.
The anodization layer is aluminum oxide which is extremely
hard and brittle, and cracks wherever the aluminum is highly
stressed, typically around the spoke holes.  The bottom of
each crack is a preferential site for corrosion and further
fatigue cracking of the underlying aluminum.   Compare the
Mavic MA-40 (anodized) and MA-2 (plain) rims, which are
otherwise identical.  The MA-40 is much more prone to
cracking and premature failure.  Oh yeah, the oxide
layer also degrades braking because it inhibits heat
conduction to the rim.

This is one instance where the typical consumer is willing
to pay more for a "feature" which looks high-tech,
but which actually degrades the performance of the product
in all aspects.

- Mark Drela
- MIT Aero & Astro