P
Peter Cole
Guest
[email protected] wrote:
> On Apr 23, 4:06 pm, Peter Cole <[email protected]> wrote:
>> The sources I cited are pretty unambiguous. It's causal.
>
> Yes, it's causal in the sources you cite. Cite a source that tests
> extrusions instead of castings, and you'll have something relevant to
> the discussion. CT some cracked rims to prove that they don't have
> void defects which could initiate cracking along the line of
> anisotropy, and you have reason to believe that anodizing breaks bike
> rims.
If your contention is that extruded aluminum parts contain typically
more void defects than castings, please cite some sources.
There are several reasons (besides anisotropy) that favor
circumferential cracking at spoke holes. The 2 most obvious are that the
rim is under substantial circumferential compression and that the
extrusion is usually thinnest at the center. For some rims, cross
section hoop forces from tire pressure also add a tension component
which favors circumferential crack/fatigue. Finally, hollow section
extrusions, like those of double wall rims, will have circumferential
weld zones, formed after the metal passes the mandrel.
The fact that other factors contribute to cracking/fatigue doesn't alter
the fact that anodizing weakens rims in fatigue. Aluminum spends perhaps
90% of its fatigue life in crack initiation mode, anodizing shortens
that phase. The effects of flaws are cumulative. It may be that rim
extrusions are so crappy that anodize treatments don't affect fatigue
life, but I doubt it, real world experience shows otherwise. Again, if
you have any source that shows otherwise please cite it.
> On Apr 23, 4:06 pm, Peter Cole <[email protected]> wrote:
>> The sources I cited are pretty unambiguous. It's causal.
>
> Yes, it's causal in the sources you cite. Cite a source that tests
> extrusions instead of castings, and you'll have something relevant to
> the discussion. CT some cracked rims to prove that they don't have
> void defects which could initiate cracking along the line of
> anisotropy, and you have reason to believe that anodizing breaks bike
> rims.
If your contention is that extruded aluminum parts contain typically
more void defects than castings, please cite some sources.
There are several reasons (besides anisotropy) that favor
circumferential cracking at spoke holes. The 2 most obvious are that the
rim is under substantial circumferential compression and that the
extrusion is usually thinnest at the center. For some rims, cross
section hoop forces from tire pressure also add a tension component
which favors circumferential crack/fatigue. Finally, hollow section
extrusions, like those of double wall rims, will have circumferential
weld zones, formed after the metal passes the mandrel.
The fact that other factors contribute to cracking/fatigue doesn't alter
the fact that anodizing weakens rims in fatigue. Aluminum spends perhaps
90% of its fatigue life in crack initiation mode, anodizing shortens
that phase. The effects of flaws are cumulative. It may be that rim
extrusions are so crappy that anodize treatments don't affect fatigue
life, but I doubt it, real world experience shows otherwise. Again, if
you have any source that shows otherwise please cite it.