Re: question of principle

In article <Wv-dnalEhc_eR9bbnZ2dnUVZ_rSjnZ2d@xxxxxxxxxxxxx>,
jim beam <spamvortex@xxxxxxxxxxxxxxx> wrote:

G.T. wrote:
jim beam wrote:
G.T. wrote:
jim beam wrote:
ok, let's see who's awake.

imagine i have a strip of extruded 6106 aluminum bar 1" wide 1/4"
thick and 12" long. it's unanodized and effectively free of surface
defects.

then, imagine i machine a sharp 1/16" wide "v" notch in the middle
of the bar to a depth of 50% thickness. finally, i load the bar in
4-point loading with the two outer load points 1/4" from the ends
and the two middle load points centered and 2" apart. the notch is
on the tensile side with respect to load.

now, at what stress will the bar yield? is it:

a. ~100% of un-notched strength?
b. <50% of un-notched strength?
c. er, don't know?

Easy. None of the above.

Greg

nope, it's definitely one of the above. c'mon, i've kept it pretty
simple - it's just a question about the influence of notching [and by
extension, surface cracking] on failure.

I'm going with the obvious but I'm sure you're going to say (a).

Greg

well, the answer is c. it would be a. if the notch was longitudinal, b.
if transverse, but since the orientation of the notch is not stated, the
correct answer is c.

the point is, all this b.s. about anodizing cracking completely fails to
address this fundamental principle. if the cracks [or notches] are not
aligned such that stress is magnified at their root, they have little or
no effect. since we see cracking rigidly adhere to the extrusion axis,
/regardless/ of anodizing crack orientation, it's obvious, to anyone
that understands this basic principle at any rate, that it must be a
material issue, not anodizing.

Nipples stress the material around the spoke hole both tangential
to the spoke hole and radially to the spoke hole. IMNSHO HTH HAND

--
Michael Press
.

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