Anodizing effect on fatigue life of aluminum alloy

In article
,
wrote:

On Apr 23, 8:12 am, Peter Cole wrote:
Peter Cole wrote:
"Fatigue Design of Aluminum Components & Structures", Sharp, Nordmark
and Menzemer 1996

You can use the Amazon "Search inside" feature to see the graph on page
100:
http://www.amazon.com/gp/reader/0070...ref=sib_dp_pt#

The graph shows very large reductions in fatigue strength for 7075
forgings after cleaning with caustic (C22) or acid (C31) baths. It also
shows drastic reductions in fatigue strength for uncleaned, anodized
samples.

From the above graph, thick (50 micrometer) anodizing, reduced the
fatigue life by a factor of about 60 (@35ksi), while even thin (2.5
micrometer) anodizing reduced it by a factor of 6.

I should point out that these sources agree with what Jobst has
explained all along: thick anodizing has a disastrous effect on fatigue
life, and even thin cosmetic anodizing can have significant
consequences. The mechanism, as described in these sources, agrees with
his causal explanation. This is science, there can be no controversy,
except via willful ignorance.

It's only causal if you believe that there are no other factors
affecting fatigue life. You could substitute anodizing for mirror
polishing, and it's not going to improve fatigue life if your
extrusion process left internal voids. Without direct observation of
cracks appearing in the anodized layer and propagating into the metal,
it's not causality. It's correlation, and not even real correlation,
as nobody has actually bothered to pin down incidence rates.

The correlation is in the material Peter cited and quoted.
Anodized structural members are substantially more fatigue prone.

--
Michael Press

Peter Cole wrote:
Peter Cole wrote:

"Fatigue Design of Aluminum Components & Structures", Sharp, Nordmark
and Menzemer 1996

You can use the Amazon "Search inside" feature to see the graph on
page 100:
http://www.amazon.com/gp/reader/0070...ref=sib_dp_pt#

The graph shows very large reductions in fatigue strength for 7075
forgings after cleaning with caustic (C22) or acid (C31) baths. It
also shows drastic reductions in fatigue strength for uncleaned,
anodized samples.

From the above graph, thick (50 micrometer) anodizing, reduced the
fatigue life by a factor of about 60 (@35ksi), while even thin (2.5
micrometer) anodizing reduced it by a factor of 6.

I should point out that these sources agree with what Jobst has
explained all along: thick anodizing has a disastrous effect on fatigue
life, and even thin cosmetic anodizing can have significant
consequences. The mechanism, as described in these sources, agrees with
his causal explanation. This is science, there can be no controversy,
except via willful ignorance.

I disagree with the last sentence. Besides willful ignorance, the cause
for controversy could be overindulgence in Kentucky Bourbon whiskey.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

agcou wrote:
On Wed, 23 Apr 2008 05:57:27 -0700, jim beam wrote:


the only willful ignorance being demonstrated here is from those trying
to make the facts fit preconception!!! yes, anodizing /can/ have a
serious affect on fatigue. BUT, if you or he had ever bothered to
observe the facts, cracking is entirely independent of anodizing crack
orientation. it is therefore NOT the cause in this case.


Another common misconception is that the substrate cracks cause anodization
layer cracks. This is clearly wrong for the same reason. The cracks
aren't oriented, therefore they are not related.

absolutely.



I think Peter realizes the obvious fact that bicycle rims are a special
case wherein annodizing does not have an appreciable effect on fatigue. As
you say, he is merely trolling. You should not feed him.

maybe, but on consideration, given that jobst has poisoned the well with
significant misinformation, and that peter cole insists on trying to
perpetuate it, i take the view that the true facts need to be aired,
regardless.

Michael Press wrote:
In article
,
wrote:

On Apr 23, 8:12 am, Peter Cole wrote:
Peter Cole wrote:
"Fatigue Design of Aluminum Components & Structures", Sharp, Nordmark
and Menzemer 1996
You can use the Amazon "Search inside" feature to see the graph on page
100:
http://www.amazon.com/gp/reader/0070...ref=sib_dp_pt#
The graph shows very large reductions in fatigue strength for 7075
forgings after cleaning with caustic (C22) or acid (C31) baths. It also
shows drastic reductions in fatigue strength for uncleaned, anodized
samples.
From the above graph, thick (50 micrometer) anodizing, reduced the
fatigue life by a factor of about 60 (@35ksi), while even thin (2.5
micrometer) anodizing reduced it by a factor of 6.
I should point out that these sources agree with what Jobst has
explained all along: thick anodizing has a disastrous effect on fatigue
life, and even thin cosmetic anodizing can have significant
consequences. The mechanism, as described in these sources, agrees with
his causal explanation. This is science, there can be no controversy,
except via willful ignorance.
It's only causal if you believe that there are no other factors
affecting fatigue life. You could substitute anodizing for mirror
polishing, and it's not going to improve fatigue life if your
extrusion process left internal voids. Without direct observation of
cracks appearing in the anodized layer and propagating into the metal,
it's not causality. It's correlation, and not even real correlation,
as nobody has actually bothered to pin down incidence rates.

The correlation is in the material Peter cited and quoted.
Anodized structural members are substantially more fatigue prone.


"orientation". look up how it affects stress concentration.

Peter Cole wrote:
wrote:
On Apr 23, 8:12 am, Peter Cole wrote:
Peter Cole wrote:
"Fatigue Design of Aluminum Components & Structures", Sharp, Nordmark
and Menzemer 1996
You can use the Amazon "Search inside" feature to see the graph on page
100:
http://www.amazon.com/gp/reader/0070...ref=sib_dp_pt#
The graph shows very large reductions in fatigue strength for 7075
forgings after cleaning with caustic (C22) or acid (C31) baths. It also
shows drastic reductions in fatigue strength for uncleaned, anodized
samples.
From the above graph, thick (50 micrometer) anodizing, reduced the
fatigue life by a factor of about 60 (@35ksi), while even thin (2.5
micrometer) anodizing reduced it by a factor of 6.
I should point out that these sources agree with what Jobst has
explained all along: thick anodizing has a disastrous effect on fatigue
life, and even thin cosmetic anodizing can have significant
consequences. The mechanism, as described in these sources, agrees with
his causal explanation. This is science, there can be no controversy,
except via willful ignorance.

It's only causal if you believe that there are no other factors
affecting fatigue life. You could substitute anodizing for mirror
polishing, and it's not going to improve fatigue life if your
extrusion process left internal voids. Without direct observation of
cracks appearing in the anodized layer and propagating into the metal,
it's not causality. It's correlation, and not even real correlation,
as nobody has actually bothered to pin down incidence rates.

The sources I cited are pretty unambiguous. It's causal.

your cite is completely out of context. those materials are not highly
anisotropic like a bike rim, and they have cracking perpendicular to
load, not axial like with bike rims.

bottom line, the principle of anodizing induced fatigue is correct, but
it's NOT OBSERVED to be the cause in our case - and extrusion flaws are.

Peter Cole wrote:
agcou wrote:
On Wed, 23 Apr 2008 05:57:27 -0700, jim beam wrote:


the only willful ignorance being demonstrated here is from those
trying to make the facts fit preconception!!! yes, anodizing /can/
have a serious affect on fatigue. BUT, if you or he had ever
bothered to observe the facts, cracking is entirely independent of
anodizing crack orientation. it is therefore NOT the cause in this
case.


Another common misconception is that the substrate cracks cause
anodization layer cracks. This is clearly wrong for the same reason.
The cracks aren't oriented, therefore they are not related.

I don't think that's a common misconception. This is the first time I've
heard it.

that's not true - i've discussed this principle here many times. and
argued it with you iirc.



I think Peter realizes the obvious fact that bicycle rims are a
special case wherein annodizing does not have an appreciable effect on
fatigue.

How could that be?

orientation!!! if not positioned to resolve stress concentration, it,
er, doesn't resolve stress concentration and therefore doesn't cause
fatigue!!!

Michael Press wrote:
In article ,
agcou wrote:

On Wed, 23 Apr 2008 05:57:27 -0700, jim beam wrote:


the only willful ignorance being demonstrated here is from those trying
to make the facts fit preconception!!! yes, anodizing /can/ have a
serious affect on fatigue. BUT, if you or he had ever bothered to
observe the facts, cracking is entirely independent of anodizing crack
orientation. it is therefore NOT the cause in this case.

Another common misconception is that the substrate cracks cause anodization
layer cracks.

Not so as I have heard. The crack _initiation_ is as
when you stress the skin under a scab. The scab is
rigid, the underlying tissue is elastic, the scab
fractures providing a stress riser in the tissue
that propagates into perfused tissue, rupturing
capillaries resulting in visible bleeding.

This is clearly wrong for the same reason. The cracks
aren't oriented, therefore they are not related.

I think Peter realizes the obvious fact that bicycle rims are a special
case wherein annodizing does not have an appreciable effect on fatigue. As
you say, he is merely trolling. You should not feed him.

You assert a special case but provide no description,
nor substantiation.



word of the day is "orientation". a scab [sic] that cracks does so
perpendicular to applied stress. from then on, it's a stress
concentration thing. if it were cracked axial to the applied stress,
the wound would not open and thus no more damage would occur. and this
is exactly the case with cracked anodizing - if the cracks are not
oriented to resolve stress concentration, they're not going to initiate
fatigue. pretty basic.

In article ,
Tom Sherman wrote:

Peter Cole wrote:
Peter Cole wrote:

I should point out that these sources agree with what Jobst has
explained all along: thick anodizing has a disastrous effect on
fatigue life, and even thin cosmetic anodizing can have significant
consequences. The mechanism, as described in these sources, agrees
with his causal explanation. This is science, there can be no
controversy, except via willful ignorance.

Other sources available on the Interwebs, which also conform what Jobst
has said on the topic, have been posted multiple times (for example from
www.anodizing.org) to no avail. The facts are unambiguous to everyone
with a reasonable ounce or two of wit.

I disagree with the last sentence. Besides willful ignorance, the
cause for controversy could be overindulgence in Kentucky Bourbon
whiskey.

Or just plain ****iness.

Tim McNamara wrote:
In article ,
Tom Sherman wrote:

Peter Cole wrote:
Peter Cole wrote:

I should point out that these sources agree with what Jobst has
explained all along: thick anodizing has a disastrous effect on
fatigue life, and even thin cosmetic anodizing can have significant
consequences. The mechanism, as described in these sources, agrees
with his causal explanation. This is science, there can be no
controversy, except via willful ignorance.

Other sources available on the Interwebs, which also conform what Jobst
has said on the topic, have been posted multiple times (for example from
www.anodizing.org) to no avail. The facts are unambiguous to everyone
with a reasonable ounce or two of wit.

seems timmy the retard can't be bothered to read the word of the day
either. "orientation" timmy. it's the key to many things. not least
of which is "anisotropy", a word used when discussing rim extrusions.



I disagree with the last sentence. Besides willful ignorance, the
cause for controversy could be overindulgence in Kentucky Bourbon
whiskey.

Or just plain ****iness.

which isn't clinical retardation.

On Apr 23, 7:35 pm, Michael Press wrote:
In article
,



wrote:
On Apr 23, 8:12 am, Peter Cole wrote:
Peter Cole wrote:
"Fatigue Design of Aluminum Components & Structures", Sharp, Nordmark
and Menzemer 1996

You can use the Amazon "Search inside" feature to see the graph on page
100:
http://www.amazon.com/gp/reader/0070...ref=sib_dp_pt#

The graph shows very large reductions in fatigue strength for 7075
forgings after cleaning with caustic (C22) or acid (C31) baths. It also
shows drastic reductions in fatigue strength for uncleaned, anodized
samples.

From the above graph, thick (50 micrometer) anodizing, reduced the
fatigue life by a factor of about 60 (@35ksi), while even thin (2.5
micrometer) anodizing reduced it by a factor of 6.

I should point out that these sources agree with what Jobst has
explained all along: thick anodizing has a disastrous effect on fatigue
life, and even thin cosmetic anodizing can have significant
consequences. The mechanism, as described in these sources, agrees with
his causal explanation. This is science, there can be no controversy,
except via willful ignorance.

It's only causal if you believe that there are no other factors
affecting fatigue life. You could substitute anodizing for mirror
polishing, and it's not going to improve fatigue life if your
extrusion process left internal voids. Without direct observation of
cracks appearing in the anodized layer and propagating into the metal,
it's not causality. It's correlation, and not even real correlation,
as nobody has actually bothered to pin down incidence rates.

The correlation is in the material Peter cited and quoted.
Anodized structural members are substantially more fatigue prone.

--
Michael Press

And apples are substantially redder than oranges. Again, it's only
causal if anodizing is the only factor affecting fatigue life. This
is not the case, as bicycle rims have high grain anisotropy and the
potential for extrusion induced flaws, which also make members more
fatigue prone. These factors are competing with the anodizing to
break your rim, and there's plenty of evidence that much of the time
they're winning.