Anodizing effect on fatigue life of aluminum alloy

Interesting article on a fatigue failure of an experimental helicopter
component"

"Anodizing and Fatigue Life", Experimental Helo / May 2007
http://www.experimentalhelo.com/Anodizing&Fatigue.pdf

The article references a paper from 2000:

"Characteristics of Fatigue Strength on Anodized 2014-T6 Aluminum Alloy."
http://sciencelinks.jp/j-east/articl...01A0137211.php

"Abstract;In order to investigate the effect of anodized film on fatigue
strength of aluminum alloy, A 2014-T 6, repeated tensile fatigue test
was conducted in laboratory air under the stress ratio, R, of 0.01 using
smooth specimen with anodized film thickness of 3.MU.m. Fatigue strength
of anodized specimen tested under R=0.01 decreased by 18-20% as compared
with that of the untreated one ... The anodized film is fractured at an
early stage of repeated tensile fatigue process, because it is too
brittle to accommodate the substrate metal. Many cracks are induced to
initiate at the substrate by flaws of the anodized film. It was pointed
out through the study that the fatigue strength of anodized aluminum
alloy is controlled by the crack initiation behavior in the substrate
induced by the rupture of the anodized film, which is related to the
deformation of substrate metal during fatigue process."

The article also references a book:

"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.

Peter Cole wrote:
Interesting article on a fatigue failure of an experimental helicopter
component"

"Anodizing and Fatigue Life", Experimental Helo / May 2007
http://www.experimentalhelo.com/Anodizing&Fatigue.pdf

The article references a paper from 2000:

"Characteristics of Fatigue Strength on Anodized 2014-T6 Aluminum Alloy."
http://sciencelinks.jp/j-east/articl...01A0137211.php

"Abstract;In order to investigate the effect of anodized film on fatigue
strength of aluminum alloy, A 2014-T 6, repeated tensile fatigue test
was conducted in laboratory air under the stress ratio, R, of 0.01 using
smooth specimen with anodized film thickness of 3.MU.m. Fatigue strength
of anodized specimen tested under R=0.01 decreased by 18-20% as compared
with that of the untreated one ... The anodized film is fractured at an
early stage of repeated tensile fatigue process, because it is too
brittle to accommodate the substrate metal. Many cracks are induced to
initiate at the substrate by flaws of the anodized film. It was pointed
out through the study that the fatigue strength of anodized aluminum
alloy is controlled by the crack initiation behavior in the substrate
induced by the rupture of the anodized film, which is related to the
deformation of substrate metal during fatigue process."

The article also references a book:

"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.


slow day peter? feel the need to do a bit of trolling? and if i told
you that hydrogen embrittlement exists, would you go ahead and conclude
that rims crack because of it? or would you bother to observe the
failure conditions first?

rim cracking has complete correlation with extrusion anisotropy, and
merely coincidental correlation with anodizing cracking. if a rim crack
orientation doesn't follow an anodizing crack orientation, and it
frequently doesn't, then to conclude that coincidence is cause is at
best sloppy and/or ignorant, at worst, an attempt to fudge the facts to
fit an underinformed preconception. simple observation shows the truth.
shame that seems to be so low down the list of priorities around here.

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.

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.

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.

it doesn't get much simpler peter cole. the human folly of ego and
attempted face saving [including trolling] will be the death of this
species - because observation of scientific fact sure doesn't seem to be
a priority.

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.

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.

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.

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?

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 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.

On Apr 23, 4:06 pm, 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.

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. Until then you just have articles written by "experts" who can
build helicopters, but not use spell check.

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.

--
Michael Press