Anodizing effect on fatigue life of aluminum alloy



P

Peter Cole

Guest
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/article/200107/000020010701A0137211.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/0070569703/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.
 
J

jim beam

Guest
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/article/200107/000020010701A0137211.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/0070569703/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.
 
P

Peter Cole

Guest
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/0070569703/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.
 
J

jim beam

Guest
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/0070569703/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 <[email protected]> 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/0070569703/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.
 
P

Peter Cole

Guest
[email protected] wrote:
> On Apr 23, 8:12 am, Peter Cole <[email protected]> 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/0070569703/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.
 
P

Peter Cole

Guest
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?
 
A

agcou

Guest
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 <[email protected]> wrote:
> [email protected] wrote:
> > On Apr 23, 8:12 am, Peter Cole <[email protected]> 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/0070569703/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.
 
M

Michael Press

Guest
In article <[email protected]>,
agcou <[email protected]> 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
 
M

Michael Press

Guest
In article
<[email protected]>,
[email protected] wrote:

> On Apr 23, 8:12 am, Peter Cole <[email protected]> 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/0070569703/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
 
T

Tom Sherman

Guest
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/0070569703/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
 
J

jim beam

Guest
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.
 
J

jim beam

Guest
Michael Press wrote:
> In article
> <[email protected]>,
> [email protected] wrote:
>
>> On Apr 23, 8:12 am, Peter Cole <[email protected]> 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/0070569703/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.
 
J

jim beam

Guest
Peter Cole wrote:
> [email protected] wrote:
>> On Apr 23, 8:12 am, Peter Cole <[email protected]> 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/0070569703/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.
 
J

jim beam

Guest
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!!!
 
J

jim beam

Guest
Michael Press wrote:
> In article <[email protected]>,
> agcou <[email protected]> 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.
 
T

Tim McNamara

Guest
In article <[email protected]>,
Tom Sherman <[email protected]> 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 pissiness.
 
J

jim beam

Guest
Tim McNamara wrote:
> In article <[email protected]>,
> Tom Sherman <[email protected]> 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 pissiness.


which isn't clinical retardation.
 
On Apr 23, 7:35 pm, Michael Press <[email protected]> wrote:
> In article
> <[email protected]>,
>
>
>
> [email protected] wrote:
> > On Apr 23, 8:12 am, Peter Cole <[email protected]> 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/0070569703/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.