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.
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.