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ASTM Selected Technical Papers
Environmentally Assisted Cracking: Science and Engineering
By
WB Lisagor
WB Lisagor
1
Head
, Metallic Materials Branch
NASA Langley Research Center
,
Hampton, VA
;
symposium chairman and editor
.
Search for other works by this author on:
TW Crooker
TW Crooker
2
National Aeronautics and Space Administration
,
Washington, DC
;
symposium chairman and editor
.
Search for other works by this author on:
BN Leis
BN Leis
3
Battelle Columbus Labs.
,
Columbus, OH
;
symposium chairman and editor
.
Search for other works by this author on:
ISBN-10:
0-8031-1276-9
ISBN:
978-0-8031-1276-6
No. of Pages:
551
Publisher:
ASTM International
Publication date:
1990

The results of an interlaboratory program conducted to evaluate variability in measurements of the threshold stress intensity factor (KISCC) and stress corrosion crack growth rates (da/dt) for aluminum alloys are summarized. Precracked specimens machined from 7075-T6 aluminum alloy plate are exposed to a 3.5% NaCl (sodium chloride) solution by eleven participating laboratories. The effects of specimen configuration, starting stress intensity level, precracking procedure, and surface grooving are statistically evaluated, and sources of both interlaboratory and intralaboratory variability are identified. Data analysis indicates that variations in crack growth rates were related to difficulties associated with visual crack length measurements, especially on face-grooved specimens, and that more effective measurement techniques would more accurately characterize stress corrosion crack growth. In addition, test duration should be determined systematically, accounting for crack length measurement resolution, time for crack arrest, and experimental interferences. Variations in KISCC were related to the procedure used to measure the final bolt load. Final load measured by specimen reloading did not correlate well with that determined by compliance and appeared sensitive to factors such as corrosion product wedging and metallurgical features on the stress corrosion crack faces. Miniature instrumented load cells were used in several tests in a parallel program to monitor load relaxation during specimen exposure and to provide an indication of final load prior to specimen reloading. The load cell output during specimen exposure indicated that perturbations observed in crack length versus time curves may be related to real changes in load and should not be considered due only to crack length measurement difficulties. Compliance solutions were experimentally determined for both modified compact and double-beam wedge loaded specimens with different face-groove geometries and the results compared with published solutions. Both crack-mouth and load-line crack opening displacements were measured, and the data were used to define a relationship to correlate deflections at these measurement locations. The resulting relationship is compared with a previous solution determined by boundary collocation. No significant statistical variation in KISCC was observed with regard to specimen type, surface grooves, or specimen orientation, indicating both specimen configurations are suitable for stress corrosion testing and differences in KISCC determination were attributed to test procedures. Results of both the interlaboratory program and the additional studies should provide important contributions toward the development of a standard test method for stress corrosion testing and analysis using precracked specimens.

1.
Stress-Corrosion Cracking in High Strength Steels and in Titanium and Aluminum Alloys
,
Brown
B. F.
, Ed.,
Naval Research Laboratory
,
Washington, DC
,
1972
.
2.
Speidel
,
M. O.
and
Hyatt
,
M. V.
,
Advances in Corrosion Science and Technology
, Vol.
2
,
1972
, pp. 115–335.
3.
Sprowls
,
D. O.
and
Brown
,
R. H.
,
Metal Progress
,
05
1962
, p. 77.
4.
Hyatt
,
M. V.
, “
Effects of Specimen Geometry and Grain Structure on SCC Behavior of Aluminum Alloys
,” Boeing Commercial Airplane Group Document D6-24470,
11
1969
.
5.
Annual Book of ASTM Standards
, Section 3, Vol.
03.02
Wear and Erosion; Metal Corrosion,
American Society for Testing and Materials
,
Philadelphia
,
1988
.
6.
Hyatt
,
M. V.
, “
Use of Precracked Specimens in Stress Corrosion Testing of High Strength Aluminum Alloys
,” Boeing Commercial Airplane Group Document D6-24466,
11
1969
.
7.
Hyatt
,
M V.
, “
Use of Precracked Specimens in Selecting Heat Treatments for Stress Corrosion Resistance in High Strength Aluminum Alloys
,” Boeing Commercial Airplane Group Document D6-24467,
11
1969
.
8.
Brown
,
B. F.
,
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, Vol.
2
,
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, pp. 171–182.
9.
Sprowls
,
D. O.
,
Shumaker
,
M. B.
,
Walsh
,
J. D.
, and
Coursen
,
J. W.
, “
Evaluation of Stress Corrosion Cracking Susceptibility Using Fracture Mechanics Techniques
,” NASA CR-124469,
National Aeronautics and Space Administration
,
31
05
1973
.
10.
Dorward
,
R. C.
and
Hasse
,
K. R.
,
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, Vol.
34
, No.
11
, pp. 395–396.
11.
Wei
,
R. P.
and
Novak
,
S. R.
,
Journal of Testing and Evaluation
 0090-3973, Vol.
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, No.
1
,
01
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, pp. 38–75.
12.
Fichter
,
W. B.
,
International Journal of Fracture
, Vol.
22
,
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, pp. 133–143.
13.
Lisagor
,
W. B.
in
Environment-Sensitive Fracture: Evaluation and Comparison of Test Methods
, ASTM STP 821,
Dean
,
Pugh
, and
Ugiansky
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1984
, pp. 80–97.
14.
LeFort
,
P.
and
Mowbray
,
D. F.
,
Journal of Testing and Evaluation
 0090-3973, Vol.
6
, No.
2
,
03
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, pp. 114–119.
15.
Novak
,
S. R.
and
Rolfe
,
S. T.
,
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, Vol.
4
, No.
3
,
1969
, pp. 701–728.
16.
Dorward
,
R. C.
,
Hasse
,
K. R.
, and
Helfrich
,
W. J.
,
Journal of Testing and Evaluation
 0090-3973, Vol.
6
, No.
4
,
1978
, pp. 268–275.
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