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ASTM Selected Technical Papers
Small-Crack Test Methods
By
JM Larsen
JM Larsen
1
Wright Laboratory
,
Materials Directorate, Wright-Patterson Air Force Base, OH 45433
;
symposium cochairman and coeditor
.
Search for other works by this author on:
JE Allison
JE Allison
2
Ford Scientific Laboratory
, P.O. Box 2053
Dearborn, MI 48121
;
symposium cochairman and coeditor
.
Search for other works by this author on:
ISBN-10:
0-8031-1469-9
ISBN:
978-0-8031-1469-2
No. of Pages:
229
Publisher:
ASTM International
Publication date:
1992

A procedure for using photomicroscopy to record the growth of small fatigue cracks is presented. Using a specially designed fatigue specimen, the method is applicable to both naturally initiated cracks and cracks initiated from a small electro-discharge machined notch. Components of the experimental apparatus, which are low cost and readily available, include a standard metallurgical microscope, a 35-mm camera with bulk film capability, an electronic flash, and a microcomputer to control the fatigue machine and record test data. The photographic record provides a direct measurement of surface crack length and documents crack interactions with microstructural features; measurement precision less than 1 μm is possible. Following a test, the photographs of small cracks are projected on a computer digitizing tablet for convenient measurement of crack length. The crack length data are then combined with fatigue cycle-count data and reduced to the form of da/dN versus ΔK (or some other appropriate crack driving force). The capabilities of the photomicroscopic method are illustrated using typical data from specimens of the alloy Ti-6Al-2Sn-4Zr-6Mo, and an assessment is made of the practical advantages and limitations of the technique. Finally, some commonly unrecognized pitfalls that routinely arise in the analysis of small-crack data are discussed, and an alternative procedure for the analysis of such data is presented.

1.
Swain
,
M. H.
, “
Monitoring Small-Crack Growth by the Replication Method
,”
Small-Crack Test Methods
, STP 1149,
Larsen
J. M.
and
Allison
J. E.
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1992
, pp. 34–56 (in this publication).
2.
Davidson
,
D. L.
, “
The Experimental Mechanics of Microcracks
,”
Small-Crack Test Methods
, STP 1149,
Larsen
J. M.
and
Allison
J. E.
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1992
, pp. 83–91 (in this publication).
3.
Papirno
,
R.
and
Parker
,
B. S.
, “
An Automatic Flash Photomicroscopic System for Fatigue Crack Initiation Studies
,”
Cyclic Stress-Strain Behavior—Analysis, Experimentation, and Failure Prediction
, STP 519,
American Society for Testing and Materials
,
Philadelphia
,
1973
, pp. 98–108.
4.
Cox
,
J. M.
, “
Pitting and Fatigue Crack Initiation of 2124-T851 Aluminum in 3.5% NaCl Solution
,” M.S. thesis,
University of Missouri
, Columbia, MO,
1979
, pp. 61–70.
5.
Larsen
,
J. M.
, “
An Automated Photomicroscopic System for Monitoring the Growth of Small Fatigue Cracks
,”
Fracture Mechanics: Seventeenth Volume
, STP 905,
Underwood
J. H.
,
Chait
R.
,
Smith
C. W.
,
Wilhelm
D. P.
,
Andrews
W. A.
, and
Newman
,
J. C.
 Jr.
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1986
, pp. 226–238.
6.
Larsen
,
J. M.
, “
The Effects of Slip Character and Crack Closure on the Growth of Small Fatigue Cracks in Titanium-Aluminum Alloys
,” Ph.D. dissertation,
Carnegie Mellon University
, Pittsburgh, PA,
1987
, also published as Wright Research and Development Center Report WRDC-TR-89-4094 (AD A220714), Wright-Patterson AFB, OH, 1990.
7.
Leverant
,
G. R.
,
Langer
,
B. S.
,
Yuen
,
A.
, and
Hopkins
,
S. W.
, “
Surface Residual Stresses, Surface Topography and the Fatigue Behavior of Ti-6Al-4V
,”
Metallurgical Transactions
, Vol.
10A
,
1979
, pp. 251–257.
8.
Hack
,
J. E.
and
Leverant
,
G. R.
, “
Influence of Compressive Residual Stress on the Crack-Opening Behavior of Part-Through Fatigue Cracks
,”
Residual Stress Effects in Fatigue
, STP 776,
American Society for Testing and Materials
,
Philadelphia
,
1982
, pp. 204–223.
9.
Johnson
,
G. A.
, “
Generating Compressive Residual Stress by CBN Grinding
,”
Proceedings of ASM Conference on Residual Stress in Design, Process and Materials Selection
,
American Society for Metals
,
Metals Park, OH
,
1987
, pp. 157–166.
10.
Koster
,
W. P.
, “
Surface Integrity of Machined Structural Components
,”
U.S. Air Force Materials Laboratory Report
70-11,
Wright-Patterson Air Force Base
, OH,
1970
.
11.
Zlatin
,
N.
and
Field
,
M.
, “
Procedures and Precautions in Machining Titanium Alloys
,”
Source Book on Titanium Alloys
,
Donachie
,
M. J.
 Jr.
, Eds.,
American Society for Metals
,
Metals Park, OH
,
1982
, pp. 342–357.
12.
Private communication,
Lambda Research Inc.
, Cincinnati, OH,
1990
.
13.
Pardee
,
W. J.
,
Morris
,
W. L.
, and
Addison
,
R. C.
, “
Quantitative Nondestructive Evaluation (NDE) for Retirement-for-Cause
,” Annual Technical Report 1 on Defense Advanced Research Projects Agency Contract MDA903-80-C-0641,
Rockwell International Science Center
, Thousand Oaks, CA,
1981
, p. 9.
14.
Hicks
,
M. A.
and
Pickard
,
A. C.
, “
A Comparison of Theoretical and Experimental Methods of Calibrating Electrical Potential Drop Technique for Crack Length Determination
,”
International Journal of Fracture
, Vol.
20
,
1982
, pp. 91–101.
15.
Tokaji
,
K.
,
Ogawa
,
T.
, and
Aoki
,
T.
, “
Small Fatigue Crack Growth in a Low Carbon Steel Under Tension-Compression and Pulsating-Tension Loading
,”
Fatigue Fracture of Engineering Materials Structures
, Vol.
13
,
1990
, pp. 31–39.
16.
Suh
,
C. M.
,
Yuuki
,
R.
, and
Kitagawa
,
H.
, “
Fatigue Microcracks in a Low Carbon Steel
,”
Fatigue Fracture Engineering Materials Structure
, Vol.
8
,
1985
, pp. 193–203.
17.
Ravichandran
,
K. S.
and
Larsen
,
J. M.
, “
Behavior of Small and Large Fatigue Cracks in Ti-24Al-11Nb: Effects of Crack Shape, Microstructure, and Closure
,” in press:
Fracture Mechanics: 22nd Symposium
, Volume
I
, STP 1131,
Ernst
H. A.
,
Saxena
A.
, and
McDowell
D. L.
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1992
, pp. 727–748.
18.
Pineau
,
A.
, “
Short Fatigue Crack Behavior in Relation to Three-Dimensional Aspects and Crack Closure Effect
,”
Small Fatigue Cracks
,
Ritchie
R. O.
and
Lankford
J.
, Eds.,
The Metallurgical Society
,
Warrendale, PA
,
1986
, pp. 191–211.
19.
Nikon Metallurgical Microscope,
OPTIPHOT
,
Instruction Manual
,
Nippon Kogaku K. K.
,
Japan
.
20.
KODAK publication F-32,
Eastman Kodak Co
, Rochester, NY,
1988
.
21.
Larsen
,
J. M.
,
Jira
,
J. R.
, and
Weerasooriya
,
T.
, “
Crack Opening Displacement Measurements on Small Cracks in Fatigue
,”
Fracture Mechanics: Eighteenth Symposium
, STP 945,
Read
D. T.
and
Reed
R. P.
, Eds.,
American Society for Testing and Materials
,
Philadelphia, PA
,
1988
, pp. 896–912.
22.
Jira
,
J. R.
,
Weerasooriya
,
T.
,
Nicholas
,
T.
, and
Larsen
,
J. M.
, “
Effects of Closure on the Fatigue Crack Growth of Small Surface Cracks in a High-Strength Titanium Alloy
,”
Mechanics of Fatigue Crack Closure
, STP 982,
Newman
,
J. C.
 Jr.
and
Elber
W.
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1988
, pp. 617–635.
23.
Jira
,
J. R.
,
Nicholas
,
T.
, and
Larsen
,
J. M.
, “
Fatigue Thresholds in Surface Flaws in Ti-6Al-2Sn-4Zr-6Mo
,”
Fatigue 87
, Vol.
IV
,
Starke
,
E. A.
 Jr.
and
Ritchie
R. O.
, Eds.,
Engineering Materials Advisory Services, Ltd.
,
West Midlands, United Kingdom
,
1987
, pp. 1851–1860.
24.
Larsen
,
J. M.
and
Jira
,
J. R.
, “
Small-Crack Closure Measurements in Titanium Alloys
,”
Experimental Mechanics
,
03
1991
, pp. 82–87.
25.
Larsen
,
J. M.
,
Nicholas
,
T.
,
Thompson
,
A. W.
, and
Williams
,
J. C.
, “
Small-Crack Growth in Titanium-Aluminum Alloys
,”
Small Fatigue Cracks
,
Ritchie
R. O.
and
Lankford
J.
, Eds.,
TMS-AIME
,
Warrendale, PA
,
1986
, pp. 499–512.
26.
Larsen
,
J. M.
,
Williams
,
J. C.
, and
Thompson
,
A. W.
, “
Crack-Closure Effects on the Growth of Small Surface Cracks in Titanium-Aluminum Alloys
,”
Mechanics of Fatigue Crack Closure
, STP 982,
Newman
,
J. C.
 Jr.
and
Elber
W.
, Eds.,
American Society for Testing and Materials
,
Philadelphia, PA
,
1988
, pp. 149–167.
27.
Sharpe
,
W. N.
,
Jira
,
J. R.
, and
Larsen
,
J. M.
, “
Real-Time Measurement of Small-Crack Opening Behavior Using an Interferometric Strain/Displacement Gage
,”
Small-Crack Test Methods
, STP 1149,
Larsen
J. M.
and
Allison
J. E.
, Eds.,
American Society for Testing and Materials
,
Philadelphia, PA
,
1992
, pp. 92–115 (in this publication).
28.
Newman
,
J. C.
, Jr.
and
Raju
,
I. S.
, “
Stress-Intensity Factor Equations for Cracks in Three Dimensional Finite Bodies
,”
Fracture Mechanics: Fourteenth Symposium—Volume I: Theory and Analysis
, STP 791,
Lewis
J. C.
and
Sines
G.
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1983
, pp. I-238–I-265.
29.
Clark
, ,
W. G.
 Jr.
, and
Hudak
, ,
S. J.
 Jr.
, “
The Analysis of Fatigue Crack Growth Rate Data
,”
Application of Fracture Mechanics to Design
,
Burke
J. J.
and
Weiss
V.
, Eds., Vol.
22
,
Plenum Press
,
1979
, pp. 67–81.
30.
Wei
,
R. P.
,
Wei
,
W.
, and
Miller
,
G. A.
, “
Effect of Measurement Precision and Data Processing Procedure on Variability in Fatigue Crack Growth-Rate Data
,
Journal of Testing and Evaluation
 0090-3973, Vol.
7
,
1979
, pp. 90–95.
31.
Newman
,
J. C.
, Jr.
, “
Fracture Mechanics Parameters for Small Fatigue Cracks
,”
Small-Crack Test Methods
, STP 1149,
Larsen
J. M.
and
Allison
J. E.
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1992
, pp. 6–33 (in this publication).
32.
American Society for Metals
, “
Electropolishing
,”
Metals Handbook
, 9th Ed., Vol.
5
,
American Society for Metals
,
Metals Park, OH
,
1982
, pp. 303–309.
33.
Vander Voort
,
G. F.
,
Metallography, Principles and Practice
,
McGraw-Hill Inc.
,
New York
,
1984
, pp. 119–125.
34.
Rowe
,
M. S.
,
Harper
,
C. E.
, Jr.
, and
Jackson
,
A.
, “
A Computer Controlled Electropolishing System
,”
Microstructural Science
, Vol.
16
,
Cialoni
H. J.
,
Blum
M. E.
,
Johnson
G. W. E.
, and
Vander Voort
G. F.
, Eds., pp. 555–564.
35.
Rowe
,
M. S.
,
Harper
,
C. E.
, Jr.
, and
Underwood
,
C. R.
, “
Computer Controlled Electropolishing System
,” United States Patent No. 4,935,865,
1990
.
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