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ASTM Selected Technical Papers
Developments in Fracture Mechanics Test Methods Standardization
By
WF Brown, Jr Jr
WF Brown, Jr Jr
1
Chief
,
Fracture Branch, NASA-Lewis Research Center
,
Cleveland, Ohio 44135
;
coeditor
.
Search for other works by this author on:
JG Kaufman
JG Kaufman
2
Alcoa Laboratories, Aluminum Company of America
?
Pittsburgh> Pa
.
15219
;
coeditor
.
Search for other works by this author on:
ISBN-10:
0-8031-0321-2
ISBN:
978-0-8031-0321-4
No. of Pages:
294
Publisher:
ASTM International
Publication date:
1977

This paper is concerned with the use of the sharply notched cylindrical specimen as an index of plane-strain fracture toughness in quality assurance of aluminum alloy products. Specifically, information is presented that relates to the use of the ASTM Tentative Method for Sharp-Notch Tension Testing with Cylindrical Specimens (E 602-76T) in quality assurance programs. The first part of this paper describes the results of an investigation into the influence of fundamental testing variables on the sharp notch strength of several high-strength aluminum alloys. The results indicate that variations in the notch root radius and eccentricity of loading (expressed in terms of the percent bending in a verification specimen) within the range permitted by the Tentative Method can contribute significantly to the scatter observed in relations between the sharp notch to yield strength ratio (NYR) and KIc. The results also show that the upper limit of KIc beyond which the NYR loses useful sensitivity to further increases in KIc decreases with decreasing specimen size (diameter). It appears that the notch strength of the smaller of the two specimens (½ and1116in. diameter; 13 and 27 mm diameter) specified in the Tentative Method will have rather limited application as an index of KIc for the tougher high-strength aluminum alloys. However, the upper limit of 1.3 presently placed on the NYR appears to be overly conservative for high-strength aluminum alloys.

The second part of the paper describes the statistical analysis of correlations between the NYR and KIc for various lots of 2124-T851 aluminum alloy plate. The purpose of the analysis was to demonstrate how the sharp-notch cylindrical specimen could be used in a quality assurance program for high-strength aluminum alloy products based on a minimum acceptable value of KIc. The results indicate that the NYR from the larger of the two specimens specified in the Tentative Method provides a better correlation with KIc than does the NYR from the smaller specimen. A modified regression analysis is introduced which establishes tighter tolerance limits for the correlations than can be obtained using conventional procedures. The consequence is an improvement in the cost effectiveness of quality control procedures using the sharply notched cylindrical specimen. A review of existing data shows that crack orientation and product thickness can influence the correlations but that for practical purposes of quality assurance, correlations based on the T-L orientation will ensure that the minimum value of KIc is exceeded in all three orientations. Thickness effects can be handled by establishing separate correlations depending on whether the plate product is greater or less than 4 in. thick. Employing the modified regression analysis, a simple quality assurance plan for fracture toughness guarantee of aluminum alloy products was developed and shown to be cost effective based on available data for the aluminum alloy 2124-T851.

1.
Brown
,
W. F.
 Jr.
,
Jones
,
M. H.
, and
Newman
,
D. P.
in
Strength and Ductility of Metals at Elevated Temperatures, ASTM STP 128
,
American Society for Testing and Materials
,
1952
, pp. 25–48.
2.
Brown
,
W. F.
 Jr.
,
Jones
,
M. H.
, and
Newman
,
D. P.
in
Proceedings
,
American Society for Testing and Materials
, Vol.
53
,
1953
, pp. 661–676.
3.
Screening Tests for High-Strength Alloys Using Sharply Notched Cylindrical Specimens
,”
Fourth Report of a Special ASTM Committee
,
Materials Research and Standards
, Vol.
2
,
03
1962
, p. 196.
4.
Kaufman
,
J. G.
,
Sha
,
G. T.
,
Kohm
,
R. F.
, and
Bucci
,
R. J.
in
Cracks and Fracture, ASTM STP 601
,
American Society for Testing and Materials
,
1976
, pp. 169–190.
5.
Jones
,
M. H.
,
Bubsey
,
R. T.
,
Succop
,
G.
, and
Brown
,
W. F.
 Jr.
,
Journal of Testing and Evaluation
 0090-3973, Vol.
2
, No.
5
,
1974
, p. 378.
6.
Kaufman
,
J. G.
in
Fracture Toughness, ASTM STP 514
,
American Society for Testing and Materials
,
1972
, pp. 82–97.
7.
Tada
,
H.
,
Paris
,
P. C.
, and
Irwin
,
G. R.
,
The Stress Analysis of Cracks Handbook
,
Del Research Corp.
,
Hellertown, Pa.
,
1973
.
8.
Nelson
,
F. G.
,
Shilling
,
P. E.
, and
Kaufman
,
J. G.
,
Engineering Fracture Mechanics
 0013-7944, Vol.
4
,
1972
, p. 33.
9.
Kaufman
,
J. G.
and
Nelson
,
F. G.
in
Fracture Toughness and Slow Stable Cracking, ASTM STP 559
,
American Society for Testing and Materials
,
1974
, pp. 74–85.
10.
The Aluminum Association Position on Fracture Toughness Requirements and Quality Control Testing
,” an Interim Report,
Aluminum Association
,
09
1974
.
11.
Kohm
,
R. F.
and
Clark
,
J. W.
, “
Statistical Analysis Techniques for Dirty Data
” presented at ASCE-EMD Speciality Conference,
University of Waterloo, Waterloo, Ont.
,
05
1976
.
12.
Vellman
,
P. F.
, “
Nonlinear Data-Smoothers: Some Definitions and Applications
,” presented at the Joint Statistical Meeting of the American Statistical Association,
Biometric Society
,
1974
.
13.
Boston
,
A. E.
and
Tukey
,
J. W.
,
Technometrics
 0040-1706, Vol.
16
,
1974
, p. 147.
14.
Tukey
,
J. W.
,
Exploratory Data Analysis
,
Wiley, New York
,
1977
.
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