ASTM B909-00
(Guide)Standard Guide for Plane Strain Fracture Toughness Testing of Non-Stress Relieved Aluminum Products
Standard Guide for Plane Strain Fracture Toughness Testing of Non-Stress Relieved Aluminum Products
SCOPE
1.1 This guide covers supplementary guidelines for plane-strain fracture toughness testing of aluminum products for which complete stress relief is not practicable. Guidelines for recognizing when residual stresses may be significantly biasing test results are presented, as well as methods for minimizing the effects of residual stress during testing. This guide also provides guidelines for correction and interpretation of data produced during the testing of these products. Test Method E399 is the standard test method to be used for plane-strain fracture toughness testing of aluminum alloys.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:B909–00
Standard Guide for
Plane Strain Fracture Toughness Testing of Non-Stress
Relieved Aluminum Products
This standard is issued under the fixed designation B 909; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2.1 corrected plane-strain fracture toughness— a test
result, designated K (corrected), which has been corrected for
q
1.1 This guide covers supplementary guidelines for plane-
residual stress bias by one of the methods outlined in this
strain fracture toughness testing of aluminum products for
guide.ThecorrectedresultisanestimationoftheK orK that
q Ic
which complete stress relief is not practicable. Guidelines for
would have been obtained in a residual stress free specimen.
recognizingwhenresidualstressesmaybesignificantlybiasing
The corrected result may be obtained from a test record which
test results are presented, as well as methods for minimizing
yielded either an invalid K or valid K , but for which there is
q Ic
the effects of residual stress during testing. This guide also
evidence that significant residual stress is present in the test
provides guidelines for correction and interpretation of data
coupon.
produced during the testing of these products. Test Method
3.2.2 invalid plane-strain fracture toughness— a test result,
E 399 is the standard test method to be used for plane-strain
designated K , that does not meet one or more validity
q
fracture toughness testing of aluminum alloys.
requirements in Test Method E 399 or ISO 12737 and may or
1.2 This standard does not purport to address all of the
may not be significantly influenced by residual stress.
safety concerns, if any, associated with its use. It is the
3.2.3 valid plane-strain fracture toughness— a test result,
responsibility of the user of this standard to establish appro-
designated K , meeting the validity requirements in Test
Ic
priate safety and health practices and determine the applica-
Method E 399 or ISO 12737 that may or may not be signifi-
bility of regulatory limitations prior to use.
cantly influenced by residual stress.
2. Referenced Documents
4. Significance and Use
2.1 ASTM Standards:
4.1 The property K , determined by Test Method E 399 or
Ic
E 399 Test Method for Plane-Strain Fracture Toughness
ISO 12737, characterizes a material’s resistance to fracture in
Testing of Metallic Materials
a neutral environment and in the presence of a sharp crack
E 561 Practice for R-Curve Determination
subjected to an applied opening force or moment within a field
E 1823 Terminology Relating to Fatigue and Fracture Test-
of high constraint to lateral plastic flow (plane strain condi-
ing
tion).AK value is considered to be a lower limiting value of
Ic
2.2 ANSI Standard:
fracture toughness associated with the plane strain state.
ANSI H35.1 Alloy and Temper Designations for Alumi-
4.1.1 Thermal quenching processes used with precipitation
num
hardened aluminum alloy products can introduce significant
2.3 ISO Standard:
residual stresses in the product. Mechanical stress relief pro-
ISO 12737 Metallic Materials–Determination of Plane
4 cedures (stretching, compression) are commonly used to re-
Strain Fracture Toughness
lieve these residual stresses in products with simple shapes.
3. Terminology However, in the case of mill products with thick cross-sections
(for example, heavy gage plate or large hand forgings) or
3.1 Definitions—Terminology in Test Method E 399 and
complex shapes (for example, closed die forgings, complex
Terminology E 1823 are applicable herein.
open die forgings, stepped extrusions, castings), complete
3.2 Definitions of Terms Specific to This Standard:
mechanical stress relief is not always possible. In other
instances residual stresses may be unintentionally introduced
This guide is under the jurisdiction ofASTM Committee B07 on Light Metals
into a product during fabrication operations such as straight-
and Alloys and is the direct responsibility of Subcommittee B07.05 on Testing.
ening, forming, or welding operations.
Current edition approved Oct. 10, 2000. Published November 2000.
2 4.1.2 Specimens taken from such products that contain
Annual Book of ASTM Standards, Vol 03.01.
Available fromAmerican National Standards Institute (ANSI), 11 W. 42nd St., residual stress will likewise themselves contain residual stress.
New York, NY 10036.
While the act of specimen extraction in itself partially relieves
Available from International Organization for Standardization (ISO), 1, rue de
Varembé, Case postale 56, CH-1211 Geneva 20, Switzerland.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B909–00
and redistributes the pattern of original stress, the remaining 5.1.3 Excessive fatigue precrack front curvature not meet-
magnitude can still be appreciable enough to cause significant ing the crack-front straightness requirements in Test Method
error in the ensuing test result. E 399 or ISO 12737.
4.1.3 Residual stress is superimposed on the applied stress 5.1.4 Unusually high loads or number of cycles required for
andresultsinanactualcrack-tipstressintensitythatisdifferent precracking relative to the same or similar alloy/products.
from that based solely on externally applied forces or displace- 5.1.5 A significant change in fracture toughness that is
ments. greater than that typically observed upon changing specimen
4.1.4 Teststhatutilizedeepedge-notchedspecimenssuchas configuration (for example, from C(T) to three point bend bar)
thecompacttensionC(T)areparticularlysensitivetodistortion or upon changing specimen plan size that cannot be explained
during specimen machining when influential residual stress is by other means. For example, if residual stress is biasing
present. In general, for those cases where such residual stresses fracture toughness tests results, then increasing the specimen
are thermal quench induced, the resulting K or K result is plan size typically results in increasing K values.
Ic q q
typically biased upward (that is, K is higher than that which
q
NOTE 1—Other factors, such as a steeply rising R-curve (Practice
would have been achieved in a residual stress free specimen).
E 561) in high toughness alloy/products, may also be responsible for K
q
The inflated values result from the combination of specimen
values increasing with increasing specimen plan size.
distortionandbendingmomentscausedbytheredistributionof
5.1.6 A nonlinear load-COD trace during the initial elastic
residual stress during specimen machining and excessive
portion of the test record. This result is indicative of the
fatigue precrack from curvature .
residual stress clamping that is being overcome to open the
4.2 This guide can serve the following purposes:
crack under the progressively increasing applied load.
4.2.1 Provide warning signs that the measured value of K
Ic
has been biased by residual stresses and may not be a lower
6. Minimizing Effects of Residual Stress on Fracture
limit value of fracture toughness.
Toughness Measurements
4.2.2 Provide experimental methods by which to minimize
6.1 When testing aluminum products that have not been
the effect of residual stress on measured fracture toughness
stress relieved, there are two approaches available to minimize
values.
or eliminate the effects of residual stress on fracture toughness
4.2.3 Suggest methods that can be used to correct residual
measurements. The first approach involves the use of one or
stress influenced values of fracture toughness to values that
more experimental methods designed to minimize the residual
approximate a fracture toughness value representative of a test
stress in test specimens. The second approach involves the use
performed without residual stress bias.
of post-test correction methods to estimate the fracture tough-
ness K or K that would have been obtained had the test
q Ic
5. Warning Signs
specimen been free of residual stress.
5.1 There are a number of warning signs that test measure-
ments are or might be biased by the presence of residual stress.
7. Experimental Methods to Minimize Effects of Residual
If any one or more of the following conditions exist, residual
Stress
stress bias of the ensuing plane strain fracture toughness test
7.1 The following considerations can be used to minimize
result should be suspected.The likelihood that residual stresses
the magnitude of residual stress in test specimens.
are biasing test results increases as the number of warning
7.1.1 To minimize the biasing influences of both distortion-
signs increase.
induced clamping (or opening) moments and precrack front
5.1.1 A temper designation of a heat treatable aluminum
curvature, the specimen thickness (B) should be as small as
product that does not indic
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