ASTM B909-00(2011)
(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
SIGNIFICANCE AND USE
The property KIc, determined by Test Method E399 or ISO 12737, characterizes a material's resistance to fracture in a neutral environment and in the presence of a sharp crack subjected to an applied opening force or moment within a field of high constraint to lateral plastic flow (plane strain condition). A KIc value is considered to be a lower limiting value of fracture toughness associated with the plane strain state.
Thermal quenching processes used with precipitation hardened aluminum alloy products can introduce significant residual stresses in the product. Mechanical stress relief procedures (stretching, compression) are commonly used to relieve these residual stresses in products with simple shapes. However, in the case of mill products with thick cross-sections (for example, heavy gage plate or large hand forgings) or complex shapes (for example, closed die forgings, complex open die forgings, stepped extrusions, castings), complete mechanical stress relief is not always possible. In other instances residual stresses may be unintentionally introduced into a product during fabrication operations such as straightening, forming, or welding operations.
Specimens taken from such products that contain residual stress will likewise themselves contain residual stress. While the act of specimen extraction in itself partially relieves and redistributes the pattern of original stress, the remaining magnitude can still be appreciable enough to cause significant error in the ensuing test result.
Residual stress is superimposed on the applied stress and results in an actual crack-tip stress intensity that is different from that based solely on externally applied forces or displacements.
Tests that utilize deep edge-notched specimens such as the compact tension C(T) are particularly sensitive to distortion during specimen machining when influential residual stress is present. In general, for those cases where such residual stresses are thermal quench induced, the ...
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 (Reapproved 2011)
Standard Guide for
Plane Strain Fracture Toughness Testing of Non-Stress
Relieved Aluminum Products
This standard is issued under the fixed designation B909; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
3.1 Definitions—Terminology in Test Method E399 and
1.1 This guide covers supplementary guidelines for plane-
Terminology E1823 are applicable herein.
strain fracture toughness testing of aluminum products for
which complete stress relief is not practicable. Guidelines for
3.2 Definitions of Terms Specific to This Standard:
recognizingwhenresidualstressesmaybesignificantlybiasing
3.2.1 corrected plane-strain fracture toughness— a test
test results are presented, as well as methods for minimizing
result, designated K (corrected), which has been corrected for
q
the effects of residual stress during testing. This guide also
residual stress bias by one of the methods outlined in this
provides guidelines for correction and interpretation of data
guide.ThecorrectedresultisanestimationoftheK orK that
q Ic
produced during the testing of these products. Test Method
would have been obtained in a residual stress free specimen.
E399 is the standard test method to be used for plane-strain
The corrected result may be obtained from a test record which
fracture toughness testing of aluminum alloys.
yielded either an invalid K or valid K , but for which there is
q Ic
evidence that significant residual stress is present in the test
1.2 This standard does not purport to address all of the
coupon.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.2.2 invalid plane-strain fracture toughness— a test result,
priate safety and health practices and determine the applica-
designated K , that does not meet one or more validity
q
bility of regulatory limitations prior to use.
requirements in Test Method E399 or ISO 12737 and may or
may not be significantly influenced by residual stress.
2. Referenced Documents
3.2.3 valid plane-strain fracture toughness— a test result,
2.1 ASTM Standards: designated K , meeting the validity requirements in Test
Ic
Method E399 or ISO 12737 that may or may not be signifi-
E399 Test Method for Linear-Elastic Plane-Strain Fracture
Toughness K of Metallic Materials cantly influenced by residual stress.
Ic
E561 Test Method forK-R Curve Determination
E1823 TerminologyRelatingtoFatigueandFractureTesting 4. Significance and Use
2.2 ANSI Standard: 4.1 The property K , determined by Test Method E399 or
Ic
ANSIH35.1 AlloyandTemperDesignationsforAluminum
ISO 12737, characterizes a material’s resistance to fracture in
a neutral environment and in the presence of a sharp crack
2.3 ISO Standard:
subjected to an applied opening force or moment within a field
ISO 12737 Metallic Materials–Determination of Plane
of high constraint to lateral plastic flow (plane strain condi-
Strain Fracture Toughness
tion).AK value is considered to be a lower limiting value of
Ic
fracture toughness associated with the plane strain state.
4.1.1 Thermal quenching processes used with precipitation
This guide is under the jurisdiction ofASTM Committee B07 on Light Metals
hardened aluminum alloy products can introduce significant
and Alloys and is the direct responsibility of Subcommittee B07.05 on Testing.
residual stresses in the product. Mechanical stress relief pro-
Current edition approved Nov. 1, 2011. Published June 2012. Originally
approved in 2000. Last previous edition approved in 2006 as B909 – 00 (2006).
cedures (stretching, compression) are commonly used to re-
DOI: 10.1520/B0909-00R11.
lieve these residual stresses in products with simple shapes.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
However, in the case of mill products with thick cross-sections
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
(for example, heavy gage plate or large hand forgings) or
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
complex shapes (for example, closed die forgings, complex
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
open die forgings, stepped extrusions, castings), complete
4th Floor, New York, NY 10036, http://www.ansi.org.
mechanical stress relief is not always possible. In other
Available from International Organization for Standardization (ISO), 1 rue de
Varembé, Case postale 56, CH-1211, Geneva 20, Switzerland, http://www.iso.ch. instances residual stresses may be unintentionally introduced
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B909 − 00 (2011)
into a product during fabrication operations such as length to width ratio (a /W) of 0.45, a difference in the height
o
straightening, forming, or welding operations. measured before and after machining the notch equal to or
4.1.2 Specimens taken from such products that contain greater than 0.003 in. (0.076 mm) is an indicator that the
residual stress will likewise themselves contain residual stress. ensuing test result will be significantly influenced by residual
While the act of specimen extraction in itself partially relieves stress.
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.
E399 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.Ingeneral,forthosecaseswheresuchresidualstresses
fracture toughness tests results, then increasing the specimen
are thermal quench induced, the resulting K or K result is
Ic q
plan size typically results in increasing K values.
q
typically biased upward (that is, K is higher than that which
q
NOTE1—Otherfactors,suchasasteeplyrisingR-curve(PracticeE561)
would have been achieved in a residual stress free specimen).
in high toughness alloy/products, may also be responsible for K values
q
The inflated values result from the combination of specimen
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-
5. Warning Signs ness K or K that would have been obtained had the test
q Ic
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
resultshouldbesuspected.Thelikelihoodthatresidualstresses
7.1 The following considerations can be used to minimize
are biasing test results increases as the nu
...
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