ASTM B771-11(2021)

Standard Test Method for Short Rod Fracture Toughness of Cemented Carbides

SIGNIFICANCE AND USE
5.1 The property KIcSR determined by this test method is believed to characterize the resistance of a cemented carbide to fracture in a neutral environment in the presence of a sharp crack under severe tensile constraint, such that the state of stress near the crack front approaches tri-tensile plane strain, and the crack-tip plastic region is small compared with the crack size and specimen dimensions in the constraint direction. A KIcSR value is believed to represent a lower limiting value of fracture toughness. This value may be used to estimate the relation between failure stress and defect size when the conditions of high constraint described above would be expected. Background information concerning the basis for development of this test method in terms of linear elastic fracture mechanics may be found in Refs (1-7).3  
5.2 This test method can serve the following purposes:  
5.2.1 To establish, in quantitative terms significant to service performance, the effects of fabrication variables on the fracture toughness of new or existing materials, and  
5.2.2 To establish the suitability of a material for a specific application for which the stress conditions are prescribed and for which maximum flaw sizes can be established with confidence.
SCOPE
1.1 This test method covers the determination of the fracture toughness of cemented carbides (KIcSR) by testing slotted short rod or short bar specimens.  
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.  
1.3 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Aug-2021
• ICS: 77.160 - Powder metallurgy
• Technical Committee: B09 - Metal Powders and Metal Powder Products
• Drafting Committee: B09.06 - Cemented Carbides

Relations

• Refers: ASTM E399-12e3 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness K<inf>Ic</inf > of Metallic Materials
• Effective Date: 15-Nov-2012
• Refers: ASTM E399-12 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness <emph type="bdit" >K<inf> Ic</inf></emph> of Metallic Materials
• Effective Date: 15-Nov-2012
• Refers: ASTM E399-12e2 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness K<inf>Ic</inf > of Metallic Materials
• Effective Date: 15-Nov-2012
• Refers: ASTM E399-12e1 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness K<inf>Ic</inf > of Metallic Materials
• Effective Date: 15-Nov-2012
• Refers: ASTM E399-09 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness <bdit>K<inf> Ic</inf></bdit> of Metallic Materials
• Effective Date: 01-Jul-2009
• Refers: ASTM E399-09e1 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness <bdit>K<inf> Ic</inf></bdit> of Metallic Materials
• Effective Date: 01-Jul-2009
• Refers: ASTM E399-08 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness <bdit>K<inf> Ic</inf></bdit> of Metallic Materials
• Effective Date: 15-Nov-2008
• Refers: ASTM E399-06 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness K_Ic of Metallic Materials
• Effective Date: 15-Dec-2006
• Refers: ASTM E399-06e2 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness <bdit>K<inf> Ic</inf></bdit> of Metallic Materials
• Effective Date: 15-Dec-2006
• Refers: ASTM E399-06e1 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness K_Ic of Metallic Materials
• Effective Date: 15-Dec-2006
• Refers: ASTM E399-05 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness K_IC of Metallic Materials
• Effective Date: 01-Apr-2005
• Refers: ASTM E399-90(1997) - Standard Test Method for Plane-Strain Fracture Toughness of Metallic Materials
• Effective Date: 01-Jan-1997

Overview

ASTM B771-11(2021), Standard Test Method for Short Rod Fracture Toughness of Cemented Carbides, specifies a procedure for determining the fracture toughness (KIcSR) of cemented carbides. This method evaluates the resistance of these hard materials to fracture in the presence of a sharp crack under severe tensile stress. By utilizing slotted short rod or short bar specimens, the standard provides a quantitative assessment that helps predict failure risk based on existing flaws and stress conditions.

Fracture toughness is a critical material property, particularly for cemented carbides used in high-performance and wear-resistant applications. Employing this international standard supports manufacturers in qualifying materials for demanding service environments and informs engineering decisions regarding fabrication processes and final use.

Key Topics

The ASTM B771-11(2021) standard covers several essential topics:

• Test Specimen Types: Instructions for preparing both short rod and short bar specimens, including dimensional tolerances and slot designs (curved and straight slot options).
• Test Methodology: Step-by-step procedures for loading specimens using chevron slots, recording load versus displacement, and evaluating crack initiation and propagation.
• Data Analysis: Guidelines for calculating KIcSR from load-displacement records, accounting for machine type (tensile test machine or distributed load system) and measuring corrections for specimen deviations.
• Validity Requirements: Criteria for valid tests, such as alignment, measurement of crack follow, residual stress limits, and specimen conformity to dimension tolerances.
• Reporting: Documentation requirements for test results, including specimen ID, environmental conditions, measurements, test observations, and any noted deviations.

Safety Notice: Users are responsible for ensuring proper safety, health, and environmental protocols, as the standard does not address all hazards associated with its application.

Applications

The ASTM B771-11(2021) test method is widely used in materials science and manufacturing sectors for:

• Material Qualification: Verifying fracture toughness of cemented carbides for use in cutting tools, mining equipment, and industrial machinery.
• Process Improvement: Assessing the influence of fabrication or processing variables such as sintering conditions, composition, or heat treatment on the toughness of cemented carbides.
• Failure Analysis: Estimating the relationship between failure stress and intrinsic or manufacturing-induced defects under specified loading conditions.
• Quality Assurance: Supporting the consistent production of reliable, high-strength carbide components by providing objective fracture toughness measurements.

By adhering to this test method, organizations benefit from reproducible, quantitative insights crucial for both new materials development and maintaining the integrity of existing products.

Related Standards

ASTM B771-11(2021) aligns with global standardization principles and references several related documents, including:

• ASTM E399: Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness of Metallic Materials, which provides context for methodologies involving plane-strain conditions.
• ASTM Standards for Metal Powders and Powder Products: Further guidance on testing and material properties relevant to cemented carbides.
• WTO TBT Principles: Compliance with internationally recognized procedures for the development and harmonization of standards.

Organizations implementing ASTM B771-11(2021) may also consider these related standards to ensure comprehensive materials testing and adherence to best practices.

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Keywords: ASTM B771-11, short rod fracture toughness, cemented carbides, KIcSR, fracture resistance, material qualification, toughness testing, carbide components, standard test method, load-displacement testing, specimen preparation, materials engineering, quality assurance, international standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B771 − 11 (Reapproved 2021)
Standard Test Method for
Short Rod Fracture Toughness of Cemented Carbides
This standard is issued under the fixed designation B771; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope where:
r = distance directly forward from the crack tip to a
1.1 Thistestmethodcoversthedeterminationofthefracture
location where the significant stress σ is calculated,
toughness of cemented carbides (K ) by testing slotted short y
IcSR
and
rod or short bar specimens.
σ = principal stress normal to the crack plane.
y
1.2 The values stated in SI units are to be regarded as
standard. The values given in parentheses are for information 3.2 Abbreviations: fracture toughness of cemented carbide,
−3/2
only.
K ,(dimensional units FL )—the material-toughness
IcSR
property measured in terms of the stress-intensity factor K by
1.3 This standard does not purport to address all of the
l
the operational procedure specified in this test method.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- 4. Summary of Test Method
mine the applicability of regulatory limitations prior to use.
4.1 This test method involves the application of an opening
1.4 This international standard was developed in accor-
load to the mouth of the short rod or short bar specimen which
dance with internationally recognized principles on standard-
contains a chevron-shaped slot. Load versus displacement
ization established in the Decision on Principles for the
across the slot at the specimen mouth is recorded autographi-
Development of International Standards, Guides and Recom-
cally.As the load is increased, a crack initiates at the point of
mendations issued by the World Trade Organization Technical
thechevronslotandslowlyadvanceslongitudinally,tendingto
Barriers to Trade (TBT) Committee.
split the specimen in half. The load goes through a smooth
2. Referenced Documents maximum when the width of the crack front is about one third
of the specimen diameter (short rod) or breadth (short bar).
2.1 ASTM Standards:
Thereafter, the load decreases with further crack growth. Two
E399Test Method for Linear-Elastic Plane-Strain Fracture
unloading-reloading cycles are performed during the test to
Toughness of Metallic Materials
measure the effects of any macroscopic residual stresses in the
3. Terminology Definitions specimen. The fracture toughness is calculated from the
−3/2
maximumloadinthetestandaresidualstressparameterwhich
3.1 stress intensity factor, K,(dimensional units FL )—
l
is evaluated from the unloading-reloading cycles on the test
the magnitude of the ideal-crack-tip stress field for mode 1 in
record.
a linear-elastic body.
NOTE 1—Values of K for mode l are given by:
5. Significance and Use
K 5limit @σ =2πr# (1)
l y 5.1 The property K determined by this test method is
IcSR
believedtocharacterizetheresistanceofacementedcarbideto
r→0
fracture in a neutral environment in the presence of a sharp
crack under severe tensile constraint, such that the state of
stress near the crack front approaches tri-tensile plane strain,
This test method is under the jurisdiction of ASTM Committee B09 on Metal
Powders and Metal Powder Products and is the direct responsibility of Subcom- and the crack-tip plastic region is small compared with the
mittee B09.06 on Cemented Carbides.
cracksizeandspecimendimensionsintheconstraintdirection.
Current edition approved Sept. 1, 2021. Published October 2021. Originally
AK valueisbelievedtorepresentalowerlimitingvalueof
approvedin1987.Lastpreviouseditionapprovedin2017asB771–11(2017).DOI: IcSR
10.1520/B0771-11R21. fracture toughness. This value may be used to estimate the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
relation between failure stress and defect size when the
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
conditions of high constraint described above would be ex-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. pected. Background information concerning the basis for
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B771 − 11 (2021)
Standard Dimensions
Standard Dimensions
Short Rod
Short Bar
(mm) (in.)
(mm) (in.)
B = 12.700 ± 0.025 0.500 ± 0.001
B = 12.700 ± 0.025 0.500 ± 0.001
W = 19.050 ± 0.075 0.750 ± 0.003
H = 11.050 ± 0.025 0.435 ± 0.001
τ = 0.381 ± 0.025 0.015 ± 0.001
W = 19.050 ± 0.075 0.750 ± 0.003
For Curved Slot Option
τ = 0.381± 0.025 0.015 ± 0.001
a = 6.350± 0.075 0.250 ± 0.003
o
For Curved Slot Option
θ = 58.0° ± 0.5°
a = 6.350± 0.075 0.250 ± 0.003
o
R = 62.23 ± 1.27 02.45 ± 0.05
θ = 58.0° ± 0.5°
For Straight Slot Option
R = 62.23 ± 1.27 2.45 ± 0.05
a = 6.744± 0.075 0.266 ± 0.003
o
For Straight Slot Option
θ = 55.2° ± 0.5°
a = 6.744 ± 0.075 0.266 ± 0.003
o
R=``
θ = 55.2° ± 0.5°
R=``
FIG. 1 Short Rod Specimen
FIG. 2 Short Bar Specimen
development of this test method in terms of linear elastic
fracture mechanics may be found in Refs (1-7).
5.2 This test method can serve the following purposes:
5.2.1 To establish, in quantitative terms significant to ser-
vice performance, the effects of fabrication variables on the
fracture toughness of new or existing materials, and
5.2.2 To establish the suitability of a material for a specific
application for which the stress conditions are prescribed and
for which maximum flaw sizes can be established with
confidence.
6. Specimen Configuration, Dimensions, and Preparation
6.1 Both the round short rod specimen and the rectangular
shaped short bar specimen are equally acceptable and have
been found to have the same calibration (5). The short rod
dimensions are given in Fig. 1; the short bar in Fig. 2.
6.2 Grip Slot—Depending on the apparatus used to test the
specimen, a grip slot may be required in the specimen front
NOTE 1—The dashed lines show the front face profile of Figs. 1 and 2
face,asshowninFig.3.Thesurfacesinthegripslotshallhave
without grip slot.
a smooth ground finish so that the contact with each grip will
FIG. 3 Short Rod and Short Bar Grip Slot in Specimen Front Face
be along an essentially continuous line along the entire grip
slot, rather than at a few isolated points or along a short
segment within the grip slot.
6.3 Crack-Guiding Slots—These may be ground using a
diamondabrasivewheelofapproximately124 63mm(4.9 6
0.1 in.) diameter, with a thickness of 0.36 6 0.01 mm (0.0140
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. 6 0.0005 in.). The resulting slots in the specimen are slightly
B771 − 11 (2021)
FIG. 4 Grip Design
thicker than the diamond wheel (0.38 6 0.02 mm, or 0.015 6
0.001 in.). A diamond concentration number of 50, and a grit
size of 150 are suggested. Dimensions are given in Fig. 1 and
Fig. 2 for two slotting options: (1) Specimens with curved slot
bottomsmadebyplungefeedingthespecimenontoadiamond
cutting wheel of a given radius, and (2) Specimens with
straight slot bottoms made by moving the specimen by a
cutting wheel. The values of a and θ for the two slot
o
configurations are chosen to cause the specimen calibration to
FIG. 5 Tensile Test Machine Test Configuration
remain constant.
7.3 Distributed Load Test Machine —An alternative special
7. Apparatus
purpose machine that has been found suitable for the test
7.1 Theprocedureinvolvestestingofchevron-slottedspeci-
requires no grip slot in the front face of the specimen. A thin
mens and recording the load versus specimen mouth opening
stainlesssteelinflatablebladderisinsertedintothechevronslot
displacement during the test.
in the mouth of the specimen. Subsequent inflation of the
7.2 Grips and Fixtures for Tensile Test Machine Loading—
bladder causes it to press against the inner surfaces of the slot,
Grip slots are required in the specimen face for this test
thusproducingthedesiredloading.Themachineprovidesload
method,asshowninFig.3.Fig.4showsthegripdesign.Grips
and displacement outputs, which must be recorded externally
shall have a hardness of 45 HRC or greater, and shall be
on a device such as an X-Y recorder.
capable of providing loads to at least 1560 N (350 lbf). The
7.4 Testing Machine Characteristics—It has been observed
gripsareattachedtothearmsoftensiletestmachinebythepin
that some grades of carbides show a “pop-in” type of behavior
and clevis arrangement shown in Fig. 5. The grip lips are
in which the load required to initiate the crack at the point of
inserted into the grip slot in the specimen, and the specimen is
the chevron slot is larger than the load required to advance the
loaded as the test machine arms apply a tensile load to the
crack just after initiation, such that the crack suddenly and
grips.Atransducerformeasuringthespecimenmouthopening
audibly jumps ahead at the time of its initiation. Occasionally,
displacement during the test, and means for automatically
the load at crack initiation can exceed the load maximum
recording the load-displacement test record, such as an X-Y
whichoccursasthecrackpassesthroughthecriticallocationin
recorder, are also required when using the tensile test machine
the specimen. When this occurs, a very stiff machine with
apparatus.Asuggesteddesignforthespecimenmouthopening
displacement gage appears in Fig. 6. The gage shall have a
−6 4
The sole instrument of this type known to the committee is the FraQ WC,
displacement resolution of 0.25 µm (10×10 in.) or better.
availablefromDijonInstrumentInc,1948MichiganAve,SaltLakeCity,UT84108.
However, it is not necessary to calibrate the displacement axis
If you are aware of alternative suppliers, please provide this information toASTM
ofthetestrecordsinceonlydisplacementratiosareusedinthe
International Headquarters. Your comments will receive careful consideration at a
data analysis. meeting of the responsible technical committee1, which you may attend.
B771 − 11 (2021)
FIG. 6 Suggested Design for a Specimen Mouth Opening Gage
controlled displacement loading is necessary in order to allow overlap somewhat in the mouth of the specimen, and because
the crack to arrest well before passing beyond the critical the cuts may not meet perfectly, the slot width near the center
location. The large pop-in load is then ignored, and the of the mouth may be larger than the width at the outside
subsequent load maximum as the crack passes through the
corners.Iftheslotwidthnearthecenterexceedstheslotwidth
critical location is used to determine K . Stiff machine
at the corners by more than 0.10 mm (0.004 in.), a test of that
IcSR
loading is also required in order to maintain crack growth
specimen by a Fractometer is invalid.
stability to well beyond the peak load in the test, where the
8.3 Specimen Testing Procedure:
second unloading-reloading cycle is initiated.
8.3.1 Load Transducer Calibration:
8. Procedure
8.3.1.1 Calibrate the output of the load cell in the test
machine to assure that the load cell output, as recorded on the
8.1 Number of Tests—A minimum of 3 replicate tests shall
load versus displacement recorder, is accurately translatable
be made.
into the actual force applied to the specimen. In those cases in
8.2 Specimen Measurement:
which a distributed load test machine is used (see 7.3), the
8.2.1 Measure and record all specimen dimensions. If the
calibration shall be performed according to the instructions in
dimensions are within the tolerances shown in Fig. 1 and Fig.
Annex A1.
2, no correction to the data need be made for out-of-tolerance
8.3.1.2 Installthespecimenonthetestmachine.Ifusingthe
dimensions. If one or more of the parameters a , W,θ orτ are
o
tensile test machine (see 7.2), operate the test machine in the
out of tolerance by up to 3 times the tolerances shown in Fig.
“displacementcontrol”mode.Bringthegripssufficientlyclose
1andFig.2,validtestsmaystillbemadebytheapplicationof
together such that they simultaneously fit into the grip slot in
the appropriate factors to account for the deviation from
thespecimenface.Thenincreasethespacingbetweenthegrips
standard dimensions (see 9.3). If the slot centering is outside
very carefully until an opening load of 10 to 30 N (2 to 7 lb)
the indicated tolerance, the crack is less likely to follow the
is applied to the specimen. Check the alignment of the
chevron slots. However, the test may still be considered
specimen with respect to the grips, and the alignment of the
successful if the crack follows the slots sufficiently well, as
discussed in 9.2. grips with respect to each other. The grips shall be centered in
the specimen grip slot to within 0.25 mm (0.010 in.). The
8.2.2 The slot thickness measurement is critical on speci-
mens to be tested on a Fractometer. It should be measured to vertical offset between the grips shall not exceed 0.13 mm
(0.005 in.). Using a magnifying glass, observe the grips in the
within 0.013 mm (0.0005 in.) at the outside corners of the slot
using a feeler gage. If a feeler gage blade enters the slot to a grip slot from each side of the specimen to assure that the
depth of 1 mm or more, the slot is said to be at least as thick specimen is properly installed. The grips should extend as far
as the blade. Because the saw cuts forming the chevron slot as possible into the grip slot, resulting in contact lines (load
B771 − 11 (2021)
9. Calculation and Interpretation of Results
9.1 Remove the specimen from the apparatus. If the two
halvesarestilljoined,breakthemapartwithawedge.Examine
the fracture surfaces for any imperfections that may have
influencedthemeasuredpeakload.Anyimperfections(suchas
a void, a surface irregularity, or a piece of foreign matter) that
is visible to the naked eye may influence the measurement if
theimperfectionislocatedbetween7.6mm(0.30in.)and14.2
mm (0.56 in.) from the mouth of the specimen. Imperfectio
...