ISO 12135:2021

Metallic materials — Unified method of test for the determination of quasistatic fracture toughness

This document specifies methods for determining fracture toughness in terms of K, δ, J and R-curves for homogeneous metallic materials subjected to quasistatic loading. Specimens are notched, precracked by fatigue and tested under slowly increasing displacement. The fracture toughness is determined for individual specimens at or after the onset of ductile crack extension or at the onset of ductile crack instability or unstable crack extension. In cases where cracks grow in a stable manner under ductile tearing conditions, a resistance curve describing fracture toughness as a function of crack extension is measured. In some cases in the testing of ferritic materials, unstable crack extension can occur by cleavage or ductile crack initiation and growth, interrupted by cleavage extension. The fracture toughness at crack arrest is not covered by this document. Special testing requirements and analysis procedures are necessary when testing weldments, and these are described in ISO 15653 which is complementary to this document. Statistical variability of the results strongly depends on the fracture type, for instance, fracture toughness associated with cleavage fracture in ferritic steels can show large variation. For applications that require high reliability, a statistical approach can be used to quantify the variability in fracture toughness in the ductile-to-brittle transition region, such as that given in ASTM E1921. However, it is not the purpose of this document to specify the number of tests to be carried out nor how the results of the tests are to be applied or interpreted.

Matériaux métalliques — Méthode unifiée d'essai pour la détermination de la ténacité quasi statique

General Information

• Status: Published
• Publication Date: 26-Jul-2021
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: ISO/TC 164/SC 4 - Fatigue, fracture and toughness testing
• Drafting Committee: ISO/TC 164/SC 4/WG 3 - Fracture toughness
• Current Stage: 6060 - International Standard published
• Start Date: 27-Jul-2021
• Due Date: 03-Apr-2021
• Completion Date: 27-Jul-2021

Relations

• Revises: ISO 12135:2016 - Metallic materials — Unified method of test for the determination of quasistatic fracture toughness
• Effective Date: 23-Apr-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 12135
Third edition
2021-07
Corrected version
2022-08
Metallic materials — Unified method
of test for the determination of
quasistatic fracture toughness
Matériaux métalliques — Méthode unifiée d'essai pour la
détermination de la ténacité quasi statique
Reference number
ISO 12135:2021(E)
© ISO 2021

---------------------- Page: 1 ----------------------
ISO 12135:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2021 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 12135:2021(E)
Contents Page
Foreword . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.2
5 General requirements . 5
5.1 General . 5
5.2 Fracture parameters . 7
5.3 Fracture toughness symbols . 8
5.4 Test specimens. 8
5.4.1 Specimen configuration and size . 8
5.4.2 Specimen preparation .13
5.5 Pre-test requirements . 19
5.5.1 Pre-test measurements . 19
5.5.2 Crack shape/length requirements. 19
5.6 Test apparatus. 19
5.6.1 Calibration . . . 19
5.6.2 Force application . 20
5.6.3 Displacement measurement . 20
5.6.4 Test fixtures . 20
5.7 Test requirements. 24
5.7.1 Three-point bend testing . 24
5.7.2 Compact tension testing . 24
5.7.3 Specimen test temperature . 24
5.7.4 Recording . 25
5.7.5 Testing rates . 25
5.7.6 Test analyses . 25
5.8 Post-test crack measurements . 25
5.8.1 General . 25
5.8.2 Initial crack length, a .25
0
5.8.3 Stable crack extension, Δa .30
5.8.4 Unstable crack extension .30
6 Determination of fracture toughness for stable and unstable crack extension .31
6.1 General . 31
6.2 Determination of plane strain fracture toughness, K . 32
lc
6.2.1 General . 32
6.2.2 Interpretation of the test record for F . 32
Q
6.2.3 Calculation of K .33
Q
6.2.4 Qualification of K as K .34
Q lc
6.3 Determination of fracture toughness in terms of δ .34
6.3.1 Determination of F and V , F and V , or F and V .34
c c u u uc uc
6.3.2 Determination of F and V . 35
m m
6.3.3 Determination of V . 36
p
6.3.4 Calculation of δ .36
0
6.3.5 Qualification of δ fracture toughness value . 37
0
6.4 Determination of fracture toughness in terms of J .38
6.4.1 Determination of F and V or q , F and V or q , or F and V or q .38
c c c u u u uc uc uc
6.4.2 Determination of F and q .38
m m
6.4.3 Determination of U .38
p
6.4.4 Calculation of J . 39
0
6.4.5 Qualification of J fracture toughness value .40
0
iii
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ISO 12135:2021(E)
7 Determination of resistance curves δ-Δa and J-Δa and initiation toughness δ
0,2BL
and J and δ and J for stable crack extension .41
0,2BL i i
7.1 General . 41
7.2 Test procedure . 41
7.2.1 General . 41
7.2.2 Multiple-specimen procedure . 41
7.2.3 Single-specimen procedure . 41
7.2.4 Final crack front straightness . 42
7.3 Calculation of J and δ . 42
7.3.1 Calculation of J . . 42
7.3.2 Calculation of δ . 42
7.4 R-curve plot . 43
7.4.1 Plot construction .44
7.4.2 Data spacing and curve fitting . 45
7.5 Qualification of resistance curves . .46
7.5.1 Qualification of J-Δa resistance curves .46
7.5.2 Qualification of δ−Δa resistance curves .46
7.6 Determination and qualification of J and δ . 47
0,2BL 0,2BL
7.6.1 Determination of J . . 47
0,2BL
7.6.2 Determination of δ .48
0,2BL
7.7 Determination of initiation toughness J and δ by scanning electron microscopy
i i
(SEM) .49
8 Test report .50
8.1 Organization .50
8.2 Specimen, material and test environment .50
8.2.1 Specimen description .50
8.2.2 Specimen dimensions.50
8.2.3 Material description .50
8.2.4 Additional dimensions .50
8.2.5 Test environment .50
8.2.6 Fatigue precracking conditions.50
8.3 Test data qualification . 51
8.3.1 Limitations . 51
8.3.2 Crack length measurements . 51
8.3.3 Fracture surface appearance . 51
8.3.4 Pop-in. 51
8.3.5 Resistance curves . 51
8.3.6 Checklist for data qualification . 51
8.4 Qualification of K . 52
lc
8.5 Qualification of δ , δ , δ or δ  . 52
c(B) u(B) uc(B) m(B)
8.6 Qualification of J , J , J or J  . 53
c(B) u(B) uc(B) m(B)
8.7 Qualification of the δ-R Curve . 53
8.8 Qualification of the J-R Curve . 53
8.9 Qualification of δ as δ . 53
0,2BL(B) 0,2BL
8.10 Qualification of J as J . 53
0,2BL(B) 0,2BL
Annex A (informative) Determination of δ and J .55
i i
Annex B (normative) Crack plane orientation .60
Annex C (informative) Example test reports .62
Annex D (informative) Stress intensity factor coefficients and compliance relationships .71
Annex E (informative) Measurement of load-line displacement q in the three-point bend test.75
Annex F (informative) Derivation of pop-in formulae .80
Annex G (informative) Analytical methods for the determination of V and U .82
p p
Annex H (informative) Guidelines for single-specimen methods .83
iv
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ISO 12135:2021(E)
Annex I (normative) Power-law fits to crack extension data (see Reference [42]) .97
Bibliography .98
v
© ISO 2021 – All rights reserved

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ISO 12135:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,
Subcommittee SC 4, Fatigue, fracture and toughness testing.
This third edition cancels and replaces the second edition (ISO 12135:2016), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— formulae to calculate CTOD have been replaced with those based on rigid rotation assumption
throughout; replacing the previous R-curve formulae based on CTOD from J. CTOD formulae for
SENBs are now those based on recent research to include the material yield to tensile strength ratio
in the CTOD formulae;
— the determination of J directly from displacement defined in terms of CMOD has been included, in
addition to the methods based on load line displacement;
— where fatigue precrack straightness requirements cannot be met due to internal residual stresses,
the application of modification techniques, originally developed for weld specimens, is now
permitted;
— the rotation correction factor for compact specimens has been revised with a new formula;
— editorial changes have been made to improve consistency of terms and definitions used throughout
the document.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
This corrected version of ISO 12135:2021 incorporates the following corrections:
— in Figure 6 a) the envelope tip angle was corrected from 60° to 30°;
vi
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---------------------- Page: 6 ----------------------
ISO 12135:2021(E)
— in 7.3.1, Formula (35) was corrected, with the addition of "Δ" before "a", to read:
2
 
2 η U γ ⋅Δa
a  
FS⋅   1−ν
pp p
0
 
J= g ⋅⋅+ 11− ;
 
 
1
05,
15, WE BW−a Wa−
  () ()
   
BB⋅ W
() N 0  0 
 
N
— in 7.3.2, Formula (38) was corrected, with the deletion of "+z", to read:
2
 
2 1−raΔ ++rB
a ()
 
FS⋅ 1−ν p pN
0
 g  +
δ = ⋅V ;
 
1 p
05,
15, WmRE
 
  1−raΔ ++rB a
()BB⋅ W p02, ()
pp N 0
 N 
— in 7.3.2, Formula (43) was corrected, with the deletion of "+z", to read:
2
 
2
a 05,,40Δa+ 46 WWa−
()
F   1−ν
0 0
 
δ = g ⋅ + ⋅V ;
 
2 p
05,
WR2 E 05,,40aa+Δ + 46W
  ()
 
BB⋅⋅W p02, 0
()
 
N
— in Table C.3 the small "v" was corrected to capital "V";
2 2
a a
   
— in Annex D, Formula (D.7) was corrected, with the replacement of 1− with 1− , to read:
   
W   W 
2 34
 
a 15,8 a a a a
 
       
g = 0,,121+−1210,,159 −14771+ ,30 ;
 
       
4
2
W  W W  W  W 
a  
   
1−
 
W
 
— in Annex H, Formula (H.13) was corrected, with the replacement of "g " with "g ", to read:
6 4
a
 
0
g
 
4
W a
   
coefficient λ= and the function to read: g .
 
4
a
W
   
0,est
g
 
4
W
 
vii
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INTERNATIONAL STANDARD ISO 12135:2021(E)
Metallic materials — Unified method of test for the
determination of quasistatic fracture toughness
1 Scope
This document specifies methods for determining fracture toughness in terms of K, δ, J and R-curves for
homogeneous metallic materials subjected to quasistatic loading. Specimens are notched, precracked
by fatigue and tested under slowly increasing displacement. The fracture toughness is determined for
individual specimens at or after the onset of ductile crack extension or at the onset of ductile crack
instability or unstable crack extension. In cases where cracks grow in a stable manner under ductile
tearing conditions, a resistance curve describing fracture toughness as a function of crack extension
is measured. In some cases in the testing of ferritic materials, unstable crack extension can occur
by cleavage or ductile crack initiation and growth, interrupted by cleavage extension. The fracture
toughness at crack arrest is not covered by this document. Special testing requirements and analysis
procedures are necessary when testing weldments, and these are described in ISO 15653 which is
complementary to this document.
Statistical variability of the results strongly depends on the fracture type, for instance, fracture
toughness associated with cleavage fracture in ferritic steels can show large variation. For applications
that require high reliability, a statistical approach can be used to quantify the variability in fracture
toughness in the ductile-to-brittle transition region, such as that given in ASTM E1921. However, it is
not the purpose of this document to specify the number of tests to be carried out nor how the results of
the tests are to be applied or interpreted.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3785, Metallic materials — Designation of test specimen axes in relation to product texture
ISO 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
stress intensity factor
K
magnitude of the elastic stress-field singularity for a homogeneous, linear-elastic body
Note 1 to entry: The stress intensity factor is a function of applied force, crack length, specimen size and specimen
geometry.
1
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ISO 12135:2021(E)
3.2
crack-tip opening displacement
δ
relative opening displacement of the crack surfaces normal to the original (undeformed) crack plane at
the tip of the fatigue precrack, evaluated using the rotation point formula
3.3
J-integral
line or surface integral that encloses the crack front from one crack surface to the other and
characterizes the local stress-strain field at the crack tip
3.4
J
loading parameter, equivalent to the J-integral (3.3), the specific values of which, experimentally
determined by this method of test (J , J , J ,…), characterize fracture toughness under elastic-plastic
c i u
conditions
3.5
stable crack extension
crack extension which stops or would stop when the applied displacement is held constant as a test
progresses under displacement control
3.6
unstable crack extension
abrupt crack extension occurring with or without prior stable crack extension (3.5)
3.7
pop-in
abrupt discontinuity in the force versus displacement record, featured as a sudden increase in
displacement and, generally, a decrease in force followed by an increase in force
Note 1 to entry: Displacement and force subsequently increase beyond their values at pop-in.
Note 2 to entry: When conducting tests by this method, pop-ins can result from unstable crack extension
(3.6) in the plane of the precrack and are to be distinguished from discontinuity indications arising from: i)
delaminations or splits normal to the precrack plane; ii) roller or pin slippage in bend or compact specimen
load trains, respectively; iii) improper seating of displacement gauges in knife edges; iv) ice cracking in low-
temperature testing; v) electrical interference in the instrument circuitry of force and displacement measuring
a
...

INTERNATIONAL ISO
STANDARD 12135
Third edition
2021-07
Metallic materials — Unified method
of test for the determination of
quasistatic fracture toughness
Matériaux métalliques — Méthode unifiée d'essai pour la
détermination de la ténacité quasi statique
Reference number
ISO 12135:2021(E)
©
ISO 2021

---------------------- Page: 1 ----------------------
ISO 12135:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 12135:2021(E)

Contents Page
Foreword .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 General requirements . 5
5.1 General . 5
5.2 Fracture parameters. 7
5.3 Fracture toughness symbols . 8
5.4 Test specimens . 8
5.4.1 Specimen configuration and size . 8
5.4.2 Specimen preparation .13
5.5 Pre-test requirements .19
5.5.1 Pre-test measurements .19
5.5.2 Crack shape/length requirements .19
5.6 Test apparatus .19
5.6.1 Calibration .19
5.6.2 Force application .20
5.6.3 Displacement measurement .20
5.6.4 Test fixtures .20
5.7 Test requirements .24
5.7.1 Three-point bend testing .24
5.7.2 Compact tension testing .24
5.7.3 Specimen test temperature.24
5.7.4 Recording .25
5.7.5 Testing rates .25
5.7.6 Test analyses .25
5.8 Post-test crack measurements .25
5.8.1 General.25
5.8.2 Initial crack length, a .25
0
5.8.3 Stable crack extension, Δa .30
5.8.4 Unstable crack extension .30
6 Determination of fracture toughness for stable and unstable crack extension .31
6.1 General .31
6.2 Determination of plane strain fracture toughness, K .32
lc
6.2.1 General.32
6.2.2 Interpretation of the test record for F .32
Q
6.2.3 Calculation of K .33
Q
6.2.4 Qualification of K as K .34
Q lc
6.3 Determination of fracture toughness in terms of δ .34
6.3.1 Determination of F and V , F and V , or F and V .34
c c u u uc uc
6.3.2 Determination of F and V .35
m m
6.3.3 Determination of V .36
p
6.3.4 Calculation of δ .36
0
6.3.5 Qualification of δ fracture toughness value .37
0
6.4 Determination of fracture toughness in terms of J .38
6.4.1 Determination of F and V or q , F and V or q , or F and V or q .38
c c c u u u uc uc uc
6.4.2 Determination of F and q .38
m m
6.4.3 Determination of U .38
p
6.4.4 Calculation of J .39
0
6.4.5 Qualification of J fracture toughness value .40
0
© ISO 2021 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 12135:2021(E)

7 Determination of resistance curves δ-Δa and J-Δa and initiation toughness δ and
0,2BL
J and δ and J for stable crack extension .41
0,2BL i i
7.1 General .41
7.2 Test procedure .41
7.2.1 General.41
7.2.2 Multiple-specimen procedure .41
7.2.3 Single-specimen procedure .41
7.2.4 Final crack front straightness .42
7.3 Calculation of J and δ .42
7.3.1 Calculation of J .42
7.3.2 Calculation of δ .42
7.4 R-curve plot .43
7.4.1 Plot construction .44
7.4.2 Data spacing and curve fitting .45
7.5 Qualification of resistance curves .46
7.5.1 Qualification of J-Δa resistance curves .46
7.5.2 Qualification of δ−Δa resistance curves .46
7.6 Determination and qualification of J and δ .47
0,2BL 0,2BL
7.6.1 Determination of J .47
0,2BL
7.6.2 Determination of δ .48
0,2BL
7.7 Determination of initiation toughness J and δ by scanning electron microscopy (SEM) .49
i i
8 Test report .49
8.1 Organization .49
8.2 Specimen, material and test environment .50
8.2.1 Specimen description .50
8.2.2 Specimen dimensions .50
8.2.3 Material description . .50
8.2.4 Additional dimensions .50
8.2.5 Test environment .50
8.2.6 Fatigue precracking conditions .50
8.3 Test data qualification .51
8.3.1 Limitations .51
8.3.2 Crack length measurements .51
8.3.3 Fracture surface appearance .51
8.3.4 Pop-in .51
8.3.5 Resistance curves .51
8.3.6 Checklist for data qualification .51
8.4 Qualification of K .52
lc
8.5 Qualification of δ , δ , δ or δ  .52
c(B) u(B) uc(B) m(B)
8.6 Qualification of J , J , J or J  .53
c(B) u(B) uc(B) m(B)
8.7 Qualification of the δ-R Curve .53
8.8 Qualification of the J-R Curve .53
8.9 Qualification of δ as δ .53
0,2BL(B) 0,2BL
8.10 Qualification of J as J .53
0,2BL(B) 0,2BL
Annex A (informative) Determination of δ and J .55
i i
Annex B (normative) Crack plane orientation .60
Annex C (informative) Example test reports .62
Annex D (informative) Stress intensity factor coefficients and compliance relationships .71
Annex E (informative) Measurement of load-line displacement q in the three-point bend test .75
Annex F (informative) Derivation of pop-in formulae .80
Annex G (informative) Analytical methods for the determination of V and U .82
p p
Annex H (informative) Guidelines for single-specimen methods .83
Annex I (normative) Power-law fits to crack extension data (see Reference [42]) .97
iv © ISO 2021 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 12135:2021(E)

Bibliography .98
© ISO 2021 – All rights reserved v

---------------------- Page: 5 ----------------------
ISO 12135:2021(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,
Subcommittee SC 4, Fatigue, fracture and toughness testing.
This third edition cancels and replaces the second edition (ISO 12135:2016), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— formulae to calculate CTOD have been replaced with those based on rigid rotation assumption
throughout; replacing the previous R-curve formulae based on CTOD from J. CTOD formulae for
SENBs are now those based on recent research to include the material yield to tensile strength ratio
in the CTOD formulae;
— the determination of J directly from displacement defined in terms of CMOD has been included, in
addition to the methods based on load line displacement;
— where fatigue precrack straightness requirements cannot be met due to internal residual stresses,
the application of modification techniques, originally developed for weld specimens, is now
permitted;
— the rotation correction factor for compact specimens has been revised with a new formula;
— editorial changes have been made to improve consistency of terms and definitions used throughout
the document.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
vi © ISO 2021 – All rights reserved

---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 12135:2021(E)
Metallic materials — Unified method of test for the
determination of quasistatic fracture toughness
1 Scope
This document specifies methods for determining fracture toughness in terms of K, δ, J and R-curves for
homogeneous metallic materials subjected to quasistatic loading. Specimens are notched, precracked
by fatigue and tested under slowly increasing displacement. The fracture toughness is determined for
individual specimens at or after the onset of ductile crack extension or at the onset of ductile crack
instability or unstable crack extension. In cases where cracks grow in a stable manner under ductile
tearing conditions, a resistance curve describing fracture toughness as a function of crack extension
is measured. In some cases in the testing of ferritic materials, unstable crack extension can occur
by cleavage or ductile crack initiation and growth, interrupted by cleavage extension. The fracture
toughness at crack arrest is not covered by this document. Special testing requirements and analysis
procedures are necessary when testing weldments, and these are described in ISO 15653 which is
complementary to this document.
Statistical variability of the results strongly depends on the fracture type, for instance, fracture
toughness associated with cleavage fracture in ferritic steels can show large variation. For applications
that require high reliability, a statistical approach can be used to quantify the variability in fracture
toughness in the ductile-to-brittle transition region, such as that given in ASTM E1921. However, it is
not the purpose of this document to specify the number of tests to be carried out nor how the results of
the tests are to be applied or interpreted.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3785, Metallic materials — Designation of test specimen axes in relation to product texture
ISO 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
stress intensity factor
K
magnitude of the elastic stress-field singularity for a homogeneous, linear-elastic body
Note 1 to entry: The stress intensity factor is a function of applied force, crack length, specimen size and specimen
geometry.
© ISO 2021 – All rights reserved 1

---------------------- Page: 7 ----------------------
ISO 12135:2021(E)

3.2
crack-tip opening displacement
δ
relative opening displacement of the crack surfaces normal to the original (undeformed) crack plane at
the tip of the fatigue precrack, evaluated using the rotation point formula
3.3
J-integral
line or surface integral that encloses the crack front from one crack surface to the other and
characterizes the local stress-strain field at the crack tip
3.4
J
loading parameter, equivalent to the J-integral (3.3), the specific values of which, experimentally
determined by this method of test (J , J , J ,…), characterize fracture toughness under elastic-plastic
c i u
conditions
3.5
stable crack extension
crack extension which stops or would stop when the applied displacement is held constant as a test
progresses under displacement control
3.6
unstable crack extension
abrupt crack extension occurring with or without prior stable crack extension (3.5)
3.7
pop-in
abrupt discontinuity in the force versus displacement record, featured as a sudden increase in
displacement and, generally, a decrease in force followed by an increase in force
Note 1 to entry: Displacement and force subsequently increase beyond their values at pop-in.
Note 2 to entry: When conducting tests by this method, pop-ins can result from unstable crack extension
(3.6) in the plane of the precrack and are to be distinguished from discontinuity indications arising from: i)
delaminations or splits normal to the precrack plane; ii) roller or pin slippage in bend or compact specimen
load trains, respectively; iii) improper seating of displacement gauges in knife edges; iv) ice cracking in low-
temperature testing; v) electrical interference in the instrument circuitry of force and displacement measuring
and recording devices.
3.8
crack extension resistance curves
R-curves
variation in δ (3.2) or J (3.4) with stable crack extension (3.5)
4 Symbols and abbreviated terms
Symbol Unit Designation
a mm Nominal crack length (for the purposes of fatigue precracking, an assigned value less
than a )
0
a mm Final crack length (a + Δa)
f 0
a mm Instantaneous crack length
i
a mm Length of machined notch
m
a mm Initial crack length
0
NOTE 1 This is not a complete list of parameters. Only the main parameters are given, other parameters are referred to in
the text.
NOTE 2 The values of all parameters used in calculations are assumed to be those measured or calculated for the
temperature of the test, unless otherwise specified.
2 © ISO 2021 – All rights reserved

---------------------- Page: 8 ----------------------
ISO 12135:2021(E)

Symbol Unit Designation
Δa mm Stable crack extension including blunting
Δa mm Crack extension limit for δ or J controlled crack extension
max
B mm Specimen thickness
B mm Specimen net thickness between side grooves
N
C m/N Specimen elastic compliance
CMOD mm Crack-mouth opening displacement, V
CTOD mm Crack tip opening displacement, δ
E GPa Modulus of elasticity at the pertinent temperature
F kN Applied force
F kN Applied force at the onset of unstable crack extension or pop-in when Δa is less than
c
0,2 mm offset from the construction line (Figure 2)
F kN Force value corresponding to the intersection of the test record with the secant line
d
(Figure 18)
F kN Maximum fatigue precracking force
f
F kN Limiting collapse load estimated for a given specimen type
L
F kN Maximum force for a test which exhibits a maximum force plateau preceding fracture
m
with no significant prior pop-ins (Figure 2)
F kN Provisiona
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 12135
ISO/TC 164/SC 4
Metallic materials — Unified method
Secretariat: ANSI
of test for the determination of
Voting begins on:
2021­04­22 quasistatic fracture toughness
Voting terminates on:
Matériaux métalliques — Méthode unifiée d'essai pour la
2021­06­17
détermination de la ténacité quasi statique
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 12135:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2021

---------------------- Page: 1 ----------------------
ISO/FDIS 12135:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 12135:2021(E)

Contents Page
Foreword .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 General requirements . 5
5.1 General . 5
5.2 Fracture parameters. 7
5.3 Fracture toughness symbols . 8
5.4 Test specimens . 8
5.4.1 Specimen configuration and size . 8
5.4.2 Specimen preparation .13
5.5 Pre-test requirements .19
5.5.1 Pre­test measurements .19
5.5.2 Crack shape/length requirements .19
5.6 Test apparatus .19
5.6.1 Calibration .19
5.6.2 Force application .20
5.6.3 Displacement measurement .20
5.6.4 Test fixtures .20
5.7 Test requirements .24
5.7.1 Three­point bend testing .24
5.7.2 Compact tension testing .24
5.7.3 Specimen test temperature.24
5.7.4 Recording .25
5.7.5 Testing rates .25
5.7.6 Test analyses .25
5.8 Post­test crack measurements .25
5.8.1 General.25
5.8.2 Initial crack length, a . . .
0 25
5.8.3 Stable crack extension, Δa . 30
5.8.4 Unstable crack extension .30
6 Determination of fracture toughness for stable and unstable crack extension .31
6.1 General .31
6.2 Determination of plane strain fracture toughness, K .
lc 32
6.2.1 General.32
6.2.2 Interpretation of the test record for F .
Q 32
6.2.3 Calculation of K .
Q 33
6.2.4 Qualification of K as K .
Q lc 34
6.3 Determination of fracture toughness in terms of δ . 34
6.3.1 Determination of F and V , F and V , or F and V .
c c u u uc uc 34
6.3.2 Determination of F and V .
m m 35
6.3.3 Determination of V .
p 36
6.3.4 Calculation of δ .
0 36
6.3.5 Qualification of δ fracture toughness value .37
0
6.4 Determination of fracture toughness in terms of J . 38
6.4.1 Determination of F and V or q , F and V or q , or F and V or q .
c c c u u u uc uc uc 38
6.4.2 Determination of F and q .
m m 38
6.4.3 Determination of U .
p 38
6.4.4 Calculation of J .
0 39
6.4.5 Qualification of J fracture toughness value .40
0
© ISO 2021 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/FDIS 12135:2021(E)

7 Determination of resistance curves δ-Δa and J-Δa and initiation toughness δ and
0,2BL
J and δ and J for stable crack extension .41
0,2BL i i
7.1 General .41
7.2 Test procedure .41
7.2.1 General.41
7.2.2 Multiple­specimen procedure .41
7.2.3 Single­specimen procedure .41
7.2.4 Final crack front straightness .42
7.3 Calculation of J and δ . 42
7.3.1 Calculation of J . 42
7.3.2 Calculation of δ­ .42
7.4 R­curve plot .43
7.4.1 Plot construction .44
7.4.2 Data spacing and curve fitting .45
7.5 Qualification of resistance curves .46
7.5.1 Qualification of J-Δa resistance curves .46
7.5.2 Qualification of δ−Δa resistance curves .46
7.6 Determination and qualification of J and δ .
0,2BL 0,2BL 47
7.6.1 Determination of J . .
0,2BL 47
7.6.2 Determination of δ .
0,2BL 48
7.7 Determination of initiation toughness J and δ by scanning electron microscopy (SEM) .49
i i
8 Test report .49
8.1 Organization .49
8.2 Specimen, material and test environment .50
8.2.1 Specimen description .50
8.2.2 Specimen dimensions .50
8.2.3 Material description . .50
8.2.4 Additional dimensions .50
8.2.5 Test environment .50
8.2.6 Fatigue precracking conditions .50
8.3 Test data qualification .51
8.3.1 Limitations .51
8.3.2 Crack length measurements .51
8.3.3 Fracture surface appearance .51
8.3.4 Pop­in .51
8.3.5 Resistance curves .51
8.3.6 Checklist for data qualification .51
8.4 Qualification of K .
lc 52
8.5 Qualification of δ , δ , δ or δ .
c(B) u(B) uc(B) m(B) 52
8.6 Qualification of J , J , J or J .
c(B) u(B) uc(B) m(B) 53
8.7 Qualification of the δ­R Curve .53
8.8 Qualification of the J­R Curve .53
8.9 Qualification of δ as δ .
0,2BL(B) 0,2BL 53
8.10 Qualification of J as J .
0,2BL(B) 0,2BL 53
Annex A (informative) Determination of δ and J .55
i i
Annex B (normative) Crack plane orientation .60
Annex C (informative) Example test reports .62
Annex D (informative) Stress intensity factor coefficients and compliance relationships .71
Annex E (informative) Measurement of load-line displacement q in the three-point bend test .75
Annex F (informative) Derivation of pop-in formulae .80
Annex G (informative) Analytical methods for the determination of V and U .82
p p
Annex H (informative) Guidelines for single-specimen methods .83
Annex I (normative) Power-law fits to crack extension data (see Reference [42]) .97
iv © ISO 2021 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 12135:2021(E)

Bibliography .98
© ISO 2021 – All rights reserved v

---------------------- Page: 5 ----------------------
ISO/FDIS 12135:2021(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,
Subcommittee SC 4, Fatigue, fracture and toughness testing.
This third edition cancels and replaces the second edition (ISO 12135:2016), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— formulae to calculate CTOD have been replaced with those based on rigid rotation assumption
throughout; replacing the previous R­curve formulae based on CTOD from J. CTOD formulae for
SENBs are now those based on recent research to include the material yield to tensile strength ratio
in the CTOD formulae;
— the determination of J directly from displacement defined in terms of CMOD has been included, in
addition to the methods based on load line displacement;
— where fatigue precrack straightness requirements cannot be met due to internal residual stresses,
the application of modification techniques, originally developed for weld specimens, is now
permitted;
— the rotation correction factor for compact specimens has been revised with a new formula;
— editorial changes have been made to improve consistency of terms and definitions used throughout
the document.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
vi © ISO 2021 – All rights reserved

---------------------- Page: 6 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 12135:2021(E)
Metallic materials — Unified method of test for the
determination of quasistatic fracture toughness
1 Scope
This document specifies methods for determining fracture toughness in terms of K, δ, J and R­curves for
homogeneous metallic materials subjected to quasistatic loading. Specimens are notched, precracked
by fatigue and tested under slowly increasing displacement. The fracture toughness is determined for
individual specimens at or after the onset of ductile crack extension or at the onset of ductile crack
instability or unstable crack extension. In cases where cracks grow in a stable manner under ductile
tearing conditions, a resistance curve describing fracture toughness as a function of crack extension
is measured. In some cases in the testing of ferritic materials, unstable crack extension can occur
by cleavage or ductile crack initiation and growth, interrupted by cleavage extension. The fracture
toughness at crack arrest is not covered by this document. Special testing requirements and analysis
procedures are necessary when testing weldments, and these are described in ISO 15653 which is
complementary to this document.
Statistical variability of the results strongly depends on the fracture type, for instance, fracture
toughness associated with cleavage fracture in ferritic steels can show largely variation. For applications
that require high reliability, a statistical approach can be used to quantify the variability in fracture
toughness in the ductile­to­brittle transition region, such as that given in ASTM E1921. However, it is
not the purpose of this document to specify the number of tests to be carried out nor how the results of
the tests are to be applied or interpreted.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3785, Metallic materials — Designation of test specimen axes in relation to product texture
ISO 7500­1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
stress intensity factor
K
magnitude of the elastic stress-field singularity for a homogeneous, linear-elastic body
Note 1 to entry: The stress intensity factor is a function of applied force, crack length, specimen size and specimen
geometry.
© ISO 2021 – All rights reserved 1

---------------------- Page: 7 ----------------------
ISO/FDIS 12135:2021(E)

3.2
crack-tip opening displacement
δ
relative opening displacement of the crack surfaces normal to the original (undeformed) crack plane at
the tip of the fatigue precrack, evaluated using the rotation point formula
3.3
J-integral
line or surface integral that encloses the crack front from one crack surface to the other and
characterizes the local stress-strain field at the crack tip
3.4
J
loading parameter, equivalent to the J-integral (3.3), the specific values of which, experimentally
determined by this method of test (J , J , J ,…), characterize fracture toughness under elastic­plastic
c i u
conditions
3.5
stable crack extension
crack extension which stops or would stop when the applied displacement is held constant as a test
progresses under displacement control
3.6
unstable crack extension
abrupt crack extension occurring with or without prior stable crack extension (3.5)
3.7
pop-in
abrupt discontinuity in the force versus displacement record, featured as a sudden increase in
displacement and, generally, a decrease in force followed by an increase in force
Note 1 to entry: Displacement and force subsequently increase beyond their values at pop-in.
Note 2 to entry: When conducting tests by this method, pop-ins can result from unstable crack extension
(3.6) in the plane of the precrack and are to be distinguished from discontinuity indications arising from: i)
delaminations or splits normal to the precrack plane; ii) roller or pin slippage in bend or compact specimen
load trains, respectively; iii) improper seating of displacement gauges in knife edges; iv) ice cracking in low-
temperature testing; v) electrical interference in the instrument circuitry of force and displacement measuring
and recording devices.
3.8
crack extension resistance curves
R-curves
variation in δ (3.2) or J (3.4) with stable crack extension (3.5)
4 Symbols and abbreviated terms
Symbol Unit Designation
a mm Nominal crack length (for the purposes of fatigue precracking, an assigned value less
than a )
0
a mm Final crack length (a + Δa)
f 0
a mm Instantaneous crack length
i
a mm Length of machined notch
m
a mm Initial crack length
0
NOTE 1 This is not a complete list of parameters. Only the main parameters are given, other parameters are referred to in
the text.
NOTE 2 The values of all parameters used in calculations are assumed to be those measured or calculated for the
temperature of the test, unless otherwise specified.
2 © ISO 2021 – All rights reserved

---------------------- Page: 8 ----------------------
ISO/FDIS 12135:2021(E)

Symbol Unit Designation
Δa mm Stable crack extension including blunting
Δa mm Crack extension limit for δ or J controlled crack extension
max
B mm Specimen thickness
B mm Specimen net thickness between side groov
...