ISO/FDIS 12135

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
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Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 12135:2021(E)
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DRAFT INTERNATIONAL STANDARDS MAY ON
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NATIONAL REGULATIONS. ISO 2021
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ISO/FDIS 12135:2021(E)
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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 .................. ......................................................................................................................... ......

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 ........................................................................................

6.2.1 General...................................................................................................................................................................................32

6.2.2 Interpretation of the test record for F .......................................................................................................

6.2.3 Calculation of K ..............................................................................................................................................................

6.2.4 Qualification of K as K ...........................................................................................................................................

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 .....................................................................

6.3.2 Determination of F and V .................................................................................................................................

6.3.3 Determination of V .....................................................................................................................................................

6.3.4 Calculation of δ ...............................................................................................................................................................

6.3.5 Qualification of δ fracture toughness value .........................................................................................37

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 .........................

6.4.2 Determination of F and q ..................................................................................................................................

6.4.3 Determination of U .....................................................................................................................................................

6.4.4 Calculation of J ................................................................................................................................................................

6.4.5 Qualification of J fracture toughness value ..........................................................................................40

7 Determination of resistance curves δ-Δa and J-Δa and initiation toughness δ and

J and δ and J for stable crack extension .........................................................................................................................41

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 ..............................................................................................

7.6.1 Determination of J ........................................................................................................................................... ....

7.6.2 Determination of δ .............................................................................................................................................

7.7 Determination of initiation toughness J and δ by scanning electron microscopy (SEM) ..49

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 ...............................................................................................................................................................................

8.5 Qualification of δ , δ , δ or δ .......................................................................................................................

8.6 Qualification of J , J , J or J ............................................................................................................................

8.7 Qualification of the δ­R Curve .................................................................................................................................................53

8.8 Qualification of the J­R Curve ...................................................................................................................................................53

8.9 Qualification of δ as δ ...........................................................................................................................................

8.10 Qualification of J as J ..............................................................................................................................................

Annex A (informative) Determination of δ and J .................................................................................................................................55

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

Annex H (informative) Guidelines for single-specimen methods .......................................................................................83

Annex I (normative) Power-law fits to crack extension data (see Reference [42]) ..........................................97

Bibliography .............................................................................................................................................................................................................................98

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This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,

This third edition cancels and replaces the second edition (ISO 12135:2016), which has been technically

— 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

— the determination of J directly from displacement defined in terms of CMOD has been included, in

— 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

— 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

Any feedback or questions on this document should be directed to the user’s national standards body. A

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

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 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

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

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

relative opening displacement of the crack surfaces normal to the original (undeformed) crack plane at

line or surface integral that encloses the crack front from one crack surface to the other and

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

crack extension which stops or would stop when the applied displacement is held constant as a test

abrupt crack extension occurring with or without prior stable crack extension (3.5)

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 mm Nominal crack length (for the purposes of fatigue precracking, an assigned value less

NOTE 1 This is not a complete list of parameters. Only the main parameters are given, other parameters are referred to in

NOTE 2 The values of all parameters used in calculations are assumed to be those measured or calculated for the