ISO 12135:2016

INTERNATIONAL ISO
STANDARD 12135
Second edition
2016-11-15
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 12135:2016(E)
©
ISO 2016

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ISO 12135:2016(E)

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ii © ISO 2016 – All rights reserved

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ISO 12135:2016(E)

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and designations . 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 .12
5.5 Pre-test requirements .18
5.5.1 Pre-test measurements .18
5.5.2 Crack shape/length requirements .19
5.6 Test apparatus .19
5.6.1 Calibration .19
5.6.2 Force application .19
5.6.3 Displacement measurement .19
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
o
5.8.3 Stable crack extension, Δa .28
5.8.4 Unstable crack extension .28
6 Determination of fracture toughness for stable and unstable crack extension .29
6.1 General .29
6.2 Determination of plane strain fracture toughness, K .30
lc
6.2.1 General.30
6.2.2 Interpretation of the test record for F .30
Q
6.2.3 Calculation of K .31
Q
6.2.4 Qualification of K as K .32
Q lc
6.3 Determination of fracture toughness in terms of δ .32
6.3.1 Determination of F and V , F and V , or F and V .32
c c u u uc uc
6.3.2 Determination of F and V .34
m m
6.3.3 Determination of V .34
p
6.3.4 Calculation of δ .34
ο
6.3.5 Qualification of δ fracture toughness value .35
ο
6.4 Determination of fracture toughness in terms of J .35
6.4.1 Determination of F and q , F and q , or F and q .35
c c u u uc uc
6.4.2 Determination of F and q .36
m m
6.4.3 Determination of U .36
p
6.4.4 Calculation of J .37
o
6.4.5 Qualification of J fracture toughness value .37
o
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ISO 12135:2016(E)

7 Determination of resistance curves δ -Δa and J-Δa and initiation toughness δ
J J0,2BL
and J and δ and J for stable crack extension .38
0,2BL Ji i
7.1 General .38
7.2 Test procedure .38
7.2.1 General.38
7.2.2 Multiple-specimen procedure .38
7.2.3 Single-specimen procedure .38
7.2.4 Final crack front straightness .38
7.3 Calculation of J and δ .39
J
7.3.1 Calculation of J .39
7.3.2 Calculation of δ .39
J
7.4 R-curve plot .40
7.4.1 Plot construction .41
7.4.2 Data spacing and curve fitting .42
7.5 Qualification of resistance curves .42
7.5.1 Qualification of J-Δa resistance curves .42
7.5.2 Qualification of δ −Δa resistance curves .43
J
7.6 Determination and qualification of J and δ .44
0,2BL J0,2BL
7.6.1 Determination of J .44
0,2BL
7.6.2 Determination of δ .45
J0,2BL
7.7 Determination of initiation toughness J and δ by scanning electron microscopy (SEM) 46
i Ji
8 Test report .46
8.1 Organization .46
8.2 Specimen, material and test environment .47
8.2.1 Specimen description .47
8.2.2 Specimen dimensions .47
8.2.3 Material description . .47
8.2.4 Additional dimensions .47
8.2.5 Test environment .47
8.2.6 Fatigue precracking conditions .47
8.3 Test data qualification .48
8.3.1 Limitations .48
8.3.2 Crack length measurements .48
8.3.3 Fracture surface appearance .48
8.3.4 Pop-in .48
8.3.5 Resistance curves .48
8.3.6 Checklist for data qualification .48
8.4 Qualification of K .49
lc
8.5 Qualification of the δ -R Curve .49
J
8.6 Qualification of the J-R Curve .50
8.7 Qualification of δ as δ .50
J0,2BL(B) J0,2BL
8.8 Qualification of J as J .50
0,2BL(B) 0,2BL
Annex A (informative) Determination of δ and J .51
Ji i
Annex B (normative) Crack plane orientation .56
Annex C (informative) Example test reports .57
Annex D (normative) Stress intensity factor coefficients and compliance relationships .66
Annex E (informative) Measurement of load-line displacement q in the three-point bend test .71
Annex F (informative) Derivation of pop-in formulae .76
Annex G (informative) Analytical methods for the determination of V and U .78
p p
Annex H (informative) Guidelines for single-specimen methods .80
Annex I (normative) Power-law fits to crack extension data (see Reference [42]) .95
Bibliography .96
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ISO 12135:2016(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
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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
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Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 4, Toughness testing — Fracture (F), Pendulum (P), Tear (T).
This second edition cancels and replaces the first edition (ISO 12135:2002), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 12135:2002/Cor 1:2008.
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INTERNATIONAL STANDARD ISO 12135:2016(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 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. 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 most cases, statistical variability of
the results is modest and reporting the average of three or more test results is acceptable. In cases of
cleavage fracture of ferritic materials in the ductile-to-brittle transition region, variability can be large
and additional tests may be required to quantify statistical variability. Special testing requirements
and analysis procedures are necessary when testing weldments and these are described in ISO 15653
which is complementary to this document.
When fracture occurs by cleavage or when cleavage is preceded by limited ductile crack extension,
it may be useful to establish the reference temperature for the material by conducting testing and
[2]
analysis in accordance with ASTM E1921.
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:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
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.
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ISO 12135:2016(E)

3.2
crack-tip opening displacement
δ
relative 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
crack-tip opening displacement
δ
J
estimate of the crack-tip opening displacement, obtained from J
3.4
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
3.5
J
loading parameter, equivalent to the J-integral, specific values of which, experimentally determined by
this method of test (J , J , J ,…), characterize fracture toughness under elastic-plastic conditions
c i u
3.6
stable crack extension
crack extension which stops or would stop when the applied displacement is held constant as a test
progresses under displacement control
3.7
unstable crack extension
abrupt crack extension occurring with or without prior stable crack extension
3.8
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 may result from unstable crack extension 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.
3.9
crack extension resistance curves
R-curves
variation in δ or J with stable crack extension
J
4 Symbols and designations
See Table 1.
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ISO 12135:2016(E)

Table 1 — Symbols and their designations
Symbol Unit Designation
a mm Nominal crack length (for the purposes of fatigue precracking, an assigned value less
than a )
o
a mm Final crack length (a + Δa)
f o
a mm Instantaneous crack length
i
a mm Length of machined notch
m
a mm Initial crack length
o
A J Plastic component of the area under the force vs. notch opening displacement diagram
p
(Figure 17)
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
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 16)
F kN Maximum fatigue precracking force
f
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 Provisional force value used for the calculation of K
Q Q
F kN Applied force at the onset of unstable crack extension or pop-in when Δa is equal to or
u
greater than than 0,2 mm offset from the construction line (Figure 2)
2
J MJ/m Experimental equivalent to the J-integral
2
J MJ/m Size sensitive fracture resistance J at onset of unstable crack extension or pop-in when
c(B)
stable crack extension is less than 0,2 mm offset from the construction line (B = speci-
men thickness in mm)
2
J MJ/m J at upper limit of J-controlled crack extension
g
2
J MJ/m Size-insensitive fracture resistance J at initiation of stable crack extension
i
2
J MJ/m Size sensitive fracture resistance J at the first attainment of a maximum force plateau
m(B)
for fully plastic behaviour (B = specimen thickness in mm)
2
J MJ/m Limit of J-R material behaviour defined by this method of test
max
2
J MJ/m Size sensitive fracture resistance J at the onset of unstable crack extension or pop-in
u(B)
when the event is preceded by stable crack extension equal to or greater than 0,2 mm
offset from the construction line (B = specimen thickness in mm)
2
J MJ/m Size sensitive fracture resistance J at the onset of unstable crack extension or pop-in
uc(B)
when stable crack extension cannot be measured (B = specimen thickness in mm)
2
J MJ/m J uncorrected for stable crack extension
o
2
J MJ/m Size insensitive fracture resistance J at 0,2 mm stable crack extension offset from the
0,2BL
construction line
2
J MJ/m Size sensitive fracture resistance J at 0,2 mm stable crack extension offset from the
0,2BL(B)
construction line (B = specimen thickness in mm)
NOTE 1 This is not a complete list of parameters. Only the main parameters are given here, other parameters are referred
to in the text.
NOTE 2 The values of all pa
...