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 2016
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved

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
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
iv © ISO 2016 – All rights reserved

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 on 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 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.
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.
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.
2 © ISO 2016 – All rights reserved

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)
J MJ/m Experimental equivalent to the J-integral
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)
J MJ/m J at upper limit of J-controlled crack extension
g
J MJ/m Size-insensitive fracture resistance J at initiation of stable crack extension
i
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)
J MJ/m Limit of J-R material behaviour defined by this method of test
max
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)
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)
J MJ/m J uncorrected for stable crack extension
o
J MJ/m Size insensitive fracture resistance J at 0,2 mm stable crack extension offset from the
0,2BL
construction line
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 parameters used in calculations are assumed to be those measured or calculated for the
temperature of the test, unless otherwise specified.
Table 1 (continued)
Symbol Unit Designation
K Stress intensity factor
MPa m
K Maximum value of K during the final stages of fatigue precracking
f
MPa m
K Plane strain linear elastic fracture toughness
lc
MPa m
K Plane strain linear elastic fracture toughness equivalent to J
J0,2BL 0,2BL
MPa m
K A provisional value of K
Q lc
MPa m
q mm Load-point displacement
R MPa Ultimate tensile strength perpendicular to crack plane at the test temperature
m
R MPa 0,2 % offset yield strength perpendicular to crack plane at the test temperature
p0,2
S mm Span between outer loading points in a three-point bend test
T °C Test temperature
U J Area under plot of force F versus specimen load-point displacement q at the load-line
U J Elastic component of U
e
U J Plastic component of U
p
V mm Notch-opening displacement
V mm Elastic component of V
e
V mm Plastic component of V
p
W mm Width of the test specimen
z mm For bend and straight-notch compact specimens, the initial distance of the notch opening
gauge measurement position from the notched edge of the specimen, either further from
the crack tip [+z in Figure 8 b)] or closer to the crack tip (−z); or, for a stepped-notch
compact specimen, the initial distance of the notch opening gauge measurement position
either beyond (+z) or before (−z) the initial load-line
δ mm Crack-tip opening displacement (CTOD) evaluated using the rotation point formula
δ mm Crack-tip opening displacement (CTOD) evaluated from J
J
δ mm Size sensitive fracture resistance δ at the onset of unstable crack extension or pop-in
c(B)
when stable crack extension is less than 0,2 mm crack offset from the construction line
(B = specimen thickness in mm)
δ mm δ at the limit of δ-controlled crack extension
g
δ mm Fracture resistance δ at initiation of stable crack extension
Ji J
δ mm Size sensitive fracture resistance δ at the first attainment of a maximum force plateau
m(B)
for fully plastic behaviour (B = specimen thickness in mm)
δ mm Limit of δ -R defined by this method of test
J,max J
δ mm Size sensitive fracture resistance δ 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)
δ mm Size sensitive fracture resistance δ at the onset of unstable crack extension or pop-in
uc(B)
when stable crack extension Δa cannot be measured (B = specimen thickness in mm)
δ mm δ uncorrected for stable crack extension
o
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 parameters used in calculations are assumed to be those measured or calculated for the
temperature of the test, unless otherwise specified.
4 © ISO 2016 – All rights reserved

Table 1 (continued)
Symbol Unit Designation
δ mm Size insensitive fracture resistance δ at 0,2 mm crack extension offset from construc-
J0,2BL J
tion line
δ mm Size sensitive fracture resistance δ at 0,2 mm stable crack extension offset from con-
J0,2BL(B) J
struction line (B = specimen thickness in mm)
ν — Poisson’s ratio
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 parameters used in calculations are assumed to be those measured or calculated for the
temperature of the test, unless otherwise specified.
5 General requirements
5.1 General
The fracture toughness of metallic materials can be characterized in terms of either specific (single
point) values (see Clause 6), or a continuous curve relating fracture resistance to crack extension over
a limited range of crack extension (see Clause 7). The procedures and parameters used to determine
fracture toughness vary depending upon the level of plasticity realized in the test specimen during
the test. Under any given set of conditions, however, any one of the fatigue-precracked test specimen
configurations specified in this method may be used to measure any of the fracture toughness
parameters considered. In all cases, tests are performed by applying slowly increasing displacements
to the test specimen and measuring the forces and displacements realized during the test. The
forces and displacements are then used in conjunction with certain pre-test and post-test specimen
measurements to determine the fracture toughness that characterizes the material’s resistance to
crack extension. Details of the test specimens and general information relevant to the determination
of all fracture parameters are given in this method. A flow-chart illustrating the way this method can
be used is presented in Figure 1. Characteristic types of force versus displacement records obtained in
fracture toughness tests are shown in Figure 2.
Figure 1 — General flowchart showing how to use the standard method of test
6 © ISO 2016 – All rights reserved

Key
a
Fracture.
b
Pop-in.
NOTE 1  F , F and F correspond to either δ , δ and δ respectively, or J , J and J respectively.
c u m c u m c u m
NOTE 2  Pop-in behaviour is a function of the testing machine/specimen compliance and the recorder response rate.
Figure 2 — Characteristics types of force versus displacement records in fracture tests
5.2 Fracture parameters
Specific (point) values of fracture toughness are determined from individual specimens to define the
onset of unstable crack extension or describe stable crack extension.
NOTE K characterizes the resistance to extension of a sharp crack so that i) the state of stress near the
lc
crack front closely approximates plane strain, and ii) the crack tip plastic zone is small compared with the
specimen crack size, thickness and ligament ahead of the crack.
K is considered a size-insensitive measurement of fracture toughness under the above conditions.
lc
Certain test criteria shall be met in order to qualify measurements of K .
lc
The parameters δ , J , δ , J , δ and J also characterize the resistance of a material to unstable
c c u u uc uc
extension of a sharp crack. However, these measurements are regarded as size-sensitive and as such
characterize only the specimen thickness tested. The specimen thickness is thus noted in millimetre
units in parentheses appended to the parameter symbol when reporting a test result.
When stable crack extension is extensive, test procedure and fracture toughness measurement shall
be performed as specified in Clause 7. Stable crack extension is characterized either in terms of crack
tip opening displacement δ and fracture toughness J parameters, or of a continuous δ - and
J0,2BL 0,2BL J
J-resistance curve. The values δ and J , regarded as specimen size insensitive, are engineering
J0,2BL 0,2BL
estimates of the onset of stable crack extension, not to be confused with the actual initiation toughness
δ and J Measurement of δ and J is described in Annex A.
Ji i. Ji i
Two procedures are available for determining δ and J . The multiple specimen procedure
0,2BL 0,2BL
requires several nominally identical specimens to be monotonically loaded, each to different amounts
of displacement. Measurements of force and displacement are made and recorded. Specimen crack
fronts are marked (e.g. by heat tinting or post-test fatiguing) after testing, thus enabling measurement
of stable crack extension on the specimen halves after each specimen is broken open. Post-test cooling
of ferritic material specimens to ensure brittle behaviour may be helpful in preserving crack front
markings prior to breaking open the specimens.
A minimum of six specimens is required by the multiple-specimen method. When material availability
is limited, a single-specimen procedure based on either unloading compliance or the potential drop
technique may be used. There is no restriction on the single-specimen procedure providing sufficient
accuracy can be demonstrated. In all cases, certain criteria are to be met before δ or J values
J0,2BL 0,2BL
and δ - or J-resistance curves are qualified by this standard method of test.
J
5.3 Fracture toughness symbols
Fracture toughness symbols identified in this document are given in Table 2.
Table 2 — Fracture toughness symbols
Size sensitive quantities
Qualifying limits
Parameter Size insensitive quantities (specific to thickness
to R-curves
B tested)
K
lc
K
K
J0,2BL
δ
c(B)
δ
Ji
δ, δ δ δ , δ (Δa )
J J0,2BL(B) J,g J,g max
δ
J0,2BL
δ , δ , δ
u(B) uc(B) m(B)
J
c(B)
J
i
J J J J (Δa )
0,2BL(B) g, g max
J
0,2BL
J , J , J
u(B) uc(B) m(B)
5.4 Test specimens
5.4.1 Specimen configuration and size
Dimensions and tolerances of specimens shall conform to Figures 3 to 5.
8 © ISO 2016 – All rights reserved

Surface roughness values in micrometres
Key
a
See Figures 6 to 8 and 5.4.2.3.
NOTE 1 Integral or attachable knife edges for clip gauge attachment may be used (see Figures 8 and 9).
NOTE 2 For starter notch and fatigue crack configuration, see Figure 6.
NOTE 3 1,0 ≤ W/B ≤ 4,0 (W/B = 2 preferred).
NOTE 4 0,45 ≤ a/W ≤ 0,70. For K determination, 0,45 ≤ a/W ≤ 0,55.
lc
The intersection of the crack starter notch tips with the two specimen surfaces shall be equally distant from the top
and bottom edges of the specimen to within 0,005 W.
Figure 3 — Proportional dimensions and tolerances for bend specimen
Surface roughness values in micrometres
Key
a
See Figures 6 to 8 and 5.4.2.3.
NOTE 1 Integral or attachable knife edges for clip gauge attachment may be used (see Figures 8 and 9).
NOTE 2 For starter notch and fatigue crack configuration, see Figure 6.
NOTE 3 0,8 ≤ W/B ≤ 4,0 (W/B = 2 preferred).
NOTE 4 0,45 ≤ a/W ≤ 0,70. For K determination, 0,45 ≤ a/W ≤ 0,55.
lc
+0,004 W
NOTE 5 Alternative pin hole diameter, ∅ 0,188 W .
The intersection of the crack starter notch tips with the two specimen surfaces shall be equally distant from the top
and bottom edges of the specimen to within 0,005 W.
Figure 4 — Proportional dimensions and tolerances for straight-notch compact specimen
10 © ISO 2016 – All rights reserved

Surface roughness values in micrometres
Key
a
See Figures 6 to 8.
NOTE 1 Integral or attachable knife edges for clip gauge attachment may be used (see Figures 8 and 9).
NOTE 2 For starter notch and fatigue crack configuration, see Figure 6.
NOTE 3 0,8 ≤ W/B ≤ 4,0 (W/B = 2 preferred).
NOTE 4 0,45 ≤ a/W ≤ 0,70. For K determination, 0,45 ≤ a/W ≤ 0,55.
lc
NOTE 5 Second step may not be necessary for some clip gauges; configuration optional providing fatigue crack
starter notch and fatigue crack fit within the envelope represented in Figure 6.
+0,004 W
Alternative pin hole diameter, ∅ 0,188 W . When this pin size in used, notch opening may be
NOTE 6
increased to 0,21 W maximum.
The intersection of the crack starter notch tips with the two specimen surfaces shall be equally distant from the top
and bottom edges of the specimen to within 0,005 W.
Figure 5 — Proportional dimensions and tolerances for stepped-notch compact specimen
The choice of specimen design shall take into consideration the likely outcome of the test (see Figure 1),
any preference for δ or J fracture toughness values, the crack plane orientation of interest (Annex B)
and the quantity and condition of test material available.
NOTE 1 All specimen designs (Figures 3 to 5) are suitable for determining K , δ and J values, although there
lc
are special procedural requirements for J values calculated from measurements made away from the load line.
Table 3 provides guidance on specimen size for K measurement.
lc
Table 3 — Minimum recommended thickness for K testing
lc
B
R
p02,
mm
E
≥0,005 0 <0,005 7 75
≥0,005 7 <0,006 2 63
≥0,006 2 <0,006 5 50
≥0,006 5 <0,006 8 44
≥0,006 8 <0,007 1 38
≥0,007 1 <0,007 5 32
≥0,007 5 <0,008 0 25
≥0,008 0 <0,008 5 20
≥0,008 5 <0,010 0 13
≥0,010 0 7
NOTE 2 When notch opening displacement V is measured on the load line, V = q for the stepped-notch compact
specimen (see Figure 5). The stepped-notch specimen is thus equally useful for the determination of values of K ,
lc
δ and J.
NOTE 3 For both the bend and compact configurations, a specimen width-to-thickness ratio (W/B) of 2 is
preferred, but values ranging from 1 to 4 for bend specimens and 0,8 to 4 for compact specimens are allowed.
Evidence suggests that specimen proportions of W/B = 4 yield slightly higher R-curves than the lesser proportions
of W/B = 2.
5.4.2 Specimen preparation
5.4.2.1 Material condition
Specimens shall be machined from material in the final heat treated and/or mechanically worked
condition.
NOTE 1 In the exceptional circumstance where a material cannot be machined in its final heat treated condition,
such final heat treatment may be carried out after machining provided that the specimen’s required dimensions
and tolerances, shape, and surface finishes are met, and full account is taken of the effects of specimen dimensions
on the metallurgical condition induced by certain heat treatments, for example, water quenching of steels.
NOTE 2 Residual stresses can influence the measurement of quasistatic fracture toughness. The effect can be
significant when test coupons are taken from material that characteristically embodies residual stress fields;
e.g. weldments, complex shapes, such as die forgings, stepped extrusions, castings where full stress relief is
not possible, or parts with intentionally-induced residual stresses. Specimens taken from such products that
contain residual stresses will likewise themselves contain residual stress. While extraction of the specimen in
itself partially relieves and redistributes the pattern of residual stress, the remaining magnitude can affect the
test result. Residual stress is superimposed on applied stress and results in actual crack-tip stress intensity that
is different from that based solely on externally applied forces or displacements. Distortion during specimen
machining, specimen configuration d
...