ISO 12111:2011

INTERNATIONAL ISO
STANDARD 12111
First edition
2011-08-15
Metallic materials — Fatigue testing —
Strain-controlled thermomechanical
fatigue testing method
Matériaux métalliques — Essais de fatigue — Méthode d'essai de
fatigue thermo-mécanique avec déformation contrôlée

Reference number
©
ISO 2011
©  ISO 2011
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ii © ISO 2011 – All rights reserved

Contents Page
Foreword .v
Introduction.vi
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Symbols.3
5 Apparatus.4
5.1 Testing machine .4
5.2 Strain measuring system.5
5.3 Heating system .5
5.4 Instrumentation for test monitoring .5
5.5 Checking and verification of the apparatus.6
6 Specimens.6
6.1 Geometry.6
6.2 Preparation of specimens.9
6.3 Machining procedure .10
6.4 Sampling and marking.10
6.5 Surface condition of the specimen.11
6.6 Dimensional check .11
6.7 Storage and handling of specimens.11
7 Procedure.12
7.1 Laboratory environment .12
7.2 Specimen mounting .12
7.3 Temperature control.12
7.4 Temperature gradients.12
7.5 Mechanical strain control .13
7.6 Thermal strain compensation .13
7.7 Temperature/mechanical strain phasing .15
7.8 Command waveforms .16
7.9 Start of test.16
7.10 Monitoring the test .17
7.11 Failure criteria.17
7.12 Failure.18
7.13 Test interruption sequence .18
8 Expression of results.18
8.1 Preliminary data.18
8.2 Reduction of recorded data.18
8.3 Analysis of results.18
9 Test report.19
9.1 Aim of the study .19
9.2 Material .19
9.3 Specimen.19
9.4 Test equipment details.19
9.5 Description of test methodology .19
9.6 Test termination technique including definition of failure.19
9.7 Deviations from specified test tolerances or recommended procedures .19
9.8 Test conditions .20
9.9 Presentation of results.20
Annex A (informative) Representative diagrams .21
Annex B (informative) Modulus of elasticity determination.24
Bibliography .25

iv © ISO 2011 – 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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 12111 was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 5, Fatigue testing.
Introduction
The fatigue lives of structural components subjected to simultaneously occurring thermal and mechanical
loadings are often of critical interest and concern to design engineers. A common approach to investigating
the behaviours of materials subjected to combined thermal and mechanical loadings is to idealize the
conditions of a critical material element on a uniaxial laboratory test specimen. The test condition is one where
cyclic, theoretically uniform, within the test section, temperature and strain fields are externally imposed,
simultaneously varied and controlled. Such a test is designated as “thermomechanical fatigue”, commonly
abbreviated as TMF.
In order to ensure reliability and consistency of results from different laboratories, it is necessary to generate
and collect all data using test methodologies that comply with an established standard.
This International Standard addresses both the generation and presentation of TMF data.

vi © ISO 2011 – All rights reserved

INTERNATIONAL STANDARD ISO 12111:2011(E)

Metallic materials — Fatigue testing — Strain-controlled
thermomechanical fatigue testing method
1 Scope
This International Standard is applicable to the TMF testing of uniaxially loaded metallic specimens under
strain control. Specifications allow for any constant cyclic amplitude of mechanical strain and temperature with
any constant cyclic mechanical strain ratio and any constant cyclic temperature-mechanical strain phasing.
NOTE A list and sketch of the most common cyclic types is shown in Annex A.
The range of cycles considered corresponds to that which is generally considered as the low-cycle fatigue
domain, that is, N ≤ 10 .
f
2 Normative references
The following referenced documents are indispensable for the application 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 7500-1:2004, Metallic materials — Verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Verification and calibration of the force-measuring system
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
ISO 12106, Metallic materials — Fatigue testing — Axial-strain-controlled method
ISO 23718, Metallic materials — Mechanical testing — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 23718 and ISO 12106 and the
following apply.
3.1
stress
σ
F /A , where F is the instantaneous force and A is the original cross-sectional area at room temperature
i o i o
3.2
original gauge length
L
o
length on the specimen between extensometer measurement points at room temperature and zero strain
NOTE This definition avoids the complexity of a continually varying gauge length due to thermal expansion and
contraction.
3.3
gauge length
L
instantaneous length on the specimen between extensometer measurement points
3.4
strain
ε
∆L/L , where ∆L is the change in length and L is the gauge length measured at room temperature
o o
3.5
total strain
ε
tot
algebraic sum of the mechanical and thermal strains:
ε = ε + ε
tot m th
3.6
thermal strain
ε
th
strain corresponding to the free expansion induced by a change in temperature
3.7
mechanical strain
ε
m
strain that is independent of temperature and is associated with the applied force on the specimen
3.8
elastic strain
strain component resulting when the stress is divided by the temperature-dependent Young's modulus
3.9
inelastic strain
strain component resulting when the elastic strain is subtracted from the mechanical strain
3.10
cycle
smallest segment of the strain-temperature-time pattern that is repeated periodically
3.11
maximum
greatest algebraic value of a variable within one cycle
3.12
minimum
least algebraic value of a variable within one cycle
3.13
mean
one-half of the algebraic sum of the maximum and minimum values of a variable
3.14
range
algebraic difference between the maximum and minimum values of a variable
3.15
amplitude
half the range of a variable
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