ISO 12108:2018

INTERNATIONAL ISO
STANDARD 12108
Third edition
2018-07
Metallic materials — Fatigue testing —
Fatigue crack growth method
Matériaux métalliques — Essais de fatigue — Méthode d'essai de
propagation de fissure en fatigue
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
4.1 Symbols . 4
4.2 Abbreviated terms for specimen identification . 5
5 Apparatus . 5
6 Specimens . 6
6.1 General . 6
6.2 Crack plane orientation . 6
6.3 Starter notch precracking details. 8
6.4 Stress-intensity factor .10
6.5 Specimen size .10
6.6 Specimen thickness .10
6.7 Residual stress . .10
7 Procedure.11
7.1 Fatigue precracking .11
7.2 Crack length measurement .11
−5
7.3 Constant-force-amplitude, Κ-increasing, test procedure for da/dN > 10 mm/cycle .12
−5
7.4 K-decreasing procedure for da/dN < 10 mm/cycle .13
8 Crack length measurement .15
8.1 Resolution .15
8.2 Interruption .15
8.3 Static force .15
8.4 Measurement interval .15
8.5 Symmetry.16
8.6 Out-of-plane cracking .16
8.7 Crack tip bifurcation .16
8.8 Non-visual crack length measurement .16
8.9 Visual crack length measurement .16
9 Calculations.16
9.1 Crack-front curvature .16
9.2 Determining the fatigue crack growth rate .17
9.2.1 General.17
9.2.2 Secant method .17
9.2.3 Incremental polynomial method .18
9.3 Determination of the fatigue crack growth threshold .18
10 Test report .18
10.1 General .18
10.2 Material .18
10.3 Test specimen .19
10.4 Precracking terminal values .19
10.5 Test conditions .19
10.6 Test analysis .20
10.7 Presentation of results .20
Annex A (normative) Compact tension (CT) specimen .27
Annex B (normative) Centre crack tension (CCT) specimen .32
Annex C (normative) Single edge notch tension (SENT) specimen .38
Annex D (normative) Single edge notch bend (SENB) specimens .41
Annex E (informative) Non-visual crack length measurement methodology — Electric
[9][12][36]
potential difference .48
Bibliography .51
iv © ISO 2018 – All rights reserved

Foreword
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URL: 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.
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 third edition cancels and replaces the second edition (ISO 12108:2012), which has been technically
revised. The main changes compared to the previous edition are as follows:
— The document has been reorganized to move the formulae and drawings for each of the test
specimens from the main body of the document into a separate normative annex for each specimen.
— Guidance on the effects of residual stress on fatigue crack growth rate data has been expanded.
Introduction
This document is intended to provide specifications for generation of fatigue crack growth rate data.
Test results are expressed in terms of the fatigue crack growth rate as a function of crack-tip stress-
[15][16][17]
intensity factor range, ΔK, as defined by the theory of linear elastic fracture mechanics
[18][19][20]
. Expressed in these terms, the results characterize a material's resis
...