ISO 15850:2014

INTERNATIONAL ISO
STANDARD 15850
Second edition
2014-02-15
Plastics — Determination of tension-
tension fatigue crack propagation
— Linear elastic fracture mechanics
(LEFM) approach
Plastiques — Détermination de la propagation de fissure par fatigue
en traction — Approche de la mécanique linéaire élastique de la
rupture (LEFM)
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 5
5 Significance and use . 5
6 Test specimens. 6
6.1 Shape and size . 6
6.2 Preparation . 9
6.3 Notching . 9
6.4 Side grooves .10
6.5 Conditioning .10
7 Apparatus .10
7.1 Test machine .10
7.2 Grips .11
7.3 Crack length measurement .11
7.4 Test atmosphere .15
8 Test procedure .15
8.1 Measurement of specimen dimensions .15
8.2 Specimen mounting .15
8.3 Loading .15
8.4 Out-of-plane crack propagation .15
8.5 Discontinuous crack propagation .15
8.6 Number of tests .15
9 Calculation and interpretation of results .16
9.1 Crack length versus number of cycles .16
9.2 Crack curvature correction .16
9.3 Crack growth rate da/dN .16
9.4 Stress intensity factor range ΔK .16
9.5 Energy release rate range ΔG .17
10 Test report .17
10.1 General .17
10.2 For fatigue crack propagation test .17
10.3 For fatigue crack propagation to failure test .18
Annex A (informative) Abnormality in the use of cyclic fatigue crack propagation test for ranking
long-term static fatigue behaviour .19
Bibliography .23
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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electrotechnical standardization.
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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
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to Trade (TBT) see the following URL: Foreword - Supplementary information.
The committee responsible for this document is ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical
properties.
This second edition cancels and replaces the first edition (ISO 15850:2002) of which it constitutes a
minor revision.
iv © ISO 2014 – All rights reserved

INTERNATIONAL STANDARD ISO 15850:2014(E)
Plastics — Determination of tension-tension fatigue crack
propagation — Linear elastic fracture mechanics (LEFM)
approach
1 Scope
This International Standard specifies a method for measuring the propagation of a crack in a notched
specimen subjected to a cyclic tensile load varying between a constant positive minimum and a constant
positive maximum value. The test results include the crack length as a function of the number of load
cycles and the crack length increase rate as a function of the stress intensity factor and energy release
rate at the crack tip. The possible occurrence of discontinuities in crack propagation is detected and
reported.
The test can be also used for the purpose of determining the resistance to crack propagation failure. In
this case, the results can be presented in the form of number of cycles to failure or total time taken to
cause crack propagation failure versus the stress intensity factor (see Annex A).
The method is suitable for use with the following range of materials:
— rigid and semi-rigid thermoplastic moulding and extrusion materials (including filled and short-
fibre-reinforced compounds) plus rigid and semi-rigid thermoplastic sheets;
— rigid and semi-rigid thermosetting materials (including filled and short-fibre-reinforced compounds)
plus rigid and semi-rigid thermosetting sheets.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 291, Plastics — Standard atmospheres for conditioning and testing
ISO 527 (all parts), Plastics — Determination of tensile properties
ISO 2818, Plastics — Preparation of test specimens by machining
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
cycle
smallest segment of a load-time or stress-time function which is repeated periodically
Note 1 to entry: The terms fatigue cycle, load cycle, and stress cycle are also commonly used.
3.2
number of cycles completed
N
number of load cycles since the beginning of a test
3.3
waveform
shape of the load-time curve within a single cycle
3.4
maximum load
P
max
highest value of the load during a cycle
Note 1 to entry: It is expressed in newtons.
Note 2 to entry: Only positive, i.e. tensile, loads are used in this test method.
3.5
minimum load
P
min
lowest value of the load during a cycle
Note 1 to entry: It is expressed in newtons.
Note 2 to entry: Only positive, i.e. tensile, loads are used in this test method.
3.6
load range
ΔP
difference between the maximum and the minimum loads in one cycle, given by:
ΔP = P − P
max min
3.7
load ratio
stress ratio
R
ratio of the minimum to the maximum load in one cycle, i.e.:
P
min
R�
P
max
3.8
stress intensity factor
K
limiting value of the product of the stress σ (r) perpendicular to the crack area at a distance r from the
crack tip and of the square root of 2πr, as r tends to zero:
Kr=limσ() 2πr
r→0
[SOURCE: ISO 13586:2000, 3.3]
1/2
Note 1 to entry: It is expressed in pascal root metres (Pa⋅m ).
Note 2 to entry: The term factor is used here because it is in common usage, even though the quantity has
dimensions.
3.9
maximum stress intensity factor
K
max
highest value of the stress intensity factor in one cycle
2 © ISO 2014 – All rights reserved

3.10
minimum stress intensity factor
K
min
lowest value of the stress intensity factor in one cycle
3.11
stress intensity factor range
ΔK
difference between the maximum and minimum stress intensity factors in one cycle, given by:
ΔK = K − K
max min
3.12
energy release rate
G
difference between the external work δU done on a body to enlarge a cracked area by an amount δA
ext
and the corresponding change in strain energy δU :
S
δU δU
extS
G= −
...