Plastics — Determination of J-R curves — Fracture toughness

This document specifies a method for determining the fracture toughness in term of J and R curves for plastics. The method is suitable for use with ductile and semi-ductile polymers and polymer blends. It is not intended to be used with materials in which the crack front cannot be distinguished from additional deformation processes in advance of the crack tip. The method is unsuitable for polymers reinforced with fibres. NOTE J-R curves, produced in accordance with this test method, characterizes the crack growth resistance that cannot be characterized by linear elastic fracture mechanics according to ISO 13586.

Plastiques — Détermination des courbes J-R — Résistance à la rupture

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TECHNICAL ISO/TS
SPECIFICATION 28660
First edition
2022-04
Plastics — Determination of J-R curves
— Fracture toughness
Plastiques — Détermination des courbes J-R — Résistance à la
rupture
Reference number
ISO/TS 28660:2022(E)
© ISO 2022
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ISO/TS 28660:2022(E)
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© ISO 2022 – All rights reserved
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ISO/TS 28660:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms, definitions and symbols .......................................................................................................................................................... 1

3.1 Terms and definitions ...................................................................................................................................................................... 1

3.2 Symbols ......................................................................................................................................................................................................... 4

4 Principle ........................................................................................................................................................................................................................ 4

5 Apparatus .................................................................................................................................................................................................................... 4

5.1 Testing machine ........................................................................................................................................... .......................................... 4

5.1.1 General ........................................................................................................................................................................................ 4

5.1.2 Test speeds .............................................................................................................................................................................. 4

5.1.3 Force indicator ..................................................................................................................................................................... 5

5.2 Displacement transducer .............................................................................................................................................................. 5

5.3 Loading rigs ............................................................................................................................................................................................... 5

6 Test specimens ....................................................................................................................................................................................................... 6

6.1 General ........................................................................................................................................................................................................... 6

6.2 Shape and size ......................................................................................................................................................................................... 6

6.3 Preparation ................................................................................................................................................................................................ 8

6.4 Notching ....................................................................................................................................................................................................... 8

7 Procedure ....................................................................................................................................................................................................................9

7.1 General ........................................................................................................................................................................................................... 9

7.2 Thickness, width of test specimens ..................................................................................................................................... 9

7.3 Conditioning.............................................................................................................................................................................................. 9

7.4 Test speed ................................................................................................................................................................................................... 9

7.5 Number of specimens ....................................................................................................................................................................... 9

7.6 Testing procedure ................................................................................................................................................................................ 9

7.7 Crack length and crack extension measurement .................................................................................................. 10

7.8 Indentation correction ................................................................................................................................................................. 11

8 Calculation and interpretation of results ..............................................................................................................................11

8.1 General ........................................................................................................................................................................................................ 11

8.2 Calculation of J integral ................................................................................................................................................................ 12

8.2.1 Estimation of the slope ..............................................................................................................................................12

8.2.2 Splitting of the total energy, U ..........................................................................................................................12

8.2.3 Calculation of corrected energy ........................................................................................................................ 13

8.2.4 Calculate J integral .........................................................................................................................................................13

9 Validation of results ......................................................................................................................................................................................13

9.1 General ........................................................................................................................................................................................................13

9.2 Construction of J-R curves ......................................................................................................................................................... 13

10 Test reports ............................................................................................................................................................................................................14

11 Precision and bias ...........................................................................................................................................................................................15

11.1 General ........................................................................................................................................................................................................ 15

11.2 Splitting of energy ............................................................................................................................................................................ 15

Annex A (informative) .....................................................................................................................................................................................................16

Bibliography .............................................................................................................................................................................................................................20

iii
© ISO 2022 – All rights reserved
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ISO/TS 28660:2022(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

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.

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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

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2,

Mechanical properties.

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.
© ISO 2022 – All rights reserved
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TECHNICAL SPECIFICATION ISO/TS 28660:2022(E)
Plastics — Determination of J-R curves — Fracture
toughness
1 Scope

This document specifies a method for determining the fracture toughness in term of J and R curves for

plastics.

The method is suitable for use with ductile and semi-ductile polymers and polymer blends. It is not

intended to be used with materials in which the crack front cannot be distinguished from additional

deformation processes in advance of the crack tip. The method is unsuitable for polymers reinforced

with fibres.

NOTE J-R curves, produced in accordance with this test method, characterizes the crack growth resistance

that cannot be characterized by linear elastic fracture mechanics according to ISO 13586.

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 291, Plastics — Standard atmospheres for conditioning and testing
ISO 2818, Plastics — Preparation of test specimens by machining

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

ISO 13586, Plastics — Determination of fracture toughness (GIC and KIC) — Linear elastic fracture

mechanics (LEFM) approach

ASTM D 6068, Standard Test Method for Determining J-R Curves of Plastic Materials

3 Terms, definitions and symbols
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 13586, ASTM D6068-96 and

the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
© ISO 2022 – All rights reserved
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ISO/TS 28660:2022(E)
3.1.1
J-integral

line or surface integral over a path that enclosed the crack front from one crack surface to the other,

used to characterise the local stress-strain field around the crack front
Note 1 to entry: See Reference [5].
Note 2 to entry: It is expressed in Joules per square meter (kJ/m ).
3.1.2
J-R curve
J-Δa
plot of resistance to stable physical crack extension
3.1.3
net thickness
distance between the roots of the side grooves in side grooved specimens
Note 1 to entry: It is expressed in millimetres (mm).
3.1.4
thickness
side to side dimension of the test specimen
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: shown in Figure 2 and Figure 3.
3.1.5
specimen width
larger initial dimension of the rectangular cross section of the test specimen
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: shown in Figure 2 and Figure 3.
3.1.6
original crack size
physical crack size at the start of testing
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: shown in Figure 2 and Figure 3.
3.1.7
original uncracked ligament

distance from the original crack front to the back edge of the specimen given as follows:

bW=−a
Note 1 to entry: It is expressed in millimetres (mm).
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ISO/TS 28660:2022(E)
3.1.8
crack size
physical crack size to the observed final crack front
Note 1 to entry: It is expressed in millimetres (mm).

Note 2 to entry: The size shall be a calculated average of several measurements along the crack front. See Figure 6

and Figure 7.
3.1.9
crack extension
increase in physical crack size given as:
Δaa=− a
pp 0
Note 1 to entry: It is expressed in millimetres (mm).
3.1.10
specimen span
distance between specimen rollers
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: Shown in Figure 1.
3.1.11
corrected energy
energy required to extend the crack
Note 1 to entry: It is expressed in Joules (J).
Note 2 to entry: See 8.1.
3.1.12
displacement
displacement measured by the transducer or extensometer
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: see Figure 8.
3.1.13
slope
slope of the linear portion of the force versus displacement curve
Note 1 to entry: see Figure 8.
3.1.14
geometrical functions
ηη ηη
el, pl
functions representing the notch depth influence
Note 1 to entry: See 8.2.4.
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ISO/TS 28660:2022(E)
3.2 Symbols
l total length of the test specimen (see Figures 2 and 3)

elastic part of total energy UT, determined from the area under the force versus displacement

Tel
(see Figure 8)

U plastic part of total energy UT, determined from the area under the force versus displacement

Tpl
(see Figure 8)
U total energy, expressed in joules (J)

U elastic part of corrected energy U, required to extend the crack, in Joules (J)

U plastic part of corrected energy U, required to extend the crack, in Joules (J)

f elastic part of displacement, expressed in millimetres (mm)
f plastic part of displacement, expressed in millimetres (mm)
4 Principle

This test method describes a multiple specimen technique for determining the J-R curves for polymeric

materials. The J-R curves consist of plot of J versus crack extension in the region of J-controlled growth

(see Figure 9). This method uses optical measurements of crack length and crack extension on the

fracture surfaces after each test.

There are two options for specimen geometries - three-point bend (SENB) and pin-loaded compact

tension (CT) specimens. The J-R curves from bend specimens represent lower bound estimation to

those obtained from compact tension specimens.

The largest possible specimen with representative microstructure is recommended. The J-R curves

tend to exhibit lower slope with increasing thickness.
The specimens are notched and tested under slowly increasing displacement.

Test carried out on specimens of different dimensions or with different notches, or specimens prepared

under different conditions, may produce results that are not comparable. Other factors, such as test

speed or conditioning of the specimens, can also influence the results. Consequently, when comparable

data are required, these factors shall be carefully controlled and recorded.
5 Apparatus
5.1 Testing machine
5.1.1 General

The machine shall be in accordance with ISO 7500-1 and ISO 9513, and meet the specification given in

5.1.2 and 5.1.3.
5.1.2 Test speeds

The tensile-testing machine shall be capable of maintaining the test speeds as specified in Table 1.

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ISO/TS 28660:2022(E)
Table 1 — Recommended test speeds
Test speed (mm/min) Tolerance (%)
0,125 ±20
0,25
0,5
20 ±10
100
200
300
500
5.1.3 Force indicator

The force measurement system shall be in accordance with class 1 according to ISO 7500-1.

5.2 Displacement transducer

The displacement is recorded during the test. The transducer shall be essentially free from inertia lag at

the test speeds being used. It shall measure the displacement with accuracy w
...

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