ISO/TS 28660:2022

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 2022
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ii
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
T
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
Foreword
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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/
3.1.1
J-integral
J
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
p
plot of resistance to stable physical crack extension
3.1.3
net thickness
B
N
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
B
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
W
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
a
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
b
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).
3.1.8
crack size
a
p
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
Δa
p
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
S
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
U
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
f
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
α
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.
3.2 Symbols
l total length of the test specimen (see Figures 2 and 3)
U
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)
T
U elastic part of corrected energy U, required to extend the crack, in Joules (J)
el
U plastic part of corrected energy U, required to extend the crack, in Joules (J)
pl
f elastic part of displacement, expressed in millimetres (mm)
el
f plastic part of displacement, expressed in millimetres (mm)
pl
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.
Table 1 — Recommended test speeds
Test speed (mm/min) Tolerance (%)
0,125 ±20
0,25
0,5
20 ±10
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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