EN ISO 178:2010

SLOVENSKI STANDARD
01-julij-2011
1DGRPHãþD
SIST EN ISO 178:2003
SIST EN ISO 178:2003/A1:2005
3ROLPHUQLPDWHULDOL'RORþDQMHXSRJLEQLKODVWQRVWL,62
Plastics - Determination of flexural properties (ISO 178:2010)
Kunststoffe - Bestimmung der Biegeeigenschaften (ISO 178:2010)
Plastiques - Détermination des propriétés en flexion (ISO 178:2010)
Ta slovenski standard je istoveten z: EN ISO 178:2010
ICS:
83.080.01 Polimerni materiali na Plastics in general
splošno
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 178
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2010
ICS 83.080.01 Supersedes EN ISO 178:2003
English Version
Plastics - Determination of flexural properties (ISO 178:2010)
Plastiques - Détermination des propriétés en flexion (ISO Kunststoffe - Bestimmung der Biegeeigenschaften (ISO
178:2010) 178:2010)
This European Standard was approved by CEN on 14 December 2010.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2010 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 178:2010: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
This document (EN ISO 178:2010) has been prepared by Technical Committee ISO/TC 61 “Plastics” in
collaboration with Technical Committee CEN/TC 249 “Plastics” the secretariat of which is held by NBN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by June 2011, and conflicting national standards shall be withdrawn at
the latest by June 2011.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 178:2003.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 178:2010 has been approved by CEN as a EN ISO 178:2010 without any modification.

INTERNATIONAL ISO
STANDARD 178
Fifth edition
2010-12-15
Plastics — Determination of flexural
properties
Plastiques — Détermination des propriétés en flexion

Reference number
ISO 178:2010(E)
©
ISO 2010
ISO 178:2010(E)
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ii © ISO 2010 – All rights reserved

ISO 178:2010(E)
Contents Page
Foreword .iv
1 Scope.1
2 Normative references.2
3 Terms and definitions .2
4 Principle .5
5 Test machine.5
5.1 General .5
5.2 Test speed.5
5.3 Supports and loading edge .6
5.4 Force- and deflection-measuring systems .6
5.5 Equipment for measuring the width and thickness of the test specimens.7
6 Test specimens.8
6.1 Shape and dimensions .8
6.2 Anisotropic materials.9
6.3 Preparation of test specimens .9
6.4 Specimen inspection.10
6.5 Number of test specimens.10
7 Atmosphere for conditioning and testing.10
8 Procedure.10
9 Calculation and expression of results .13
9.1 Flexural stress .13
9.2 Flexural strain .13
9.3 Flexural modulus.14
9.4 Statistical parameters .14
9.5 Significant figures .14
10 Precision .15
11 Test report.15
Annex A (informative) Precision statement.16
Annex B (informative) Influence of changes in test speed on the measured values of flexural
properties .18
Bibliography.19

ISO 178:2010(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.
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 178 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical
properties.
This fifth edition cancels and replaces the fourth edition (ISO 178:2001), which has been technically revised to
[2]
harmonize it with ISO 527-2 with respect to the test speeds used for the determination of the flexural
modulus and for the determination of other flexural properties. This has been done by specifying two methods,
method A and method B. Method A is identical to the method specified in previous editions of ISO 178, i.e. it
uses the same strain rate throughout the test, whereas method B uses two different strain rates (see 1.8 for
details).
It also incorporates the Amendment ISO 178:2001/Amd.1:2004.
iv © ISO 2010 – All rights reserved

INTERNATIONAL STANDARD ISO 178:2010(E)

Plastics — Determination of flexural properties
1 Scope
1.1 This International Standard specifies a method for determining the flexural properties of rigid (see 3.12)
and semi-rigid plastics under defined conditions. A standard test specimen is defined, but parameters are
included for alternative specimen sizes for use where appropriate. A range of test speeds is included.
1.2 The method is used to investigate the flexural behaviour of the test specimens and to determine the
flexural strength, flexural modulus and other aspects of the flexural stress/strain relationship under the
conditions defined. It applies to a freely supported beam, loaded at midspan (three-point loading test).
1.3 The method is suitable for use with the following range of materials:
⎯ thermoplastic moulding, extrusion and casting materials, including filled and reinforced compounds in
addition to unfilled types; rigid thermoplastics sheets;
⎯ thermosetting moulding materials, including filled and reinforced compounds; thermosetting sheets.
[5] [6]
In agreement with ISO 10350-1 and ISO 10350-2 , this International Standard applies to fibre-reinforced
compounds with fibre lengths u 7,5 mm prior to processing. For long-fibre-reinforced materials (laminates)
[7]
with fibre lengths > 7,5 mm, see ISO 14125 .
The method is not normally suitable for use with rigid cellular materials or sandwich structures containing
[3] [4]
cellular material. In such cases, ISO 1209-1 and/or ISO 1209-2 can be used.
NOTE For certain types of textile-fibre-reinforced plastic, a four-point bending test is preferred. This is described in
ISO 14125.
1.4 The method is performed using specimens which may be either moulded to the specified dimensions,
machined from the central section of a standard multipurpose test specimen (see ISO 20753) or machined
from finished or semi-finished products, such as mouldings, laminates, or extruded or cast sheet.
1.5 The method specifies the preferred dimensions for the test specimen. Tests which are carried out on
specimens of different dimensions, or on specimens which are prepared under different conditions, can
produce results which are not comparable. Other factors, such as the test speed and the conditioning of the
specimens, can also influence the results.
NOTE Especially for semi-crystalline polymers, the thickness of the oriented skin layer, which is dependent on the
moulding conditions, also affects the flexural properties.
1.6 The method is not suitable for the determination of design parameters but can be used in materials
testing and as a quality control test.
1.7 For materials exhibiting non-linear stress/strain behaviour, the flexural properties are only nominal. The
equations given have been derived assuming linear elastic behaviour and are valid for deflections of the
specimen that are small compared to its thickness. With the preferred specimen (which measures
80 mm × 10 mm × 4 mm) at the conventional flexural strain of 3,5 % and a span-to-thickness ratio, L/h, of 16,
the deflection is 1,5h. Flexural tests are more appropriate for stiff and brittle materials showing small
deflections at break than for very soft and ductile ones.
ISO 178:2010(E)
1.8 Contrary to the previous editions of this International Standard, this edition specifies two methods,
method A and method B. Method A is identical to the method in previous editions of this International
Standard, i.e. it uses a strain rate of 1 %/min throughout the test. Method B uses two different strain rates:
1 %/min for the determination of the flexural modulus and 5 %/min or 50 %/min, depending on the ductility of
the material, for the determination of the remainder of the flexural stress-strain curve.
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 293, Plastics — Compression moulding of test specimens of thermoplastic materials
ISO 294-1:1996, Plastics — Injection moulding of test specimens of thermoplastic materials — Part 1: General
principles, and moulding of multipurpose and bar test specimens
ISO 295, Plastics — Compression moulding of test specimens of thermosetting materials
ISO 2602, Statistical interpretation of test results — Estimation of the mean — Confidence interval
ISO 2818, Plastics — Preparation of test specimens by machining
ISO 7500-1, 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 extensometers used in uniaxial testing
ISO 10724-1, Plastics — Injection moulding of test specimens of thermosetting powder moulding compounds
(PMCs) — Part 1: General principles, and moulding of multipurpose test specimens
ISO 16012, Plastics — Determination of linear dimensions of test specimens
ISO 20753, Plastics — Test specimens
ISO 23529, Rubber — General procedures for preparing and conditioning test pieces for physical test
methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
test speed
v
rate of relative movement between the specimen supports and the loading edge
NOTE It is expressed in millimetres per minute (mm/min).
3.2
flexural stress
σ
f
nominal stress at the outer surface of the test specimen at midspan
NOTE It is calculated from the relationship given in 9.1, Equation (5), and is expressed in megapascals (MPa).
2 © ISO 2010 – All rights reserved

ISO 178:2010(E)
3.3
flexural stress at break
σ
fB
flexural stress at break of the test specimen (see Figure 1, curves a and b)
NOTE It is expressed in megapascals (MPa).
3.4
flexural strength
σ
fM
maximum flexural stress sustained by the test specimen during a bending test (see Figure 1, curves a and b)
NOTE It is expressed in megapascals (MPa).
3.5
flexural stress at conventional deflection
σ
fc
flexural stress at the conventional deflection, s , defined in 3.7 (see also Figure 1, curve c)
C
NOTE It is expressed in megapascals (MPa).
3.6
deflection
s
distance over which the top or bottom surface of the test specimen at midspan deviates from its original
position during flexure
NOTE It is expressed in millimetres (mm).
3.7
conventional deflection
s
C
deflection equal to 1,5 times the thickness, h, of the test specimen
NOTE 1 It is expressed in millimetres (mm).
NOTE 2 Using a span, L, of 16h, the conventional deflection corresponds to a flexural strain (see 3.8) of 3,5 %.
3.8
flexural strain
ε
f
nominal fractional change in length of an element of the outer surface of the test specimen at midspan
NOTE 1 It is expressed as a dimensionless ratio or a percentage (%).
NOTE 2 It is calculated in accordance with the relationships given in 9.2, Equations (6) and (7).
ISO 178:2010(E)
Curve a Specimen that breaks before yielding.
Curve b Specimen that gives a maximum and then breaks before the conventional deflection, s .
C
Curve c Specimen that neither gives a maximum nor breaks before the conventional deflection, s .
C
Figure 1 — Typical curves of flexural stress, σ , versus flexural strain, ε , and deflection, s
f f
3.9
flexural strain at break
ε
fB
flexural strain at which the test specimen breaks (see Figure 1, curves a and b)
NOTE It is expressed as a dimensionless ratio or a percentage (%).
3.10
flexural strain at flexural strength
ε
fM
flexural strain at maximum flexural stress (see Figure 1, curves a and b)
NOTE It is expressed as a dimensionless ratio or a percentage (%).
3.11
modulus of elasticity in flexure
flexural modulus
E
f
ratio of the stress difference, σ − σ , to the corresponding strain difference, ε (= 0,002 5) − ε (= 0,000 5)
f2 f1 f2 f1
[see 9.3, Equation (9)]
NOTE 1 It is expressed in megapascals (MPa).
NOTE 2 The flexural modulus is only an approximate value of Young's modulus of elasticity.
4 © ISO 2010 – All rights reserved

ISO 178:2010(E)
3.12
rigid plastic
plastic that has a modulus of elasticity in flexure or, if that is not applicable, then in tension, greater than
700 MPa
[1]
[ISO 472 ]
3.13
span between specimen supports
L
distance between the points of contact between the test specimen and the test specimen supports (see
Figure 2)
NOTE It is expressed in millimetres (mm).
3.14
flexural strain rate
r
rate at which the flexural strain (see 3.8) increases during a test
−1 −1
NOTE It is expressed in reciprocal seconds (s ) or percent per second (%⋅s ).
4 Principle
A test specimen of rectangular cross-section, resting on two supports, is deflected by means of a loading edge
acting on the specimen midway between the supports. The test specimen is deflected in this way at a
constant rate at midspan until rupture occurs at the outer surface of the specimen or until a maximum strain of
5 % (see 3.8) is reached, whichever occurs first. During this procedure, the force applied to the specimen and
the resulting deflection of the specimen at midspan are measured.
5 Test machine
5.1 General
The machine shall comply with ISO 7500-1 and ISO 9513 and the requirements given in 5.2 to 5.4.
5.2 Test speed
The test machine shall be capable of maintaining the test speed (see 3.1), as specified in Table 1.
Table 1 — Recommended values of the test speed, v
Test speed, v Tolerance
mm/min %
a
1 ±20
2 ±20
5 ±20
10 ±20
20 ±10
50 ±10
100 ±10
200 ±10
500 ±10
a
The lowest speed is used for specimens with thicknesses between 1 mm
and 3,5 mm (see also 8.5).
ISO 178:2010(E)
5.3 Supports and loading edge
Two supports and a central loading edge shall be arranged as shown in Figure 2. The supports and the
loading edge shall be parallel to within ±0,2 mm over the width of the test specimen.
The radius, R , of the loading edge and the radius, R , of the supports shall be as follows:
1 2
R = 5,0 mm ± 0,2 mm;
R = 2,0 mm ± 0,2 mm for test specimen thicknesses u 3 mm;
R = 5,0 mm ± 0,2 mm for test specimen thicknesses > 3 mm.
The span, L, shall be adjustable.

Key
1 test specimen h thickness of specimen
F applied force l length of specimen
R radius of loading edge L length of span between supports
R radius of supports
Figure 2 — Position of test specimen at start of test
5.4 Force- and deflection-measuring systems
5.4.1 Force-measuring system
The force-measuring system shall comply with the requirements of class 1 as defined in ISO 7500-1.
5.4.2 Deflection-measuring system
The deflection-measuring system shall comply with the requirements of class 1 as defined in ISO 9513. This
shall be valid over the whole range of deflections to be measured. Non-contact systems may be used
provided they meet the accuracy requirements stated above. The measurement system shall not be
influenced by machine compliance.
6 © ISO 2010 – All rights reserved

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