SIST EN ISO 178:2019
(Main)Plastics - Determination of flexural properties (ISO 178:2019)
Plastics - Determination of flexural properties (ISO 178:2019)
This document specifies a method for determining the flexural properties of rigid and semi-rigid plastics under defined conditions. A preferred test specimen is defined, but parameters are included for alternative specimen sizes for use where appropriate. A range of test speeds is included.
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).
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.
In agreement with ISO 10350-1[5] and ISO 10350-2[6], this document applies to fibre-reinforced compounds with fibre lengths ≤7,5 mm prior to processing. For long-fibre-reinforced materials (laminates) with fibre lengths >7,5 mm, see ISO 14125[7].
The method is not normally suitable for use with rigid cellular materials or sandwich structures containing cellular material. In such cases, ISO 1209-1[3] and/or ISO 1209-2[4] can be used.
NOTE 1 For certain types of textile-fibre-reinforced plastic, a four-point bending test is used. This is described in ISO 14125.
The method is performed using specimens which can 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.
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 2 Especially for injection moulded semi-crystalline polymers, the thickness of the oriented skin layer, which is dependent on the moulding conditions, also affects the flexural properties.
The method is not suitable for the determination of design parameters but can be used in materials testing and as a quality control test.
Kunststoffe - Bestimmung der Biegeeigenschaften (ISO 178:2019)
Dieses Dokument legt ein Verfahren zur Ermittlung der Biegeeigenschaften von steifen und halbsteifen Kunststoffen unter definierten Bedingungen fest. Ein bevorzugter Probekörper wird festgelegt, jedoch sind die Parameter für andere gegebenenfalls anzuwendende Probekörpergrößen enthalten. Ein Bereich von Prüfgeschwindigkeiten ist enthalten.
Das Verfahren wird für die Untersuchung des Biegeverhaltens der Probekörper und für die Bestimmung der Biegefestigkeit, des Biegemoduls und anderer Gesichtspunkte der Beziehung Biegespannung/Biegedehnung unter den definierten Bedingungen eingesetzt. Es bezieht sich auf einen frei unterstützten Biegebalken, der mittig belastet wird (Dreipunkt-Biegeversuch).
Das Prüfverfahren ist zur Anwendung auf folgende Werkstoffgruppen geeignet:
— thermoplastische Formmassen, Extrusions- und Vergussmassen, einschließlich gefüllter und verstärkter Compounds in Ergänzung zu ungefüllten Sorten; steife thermoplastische Platten;
— duroplastische Formmassen, einschließlich gefüllter und verstärkter Compounds; duro¬plastische Platten.
In Übereinstimmung mit ISO 10350 1 [5] und ISO 10350 2 [6] gilt dieses Dokument für faserverstärkte Compounds mit Faserlängen ≤ 7,5 mm vor der Verarbeitung. In Bezug auf langfaserverstärkte Werkstoffe (Laminate) mit Faserlängen > 7,5 mm siehe ISO 14125 [7].
Das Verfahren ist üblicherweise nicht für Hartschäume oder Schicht Verbundwerkstoffe geeignet, die geschäumte Strukturen enthalten. In solchen Fällen können ISO 1209 1 [3] und/oder ISO 1209 2 [4] angewendet werden.
ANMERKUNG 1 Für bestimmte Sorten textilfaserverstärkter Kunststoffe wird ein Vierpunktbiegeversuch angewendet. Dies ist in ISO 14125 beschrieben.
Das Verfahren wird mit Probekörpern durchgeführt, die direkt in den festgelegten Maßen gegossen, aus dem Mittelteil eines Standard Vielzweckprobekörpers (siehe ISO 20753) herausgearbeitet oder aus fertigen oder halbfertigen Produkten wie Formteilen, Laminate oder extrudierten oder gegossenen Platten aus¬gearbeitet werden können.
Das Verfahren legt die bevorzugten Maße für den Probekörper fest. Prüfungen an Probekörpern mit abweichenden Maßen oder Probekörpern, die unter anderen Bedingungen hergestellt wurden, können zu Ergebnissen führen, die nicht vergleichbar sind. Andere Einflüsse, wie z. B. die Prüfgeschwindigkeit und das Konditionieren der Probekörper können ebenfalls die Prüfergebnisse beeinflussen.
ANMERKUNG 2 Besonders bei spritzgegossenen teilkristallinen Polymeren wirkt sich die Dicke der orientierten Außenhaut, die von den Spritzgießbedingungen abhängt, auch auf die Biegeeigenschaften aus.
Das Verfahren ist nicht für die Bestimmung von Konstruktionseigenschaften geeignet, kann jedoch für Materialprüfungen und in der Qualitätskontrolle eingesetzt werden.
Plastiques - Détermination des propriétés en flexion (ISO 178:2019)
Le présent document spécifie une méthode pour la détermination des propriétés en flexion des plastiques rigides et semi-rigides dans des conditions définies. Une éprouvette recommandée est définie, mais des paramètres sont inclus pour d'autres dimensions d'éprouvettes lorsque l'usage est approprié. Une gamme de vitesses d'essai est incluse.
La méthode est utilisée pour l'étude du comportement en flexion des éprouvettes et pour la détermination de la résistance en flexion, du module en flexion et d'autres aspects des relations entre la contrainte et la déformation en flexion dans les conditions définies. Elle s'applique à une poutre supportée sans contrainte, chargée au milieu de sa portée (essai de chargement en trois points).
La méthode est adaptée à la gamme de matériaux suivants:
— matériaux thermoplastiques pour moulage, extrusion et coulée, y compris les compositions chargées et renforcées en plus des types non chargés; feuilles thermoplastiques rigides;
— matériaux thermodurcissables pour moulage, y compris les compositions chargées et renforcées; feuilles thermodurcissables.
En accord avec l'ISO 10350-1[5] et l'ISO 10350-2,[6] le présent document s'applique aux compositions renforcées de fibres dont les longueurs avant mise en œuvre sont inférieures ou égales à 7,5 mm. Pour les matériaux renforcés de fibres longues (stratifiés) avec des longueurs de fibres supérieures à 7,5 mm, voir l'ISO 14125[7].
La méthode n'est normalement pas adaptée pour utilisation avec des matériaux alvéolaires rigides ou à structures sandwich contenant des matériaux alvéolaires. Dans ces cas, les normes ISO 1209-1[3] et/ou ISO 1209-2[4] peuvent être utilisées.
NOTE 1 Pour certains types de plastiques renforcés de fibres textiles, un essai de flexion en quatre points est utilisé. Ce dernier est décrit dans l'ISO 14125.
La méthode est réalisée à l'aide d'éprouvettes qui peuvent être soit moulées aux dimensions spécifiées, soit usinées à partir de la partie centrale d'une éprouvette normalisée à usages multiples (voir l'ISO 20753) ou usinées à partir de produits finis ou semi-finis, tels que des pièces moulées, des stratifiés ou des feuilles extrudées ou coulées.
La méthode spécifie les dimensions recommandées pour les éprouvettes. Des essais réalisés avec des éprouvettes de dimensions différentes ou avec des éprouvettes préparées dans des conditions différentes peuvent donner des résultats qui ne sont pas comparables. D'autres facteurs, tels que la vitesse d'essai et le conditionnement des éprouvettes, peuvent également influer sur les résultats.
NOTE 2 En fonction des conditions de moulage, pour les polymères semi-cristallins moulés par injection en particulier, l'épaisseur de la couche (peau) orientée affecte les propriétés en flexion.
La méthode n'est pas adaptée pour la détermination des paramètres de calcul mais elle peut être utilisée pour les essais de matériaux et comme essai dans un contrôle qualité.
Polimerni materiali - Določanje upogibnih lastnosti (ISO 178:2019)
Ta dokument določa metodo za določanje upogibnih lastnosti togih in poltogih polimernih materialov pri določenih pogojih. Določen je prednostni preskušanec, vendar so dodani parametri za druge velikosti preskušancev za uporabo po potrebi. Vključen je nabor preskusnih hitrosti.
Metoda se uporablja za preučevanje upogibnih lastnosti preskušancev in za določanje
upogibne trdnosti, modula upogibnosti in drugih vidikov razmerja upogibna napetost/deformacija pri določenih pogojih. Uporablja se za prosto podprt nosilec, obremenjen na sredini (preskus z obremenitvijo v treh točkah).
Metoda je ustrezna za naslednje vrste materialov:
– plastomerni materiali za oblikovanje, ekstrudiranje in ulivanje, vključno s polnjenimi, nepolnjenimi in ojačenimi spojinami; trde plastomerne plošče;
– termoreaktivni materiali za oblikovanje, vključno s polnjenimi in ojačenimi spojinami; termoreaktivne plošče.
V skladu s standardoma ISO 10350-1[5] in ISO 10350-2[6] se ta dokument nanaša na spojine, ojačene z vlakni dolžine ≤ 7,5 mm pred predelavo. Za z dolgimi vlakni ojačene materiale (laminate) z dolžino vlaken > 7,5 mm glej ISO 14125[7].
Metoda običajno ni primerna za trde penjene materiale ali strukture tipa »sendvič«, ki vsebujejo penjeni material. V takih primerih se uporablja ISO 1209-1[3] in/ali ISO 1209-2[4].
OPOMBA 1: Za nekatere vrste polimernih materialov, ojačenih s tekstilnimi vlakni, se uporablja štiritočkovni preskus upogibanja. Ta je opisan v standardu ISO 14125.
Metoda se izvaja s preskušanci, ki so lahko oblikovani na določene mere,
strojno obdelani iz osrednjega dela standardnega večnamenskega preskusnega vzorca (glej ISO 20753) ali strojno obdelani iz končnih izdelkov ali polizdelkov, kot so oblikovanci, laminati ali ekstrudirane oziroma lite plošče.
Metoda določa prednostne dimenzije preskusnih vzorcev. Preskusi, ki se opravljajo
na preskušancih drugih velikosti ali na preskušancih, ki so pripravljeni pod drugačnimi pogoji, lahko dajo rezultate, ki niso primerljivi. Na rezultate lahko vplivajo tudi drugi dejavniki, kot sta hitrost preskušanja in priprava preskušancev.
OPOMBA 2: Debelina usmerjenega vrhnjega sloja, ki je odvisna od pogojev oblikovanja, vpliva tudi na upogibne lastnosti, zlasti za polkristalinične polimere, oblikovane z brizganjem.
Metoda ni primerna za ugotavljanje parametrov zasnove, lahko pa se uporabi za preskušanje materialov
in kot preskus za nadzor kakovosti.
General Information
Relations
Related Packages
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 178:2019
01-julij-2019
Nadomešča:
SIST EN ISO 178:2011
SIST EN ISO 178:2011/A1:2014
Polimerni materiali - Določanje upogibnih lastnosti (ISO 178:2019)
Plastics - Determination of flexural properties (ISO 178:2019)
Kunststoffe - Bestimmung der Biegeeigenschaften (ISO 178:2019)
Plastiques - Détermination des propriétés en flexion (ISO 178:2019)
Ta slovenski standard je istoveten z: EN ISO 178:2019
ICS:
83.080.01 Polimerni materiali na Plastics in general
splošno
SIST EN ISO 178:2019 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 178:2019
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SIST EN ISO 178:2019
EN ISO 178
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2019
EUROPÄISCHE NORM
ICS 83.080.01 Supersedes EN ISO 178:2010
English Version
Plastics - Determination of flexural properties (ISO
178:2019)
Plastiques - Détermination des propriétés en flexion Kunststoffe - Bestimmung der Biegeeigenschaften (ISO
(ISO 178:2019) 178:2019)
This European Standard was approved by CEN on 23 March 2019.
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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 178:2019 E
worldwide for CEN national Members.
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SIST EN ISO 178:2019
EN ISO 178:2019 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 178:2019
EN ISO 178:2019 (E)
European foreword
This document (EN ISO 178:2019) 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 November 2019, and conflicting national standards
shall be withdrawn at the latest by November 2019.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 178:2010.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 178:2019 has been approved by CEN as EN ISO 178:2019 without any modification.
3
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SIST EN ISO 178:2019
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SIST EN ISO 178:2019
INTERNATIONAL ISO
STANDARD 178
Sixth edition
2019-04
Plastics — Determination of flexural
properties
Plastiques — Détermination des propriétés en flexion
Reference number
ISO 178:2019(E)
©
ISO 2019
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SIST EN ISO 178:2019
ISO 178:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
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SIST EN ISO 178:2019
ISO 178:2019(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 2
4 Principle . 5
5 Test machine . 5
5.1 General . 5
5.2 Test speed . 6
5.3 Supports and loading edge . 6
5.4 Force- and deflection-measuring systems . 6
5.4.1 Introductory remarks . 6
5.4.2 Definition of precision and accuracy requirements . 6
5.4.3 Deflection measurement . 8
5.5 Equipment for measuring the width and thickness of the test specimens . 9
6 Test specimens. 9
6.1 Shape and dimensions . 9
6.1.1 General. 9
6.1.2 Preferred specimen type . 9
6.1.3 Other test specimens .10
6.2 Anisotropic materials .10
6.3 Preparation of test specimens .11
6.3.1 From moulding, extrusion and casting compounds .11
6.3.2 From sheets .11
6.4 Specimen inspection .11
6.5 Number of test specimens .12
7 Atmosphere for conditioning and testing .12
8 Procedure.12
9 Calculation and expression of results .16
9.1 Flexural stress .16
9.2 Flexural strain .16
9.3 Flexural modulus .16
9.4 Statistical parameters .17
9.5 Significant figures .17
10 Precision .17
11 Test report .17
Annex A (informative) Precision statement .19
Annex B (informative) Influence of changes in test speed on the measured values of
flexural properties .21
Annex C (normative) Compliance correction for Type III-tests .22
Annex D (informative) Relation between tensile and flexural modulus: Theoretical
expectations and experimental observations .24
Bibliography .25
© ISO 2019 – All rights reserved iii
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SIST EN ISO 178:2019
ISO 178:2019(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.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
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 the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical properties.
This sixth edition cancels and replaces the fifth edition (ISO 178:2010), which has been technically
revised. It also incorporates the Amendment ISO 178:2010/Amd.1:2013. The main changes compared to
the previous edition are as follows:
— differentiating calibration requirements according to the type of test;
— the introduction of deflectometers;
— the reinstatement of procedures for compliance correction;
— the addition of a new Annex D showing the relation between tensile and flexural modulus.
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.
iv © ISO 2019 – All rights reserved
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SIST EN ISO 178:2019
INTERNATIONAL STANDARD ISO 178:2019(E)
Plastics — Determination of flexural properties
1 Scope
This document specifies a method for determining the flexural properties of rigid and semi-rigid
plastics under defined conditions. A preferred test specimen is defined, but parameters are included for
alternative specimen sizes for use where appropriate. A range of test speeds is included.
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).
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 document applies to fibre-reinforced
compounds with fibre lengths ≤7,5 mm prior to processing. For long-fibre-reinforced materials
[7]
(laminates) with fibre lengths >7,5 mm, see ISO 14125 .
The method is not normally suitable for use with rigid cellular materials or sandwich structures
[3] [4]
containing cellular material. In such cases, ISO 1209-1 and/or ISO 1209-2 can be used.
NOTE 1 For certain types of textile-fibre-reinforced plastic, a four-point bending test is used. This is described
in ISO 14125.
The method is performed using specimens which can 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.
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 2 Especially for injection moulded semi-crystalline polymers, the thickness of the oriented skin layer,
which is dependent on the moulding conditions, also affects the flexural properties.
The method is not suitable for the determination of design parameters but can be used in materials
testing and as a quality control test.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 294-1:2017, Plastics — Injection moulding of test specimens of thermoplastic materials — Part 1:
General principles, and moulding of multipurpose and bar test specimens
© ISO 2019 – All rights reserved 1
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SIST EN ISO 178:2019
ISO 178:2019(E)
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 — 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 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
3 Terms, definitions and symbols
For the purposes of this document, the following terms and definitions 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
test speed
v
rate of relative movement between the specimen supports and the loading edge
Note 1 to entry: 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 1 to entry: It is calculated from the relationship given in Formula (5).
Note 2 to entry: It is expressed in megapascals (MPa).
3.3
flexural stress at break
σ
fB
flexural stress at break of the test specimen
Note 1 to entry: It is expressed in megapascals (MPa).
Note 2 to entry: See Figure 1, curves a and b.
3.4
flexural strength
σ
fM
maximum flexural stress (3.2) sustained by the test specimen during a bending test
Note 1 to entry: It is expressed in megapascals (MPa).
Note 2 to entry: See Figure 1, curves a and b.
2 © ISO 2019 – All rights reserved
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SIST EN ISO 178:2019
ISO 178:2019(E)
3.5
flexural stress at conventional deflection
σ
fc
flexural stress at the conventional deflection, s (3.7)
C
Note 1 to entry: It is expressed in megapascals (MPa).
Note 2 to entry: See also Figure 1, curve c.
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 1 to entry: It is expressed in millimetres (mm).
3.7
conventional deflection
s
C
deflection (3.6) equal to 1,5 times the thickness, h, of the test specimen
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: Using a span, L, of 16h, the conventional deflection corresponds to a flexural strain (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 to entry: It is expressed as a dimensionless ratio or a percentage (%).
Note 2 to entry: It is calculated in accordance with the relationships given in Formulae (6) and (7).
© ISO 2019 – All rights reserved 3
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SIST EN ISO 178:2019
ISO 178:2019(E)
Key
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
Note 1 to entry: It is expressed as a dimensionless ratio or a percentage (%).
Note 2 to entry: See Figure 1, curves a and b.
3.10
flexural strain at flexural strength
ε
fM
flexural strain at maximum flexural stress
Note 1 to entry: It is expressed as a dimensionless ratio or a percentage (%).
Note 2 to entry: See Figure 1, curves a and b.
3.11
modulus of elasticity in flexure
flexural modulus
E
f
ratio of the stress difference, σ − σ , to the corresponding strain difference,
f2 f1
ε (= 0,002 5) − ε (= 0,000 5)
f2 f1
Note 1 to entry: It is expressed in megapascals (MPa).
Note 2 to entry: The flexural modulus is only an approximate value of Young's modulus.
Note 3 to entry: See Formula (9).
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SIST EN ISO 178:2019
ISO 178:2019(E)
3.12
rigid plastic
plastic that has a modulus of elasticity in flexure (3.11) or, if that is not applicable, then in tension, greater
than 700 MPa under a given set of conditions
[SOURCE: ISO 472:2013, 2.884, modified — Note to entry has been omitted.]
3.13
semi rigid plastic
plastic that has a modulus of elasticity in flexure (3.11) or, if that is not applicable, then in tension,
between 70 MPa and 700 MPa under a given set of conditions
[SOURCE: ISO 472:2013, 2.909, modified — Note to entry has been omitted.]
3.14
span between specimen supports
L
distance between the points of contact between the test specimen and the test specimen supports
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: See Figure 2.
3.15
flexural strain rate
r
rate at which the flexural strain (3.8) increases during a test
−1
Note 1 to entry: It is expressed in percent per minute (% ⋅ min ).
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.
This document specifies two methods: method A and method B. Method A 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.
NOTE 1 The strain rates mentioned above are to be interpreted as nominal ones. Nominal test speeds are
calculated using Formula (4). For the machine settings the best fitting ones are selected from Table 1.
NOTE 2 For materials exhibiting nonlinear stress/strain behaviour, the flexural properties are only
nominal. The formulae 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.
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.
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ISO 178:2019(E)
5.2 Test speed
The test machine shall be capable of maintaining the test speed, 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).
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;
1
R = 2,0 mm ± 0,2 mm for test specimen thicknesses ≤3 mm;
2
R = 5,0 mm ± 0,2 mm for test specimen thicknesses >3 mm.
2
The span, L, shall be adjustable.
5.4 Force- and deflection-measuring systems
5.4.1 Introductory remarks
Flexural tests, according to the specific requirements on the data to be obtained, can be differentiated in
several classes, comprising different complexity and requirements on accuracy. This starts with simple
tests for obtaining flexural strength only on the one hand and on the other hand necessitates the use of
a deflectometer to obtain the deflection accurately and free of compliance effects of the machine. The
compliance of flexural testing machines has several possible sources (play and deformations in fixtures,
deformations in the load train, and deformations of the load cell). Precise and true determination of
deflection is especially important for the determination of the flexural modulus, for which the use of
uncorrected crosshead displacement is not suitable. For a repeatable determination of flexural modulus
results a compliance correction shall be applied or, preferably, a deflectometer shall be used.
5.4.2 Definition of precision and accuracy requirements
Table 2 defines objectives of testing in increasing order of test complexity and appertaining need for
accuracy. A good precision without absolute accuracy as indicated in type III-tests can be sufficient in
many quality control environments when properties are to be supervised over periods of time only.
Accurate, meaning true and precise, results as indicated in type IV-tests are needed if the results are to
be compared between laboratories. Different types of deflection measurement and different accuracy
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SIST EN ISO 178:2019
ISO 178:2019(E)
requirements for the deflection measurement are therefore defined, based on the needs on precision
and trueness of the test results.
Key
1 test specimen h thickness of specimen
2 sup
...
SLOVENSKI STANDARD
oSIST prEN ISO 178:2017
01-julij-2017
3ROLPHUQLPDWHULDOL'RORþDQMHXSRJLEQLKODVWQRVWL ,62',6
Plastics - Determination of flexural properties (ISO/DIS 178:2017)
Kunststoffe - Bestimmung der Biegeeigenschaften (ISO/DIS 178:2017)
Plastiques - Détermination des propriétés en flexion (ISO/DIS 178:2017)
Ta slovenski standard je istoveten z: prEN ISO 178
ICS:
83.080.01 Polimerni materiali na Plastics in general
splošno
oSIST prEN ISO 178:2017 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN ISO 178:2017
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oSIST prEN ISO 178:2017
DRAFT INTERNATIONAL STANDARD
ISO/DIS 178
ISO/TC 61/SC 2 Secretariat: SAC
Voting begins on: Voting terminates on:
2017-05-09 2017-07-31
Plastics — Determination of flexural properties
Plastiques — Détermination des propriétés en flexion
ICS: 83.080.01
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 178:2017(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2017
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oSIST prEN ISO 178:2017
ISO/DIS 178:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
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ii © ISO 2017 – All rights reserved
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oSIST prEN ISO 178:2017
ISO/DIS 178:2017(E)
Contents Page
Foreword . iv
1 Scope .1
2 Normative references .2
3 Terms and definitions .2
4 Principle .5
5 Test machine .6
6 Test specimens .9
7 Atmosphere for conditioning and testing . 12
8 Procedure . 13
9 Calculation and expression of results . 16
10 Precision . 18
11 Test report . 18
Annex A (informative) Precision statement . 20
Annex B (informative) Influence of changes in test speed on the measured values of
flexural properties . 22
Annex C (normative) Compliance compensation as per Type of test III . 23
Annex D (informative) Relation between tensile and flexural modulus . 26
Bibliography . 27
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oSIST prEN ISO 178:2017
ISO/DIS 178:2017(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.
For an explanation on the meaning of ISO specific terms and 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 the following URL:
www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical
properties.
This sixth edition cancels and replaces the fifth edition (ISO 178:2010), which has been technically
revised. It also incorporates the information that was given in Amendment ISO 178:2010/Amd.1:2013.
The major technical changes are the introduction of deflectometers and the reinstatement of
procedures for compliance correction.
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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.
In agreement with ISO 10350-1 [5] and ISO 10350-2 [6], this International Standard applies to fibre-
reinforced compounds with fibre lengths ≤ 7,5 mm prior to processing. For long-fibre-reinforced
materials (laminates) with fibre lengths > 7,5 mm, see ISO 14125 [7].
The method is not normally suitable for use with rigid cellular materials or sandwich structures
containing cellular material. In such cases, ISO 1209-1 [3] and/or ISO 1209-2 [4] 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 injection moulded 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.
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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 293, Plastics — Compression moulding of test specimens of thermoplastic materials
ISO 294-1, 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 — 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 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.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
IEC Electropedia: available at http://www.electropedia.org/
ISO Online browsing platform: available at http://www.iso.org/obp
3.1
test speed
v
rate of relative movement between the specimen supports and the loading edge
Note 1 to entry: It is expressed in millimetres per minute (mm/min).
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3.2
flexural stress
σ
f
nominal stress at the outer surface of the test specimen at midspan
Note 1 to entry: It is calculated from the relationship given in 9.1, Equation (5).
Note 2 to entry: It is expressed in megapascals (MPa).
3.3
flexural stress at break
σ
fR
flexural stress at break of the test specimen (see Figure 1, curves a and b)
Note 1 to entry: 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 1 to entry: 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 1 to entry: 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 1 to entry: 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 to entry: It is expressed in millimetres (mm).
Note 2 to entry: Using a span, L, of 16h, the conventional deflection corresponds to a flexural strain (see 3.8) of
3,5 %.
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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 to entry: It is expressed as a dimensionless ratio or a percentage (%).
Note 2 to entry: It is calculated in accordance with the relationships given in 9.2, Equations (6) and (7).
Key
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 1 to entry: 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 1 to entry: It is expressed as a dimensionless ratio or a percentage (%).
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3.11
modulus of elasticity in flexure
flexural modulus
E
f
ratio of the stress difference, σ − σ , to the corresponding strain difference,
f2 f1
ε (= 0,0025) − ε (= 0,0005) [see 9.3, Equation (9)]
f2 f1
Note 1 to entry: It is expressed in megapascals (MPa).
Note 2 to entry: The flexural modulus is only an approximate value of Young's modulus of elasticity.
3.12
rigid and semi rigid plastic
rigid plastic has a modulus of elasticity in flexure or, if that is not applicable, then in tension, greater
than 700 MPa. Semi rigid plastic has a modulus of elasticity in flexure or, if that is not applicable, then in
tension, between 70 MPa and 700 MPa under a given set of conditions
[SOURCE: ISO 472:2013, 2.884 and 2.909, modified]
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 1 to entry: 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
Note 1 to entry: It is expressed in percent per minute (% ⋅ min ).
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.
This International Standard specifies two methods, method A and method B. Method A 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.
NOTE 1 The strain rates mentioned above are to be interpreted as nominal ones. Nominal test speeds are
calculated using equation (4). For the machine settings the best fitting ones are selected from Table 1.
NOTE 2 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.
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ISO/DIS 178:2017(E)
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).
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;
1
R = 2,0 mm ± 0,2 mm for test specimen thicknesses ≤ 3 mm;
2
R = 5,0 mm ± 0,2 mm for test specimen thicknesses > 3 mm.
2
The span, L, shall be adjustable.
5.4 Force- and deflection-measuring systems
5.4.1 Introductory remarks
Flexural tests, according to the specific requirements on the data to be obtained, can be differentiated in
several classes, comprising different complexity and requirements on accuracy. This starts with simple
tests for obtaining flexural strength only on the one hand and on the other hand necessitates the use of
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ISO/DIS 178:2017(E)
a deflectometer to obtain the deflection accurately and free of compliance effects of the machine. The
compliance of flexural testing machines has several possible sources (play and deformations in fixtures,
deformations in the load train, and deformations of the load cell). Precise and true determination of
deflection is especially important for the determination of the flexural modulus, for which the use of
uncorrected crosshead displacement is not suitable. For a repeatable determination of flexural modulus
results a compliance compensation shall be applied or, preferably, a deflectometer shall be used.
5.4.2 Definition of precision and accuracy requirements
Table 2 defines objectives of testing in increasing order of test complexity and appertaining need for
accuracy. A good precision without absolute accuracy as indicated in case III may be sufficient in many
quality control environments when properties are to be supervised over periods of time only. Accurate,
meaning true and precise, results as indicated in case IV are needed if the results are to be compared
between laboratories. Different types of deflection measurement and different accuracy requirements
for the deflection measurement are therefore defined, based on the needs on precision and accuracy of
the test results. See also ISO 5725-1.
Key
1 test specimen h thickness of specimen
2 support base plate F applied force
3 deflectometer position l length of specimen
R radius of loading edge L length of span between supports
1
R radius of supports
2
Figure 2 — Position of test specimen and deflectometer at start of test
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Table 2 — Types of tests and calibration requirements
Types (I-IV)
of tests in increasing order of complexity and requirements for accuracy
Required objective Stress/strength Stress/strength/ Stress/strength/ Stress/strength/
of testing only strains > 1% strains/repeatable strains/accurate
and precise modulus
modulus
Property I II III IV
σ
× ×
× ×
fB
σ
× ×
× ×
fM
σ
× ×
×
fC
σ
× ×
×
fC
σ × ×
×
fB
σ × ×
×
fM
E × ×
f
Calibration requirement
Force ISO 7500-1, class 1
Deflection — ISO 9513/class 2 ISO 9513/class 2 ISO 9513/class 1
measurement plus condition set in plus condition set in
clause 5.4.2.1 clause 5.4.2.1
Type of deflection — Crosshead Crosshead Direct
measurement displacement displacement with measurement using
compliance a deflectometer
correction
5.4.2.1 Deflection measurement
The machine shall be capable of continuously recording the crosshead displacement with an accuracy
conforming to the class of ISO 9513 indicated in Table 2. 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.
When determining the flexural modulus as indicated in case III and IV, the deflection-measuring system
shall be capable of measuring the change in deflection to an accuracy of 1 % of the relevant value or
better, corresponding to ±3,4 µm for a support span, L, of 64 mm and a specimen thickness, h, of
4,0 mm (see Figure 3). Other support spans and specimen thicknesses will lead to different
requirements for the accuracy of the deflection-measuring system.
For the determination of the flexural modulus using the crosshead displacement as indicated in case III,
the latter shall be corrected for the compliance of the machine. If the machine is equipped with built in
routines for compliance correction these shall preferably be applied. If such routines are not available
the procedure given in Annex C shall be used
NOTE Annex C also gives some explanation of the possible sources of machine compliance.
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oSIST prEN ISO 178:2017
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The use of a deflectometer further reduces errors introduced by the test setup and is therefore
preferred.
Any deflection indicator capable of measuring deflection to the accuracy specified above is suitable.
Key
σ flexural stress
ε flexural strain
s corresponding deflection for a specimen thickness of 4 mm and a span between supports of 64 mm
Figure 3 — Accuracy requirements for determination of flexural modulus
5.5 Equipment for measuring the width and thickness of the test specimens
Use micrometers with an accuracy of ±0,01 mm.
Use measuring tips that allow to determine the thickness centrally within the measuring range and the
width at half height as indicated in Figure 5.
Different geometry of the contact faces of the measuring tips , i.e. circular, rectangular or sharp edges,
are acceptable. Spherical tip faces shall have a radius ≥ 50 mm. Flat tips are recommended. The face
diameter of cylindrical measuring tips shall be between 1,5 mm and 6,4 mm. Rectangular faces of
measuring tips shall have a long side of 4 mm to 6,4 mm length
It is recommended to use such a configuration that allows determining the width and the thickness with
the same instrument.
6 Test specimens
6.1 Shape and dimensions
6.1.1 General
The dimensions of the test specimens shall comply with the relevant material standard and, as
applicable, with 6.1.2 or 6.1.3. Otherwise, the type of specimen shall be agreed between the interested
parties.
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6.1.2 Preferred specimen type
The dimensions, in millimetres, of the preferred test specimen are:
length, l: 80,0 ± 2
width, b: 10,0 ± 0,2
thickness, h: 4,0 ± 0,2
In any one test specimen, the thickness within the central one third of the length shall not deviate by
more than 2 % from its mean value. The width shall not deviate from its mean value within this part of
the specimen by more than 3 %. The specimen cross section shall preferably be rectangular, with no
rounded edges, except as explained in the Note in 6.4.
The preferred specimen may be machined from the central part of a multipurpose test specimen
complying with ISO 20753.
6.1.3 Other test specimens
When it is not possible or desirable to use the preferred test specimen, use a specimen with the
dimensions given in Table 3.
NOTE Certain specifications require that test specimens from sheets of thickness greater than a specified
upper limit be reduced to a standard thickness by machining one face only. In such cases, it is conventional
practice to place the test specimen such that the original surface of the specimen is in contact with the two
supports and the force is applied by the central loading edge to the machined surface of the specimen.
Table 3 — Values of specimen width, b, in relation to thickness, h
Dimensions in millimetres
Nominal thickness Width
a
h b (±0,5)
1 ≤ h ≤ 3 25,0
3 < h ≤ 5 10,0
5 < h ≤ 10 15,0
10 < h ≤ 20 20,0
20 < h ≤ 35 35,0
35 < h ≤ 50 50,0
a
For materials with very coarse fillers, the minimum width shall be
30 mm.
6.2 Anisotropic materials
6.2.1 In the case of materials having flexural properties that depend on direction, the test specimens
shall be chosen so that the flexural stress will be applied in the same manner and direction as would be
experienced in the end-use application, if known. The relationship between the test specimen and the
end-product envisaged will determine the feasibility of using standard test specimens.
© ISO 2017 – All rights reserved
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oSIST prEN ISO 178:2017
ISO/DIS 178:2017(E)
NOTE The position or orientation and the dimensions of the test specimens sometimes have a very significant
influence on the test results.
6.2.2 When the material shows a significant difference (> 20 %) in flexural properties in two principal
directions, it shall be tested in these two directions. The orientation of the test specimen relative to the
principal directions shall be recorded (see Figure 4).
Key
L product length direction b width of test specimen
W product width direction h thickness of test specimen
Position of specimen Direction of product Direction of force
LN Length
Normal
WN Width
LP Length
Parallel
WP Width
Figure 4 — Position of test specimen in relation to product direction and direction of force
6.3 Preparation of test specimens
6.3.1 From moulding, extrusion and casting compounds
Specimens shall be prepared in accordance with the relevant material specification. When none exists,
and unless otherwise specified, specimens shall be either directly compression-moulded in accordance
with ISO 293 or ISO 295 or injection-moulded in accordance with ISO 294-1 or ISO 10724-1, as
appropriate.
© ISO 2017 – All rights reserved
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oSIST prEN ISO 178:2017
ISO/DIS 178:2017(E)
6.3.2 From sheets
Specimens shall be machined from sheets or from finished or semi-finished products in accordance
with ISO 2818.
6.4 Specimen inspection
The specimens shall be free of twist and preferably have mutually perpendicular surfaces (see,
however, the Note to entry). All surfaces and edges shall be free from sink marks, scratches, pits and
flash.
The specimens shall be checked for conformity with these requirements by visual observation against a
straight edge, carpenter's square or flat plate, and by measuring with micrometer calipers.
Specimens showing measurable or observable departure from one or more of these requirements shall
be rejected or machined to proper siz
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