SIST EN ISO 75-3:2025

SLOVENSKI STANDARD
01-oktober-2025
Polimerni materiali - Določanje temperature upogiba pod obremenitvijo -
Duromerni (termoreaktivni) laminati z visoko trdnostjo in polimeri, ojačeni z
dolgimi vlakni (ISO 75-3:2025)
Plastics - Determination of temperature of deflection under load - Part 3: High-strength
thermosetting laminates and long-fibre-reinforced plastics (ISO 75-3:2025)
Kunststoffe- Bestimmung der Wärmeformbeständigkeitstemperatur - Teil 3:
Hochbeständige härtbare Schichtstoffe und langfaserverstärkte Kunststoffe (ISO 75-
3:2025)
Plastiques - Détermination de la température de fléchissement sous charge - Partie 3:
Stratifiés thermodurcissables à haute résistance et plastiques renforcés de fibres
longues (ISO 75-3:2025)
Ta slovenski standard je istoveten z: EN ISO 75-3:2025
ICS:
83.080.10 Duromeri Thermosetting materials
83.120 Ojačani polimeri Reinforced plastics
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 75-3
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2025
EUROPÄISCHE NORM
ICS 83.080.10; 83.120 Supersedes EN ISO 75-3:2004, EN ISO 75-
3:2004/AC:2006
English Version
Plastics - Determination of temperature of deflection
under load - Part 3: High-strength thermosetting laminates
and long-fibre-reinforced plastics (ISO 75-3:2025)
Plastiques - Détermination de la température de Kunststoffe- Bestimmung der
fléchissement sous charge - Partie 3: Stratifiés Wärmeformbeständigkeitstemperatur - Teil 3:
thermodurcissables à haute résistance et plastiques Hochbeständige härtbare Schichtstoffe und
renforcés de fibres longues (ISO 75-3:2025) langfaserverstärkte Kunststoffe (ISO 75-3:2025)
This European Standard was approved by CEN on 9 August 2025.

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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye 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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 75-3:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 75-3:2025) 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 SIS.
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 February 2026, and conflicting national standards
shall be withdrawn at the latest by February 2026.
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 75-3:2004.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
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, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 75-3:2025 has been approved by CEN as EN ISO 75-3:2025 without any modification.

International
Standard
ISO 75-3
Third edition
Plastics — Determination of
2025-07
temperature of deflection under
load —
Part 3:
High-strength thermosetting
laminates and long-fibre-reinforced
plastics
Plastiques — Détermination de la température de fléchissement
sous charge —
Partie 3: Stratifiés thermodurcissables à haute résistance et
plastiques renforcés de fibres longues
Reference number
ISO 75-3:2025(en) © ISO 2025
ISO 75-3:2025(en)
© ISO 2025
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 75-3:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Apparatus . 2
5.1 Means of producing a flexural stress .2
5.2 Heating equipment .2
5.3 Weights .2
5.4 Temperature-measuring instrument .2
5.5 Deflection-measuring instrument .2
5.6 Micrometers and gauges .2
6 Test specimens . 2
6.1 General .2
6.2 Shape and dimensions .2
6.3 Specimen inspection .3
6.4 Number of test specimens .3
6.5 Test-specimen preparation .3
6.6 Annealing .3
7 Conditioning and drying . 3
8 Procedure . 4
8.1 Calculation of the force to be applied .4
8.2 Initial temperature of the heating equipment .4
8.3 Measurement .4
9 Expression of results . 5
10 Precision . 5
11 Test report . 5
Annex A (informative) Precision data . 6
Bibliography .11

iii
ISO 75-3:2025(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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 www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical
behavior, in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 249, Plastics, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 75-3:2004), which has been technically
revised.
The main changes are as follows:
— the Introduction, Scope (Clause1) and Principle clauses (Clause 4) have been updated;
— the normative references and the bibliography have been updated;
— the span definition has been changed by using a formula in accordance with ISO 178;
— preferred specimen thickness dimensions have been added;
— examples of initial deflection, error and standard deflection calculations have been added;
— a precision statement has been added as a new Annex A.
A list of all parts in the ISO 75 series can be found on the ISO website.
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 75-3:2025(en)
Introduction
The first edition (1993) of this document described a method for the determination of the temperature of
deflection under load (bending stress) of high-strength thermosetting laminates and compression-moulded
long-fibre reinforced plastics. The test load used was not a fixed load, as in ISO 75-2, but a function (1/10) of
the ultimate or specified load applied flatwise on specimen.
In the second edition of (2004) this document, the test load is determined as a fraction of the flexural
modulus of the material under test. This has the advantage that the test load is a fraction of the flexural
strength of the material and allowed the method to be applied to materials with a wide range of flexural
moduli. The test determines the temperature-dependent decrease in the flexural modulus. Because tensile
modulus and tensile strength are not necessarily related, using the flexural modulus to determine the test
load leads to more readily comparable descriptions of material behaviour.
The flexural strain increase at which the temperature of deflection under load is measured had been
increased from 0,1 % to 0,2 % to obtain greater commonality with ISO 75-2.
In this third edition, the calculation of the span value has been updated to conform with a similar and widely
used standard (i.e. ISO 178).
It is also reconfirmed that the determination of the temperature under load method described in the ISO 75
series has a great range of applicability. More in details, this method is suitable for use with the following
range of materials:
— thermosetting moulding materials, reinforced compounds, with fibre length, prior to processing, greater
than 7,5 mm; thermosetting sheets.
Despite the title clearly mention thermosetting based materials, the method has been validated also for:
— thermoplastic moulding, extrusion and casting materials, reinforced compounds, with fibre length, prior
to processing, greater than 7,5 mm; rigid thermoplastics sheets.
The method addressed in this document specifies the following parameters:
— the span that depends on the thickness of the specimen;
— the standard deflection, Δs, is a function of the flexural-strain increase, Δε (defined in this document),
f
the span and the thickness;
— the flexural stress is a fraction (1/1 000) of the initial (room-temperature) flexural modulus of the
material under test.
v
International Standard ISO 75-3:2025(en)
Plastics — Determination of temperature of deflection
under load —
Part 3:
High-strength thermosetting laminates and long-fibre-
reinforced plastics
1 Scope
This document specifies a method used for the determination of the temperature of deflection under load of
specified plastics (including fibre-reinforced plastics in which the fibre length is, prior to processing, greater
than 7,5 mm) under defined conditions. A number of different test conditions are defined, depending on the
anticipated specimen dimensions.
For additional information, see ISO 75-1:2020, Clause 1.
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 75-1:2020, Plastics — Determination of temperature of deflection under load — Part 1: General test method
ISO 295, Plastics — Compression moulding of test specimens of thermosetting materials
ISO 1268 (all parts), Fibre-reinforced plastics — Methods of producing test plates
ISO 2818, Plastics — Preparation of test specimens by machining
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 14125, Fibre-reinforced plastic composites — Determination of flexural properties
ISO 16012, Plastics — Determination of linear dimensions of test specimens
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 75-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
See ISO 75-1:2020, Clause 4.
This method does not specify a preferred thickness value for the test specimen but define a suitable range.

ISO 75-3:2025(en)
Nevertheless, it is necessary to consider that many of the testing parameters will depend on the thickness value.
Furthermore, most of the testing machines available have a distance between the test-specimen supports
(span) fixed at predefined values. For this reason, some suggested specimen thicknesses will be presented in
the following. As an alternative, specimen-thickness may be reduced by machining.
5 Apparatus
5.1 Means of producing a flexural stress
The means of producing the flexural stress shall be in accordance with ISO 75-1:2020, 5.1.
The span (distance between the points of contact between the test specimen and the test specimen supports)
shall be adjustable and its value is calculated by Formula (1):
Lh=3()0±1 (1)
where
L is the span, in mm;
h is the test specimen thickness, in mm.
NOTE 1 Formula (1) is provided by using the same approach used in ISO 178.
NOTE 2 The interlaboratory study reported in Annex A has demonstrated that, at least with the materials involved
in the experimental campaign, a deviation of about 7 % does not affect the final HDT value measure
...