SIST EN ISO 28079:2026

SLOVENSKI STANDARD
01-april-2026
Trde kovine - Preskus žilavosti po Palmqvistu (ISO 28079:2026)
Hardmetals - Palmqvist toughness test (ISO 28079:2026)
Hartmetalle - Palmqvist-Härteprüfung (ISO 28079:2026)
Métaux-durs - Essai de ténacité de Palmqvist (ISO 28079:2026)
Ta slovenski standard je istoveten z: EN ISO 28079:2026
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
77.160 Metalurgija prahov Powder metallurgy
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 28079
EUROPEAN STANDARD
NORME EUROPÉENNE
January 2026
EUROPÄISCHE NORM
ICS 77.040.10; 77.160
English Version
Hardmetals - Palmqvist toughness test (ISO 28079:2026)
Métaux-durs - Essai de ténacité de Palmqvist (ISO Hartmetalle - Palmqvist-Härteprüfung (ISO
28079:2026) 28079:2026)
This European Standard was approved by CEN on 10 January 2026.

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
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 28079:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 28079:2026) has been prepared by Technical Committee ISO/TC 119 "Powder
metallurgy" in collaboration with CCMC.
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 July 2026, and conflicting national standards shall be
withdrawn at the latest by July 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.
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 28079:2026 has been approved by CEN as EN ISO 28079:2026 without any modification.

International
Standard
ISO 28079
Second edition
Hardmetals — Palmqvist toughness
2026-01
test
Métaux-durs — Essai de ténacité de Palmqvist
Reference number
ISO 28079:2026(en) © ISO 2026
ISO 28079:2026(en)
© ISO 2026
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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CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 28079:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions .1
3.2 Symbols .1
4 Test pieces and sample preparation . 2
4.1 Test piece size and sampling .2
4.2 Surface preparation .2
4.3 Surface condition .2
5 Apparatus . 3
5.1 General .3
5.2 Indentation .3
5.3 Indentation and crack measurement .3
6 Procedure and conditions of testing . 3
6.1 Indentations .3
6.2 Indentation and crack length measurement .3
6.3 Test validity .5
7 Analysis . . 5
7.1 Vickers hardness .5
7.2 Toughness .5
8 Measurement uncertainty . 6
9 Test report . 6
Annex A (informative) Report pro forma — Palmqvist toughness measurements on hardmetals . 7
Bibliography . 9

iii
ISO 28079:2026(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 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).
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 119, Powder metallurgy, Subcommittee
SC 4, Sampling and testing methods for hardmetals, in collaboration with the European Committee for
Standardization (CEN), in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 28079:2009), which has been technically
revised.
The main changes are as follows:
— References to ISO 3878 replaced by ISO 6507-1, ISO 6507-2 and ISO 6507-3;
— Clause 3, symbol “H” for hardness replaced by “HV” for Vickers Hardness;
nd
— Subclause 4.1, 2 paragraph: last sentence deleted;
— Modification of the note in 4.1;
— Subclause 4.2 “Surface preparation” modified;
— Modification in 4.3 “surface condition”;
— Formula 1 modified, according to modifications in Clause 3;
— Deletion of the note in 7.1;
— Calculation example for Formula (10) added as A.3.
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.

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ISO 28079:2026(en)
Introduction
Good test methods are those which enable a user or manufacturer to clearly discriminate between different
materials.
Fracture toughness values are required for three reasons:
— for product design and performance assessment;
— for selection of materials;
— for quality control.
1)
A specific International Standard for the toughness of hardmetals has not been developed to date,
primarily because of the difficulty of introducing stable precracks into these tough but hard materials.
However, Palmqvist tests for toughness are widely used because of their perceived apparent simplicity.
Cracks are formed at the corners of Vickers hardness indentations and these can be used to calculate a
nominal surface toughness value. This value is sensitive to the method of measurement and to the method
of surface preparation of the sample. This document outlines good practice to minimize uncertainties due to
these issues.
There are several possible methods for the measurement of the fracture toughness of hardmetals. The
−3/2
results can be expressed either as a stress intensity factor, in MN·m , or as a fracture surface energy,
−2 −3/2 −3/2
in J·m . The range of values for typical WC/Co hardmetals is from 7 MN·m to 25 MN·m . There is a
general inverse trend of hardness against fracture toughness (see References [1] and [2]).
When applied unqualified to hardmetals, “toughness” can have several meanings.
−3/2
a) Plane-strain fracture toughness, K , in MN·m , is a value obtained from tests on specimens with
Ic
appropriate geometries for plane-strain conditions and containing a well-defined geometry of crack.
There is no standard method for hardmetals and different organizations use different test methods for
introducing the precrack.
b) Strain-energy release rate (or work of fracture), G, is an alternative expression for toughness, often
2 2
obtained by converting plane-strain toughness, K, to G [i.e. G = K /E(1 − ν ), where E is Young’s modulus
−2
and ν is Poisson's ratio]. G has units of J·m . Again, there is no standard method.
c) Palmqvist toughness, W, is a value obtained by measuring the total length of cracks emanating from the
four corners of a Vickers hardness indentation. For a given indentation load, the shorter the crack, the
tougher the hardmetal.
d) Finally, toughness is also widely used, in a loose sense, to describe the empirical relation between
perceived resistance to dynamic impacts. This is neither standardized nor quantified, but is clearly
important for many industrial applications of hard materials. Also, principally for hardmetals, it can
be more realistically assessed through either fatigue tests or high-rate strength tests, rather than a
conventional fracture toughness test.
There is a considerable body of published information on Palmqvist toughness tests for hardmetals (see
References [5] to [29]). Palmqvist toughness, W, is a toughness value obtained by measuring the crack
lengths at the corners of a Vickers indentation. It can be evaluated by making indentations either at a single
load, usually 30 kgf, or from the inverse of the slope of a plot of crack length against load for a range of applied
loads. For hardmetals, the crack depth profile is normally of the Palmqvist type, i.e. independent shallow
arcs emanating from each indentation corner. The measurement of surface crack length is, however, open
1) Terminology — There is a range of terms used for this type of material, especially including cemented carbides and/
or cermets, as well as hardmetals. The word “hardmetals” has been used in this document. It includes all hard materials
based on carbides that are bonded with a metal. In ISO 3252 terminology, “hardmetal” is stated to be “a sintered material
characterized by high strength and wear resistance, comprising carbides of refractory metals as the main component
together with a metallic binder phase”. “Cemented carbide” is synonymous with “hardmetal”. A “cermet” is defined as
“a sintered material containing at least one metallic phase and at least one non-metallic phase, generally of a ceramic
nature”.
v
ISO 28079:2026(en)
to operator error. It is widely recognized that test surfaces are carefully prepared to remove the effects of
residual surface stresses (see Reference [8]). The test also has a poor fracture-mechanics pedigree because
of the uncertainties associated with residual stresses introduced by the indentation.
One advantage of the Palmqvist method is that parallel measurements are made of sample hardness, which
is required for quality-control purposes. The crack length, and thus toughness measurements, do not
therefore require much more effort and can yield equally useful material characterization data, provided
the measurements are obtained carefully in line with the methods proposed in this document.
This document is based on a “Good Practice Guide for the Measurement of Palmqvist Toughness” published
by the UK National Physical Laboratory in 1998. This document recommends good practice to minimize
levels of uncertainty in the measurement process. The procedure has been validated through underpinning
2)
technical work within the VAMAS framework (see Reference [29]). An interlaboratory exercise was
conducted to generate underpinning technical information on toughness tests for hardmetals. More than
ten industrial organizations participated, either by correspondence, supply of materials or by conducting
tests. Eight organizations were able to complete Palmqvist tests. Good statistics were obtained on the
Palmqvist data that enabled a quantitative assessment of uncertainties to be performed for this relatively
simple test. Single-edge precracked beam data was thought to be closest to the “true” value, and the mean
values from the Palmqvist test data compared reasonably well with these results. However, care was needed
in test piece preparation to ensure a good correlation between data from the Palmqvist tests and the single-
edge precracked beam results.
2) VAMAS, Versailles Project on Advanced Materials and Standards, supports trade in high technology products through
international collaborative projects aimed at providing the technical basis for drafting codes of practice and specifications
for advanced materials. The scope of the collaboration embraces all agreed aspects of enabling science and technology,
i.e. databases, test methods, design methods, and materials technology, which are required as a precursor to the drafting
of standards for advanced materials. VAMAS activity emphasises collaboration on pre-standards measurement research,
intercomparison of test results, and consolidation of existing views on priorities for standardization action. Through this
activity, VAMAS fosters the development of internationally acceptable standards for advanced materials by the various
existing standards agencies.
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