CEN ISO/TR 20659-1:2024

SLOVENSKI STANDARD
01-september-2024
Reološke preskusne metode - Osnovni principi in medlaboratorijske primerjave -
1. del: Določanje meje plastičnosti (ISO/TR 20659-1:2024)
Rheological test methods - Fundamentals and interlaboratory comparisons - Part 1:
Determination of the yield point (ISO/TR 20659-1:2024)
Méthodes d'essai rhéologiques - Principes fondamentaux et comparaisons
interlaboratoires - Partie 1: Détermination du seuil d'écoulement (ISO/TR 20659-1:2024)
Ta slovenski standard je istoveten z: FprCEN ISO/TR 20659-1
ICS:
87.040 Barve in laki Paints and varnishes
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

Technical
Report
ISO/TR 20659-1
First edition
Rheological test methods —
2024-03
Fundamentals and interlaboratory
comparisons —
Part 1:
Determination of the yield point
Méthodes d'essai rhéologiques — Principes fondamentaux et
comparaisons interlaboratoires —
Partie 1: Détermination du seuil d'écoulement
Reference number
ISO/TR 20659-1:2024(en) © ISO 2024

ISO/TR 20659-1:2024(en)
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii
ISO/TR 20659-1:2024(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Goal of the interlaboratory test . 1
5 Metrological determination of the yield point . 2
5.1 General .2
5.2 Shear rate-controlled rotational test .2
5.3 Yield point evaluation using flow curve regression models .2
5.4 Shear stress-controlled rotational test .4
5.5 E valuation methods for yield points .4
5.5.1 General .4
5.5.2 Axis intercept for presentation of the flow curve using a linear scale .4
5.5.3 Plateau value for presentation of the flow curve using a logarithmic scale .5
5.5.4 Yield point evaluation at a reference value .5
5.5.5 Methods with regression lines for presentation in the lg γ/lg τ diagram .6
5.5.6 Rotational test: viscosity maximum method .7
5.5.7 Tests with constant shear rate .8
5.5.8 Creep test .9
5.5.9 Oscillatory test: amplitude sweep .10
6 Results of the comparative testing programme .12
6.1 Performance of the tests . 12
6.1.1 Preliminary tests . 12
6.1.2 Comparative testing programme . 12
6.2 Measuring samples . 12
6.3 Method used for determination of the yield point . 13
7 Result. 14
8 Rheometer calibration and measurement uncertainty .15
Annex A (informative) Explanatory notes .16
Bibliography . 17

iii
ISO/TR 20659-1:2024(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 35, Paints and varnishes, Subcommittee SC 9,
General test methods for paints and varnishes.
A list of all parts in the ISO 20659 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
Technical Report ISO/TR 20659-1:2024(en)
Rheological test methods — Fundamentals and
interlaboratory comparisons —
Part 1:
Determination of the yield point
1 Scope
This document gives information on an interlaboratory comparison for the determination of the yield point,
using rheological test methods. The yield point is the shear stress τ below which a material does not flow.
This document provides examples of fields of applications, in which important material properties are
characterized with the aid of the yield point. These fields of application include:
— effectiveness of rheological additives;
— shelf life (e.g. with regard to sedimentation, separation and flocculation);
— stability of the structure at rest;
— behaviour when starting to pump;
— use in scraper systems;
— wet-film thickness;
— levelling and sagging behaviour (e.g. without brushmarks or sag formation);
— orientation of effect pigments.
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 3219-1, Rheology — Part 1: Vocabulary and symbols for rotational and oscillatory rheometry
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3219-1.
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 Goal of the interlaboratory test
In the interlaboratory test, different possibilities for determining the yield point using the preferred methods
were considered.
ISO/TR 20659-1:2024(en)
The samples used in the comparative testing programme consisted of different waterborne basecoats
with lower yield points and dispersions with distinctly higher yield points. The samples also included the
following limited cases:
— very low yield points (<1 Pa), at which the range of elastic deformation is so low that the material can also
be approximately considered as a liquid at the state of rest;
— materials of which the internal structure is disintegrated only stepwise so that a transition range is
occurring and a yield zone rather than a punctual yield point is determined.
Furthermore, a non-Newtonian reference sample from the the National Metrology Institute of Germany
(PTB) was also included in the comparative testing programme.
Some background information on the original interlaboratory test is given in Annex A.
5 Metrological determination of the yield point
5.1 General
Clause 5 briefly describes all the methods in use at the time of publication. In principle, the yield point
depends on the temperature, the pressure and the thermal and mechanical history of the material. A detailed
specification of the measuring profile is therefore a precondition for reproducible measurements.
5.2 Shear rate-controlled rotational test

The shear rate γ is specified in the form of a ramp, as shown in Figure 1.
Key
 shear rate
γ
t time
Figure 1 — Shear rate/time function as a ramp
5.3 Yield point evaluation using flow curve regression models

With a linear representation of the flow curve (usually the shear stress τ as a function of the shear rate γ ),
the yield point is determined as the axis intercept on the τ axis (Figure 2).

ISO/TR 20659-1:2024(en)
Key
τ shear stress
τ Bingham yield point
B
K consistency index according to Bingham
B
 shear rate
γ
1 chosen shear rate range
Figure 2 — Flow curve regression according to Bingham
This yield point value depends not only on the specified ramp period, but also on the chosen shear rate range
and the chosen regression model. In industrial laboratories, the models according to Bingham, Casson or
Herschel/Bulkley are widely used.
The mod
...