ISO 5629:2017

INTERNATIONAL ISO
STANDARD 5629
Second edition
2017-12
Paper and board — Determination of
bending stiffness — Resonance method
Papier et carton — Détermination de la résistance à la flexion —
Méthode par résonance
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus (see Figure 1) . 2
6 Sampling . 2
7 Conditioning . 3
8 Preparation of the test piece . 3
9 Procedure. 3
9.1 General . 3
9.2 Procedure A . 3
9.2.1 Grammage . 3
9.2.2 Resonant length . 3
9.3 Procedure B . 4
9.3.1 Mean grammage . 4
9.3.2 Resonant length . 4
10 Expression of results . 4
10.1 General . 4
10.2 Procedure A . 4
10.3 Procedure B . 5
10.4 Approximate results . 5
11 Precision — Repeatability . 5
12 Test report . 6
Annex A (informative) Theoretical basis of test method . 9
Annex B (informative) Precision .10
Bibliography .12
Foreword
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URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps, Subcommittee
SC 2, Test methods and quality specifications for paper and board.
This second edition cancels and replaces the first edition (ISO 5629:1983), of which it constitutes a
minor revision.
The main changes compared with the previous edition are as follows:
— Annex B with precision data has been added;
— Bibliography has been added.
iv © ISO 2017 – All rights reserved

Introduction
There are many methods of measuring the resistance of paper and board to bending forces. Because of
the visco-elastic nature of the material, results will depend to a considerable extent on the test method
used. In this method, the bending stiffness is determined under dynamic conditions (vibration) using
only a relatively small bending angle.
INTERNATIONAL STANDARD ISO 5629:2017(E)
Paper and board — Determination of bending stiffness —
Resonance method
1 Scope
This document specifies a method for the determination of bending stiffness using the resonance method.
This method gives only a single result for each test piece tested, although in general, bending stiffness
values may depend on which surface of the material forms the inner surface of the arc resulting from
bending forces.
The bending stiffness of a very wide range of papers and boards can be measured using this method.
However, for some materials, such as those listed below, the measured numerical values will not be
strictly identical with bending stiffness as defined in 3.1:
a) multi-ply papers and boards in which the component plies can move separately during a test;
b) papers and boards with appreciable curl, especially if the axis of the curl is in the long direction
of the test piece;
c) some soft papers with grammage below about 40 g/m .
This method is not applicable to corrugated boards.
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 186, Paper and board — Sampling to determine average quality
ISO 187, Paper, board and pulps — Standard atmosphere for conditioning and testing and procedure for
monitoring the atmosphere and conditioning of samples
ISO 536, Paper and board — Determination of grammage
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:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
bending stiffness
S
moment of the resistance per unit width that a paper or board offers to bending in the region of elastic
deformation. It can be defined mathematically by Formula (1):
EI
S= (1)
b
where
E is the modulus of elasticity, i.e. Young's modulus;
I is the second moment of area (moment of inertia) of the cross-sectional area, about an axis
through the centre of that area, in its plane, and perpendicular to the direction of bending;
b is the width of the test piece.
4 Principle
Determination, under standard conditions, of the vibrational resonant length of a test piece clamped at
one end. Calculation of the bending stiffness from this value and the grammage of the material.
The vibrational resonant length of a material, in one direction, when it is subjected to vibration of a
given frequency, depends on its bending stiffness in that direction and its grammage.
5 Apparatus (see Figure 1)
Usual laboratory apparatus and the following.
5.1 Clamping system.
The clamp shall consist of two flat parallel metal plates which can be so adjusted as to give a separation
and a clamping pressure such as to just permit the test piece to be pulled through the clamp. The clamp
shall be so arranged that a test piece can project vertically in both directions through the clamp. The
dimensions of the clamp are not critical, but the width shall be greater than the width of the test piece
used. Generally, a width of slightly more than 25 mm is satisfactory.
The upper edges of the clamp may be rounded, in which case, the radius of curvature shall be less
than 0,1 mm.
1)
5.2 Means of vibrating the clamp in a horizontal plane, perpendicularly to the plane of the paper, at
a frequency of 25,0 Hz ± 0,1 Hz with an amplitude of not greater than 0,2 mm .
5.3 Means of measuring the length of test piece, projecting above the upper edge of the clamp.
5.4 Stroboscopic lamp, operating at the same frequency and in the same phase as the vibrator, for
illuminating the top edge of the test piece.
5.5 Optional components.
5.5.1 Magnifier, which can be adjusted for viewing the top edge of the test piece.
5.5.2 Movable lower clamp, of non-critical construction, so arranged that with its aid, the test piece
can be pulled (and for some materials, pushed) through the vibrating clamp. This clamp may be suitably
coupled to a measuring device, enabling the resonant length to be read directly from a scale.
6 Sampling
Select at least 10 specimens from a sample
...