ISO 1288-2:2016

INTERNATIONAL ISO
STANDARD 1288-2
First edition
2016-02-15
Glass in building — Determination of
the bending strength of glass —
Part 2:
Coaxial double-ring test on flat
specimens with large test surface areas
Verre dans la construction — Détermination de la résistance du verre
à la flexion —
Partie 2: Essais avec doubles anneaux concentriques sur éprouvettes
planes, avec de grandes surfaces de sollicitation
Reference number
©
ISO 2016
© ISO 2016, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Principle of test method . 2
6 Apparatus . 3
6.1 Testing machine . 3
6.2 Loading device. 4
6.2.1 Ring load . 4
6.2.2 Surface pressure regulator . 4
6.3 Measuring instruments . 5
7 Sample . 5
7.1 Shape and dimensions of the specimens . 5
7.2 Sampling and preparation of specimens . 5
7.2.1 Cutting and handling . 5
7.2.2 Conditioning . 5
7.2.3 Examination . 6
7.2.4 Adhesive film . 6
7.3 Number of specimens . 6
8 Procedure. 6
8.1 Temperature . 6
8.2 Humidity . 6
8.3 Thickness measurement . 6
8.4 Base plate . 6
8.5 Positioning of specimen and loading ring . 6
8.6 Load application . 7
8.7 Loading rate . 7
8.8 Location of the origin . 7
8.9 Assessment of residual stresses . 7
9 Evaluation . 8
9.1 Limitation of the evaluation . 8
9.2 Calculation of bending strength . 8
10 Test report . 9
Annex A (informative) Example of a device for keeping the gas pressure, p, in line with the
piston force, F .11
Bibliography .14
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 WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 160, Glass in building, Subcommittee SC 2, Use
considerations
ISO 1288 consists of the following parts, under the general title Glass in building — Determination of the
bending strength of glass:
— Part 1: Fundamentals of testing glass
— Part 2: Coaxial double ring test on flat specimens with large test surface areas
— Part 3: Test with specimen supported at two points (four point bending)
— Part 4: Testing of channel shaped glass
— Part 5: Coaxial double ring test on flat specimens with small test surface areas
iv © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 1288-2:2016(E)
Glass in building — Determination of the bending
strength of glass —
Part 2:
Coaxial double-ring test on flat specimens with large test
surface areas
1 Scope
This part of ISO 1288 specifies a method for determining the bending strength of glass for use in
buildings, excluding the effects of the edges.
The limitations of this part of ISO 1288 are described in ISO 1288-1.
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 48, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD
and 100 IRHD)
ISO 1288-1, Glass in building - Determination of the bending strength of glass - Part 1: Fundamentals of
testing glass
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
bending stress
tensile bending stress induced in the surface of a specimen
Note 1 to entry: For testing purposes, the bending stress should be uniform over a specified part of the surface.
3.2
effective bending stress
weighted average of the tensile bending stresses, calculated by applying a factor to take into account
non-uniformity of the stress field
3.3
bending strength
tensile bending stress or effective bending stress which leads to breakage of the specimen
3.4
equivalent bending strength
apparent bending strength of patterned glass, for which the irregularities in the thickness do not allow
precise calculation of the bending stress
4 Symbols
A effective surface area of quasi-uniform stress m
E modulus of elasticity (Young’s modulus) of the specimen Pa
NOTE For soda lime silicate glass (see ISO 16293-1), a value of 70 GPa is used.
F piston force N
F piston force upon breakage, “breaking force” N
max
F force transmitted by the loading ring to the specimen, “ring load” N
ring
h thickness or average thickness of specimen m
L side length of the square specimens m
μ Poisson number of specimen
NOTE For soda lime silicate glass (see ISO 16293-1), a value of 0,23 is used.
p gas pressure on the surface area defined by the loading ring Pa
p(F) nominal gas pressure as a function of the piston force Pa
p (F ) nominal gas pressure upon breakage Pa
max max
r location coordinate m
r radius of loading ring m
r radius of supporting ring m
r average specimen radius (for evaluation) m
3m
σ stress Pa
σ bending strength Pa
bB
σ equivalent bending strength Pa
beqB
t time s
ΔF/Δt rate at which piston force rises N/s
F*, p*, σ* non-dimensional quantities corresponding to F, p and σ [see Formulae (1) to (5)]
5 Principle of test method
The square specimen, of side length, L, and having virtually plain parallel surfaces, is placed loosely
on a supporting ring (a circular ring with a radius r ). The specimen is subjected to a load, F , by
2 ring
means of a loading ring (radius r ), which is arranged concentrically to the supporting ring. In addition,
the area, A, defined by the loading ring 0 < r < r is placed under gas pressure, p, which has a specific
relationship with the ring load, F (see Figure 1).
ring
When the specimen is subjected to the ring load and the associated gas pressure, depending upon
the dimensions r , r , L, and h, a radial tensile stress field, which is sufficiently homogeneous for the
1 2
test purpose, is developed on the convexly bent surface over the area defined by the loading ring (see
References [2], [3], [4]). The tangential tensile stress is equal to the radial tensile stress at the central
point (r = 0) of the specimen, but decreases as the radius, r, increases.
2 © ISO 2016 – All rights reserved

Outside the loading ring, the radial and tangential stresses fall sharply towards the edge of the
specimen, so that the risk of breakage outside the loading ring is low. On the edge of the specimen itself,
the radial stress is zero and the tangential stress is a compressive stress, this being the case on both the
concavely and the convexly bent sides of the specimen. The edge of the specimen is thus always under
tangential compressive stress (see ISO 1288-1).
By increasing the force, F, and the gas pressure, p, the tensile stress in the central part of the specimen
is increased at a constant rate [see (6.1 b)] until breakage, so the origin of the break can be expected to
occur in the surface area subjected to maximum tensile stress within the loading ring.
With the test apparatus as shown in Figure 1, a force, pA, acts against the piston force, F, due to the gas
pressure, p. The force transferred by the loading ring is F = F - pA. Thus a distinction should be made
ring
between the piston force and the ring load.
The bending strength, σ , or equivalent bending strength, σ , is calculated from the maximum
bB beqB
value, F , of the piston force, measured at the time of breakage, and the thickness, h, of the specimen,
max
taking into account the prescribed dimensions of the specimen and various characteristic material
values. This assumes that the gas pressure, p, follows the piston force, F, according to the nominal
function p(F), (see Figure 3).
6 Apparatus
6.1 Testing machine
The bending test shall be carried out using a suitable bending testing machine, which shall incorporate
the following features.
a) The stressing of the specimen shall be capable of being applied from zero up to a maximum value in
a manner which minimizes shock and is stepless.
b) The stressing device shall be capable of the specified rate of stressing.
c) The testing machine shall incorporate a load measuring device with a limit of error of ±2,0 % within
the measuring range.
Key
1 loading ring
2 specimen
3 supporting ring
Figure 1 — Basic diagram of test apparatus
Key
1 specimen
a
2 rigid base plate, preferably made of steel, with supporting ring (radius r )
3 rubber profile, adapted to the supporting ring, 3 mm thick, with a hardness (40 ± 10) IRHD (in accordance with
ISO 48)
a
4 rigid loading ring (radius r ), preferably made of steel
5 force transmitting component, with a ball mechanism to ensure the force is centred in the loading ring
6 rubber profile, adapted to the loading ring, 3 mm thick with a hardness (40 ± 10) IRHD (in accordance with
b
ISO 48)
c
7 adjustment jaws for centring the specimen
8 contact circle of the loading ring
9 contact circle of the supporting ring
a
The radius of curvature of the bearing surface of the ring is 5 mm.
b
In the case of specimens which are patterned on the loading ring side, a sponge rubber profile approximately
5 mm thick should also be used to ensure an adequate seal for the gas pressure.
c
The jaws are removed before the bending test is started, in order that the edge of the specimen is not clamped.
Figure 2 — Loading device
6.2 Loading device
6.2.1
...