ISO 21712:2020

INTERNATIONAL ISO
STANDARD 21712
First edition
2020-03
Fine ceramics (advanced ceramics,
advanced technical ceramics) — Test
method for flexural bond strength of
ceramics
Céramiques techniques (céramiques avancées, céramiques techniques
avancées) – Méthodes d’essai pour déterminer la résistance
d’adhésion en flexion des céramiques
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 4
5.1 Testing machine . 4
5.2 Test fixture . 4
5.2.1 General. 4
5.2.2 Bearings . 4
5.2.3 Positioning of bearings . 4
5.2.4 Fixture material . 4
5.3 Micrometer . 4
6 Test specimens. 4
6.1 Specimen size . 4
6.1.1 Type A specimens . 4
6.1.2 Type B specimens . 5
6.1.3 Chamfering and rounded edge . 5
6.2 Specimen preparation . 7
6.2.1 General. 7
6.2.2 Custom machining procedure . 7
6.2.3 Component-matched procedure . 7
6.2.4 Basic machining procedure . 7
6.2.5 Parallelism, orthogonality and chamfer sizes . 8
6.2.6 Handling of specimens . . 8
6.2.7 Number of specimens . 8
7 Procedure. 8
8 Calculation .11
9 Test report .12
Foreword
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iv © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 21712:2020(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for flexural bond strength of
ceramics
1 Scope
This document specifies a test method for determining the flexural bond strength of ceramic/ceramic
joints or ceramic/metal joints at room temperature. The substrate materials, for example ceramic or
metal, are both monolithic. This method can be used to test the interfacial bond strength of the joint
under bending conditions. It can be used for the development of joining materials and/or for the quality
control of joints, the characterization and generating design data purposes.
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 3611, Geometrical product specifications (GPS) — Dimensional measuring equipment: Micrometers for
external measurements — Design and metrological characteristics
ISO 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 14704:2016, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for
flexural strength of monolithic ceramics at room temperature
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
flexural bond strength
maximum stress at fracture at the bond interface of a specified beam containing the ceramic/ceramic
joint or the ceramic/metal joint subjected to bending
3.2
four-point flexure
configuration of flexural test where a specimen is subjected to equal loads through two bearings
symmetrically located between two support bearings
Note 1 to entry: See Figure 1 a) and b).
Note 2 to entry: The bearings may be cylindrical rollers or cylindrical bearings.
3.3
four-point 1/4 point flexure
specific configuration of four-point flexural test where the inner bearings are situated one-quarter of
the support span away from the two outer bearings
Note 1 to entry: See Figure 1 a) and Table 1.
3.4
four-point 1/3 point flexure
specific configuration of four-point strength test where the inner bearings are situated one-third of the
support span away from the two outer bearings
Note 1 to entry: See Figure 1 b) and Table 1.
3.5
semi-articulating fixture
test fixture designed to apply uniform and even loading to test specimens that have flat and parallel
surfaces
3.6
fully articulating fixture
test fixture designed to apply uniform and even loading to specimens that may have uneven, non-
parallel or twisted surfaces
4 Principle
A beam-type specimen containing the specific bond joint with a rectangular cross-section or circular
cross-section is loaded in flexure until fracture. The load at fracture, the geometry of the test fixture
and specimen dimensions are used to compute the flexural bond strength, which is a measure of the
bond strength. The material or joining interface is assumed to be linearly elastic.
2 © ISO 2020 – All rights reserved

a)  Four-point 1/4 point flexure
b)  Four-point 1/3 point flexure
Key
1 loading bearings b width
2 support bearings δ thickness
3 interface L outer span
a distance between loading and support bearings L inner span
Figure 1 — Flexural bond test configurations
Table 1 — Dimensions of flexural bond test configurations
Dimensions in millimetres
Bending Diameters of
Specimen L (outer span) L (inner span) a
1 2
type bearings
Four-point
A-I, B-I 40 ± 0,1 20 ± 0,1 10 ± 0,1 4,5 to 5,0
1/4
Four-point
A-II, B-II 30 ± 0,1 10 ± 0,1 10 ± 0,1 4,5 to 5,0
1/3
Four-point A-III, A-IV,
30 ± 0,1 10 ± 0,1 10 ± 0,1 4,0 to 6,0
1/3 B-III, B-IV
Four-point
A-V, A-VI, B-V, B-VI (4,5~10,5)δ ± 0,5 (1,5~3,5)δ ± 0,5 (1,5~3,5)δ ± 0,5 4,0 to 6,0
1/3
5 Apparatus
5.1 Testing machine
A suitable testing machine capable of applying a uniform crosshead speed shall be used. The testing
machine shall have the function for recording the peak load applied to the test specimen. The testing
machine shall fulfil the requirements of ISO 7500-1, Class 1, with an accuracy of 1 % of the indicated
load at fracture.
5.2 Test fixture
5.2.1 General
The test adopts four-point flexure configurations, as illustrated in Figure 1. The four-point 1/4 point
configuration is recommended. The fixture shall have bearings that are free to roll, as described in
5.2.2, in order to eliminate frictional constraints when the specimen surfaces expand or contract during
loading. In addition, the fixture shall be designed so that it can articulate or tilt to ensure uniform
loading to the specimen. The articulation is designed so that bearing parts of the fixture can rotate, as
shown in ISO 14704:2016, Figure B.1. The bearing parts should also provide articulation to ensure that
all bearing contacts can apply uniform load to the specimen surfaces. Semi-articulated fixtures, which
have pairs of upper and lower bearings articulating to match the specimen surfaces, may be used with
specimens that have flat and parallel surfaces, as illustrated in ISO 14704:2016, Figures B.2 a) and B.3
a). Fully articulated fixtures have more moving parts and are necessary for specimens that do not have
flat and parallel surfaces, as illustrated in ISO 14704:2016, Figures B
...