Fine ceramics (advanced ceramics, advanced technical ceramics) — Mechanical properties of monolithic ceramics at room temperature — Determination of flexural strength by the ring-on-ring test

This document specifies a method for the determination of the nominal equibiaxial flexural strength by the ring-on-ring test of advanced monolithic technical ceramic materials at room temperature. This document is applicable to materials with a grain size less than 100 µm.

Céramiques techniques — Propriétés mécaniques des céramiques monolithiques à température ambiante — Détermination de la résistance à la flexion à l'aide de doubles anneaux

General Information

Status
Published
Publication Date
07-Nov-2018
Technical Committee
Drafting Committee
Current Stage
6060 - International Standard published
Start Date
08-Nov-2018
Completion Date
08-Nov-2018
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ISO 17167:2018 - Fine ceramics (advanced ceramics, advanced technical ceramics) -- Mechanical properties of monolithic ceramics at room temperature -- Determination of flexural strength by the ring-on-ring test
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INTERNATIONAL ISO
STANDARD 17167
First edition
2018-11
Fine ceramics (advanced ceramics,
advanced technical ceramics) —
Mechanical properties of monolithic
ceramics at room temperature —
Determination of flexural strength by
the ring-on-ring test
Céramiques techniques — Propriétés mécaniques des céramiques
monolithiques à température ambiante — Détermination de la
résistance à la flexion à l'aide de doubles anneaux
Reference number
ISO 17167:2018(E)
ISO 2018
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ISO 17167:2018(E)
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© ISO 2018

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Published in Switzerland
ii © ISO 2018 – All rights reserved
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ISO 17167:2018(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Significance and use .......................................................................................................................................................................................... 2

6 Apparatus ..................................................................................................................................................................................................................... 2

6.1 Test machine ............................................................................................................................................................................................. 2

6.2 Test jig ............................................................................................................................................................................................................. 3

6.3 Calliper or alternative calibrated device for the measurement of the test piece thickness . 4

6.4 Device for measuring the temperature and humidity ........................................................................................... 4

7 Test pieces ................................................................................................................................................................................................................... 4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Dimensions and tolerances .......................................................................................................................................................... 5

7.3 Surface finish ............................................................................................................................................................................................ 6

7.3.1 General...................................................................................................................................................................................... 6

7.3.2 Surface finishing I: as-fired ..................................................................................................................................... 7

7.3.3 Surface finishing II: grinding/lapping/polishing ................................................................................. 7

7.3.4 Surface finish III: finishing by agreed procedure ................................................................................. 7

7.3.5 Check of dimensions ..................................................................................................................................................... 7

7.3.6 General requirements .................................................................................................................................................. 8

7.3.7 Number of test pieces .................................................................................................................................................. 8

7.4 Precautions ................................................................................................................................................................................................ 8

8 Procedure..................................................................................................................................................................................................................... 8

9 Calculations................................................................................................................................................................................................................ 9

10 Test report ................................................................................................................................................................................................................10

Annex A (informative) Typical fracture patterns of ceramic test pieces after a ring-on-ring test ....11

Bibliography .............................................................................................................................................................................................................................13

© ISO 2018 – All rights reserved iii
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ISO 17167:2018(E)
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).

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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.

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 © ISO 2018 – All rights reserved
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INTERNATIONAL STANDARD ISO 17167:2018(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Mechanical properties of monolithic ceramics
at room temperature — Determination of flexural strength
by the ring-on-ring test
1 Scope

This document specifies a method for the determination of the nominal equibiaxial flexural strength by

the ring-on-ring test of advanced monolithic technical ceramic materials at room temperature.

This document is applicable to materials with a grain size less than 100 µm.
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 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/IEC 17025, General requirements for the competence of testing and calibration laboratories

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
equibiaxial flexural strength

maximum nominal stress at the test piece surface supported by the material at the instant of failure

when loaded in linear elastic equibiaxial bending by the ring-on-ring test

Note 1 to entry: The ring-on-ring test for the determination of flexural strength is often referred to as biaxial

bending test or equibiaxial bending test (see Reference [1]). These names should not be used without the

reference to the ring-on-ring test conditions as there are some other test arrangements for which the term is

used or could also be used, such as the ball-on-three-balls test, the punch-on-three-balls test, the ball-on-ring

test and the punch-on-ring test.
4 Principle

A round discoidal test piece with a constant thickness is positioned between two concentric rings of

different diameters and loaded by an axial force.

The nominal equibiaxial flexural strength is calculated from the axial force which acts during the

moment of fracture, the geometry of the test piece and the test arrangement, as well as the Poisson

ratio of the test piece material.
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ISO 17167:2018(E)
5 Significance and use

This test is intended to be used for material development and characterization, quality control and

design data acquisition purposes. The strength level determined by the test is calculated on the

basis of linear elastic bending behaviour of a round, disk-like thin plate on the assumption that the

material being tested is elastically homogeneous and isotropic and shows a linear (Hooke) stress-strain

behaviour.

The result obtained from a strength test is determined by a large number of factors associated with

the microstructure of the material, the surface finishing procedure applied in preparation of the test

pieces, the size and shape of the test piece, the mechanical function of the testing apparatus, the rate

of load application and the relative humidity (RH) of the ambient atmosphere. As a consequence of the

brittle nature of ceramics, there is usually a considerable range of results obtained from a number of

nominally identical test pieces. These factors combined mean that caution in the interpretation of test

results is required. For many purposes, and as described in this document, the results of strength tests

can be described in terms of a mean value and a standard deviation. Further statistical evaluation of

results is required for design data acquisition and can be desirable for other purposes (see ISO 20501).

This method places closely defined restrictions on the size and shape of the test piece and on the

function of the test apparatus in order to minimize the errors that can arise as a consequence of the test

procedure.

NOTE The basis for the choice of dimensions and tolerances of test pieces and of the requirements of the test

jig can be found in ISO 6474-1, ASTM C1499 and Reference [1].

All other test factors are required to be stated in the test report (see Clause 10) in order to allow inter-

comparison of material behaviours. It is not possible rigorously to standardize particular surface

finishes since these are not absolutely controllable in mechanical terms. The inclusion of a standard

grinding procedure (see 7.3) as one of the surface finish options in this method is intended to provide a

means of obtaining a minimum amount of residual grinding damage to the test material.

WARNING — The extrapolation of equibiaxial flexural strength data to other geometries of

stressing, to single-axial stressing, to other rates of stressing or to other environments should

be viewed with caution.

The information about the origin of fracture in an equibiaxial flexural strength test can be a valuable

guide to the nature and position of strength-limiting defects. Fractography of test pieces is highly

recommended (see e.g. ASTM C1499, Reference [1], Reference [2]) and Annex A. In particular, the test

can identify fracture origins as being edge defects (caused by edge preparation), surface defects (caused

by surface preparation) or internal defects (caused by manufacturing inhomogeneities such as pores,

large grains or impurity concentrations). Not all advanced monolithic technical ceramics are amenable

to clear fractography.
6 Apparatus
6.1 Test machine

The test machine shall be capable of applying a force over a ball or a suitable articulation device in

that way that the loading ring acts perpendicular to the surface of the test piece so that the two rings

(loading ring and support ring) have uniform contact to the face surfaces of the test piece.

The machine shall be capable of applying the force shock-free and with controlled force or displacement.

The test machine shall be equipped for recording the maximum force applied to the test piece. The

accuracy of the test machine shall be in accordance with ISO 7500-1, grade 1.
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ISO 17167:2018(E)
6.2 Test jig

The test jig for the ring-on-ring test shall be as specified below in order to minimize misalignments and

frictional forces applied to the test piece.

NOTE 1 The precise construction of the test jig is not fixed in this document but the function is.

A schematic test setup for the examination of the nominal equibiaxial flexural strength by the double-

ring flexural test is shown in Figure 1.
Key
1 loading ring d contact diameter of the loading ring
2 thin adhesive film on the test piece d contact diameter of the support ring
3 test piece D diameter of the test piece
4 rubber film under the test piece F force applied
5 support ring r contact radius

Figure 1 — Example of a test setup for the determination of flexural strength by the ring-on-

ring test

The test jig shall consist of two concentric rings of different diameters, namely the support ring (large),

and the loading ring (small), see Figure 1.
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ISO 17167:2018(E)
The following standard dimensions shall be observed:
— contact diameter of the loading ring, d : (12 ± 0,1) mm;
— contact diameter of the support ring, d : (30 ± 0,1) mm;

— radius of curvature of the rings in the region of contact with the test piece surface, r: (2 ± 0,2) mm.

NOTE 2 This test setup has been used for decades to characterize the stress of advanced technical alumina

ceramics for orthopaedic implants (see ISO 6474-1).

A suitable centring device or procedure for the test jig shall be used ensuring a centred positioning of

the loading ring, the test piece and the support ring to one another within 0,2 mm.

Either the support ring or the loading ring shall be fixed to the punch of the test machine used so that

an adjustment of the rings to the test piece is also possible if the test piece is not perfectly coplanar flat.

The two rings shall be made from hardened steel with a Vickers hardness greater than 500 HV or

greater than 40 HRC (Rockwell C-scale), or another material with at least the hardness of the material

tested (e.g. hard metal, ceramic) to minimize damage to the rings which can occur during the fracture.

To compensate small deviations of the surface flatness of the discoidal test piece, a thin rubber film

with a thickness of (0,6 ± 0,1) mm and a shore A hardness of (60 ± 5) shall be positioned between the

support ring and the test piece.

The flatness (and/or waviness) of the loading and the supporting rings shall be equal or smaller than

0,02 mm.

6.3 Calliper or alternative calibrated device for the measurement of the test piece

thickness

For the determination of the test piece dimensions, a calibrated calliper or an alternative calibrated

device with a resolution ≤ 0,1 % of the dimension to be measured shall be used.

It means that the resolution of the measurement device for the test piece thickness shall be ≤ 0,002 mm

and for the test piece diameter ≤ 0,04 mm.
6.4 Device for measuring the temperature and humidity

A device for measuring the temperature with a resolution of at least 1 °C and a humidity measuring

device with a resolution of at least 5 % RH shall be used.
7 Test pieces
7.1 General

The test pieces shall be prepared by processes in accordance with the technologies used during the

production of the products. They may either be specially processed to, or close to, the final required

dimensions specified in 7.2, or may be machined from larger blocks or components.

NOTE 1 The strength of many types of advanced monolithic technical ceramics is strongly

...

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