ISO/PRF 19634
(Main)Fine ceramics (advanced ceramics, advanced technical ceramics) — Ceramic composites — Notations and symbols
Fine ceramics (advanced ceramics, advanced technical ceramics) — Ceramic composites — Notations and symbols
ISO 19634:2017 defines the symbols to be used to represent physical, mechanical and thermal characteristics, as determined by methods described in relevant ISO publications, for ceramic matrix composites. It is aimed at avoiding confusion in reporting measurements and characteristics of products. Where possible, the definitions are in accordance with the relevant parts of ISO 80000. In addition, the symbols used in undertaking measurements of these characteristics are also defined.
Céramiques techniques — Céramiques composites — Notations et symboles
L'ISO 19634 :2017 définit les symboles à utiliser pour représenter les caractéristiques physiques, mécaniques et thermiques, telles que déterminées par les méthodes décrites dans les publications ISO concernées, pour les composites à matrice céramique. Il vise à éviter toute confusion dans les rapports de mesures et de caractéristiques des produits. Dans toute la mesure du possible, les définitions sont conformes aux parties pertinentes de l'ISO 80000. En outre, les symboles utilisés pour la mesure de ces caractéristiques sont également définis.
General Information
Relations
Standards Content (Sample)
International
Standard
ISO 19634
Second edition
Fine ceramics (advanced ceramics,
advanced technical ceramics) —
Ceramic composites — Notations
and symbols
Céramiques techniques — Céramiques composites — Notations et
symboles
PROOF/ÉPREUVE
Reference number
ISO 19634:2025(en) © ISO 2025
ISO 19634:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
ISO 19634:2025(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Nomenclature and symbols . 4
4.1 Nomenclature .4
4.2 Symbols .5
5 Significance and use .13
5.1 Significance . . . 13
5.2 Use . 13
PROOF/ÉPREUVE
iii
ISO 19634:2025(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 206, Fine ceramics, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 184, Advanced technical
ceramics, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This second edition cancels and replaces the first edition (ISO 19634:2017), which has been technically
revised.
The main changes are as follows:
— revision and addition of certain symbols and notations.
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.
PROOF/ÉPREUVE
iv
International Standard ISO 19634:2025(en)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Ceramic composites — Notations and symbols
1 Scope
This document specifies the symbols to be used to represent physical, mechanical and thermal characteristics,
as determined by methods described in relevant International Standards, for ceramic matrix composites.
This document also specifies the symbols used in undertaking measurements of these characteristics.
This document specifies symbols that are in accordance with the relevant parts of ISO 80000 where possible.
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 80000-4, Quantities and units — Part 4: Mechanics
ISO 80000-5, Quantities and units — Part 5: Thermodynamics
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 80000-4 and ISO 80000-5 and the
following apply.
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/
3.1
ceramic matrix composite
ceramic, carbon or glass matrix containing reinforcement distributed in one or more spatial directions
3.2
unidirectional ceramic matrix composite
1D material
ceramic matrix composite (3.1), the reinforcement of which is distributed in one single direction
Note 1 to entry: See Figure 1.
PROOF/ÉPREUVE
ISO 19634:2025(en)
Key
1 direction of reinforcement
2 direction of the greater transverse dimension (width), perpendicular to direction 1
3 direction of the smaller transverse dimension (thickness), perpendicular to direction 1
NOTE When the width and the thickness are equal, then directions 2 and 3 are equivalent and can be chosen freely.
Figure 1 — Schematic diagram of a 1D material
3.3
in-plane reinforced ceramic matrix composite
2D material
ceramic matrix composite (3.1), where the reinforcements are placed along at least two directions in a single plane
Note 1 to entry: See Figure 2.
Key
1 direction of the greater fraction of reinforcement
2 direction perpendicular to direction 1 in the plane of reinforcement (not necessarily a direction of
reinforcement)
3 direction perpendicular to the plane of reinforcement
NOTE 1 Strictly more than one direction of fibrous reinforcement, all contained within one plane (in the present
case, there are three directions of reinforcement in plane (1,2)).
PROOF/ÉPREUVE
ISO 19634:2025(en)
NOTE 2 When several directions have an equal fraction of reinforcement, it shall be stated which direction is
chosen as direction 1 in relation to the reinforcement structure (for example, orthogonal reinforced fabric: warp in
direction 1, weft in direction 2).
Figure 2 — Schematic diagram of a 2D material
3.4
multidirectional ceramic matrix composite
xD (2 < x ≤ 3) material
ceramic matrix composite (3.1), where the reinforcement is spatially distributed in at least three directions
not in a single plane
Note 1 to entry: See Figures 3 and 4.
Figure 3 — Schematic diagram of a xD (2 < × ≤ 3) material
PROOF/ÉPREUVE
ISO 19634:2025(en)
Key
1 direction of the greater fraction of reinforcement
2 direction perpendicular to direction 1
3 direction perpendicular to the plane containing directions 1 and 2
NOTE 1 When several directions have equal fraction of reinforcement, it shall be stated which direction is chosen as
direction 1, in relation to the reinforcement structure. When it is possible to define a plane of reinforcement, direction
2 will be chosen in this plane perpendicular to direction 1(direction 2 is not necessarily a direction of reinforcement),
and direction 3 will be perpendicular to the plane containing directions 1 and 2. When it is not possible to define a
plane of reinforcement, direction 2 is chosen arbitrarily, but perpendicular to direction 1 and shall be clearly identified.
Figure 4 — Schematic diagram of a 3D material
4 Nomenclature and symbols
4.1 Nomenclature
Composites with continuous reinforcements constitute a specific class of these materials. Several subclasses
of ceramic matrix composites with continuous reinforcements can be distinguished.
The symbol F/I/M applies usually to ceramic matrix composites:
— F indicates the chemical nature of fibrous reinforcement: C stands for carbon, SiC for silicon carbide,
Al O for alumina, etc.
2 3
— I indicates the chemical nature of fibre/matrix interphase: C stands for carbon, BN for boron nitride,
LaPO for monazite, etc.
— M indicates the chemical nature of matrix: C for carbon, SiC for silicon carbide, Al O for alumina.
2 3
EXAMPLE 1 A ceramic matrix composite composed of a silicon carbide fibre, a carbon interphase and a silicon
carbide matrix is denoted by SiC/C/SiC.
More complex symbols can be used to describe the constituents with a greater degree of precision.
EXAMPLE 2 For a composite composed of a carbon fibre, a multi-layered interphase of four alternate layers of
carbon and silicon carbide, and a silicon carbide matrix, the symbol is: C /[C/SiC] /SiC .
f 4 m
PROOF/ÉPREUVE
ISO 19634:2025(en)
4.2 Symbols
The symbols used for the various mechanical and thermal quantities are given in Tables 1 to 4.
PROOF/ÉPREUVE
ISO 19634:2025(en)
PROOF/ÉPREUVE
Table 1 — Symbols related to physical quantities
Quantity Symbol Definition Unit Remark
Density ρ Ratio of the mass of a body to its volume kg/m
Apparent density ρ Ratio of the mass of the body to its total volume kg/m
a
Bulk density ρ Ratio of the mass of the dry material of a porous body to kg/m Bulk volume = sum of volumes of solid material, open
b
its volume pores and closed pores
Linear density t Ratio of the mass of a multifilament tow to its length tex Tex is the mass in grams per 1 000 m
Porosity P Ratio of the total volume of pores in a porous body to its —
total volume
Apparent porosity P Ratio of the volume of open pores to total volume —
a
Mass m Quantity of matter in a body g
Phase volume fraction V Fractional volume of phase of type j determined from —
f,j
micrographs of polished cross-sections
ISO 19634:2025(en)
PROOF/ÉPREUVE
Table 2 — Symbols related to geometrical quantities of test pieces
Quantity Symbol Definition Unit Remark
Length
Total length l, l Total length of the test piece mm
t
Part of the test specimen that has uniform and minimum
Calibrated length l mm
cross-section area
Initial length l Initial length of test piece in thermal expansion meas- mm
urement
Gauge length L Initial distance between reference points on the test mm
piece in the calibrated length
Distance between outer rollers L Outer support span in three or four-point bending con- mm
a
In flexural strength and modulus testing
figuration
Distance between inner rollers L Inner loading span in four-point bending configuration mm In flexural strength and modulus testing
i
Cross-section S Cross-section area mm
Initial cross-section area S Cross-section area of the test piece within the calibrated mm
length at room temperature before loading
NOTE 1 When the material is protected by a surface treatment, two initial cross-section areas can be defined:
— Apparent cross-section area S Area of the cross-section mm
0,a
— Effective cross-section area S Area corrected by a factor, to account for the presence of mm
0,e
a surface layer
Distance between notches L In inter-laminar shear testing, the spacing between mm
opposite notches
Shear section Section located between the notches of test sample mm
Initial shear section area S Shear section area before test between the notches of
the test piece at roo
...
ISO/DISPRF 19634
ISO/TC 206
Secretariat: JISC
Date: 2025-07-11-12
Fine ceramics (advanced ceramics, advanced technical ceramics) —
Ceramic composites — Notations and symbols
Céramiques techniques — Céramiques composites — Notations et symboles
DIS stage
Warning for WD’s and CD’s
This document is not an ISO International Standard. It is distributed for review and comment. It is subject to change
without notice and may not be referred to as an International Standard.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which
they are aware and to provide supporting documentation.
PROOF
ISO/DISPRF 19634:20242025(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
iii
ISO/DISPRF 19634:20242025(en)
Contents
Foreword . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Nomenclature and symbols . 6
5 Significance and use . 16
Foreword . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Nomenclature and symbols . 6
5 Significance and use . 16
iv
ISO/DISPRF 19634:20242025(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.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.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics., in collaboration with the
European Committee for Standardization (CEN) Technical Committee CEN/TC 184, Advanced technical
ceramics, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This second edition cancels and replaces the first edition (ISO 19634:2017).), which has been technically
revised.
The main changes are as follows:
— revision and addition of certain symbols and notations.
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.
v
ISO/DISPRF 19634:20242025(en)
Fine ceramics (advanced ceramics, advanced technical ceramics) —
Ceramic composites — Notations and symbols
1 Scope
This document specifies the symbols to be used to represent physical, mechanical and thermal characteristics,
as determined by methods described in relevant International Standards, for ceramic matrix composites. This
document also specifies the symbols used in undertaking measurements of these characteristics.
This document specifies symbols that are in accordance with the relevant parts of ISO 80000 where possible.
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 80000-4, Quantities and units — Part 4: Mechanics
ISO 80000-5, Quantities and units — Part 5: Thermodynamics
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 80000-4 and ISO 80000-5 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
3.1
ceramic matrix composite
ceramic, carbon or glass matrix containing reinforcement distributed in one or more spatial directions
3.2
unidirectional ceramic matrix composite
1D material
ceramic matrix composite (3.1Error! Reference source not found.), the reinforcement of which is distributed
in one single direction
Note 1 to entry: See Figure 10.
ISO/DISPRF 19634:20242025(en)
Key
1 direction of reinforcement
2 direction of the greater transverse dimension (width), perpendicular to direction 1
3 direction of the smaller transverse dimension (thickness), perpendicular to direction 1
NOTE When the width and the thickness are equal, then directions 2 and 3 are equivalent and can be chosen freely.
1 direction of reinforcement
2 direction of the greater transverse dimension (width), perpendicular to direction 1
3 direction of the smaller transverse dimension (thickness), perpendicular to direction 1
NOTE When the width and the thickness are equal, then directions 2 and 3 are equivalent and can be chosen freely.
Figure 1 — Schematic diagram of a 1D material
3.3
in-plane reinforced ceramic matrix composite
2D material
ceramic matrix composite (3.1Error! Reference source not found.), where the reinforcements are placed
along at least two directions in a single plane
Note 1 to entry: See Figure 20.
ISO/DISPRF 19634:20242025(en)
Key
1 direction of the greater fraction of reinforcement
2 direction perpendicular to direction 1 in the plane of reinforcement (not necessarily a direction of reinforcement)
3 direction perpendicular to the plane of reinforcement
NOTE 1 Strictly more than one direction of fibrous reinforcement, all contained within one plane (in the present case, there are three
directions of reinforcement in plane (1,2)).
NOTE 2 When several directions have an equal fraction of reinforcement, it shall be stated which direction is chosen as direction 1 in
relation to the reinforcement structure (for example, orthogonal reinforced fabric: warp in direction 1, weft in direction 2).
1 direction of the greater fraction of reinforcement
2 direction perpendicular to direction 1 in the plane of reinforcement (not necessarily a direction of reinforcement)
3 direction perpendicular to the plane of reinforcement
NOTE 1 Strictly more than one direction of fibrous reinforcement, all contained within one plane (in the present case,
there are three directions of reinforcement in plane (1,2)).
ISO/DISPRF 19634:20242025(en)
NOTE 2 When several directions have an equal fraction of reinforcement, it shall be stated which direction is chosen
as direction 1 in relation to the reinforcement structure (for example, orthogonal reinforced fabric: warp in direction 1,
weft in direction 2).
Figure 2 — Schematic diagram of a 2D material
3.4
multidirectional ceramic matrix composite
yDxD (2 < y ≤x ≤ 3) material
ceramic matrix composite (3.1Error! Reference source not found.), where the reinforcement is spatially
distributed in at least three directions not in a single plane
Note 1 to entry: See Figures 30 and 40.
Figure 3 — Schematic diagram of a xD (2 < × ≤ 3) material
ISO/DISPRF 19634:20242025(en)
Key
1 direction of the greater fraction of reinforcement
2 direction perpendicular to direction 1
3 direction perpendicular to the plane containing directions 1 and 2
NOTE 1 When several directions have equal fraction of reinforcement, it shall be stated which direction is chosen as direction 1, in
relation to the reinforcement structure. When it is possible to define a plane of reinforcement, direction 2 will be chosen in this
plane perpendicular to direction 1(direction 2 is not necessarily a direction of reinforcement), and direction 3 will be
perpendicular to the plane containing directions 1 and 2. When it is not possible to define a plane of reinforcement, direction 2 is
chosen arbitrarily, but perpendicular to direction 1 and shall be clearly identified.
ISO/DISPRF 19634:20242025(en)
1 direction of the greater fraction of reinforcement
2 direction perpendicular to direction 1
3 direction perpendicular to the plane containing directions 1 and 2
NOTE 1 When several directions have equal fraction of reinforcement, it shall be stated which direction is chosen as
direction 1, in relation to the reinforcement structure. When it is possible to define a plane of reinforcement, direction 2
will be chosen in this plane perpendicular to direction 1(direction 2 is not necessarily a direction of reinforcement), and
direction 3 will be perpendicular to the plane containing directions 1 and 2. When it is not possible to define a plane of
reinforcement, direction 2 is chosen arbitrarily, but perpendicular to direction 1 and shall be clearly identified.
Figure 4 — Schematic diagram of a 3D material
4 Nomenclature and symbols
4.1 4.1 Nomenclature
Composites with continuous reinforcements constitute a specific class of these materials. Several subclasses
of ceramic matrix composites with continuous reinforcements can be distinguished.
The symbol F/I/M applies usually to ceramic matrix composites:
— F indicates the chemical nature of fibrous reinforcement: C stands for carbon, SiC for silicon carbide, Al O
2 3
for alumina, etc.
— I indicates the chemical nature of fibre/matrix interphase: C stands for carbon, BN for boron nitride, LaPO
for monazite, etc.
— M indicates the chemical nature of matrix: C for carbon, SiC for silicon carbide, Al O for alumina.
2 3
EXAMPLE 1 A ceramic matrix composite composed of a silicon carbide fibre, a carbon interphase and a silicon carbide
matrix is denoted by SiC/C/SiC.
More complex symbols can be used to describe the constituents with a greater degree of precision.
EXAMPLE 2 For a composite composed of a carbon fibre, a multi-layered interphase of four alternate layers of carbon
and silicon carbide, and a silicon carbide matrix, the symbol is: Cf/[C/SiC]4/SiCm.
4.2 4.2 Symbols
The symbols used for the various mechanical and thermal quantities are given in Tables 10 to 40.
ISO/DISPRF 19634:20242025(en)
Table 1 — Symbols related to physical quantities
Quantity Symbol Definition Unit Remark
Density ρ Ratio of the mass of a body
...
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