ISO 19634:2026

Norme
internationale
ISO 19634
Deuxième édition
Céramiques techniques —
2026-02
Céramiques composites —
Notations et symboles
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Ceramic composites — Notations and symbols
Numéro de référence
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2026
Tous droits réservés. Sauf prescription différente ou nécessité dans le contexte de sa mise en œuvre, aucune partie de cette
publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,
y compris la photocopie, ou la diffusion sur l’internet ou sur un intranet, sans autorisation écrite préalable. Une autorisation peut
être demandée à l’ISO à l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.
ISO copyright office
Case postale 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Genève
Tél.: +41 22 749 01 11
E-mail: copyright@iso.org
Web: www.iso.org
Publié en Suisse
ii
Sommaire Page
Avant-propos .iv
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 1
4 Nomenclature et symboles . 5
4.1 Nomenclature .5
4.2 Symboles .5
5 Signification et utilisation .16
5.1 Signification .16
5.2 Utilisation .16

iii
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes nationaux
de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est en général
confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude a le droit de faire
partie du comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l’ISO participent également aux travaux. L’ISO collabore étroitement avec
la Commission électrotechnique internationale (IEC) en ce qui concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d’approbation requis pour les différents types de documents ISO. Le présent document
a été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2
(voir www.iso.org/directives).
L’ISO attire l’attention sur le fait que la mise en application du présent document peut entraîner l’utilisation
d’un ou de plusieurs brevets. L’ISO ne prend pas position quant à la preuve, à la validité et à l’applicabilité de
tout droit de brevet revendiqué à cet égard. À la date de publication du présent document, l’ISO n’avait pas
reçu notification qu’un ou plusieurs brevets pouvaient être nécessaires à sa mise en application. Toutefois,
il y a lieu d’avertir les responsables de la mise en application du présent document que des informations
plus récentes sont susceptibles de figurer dans la base de données de brevets, disponible à l’adresse
www.iso.org/brevets. L’ISO ne saurait être tenue pour responsable de ne pas avoir identifié tout ou partie de
tels droits de brevet.
Les appellations commerciales éventuellement mentionnées dans le présent document sont données pour
information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion de
l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles techniques au
commerce (OTC), voir www.iso.org/avant-propos.
Le présent document a été élaboré par le comité technique ISO/TC 206, Céramiques techniques, en
collaboration avec le comité technique CEN/TC 184, Céramiques techniques avancées, du Comité européen
de normalisation (CEN) conformément à l’Accord de coopération technique entre l’ISO et le CEN (Accord de
Vienne).
Cette deuxième édition annule et remplace la première édition (ISO 19634:2017), qui a fait l’objet d’une
révision technique.
Les principales modifications sont les suivantes :
— révision et ajout de certains symboles et notations.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes se
trouve à l’adresse www.iso.org/fr/members.html.

iv
Norme internationale ISO 19634:2026(fr)
Céramiques techniques — Céramiques composites —
Notations et symboles
1 Domaine d’application
Le présent document spécifie les symboles à utiliser pour représenter les caractéristiques physiques,
mécaniques et thermiques, telles que déterminées par les méthodes décrites dans les Normes internationales
concernées, pour les composites à matrice céramique. Le présent document spécifie également les symboles
utilisés pour la mesure de ces caractéristiques.
Le présent document spécifie, dans la mesure du possible, les symboles qui sont conformes aux parties
pertinentes de la série ISO 80000.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l’édition citée s’applique. Pour
les références non datées, la dernière édition du document de référence s’applique (y compris les éventuels
amendements).
ISO 80000-4, Quantities and units — Part 4: Mechanics
ISO 80000-5, Quantities and units — Part 5: Thermodynamics
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions donnés dans l’ISO 80000-4 et l’ISO 80000-5
ainsi que les suivants, s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en normalisation,
consultables aux adresses suivantes :
— ISO Online browsing platform : disponible à l’adresse https:// www .iso .org/ obp
— IEC Electropedia : disponible à l’adresse https:// www .electropedia .org/
3.1
composite à matrice céramique
matrice en céramique, en carbone ou en verre contenant un renfort orienté dans une ou plusieurs directions
spatiales
3.2
composite à matrice céramique unidirectionnel
matériau 1D
composite à matrice céramique (3.1) dont le renfort est orienté dans une seule direction
Note 1 à l'article: à l’article : Voir Figure 1.

Légende
1 direction du renfort
2 dimension transversale la plus grande (largeur), perpendiculaire à la direction 1
3 dimension transversale la plus petite (épaisseur), perpendiculaire à la direction 1
NOTE Lorsque la largeur et l’épaisseur sont égales, les directions 2 et 3 sont équivalentes et peuvent être choisies
de manière quelconque.
Figure 1 — Schéma d’un matériau 1D
3.3
composite à matrice céramique renforcé dans un plan
matériau 2D
composite à matrice céramique (3.1) dont le renfort est orienté selon au moins deux directions dans un seul
plan
Note 1 à l'article: à l’article : Voir Figure 2.

Légende
1 direction de la plus grande fraction de renfort
2 direction perpendiculaire à la direction 1 dans le plan du renfort (n’est pas nécessairement une direction de
renfort)
3 direction perpendiculaire au plan du renfort
NOTE Strictement plus d’une direction de renfort fibreux, toutes les directions étant dans le même plan (dans le
cas présent, il y a trois directions de renfort dans le plan (1,2)).
Lorsque plusieurs directions ont une fraction de renfort égale, il faut préciser quelle direction est choisie
comme direction 1 par rapport à la structure du renfort (par exemple pour un textile à renfort orthogonal :
chaîne dans la direction 1, trame dans la direction 2).
Figure 2 — Schéma d’un matériau 2D
3.4
composite à matrice céramique multidirectionnel
matériau xD (2 < x ≤ 3)
composite à matrice céramique (3.1) dont le renfort est orienté dans l’espace dans au moins trois directions
qui ne sont pas dans un même plan
Note 1 à l'article: à l’article : Voir Figures 3 et 4.

Figure 3 — Schéma d’un matériau xD (2 < × ≤ 3)
Légende
1 direction de la plus grande fraction de renfort
2 direction dans le plan perpendiculaire à la direction 1
3 direction perpendiculaire au plan contenant les directions 1 et 2
Lorsque plusieurs directions ont une fraction de renfort égale, il faut préciser quelle direction est choisie
comme direction 1 par rapport à la structure du renfort. Lorsqu’il est possible de définir un plan de renfort,
la direction 2 est choisie dans le plan perpendiculaire à la direction 1 (la direction 2 n’est pas nécessairement
une direction de renfort) et la direction 3 est perpendiculaire au plan contenant les directions 1 et 2.
Lorsqu’il est impossible de définir un plan de renfort, la direction 2 est choisie de manière arbitraire, mais
elle est perpendiculaire à la direction 1 et doit être clairement identifiée.
Figure 4 — Schéma d’un matériau 3D

4 Nomenclature et symboles
4.1 Nomenclature
Les composites à renforts continus constituent une classe spécifique de ces matériaux. Plusieurs sous-
classes de composites à matrice céramique à renforts continus peuvent être distinguées.
Le symbole F/I/M s’applique généralement aux composites à matrice céramique :
— F indique la composition chimique du renfort fibreux : C pour le carbone, SiC pour le carbure de silicium,
Al O pour l’alumine, etc.
2 3
— I indique la composition chimique de l’interface fibre/matrice : C pour le carbone, BN pour le nitrure de
bore, LaPO pour la monazite, etc.
— M indique la composition chimique de la matrice : C pour le carbone, SiC pour le carbure de silicium,
Al O pour l’alumine.
2 3
EXEMPLE 1 Un composite à matrice céramique constitué de fibre de carbure de silicium, d’une interphase carbone
et d’une matrice de carbure de silicium se note : SiC/C/SiC.
Des notations plus complexes peuvent également être employées pour décrire plus précisément les
constituants.
EXEMPLE 2 Un composite à matrice céramique constitué de fibres de carbone avec une interphase séquencée de
quatre couches de carbone alternées avec quatre couches de carbure de silicium et une matrice de carbure de silicium
s’écrit : C /[C/SiC] /SiC .
f 4 m
4.2 Symboles
Les symboles utilisés pour les différentes grandeurs mécaniques et thermiques sont indiqués dans les
Tableaux 1 à 4.
Tableau 1 — Symboles relatifs aux grandeurs physiques
Grandeur Symbole Définition Unité Remarque
Masse volumique ρ Rapport de la masse d’un corps à son volume kg/m
Masse volumique apparente ρ Rapport de la masse du matériau à son volume kg/m
a
total
Masse volumique réelle ρ Rapport de la masse du matériau sec d’un kg/m Volume apparent = somme des volumes du
b
corps poreux et de son volume apparent matériau solide, des pores ouverts et des
pores fermés
Rapport de la masse d’un fil multifilamentaire
Masse linéique t tex Tex est la masse en grammes de 1 000 m
à sa longueur
Porosité P Rapport du volume total de pores au volume —
total du matériau
Porosité apparente P Rapport du volume des pores ouverts au —
a
volume total
Masse m Quantité de matière dans un corps g
Fraction volumique de phase V Fraction volumique de phase de type j déter- —
f,j
minée à partir des micrographies de sections
polies
Tableau 2 — Symboles relatifs aux grandeurs géométriques des éprouvettes
Grandeur Symbole Définition Unité Remarque
Longueur
Longueur totale l Longueur totale de l’éprouvette mm
t
Partie de l’éprouvette qui possède une section
Longueur utile L mm
transversale uniforme minimale
Longueur initiale l Longueur initiale de l’éprouvette lors de la mm
mesure de la dilatation thermique
Longueur de jauge L Distance initiale entre des points de référence mm
dans la longueur utile de l’éprouvette
Distance entre les appuis L Distance entre les supports de l’éprouvette en mm Essais de résistance et de module d’élasticité
a
flexion en trois ou quatre points en flexion
Distance entre les points de chargement d’une Essais de résistance et de module d’élasticité
Distance entre les couteaux supérieurs L mm
i
éprouvette de flexion en quatre points en flexion
Aire de la section S Aire de la section transversale de l’éprouvette mm
Aire initiale de la section S Aire de la section de l’éprouvette dans la lon- mm
gueur utile à la température ambiante avant
chargement
NOTE 1 Lorsque le matériau est protégé par un traitement de surface, deux sections initiales peuvent être définies :
—  Aire de la section apparente S Aire de la section mm
0,a
—  Aire de la section effective S Aire corrigée par un facteur pour tenir mm
0,e
compte de la présence d’une couche superfi-
cielle
Distance entre les entailles L Pour les essais de cisaillement interlaminaire, mm
la distance entre les entailles opposées
Section de cisaillement Section située entre les entailles de l’échantil- mm
lon pour essai
Aire initiale de la section de cisaillement S Aire de la section de cisaillement entre les
entailles de l’éprouvette à la température
ambiante avant l’essai
...

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 temperatu
...

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 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 its kg/m Bulk volume = sum of volumes of solid material, open
b
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
Fractional volume of phase of type j determined from
Phase volume fraction Vf,j —
...

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 temperatu
...

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 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 its kg/m Bulk volume = sum of volumes of solid material, open
b
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
Fractional volume of phase of type j determined from
Phase volume fraction Vf,j —
...