ISO/FDIS 24831

FINAL DRAFT
International
Standard
ISO/TC 206
Fine ceramics (advanced ceramics,
Secretariat: JISC
advanced technical ceramics) —
Voting begins on:
Mechanical properties of ceramic
2026-09-21
matrix composite at ambient
Voting terminates on:
temperature in air atmospheric
2026-11-16
pressure — Determination of leak
strength of tubes
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
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INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 206
Fine ceramics (advanced ceramics,
Secretariat: JISC
advanced technical ceramics) —
Voting begins on:
Mechanical properties of ceramic
matrix composite at ambient
Voting terminates on:
temperature in air atmospheric
pressure — Determination of leak
strength of tubes
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 SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
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MADE IN NATIONAL REGULATIONS.
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Significance and use . 2
6 Apparatus . 2
6.1 Pressurizing system .2
6.2 Passive seal fixture .3
6.3 Adhesive .3
6.4 Pressurization medium .3
6.5 Strain measurement .4
6.5.1 General .4
6.5.2 Strain gauge .4
6.5.3 Digital image correlation (DIC) .4
7 Measurement of test specimen dimensions. 4
8 Test specimen dimensions . 4
9 Specimen preparation . . 5
10 Test modes and rates . 5
11 Test procedure . 5
11.1 Pressure cell .5
11.2 Measurement of test specimen dimensions .6
11.3 Specimen bonding .6
11.4 Setting-up of strain measurement means .6
11.5 Specimen mounting . .7
11.6 Measurement .7
11.7 Leak location of test specimen .7
11.8 Test validity .7
11.9 Number of test specimens .7
12 Calculation of results . 8
12.1 Hoop tensile stress and strain .8
12.2 Pressure-strain curves .8
12.3 Stress-strain curves .10
12.4 Leak strength .11
13 Statistics . .11
14 Test report .12
Annex A (informative) Test setup of leak properties of the tube specimen .13
Bibliography . 14

iii
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
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This document was prepared by Technical Committee ISO/TC 206, Fine Ceramics.
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iv
FINAL DRAFT International Standard ISO/FDIS 24831:2026(en)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Mechanical properties of ceramic matrix
composite at ambient temperature in air atmospheric
pressure — Determination of leak strength of tubes
1 Scope
This document specifies a method for determining the leak strength of ceramic matrix composite (CMC)
tubes with fibre-reinforcement at room temperature in air atmospheric pressure. This document provides
information on the stress-strain response, such as leak strength, and corresponding hoop tensile strain.
This document applies primarily to ceramic matrix composite tubes with continuous fibre reinforcement:
uni-directional (1-D), bi-directional (2-D), tri-directional (xD, 2< x <3).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3611, Geometrical product specifications (GPS) — Dimensional measuring equipment — Design and
metrological characteristics of micrometers for external measurements
ISO 20507, Fine ceramics (advanced ceramics, advanced technical ceramics) —Vocabulary
ASTM E251-92, Test Methods for performance characteristics of metallic bonded resistance strain gauges
ASTM E2208-02, Standard Guide for Evaluating Non-Contacting Optical Strain Measurement Systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20507 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
total length
L
t
length including ends of the tube specimen
3.2
calibrated length
L
c
part of the test specimen that has uniform and minimum external diameter
[SOURCE: ISO 21971:2019,3.1]
3.3
gauge length
L
g
initial distance between reference points on the test specimen in the calibrated length
[SOURCE: ISO 21971:2019,3.2]
3.4
leak pressure
P
l
internal pressure corresponding to the tube specimen when leakage occurs during the test
3.5
leak strength
σ
l
hoop stress corresponding to leak pressure (3.4)
Note 1 to entry: The leak pressure is not enough to cause fibre breakage, therefore, the tube specimen still has a
complete integrity geometry.
4 Principle
Closed-end seal fittings incorporating a high-strength adhesive seal against the test specimen tube of
specified dimensions are used at room temperature. Both axial and hoop stress act on the tube specimen
at the same time during leak properties test of CMC tube specimen. Pressure medium is pumped into the
test specimen at a constant volume flow rate. The tube specimen is loaded to leakage and the corresponding
test time, internal pressure, and strain data are recorded. The leak strength of the specimen are calculated
based on the test data and curves.
The end fitting incorporating a high-strength adhesive shall ensure that there is no leakage of pressurized
medium from the seal area during loading.
5 Significance and use
Unlike hoop strength tests, which lead to severe fracture of CMC tubes, this standard specifies a method for
determining the liquid pressure leak strength under low internal pressure. Leakage arises from microscopic
matrix damage, with no extensive fibre breakage. The CMC tube remains intact in its original shape once the
leak strength is reached.
This standard is intended to assess the influences of pore characteristics (quantity, size and connectivity),
reinforcement weaving architecture and tube geometry (wall thickness and diameter) on the leakage
resistance of CMC tubes. Test data can support material development, production quality control, material
comparison and performance characterization of CMC tubular components
6 Apparatus
6.1 Pressurizing system
Pressurizing system should be designed with sufficient safety protection device, in case of overpressure,
leakage and other dangers, to ensure the safety of staff and equipment (see Figure A.1).
Special consideration shall be given to the following items.
a) Pump, shall be able to apply a continuously increasing and uniform internal pressure to the tube
specimen. The pump should not produce a pressure surge with each stroke.
b) Valves, shall include the following functions: control, regulation, and safety.

c) Pressure sensor, of adequate capacity, shall be used to monitor system pressure and to record the fluid
pressure attained. The accuracy of pressure sensor shall be better than 1 % of the test value.
6.2 Passive seal fixture
Passive seal fixture transmits the pressure medium applied by the pressurizing system to the tube specimen.
Seal fixture mainly consists of left end fitting, right end fitting and seal bolt. Left end fitting provides bonding
area on both the OD and the ID zones of the tube specimen, and there is a channel to induce pressurized
medium into the tube specimen. Right end fitting has a vent hole to ensure that all free gases shall be vented
prior to test. The seal bolt is used to seal vent hole. An example of the tube specimen closed-end seal fixture
is shown in Figure 1. The tube specimen is recommended to fit into the bonding cavity with a thin (~0,1 to
[2]
0,2 mm) space for adhesive, providing uniform gluing zone between the tube specimen and the end fitting .
Insufficient b
...