ISO 15733:2001

INTERNATIONAL ISO
STANDARD 15733
First edition
2001-02-01
Fine ceramics (advanced ceramics,
advanced technical ceramics) — Test
method for tensile stress-strain behaviour
of continuous, fibre-reinforced composites
at room temperature
Céramiques techniques — Méthode d'essai de comportement à la
contrainte en traction des composites renforcés de fibres continues, à
température ambiante
Reference number
ISO 15733:2001(E)
©
ISO 2001

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ISO 15733:2001(E)
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ii © ISO 2001 – All rights reserved

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ISO 15733:2001(E)
Contents Page
Foreword.iv
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Symbols and designations .3
5 Principle.5
6 Apparatus .5
6.1 Testing machine.5
6.2 Test piece gripping.5
6.3 Strain measurement .7
6.4 Data acquisition .7
6.5 Dimension measurement .7
7 Test piece .7
7.1 Test piece geometry .7
7.2 Test piece preparation .9
7.3 Number of test piece .10
7.4 Valid test.10
7.5 End tabs.10
8 Test conditions .11
8.1 Verification of axial alignment.11
8.2 Test modes and rates.11
9 Procedure .11
9.1 Test piece dimensions .11
9.2 Preparation for testing .11
9.3 Completion of testing.11
9.4 Post test.12
9.5 Calculation of results .12
10 Test report .17
10.1 Test set .17
10.2 Individual tests.18
Annex A (normative) Alignment verification .22
Annex B (informative) Test piece geometries .24
Bibliography.27
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ISO 15733:2001(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 15733 was prepared by Technical Committee ISO/TC 206, Fine ceramics.
Annex A forms a normative part of this International Standard, annex B is for information only.
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INTERNATIONAL STANDARD ISO 15733:2001(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for tensile stress-strain behaviour of
continuous, fibre-reinforced composites at room temperature
1 Scope
This International Standard specifies the determination of in-plane tensile behaviour including stress-strain
response under monotonic uniaxial testing of continuous fiber-reinforced ceramic matrix composites (CFRCMCs) at
ambient temperature.
This International Standard addresses, but is not restricted to, various suggested test piece geometries, test piece
fabrication methods, testing modes, testing rates, allowable bending, data collection and reporting procedures. This
International Standard applies primarily to ceramic and/or glass matrix composites with continuous fiber
reinforcement: uni-directional (1-D), bi-directional (2-D) and tri-directional (3-D) or other multi-directional
reinforcements. Carbon fiber-reinforced carbon matrix (C/C) composites may also be tested using this International
Standard, although caution is advised since this International Standard was developed primarily for CFRCMCs and
any accommodations unique to C/C composites have not been included.
Values expressed in this International Standard are in accordance with the International System of Units (SI).
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 286-1:1988, ISO system of limits and fits — Part 1: Bases of tolerances, deviations and fits.
ISO 3611:1978, Micrometer callipers for external measurement.
ISO 6892:1998, Metallic materials — Tensile testing at ambient temperature.
ISO 7500-1:1999, Metallic materials — Verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Verification and calibration of the force-measuring system.
ISO 9513:1999, Metallic materials — Calibration of extensometers used in uniaxial testing.
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
fine ceramic (advanced ceramic, advanced technical ceramic)
highly-engineered, high-performance predominately non-metallic, inorganic, ceramic material having specific
functional attributes
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ISO 15733:2001(E)
3.2
axial strain
average longitudinal strain measured at the surface on opposite sides of the longitudinal axis of symmetry of the
test piece by strain-sensing devices located at the mid length of the reduced section
3.3
bending strain
difference between the strain at the surface and the axial strain
NOTE In general, the bending strain varies from point to point around and along the reduced section of the test piece.
3.4
breaking force
force at which fracture occurs
3.5
ceramic matrix composite
material consisting of two or more materials (insoluble in one another), in which the major, continuous component
(matrix component) is a ceramic, while the secondary component(s) (reinforcing component) may be ceramic,
glass-ceramic, glass, metal or organic in nature; these components are combined on a macroscale to form a useful
engineering material possessing certain properties or behaviour not possessed by the individual constituents
3.6
continuous fiber-reinforced ceramic matrix composite (CFRCMC)
ceramic matrix composite in which the reinforcing phase consists of a continuous fiber, continuous yarn or a woven
fabric
3.7
fracture strength
tensile stress which the material sustains at the instant of fracture
NOTE Fracture strength is calculated from the force at fracture during a tensile test carried to rupture and the original
cross-sectional area of the test piece.
3.8
gauge length
original length of that portion of the test piece over which strain or change of length is determined
3.9
irrecoverable cumulative damage energy (also known as, modulus of toughness)
strain energy per unit volume required to stress the material from zero to final fracture indicating the ability of the
material to absorb energy beyond the elastic range (i.e., inherent damage tolerance of the material)
3.10
matrix-cracking stress
the applied tensile stress at which the matrix cracks into a series of roughly parallel blocks perpendicular to the
tensile stress
3.11
modulus of elasticity
the ratio of stress to corresponding strain less than the proportional limit
3.12
proportional limit stress
the greatest stress which a material is capable of sustaining without any deviation from proportionality of stress to
strain (Hooke's law)
3.13
percent bending
the bending strain times 100 divided by the axial strain
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ISO 15733:2001(E)
3.14
recoverable elastic energy (also known as, modulus of resilience)
strain energy per unit volume required to elastically stress the material from zero to the proportional limit indicating
the ability of the material to absorb energy when deformed elastically and return it when the force is removed
3.15
slow crack growth
sub-critical crack growth (extension) which may result from, but is not restricted to, such mechanisms as
environmentally-assisted stress corrosion or diffusive crack growth
3.16
tensile strength
the maximum tensile stress which a material is capable of sustaining
NOTE Tensile strength is calculated from the maximum force during a tensile test carried to rupture and the original cross-
sectional area of the test piece.
3.17
test series
a discrete group of tests on individual test pieces conducted within a discrete period of time on a particular material
configuration, test piece geometry, test condition or other uniquely definable qualifier (e.g., a test series composed
of material A comprising ten test pieces of geometry B tested at a fixed rate in strain control to final fracture in
ambient air)
4 Symbols and designations
Symbols used throughout this International Standard and their designations are given in Table 1.
Table 1 — Symbols and designations
Symbol Designation Unit References
2
A Surface area mm 9.5.1
equations 1, 2a, 2b
d
Thickness mm Tables 2, 3
Figures 3, 4
E Elastic modulus (Young’s modulus) MPa 9.5.7
equation 6, Figure 6
3
E Recoverable elastic energy (modulus of resilience) J/m 9.5.10
R
equation 7
3
E Irrecoverable cumulative damage energy (modulus of toughness) J/m 9.5.11
T
equations 8, 9
F
Force N 9.5.1
equation 1
F Force at fracture N 9.5.5
f
equation 5
F Maximum force N 9.5.3
m
equation 4
l Length, extensometer or test piece at any time mm 9.5.2
equation 3
l
Length, original extensometer or test piece mm 9.5.2
0
equation 3
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ISO 15733:2001(E)
Table 1 (continued)
Symbol Designation Unit References
L Length, total for straight-sided test piece geometry mm Table 3
Figure 4
L
Length, gauge for contoured test piece geometry mm Table 2
1
Figure 3
L Length, total for contoured test piece geometry mm Table 2
2
Figure 3
n Number of valid tests 1 10.1, g)
n Number of total tests 1 10.1, g)
T
R Radius, blend for contoured test piece geometry mm Table 2
Figure 3
SD Standard deviation var. equation 11
R Tensile strength at fracture MPa 9.5.5
f
equation 5
R Ultimate tensile strength MPa 9.5.3
m
equation 4
V
Coefficient of variation var. equation 12
W Width, total for straight-sided test piece geometry mm Table 2
Figure 4
W Width, gauge for contoured test piece geometry mm Table 2
1
Figure 3
W Width, grip for contoured test piece geometry mm Table 2
2
Figure 3
Mean 1 equation 10
X
Strain, normal mm/mm 9.5.2
�
equation 3
� Strain, corresponding to R mm/mm 9.5.6
f f
Figure 6
Strain, corresponding to R mm/mm 9.5.4
�
m
m
mm/mm 9.5.9
� Strain, corresponding to �
0 0
Figure 6
Stress, normal MPa 9.5.1
�
equation 1
Stress, proportional limit MPa 9.5.8
�
0
Figures 6, 7
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ISO 15733:2001(E)
5Principle
This International Standard is for material development, material comparison, quality assurance, characterization,
reliability and design data generation. Dissimilar material response of CFRCMCs in tension and compression
prevents unambiguous characterization of material behaviour from flexural tests. Therefore, uniaxially-tested and
uniformly-stressed tensile tests can provide information on fundamental material behaviour including stress-strain
response, proportional limit and ultimate strengths, elastic constants, and strain-energy absorption.
This test consists of testing a test piece to fracture using a uniaxial tensile force for the purpose of determining
tensile stress-strain response, various tensile strengths and corresponding strains, elastic constants and various
deformation energies. Generally, this test is carried out under conditions of ambient temperature and environment.
6 Apparatus
6.1 Testing machine
The testing machine shall be verified in accordance with ISO 7500-1 and shall be of at least grade 1,0 unless
otherwise specified.
6.2 Test piece gripping
Various types of gripping device may be used to transmit the measured force applied by the testing machine to the
test piece. The brittle nature of the matrices of CFRCMCs requires a uniform interface between the grip
components and the gripped section of the test piece in order to minimize crack initiation and fracture of the test
piece in the gripped section. Gripping devices can be classified generally as those employing active and those
employing passive grip interfaces.
6.2.1 Active grip interfaces
Active grip interfaces require continuous application of a mechanically-, hydraulically- or pneumatically-derived
force (pressure) to transmit the force applied by the test machine to the test piece. Sufficient lateral pressure shall
be applied to prevent slippage between the grip face and the test piece. Grip surfaces that are scored or serrated
with a pattern similar to that of a single-cut file have been found to be satisfactory. See Figure 1.
NOTE Generally, these types of grip interface cause a force to be applied perpendicular to the surface of the gripped
section of the test piece. Transmission of the uniaxial force applied by the test machine is then accomplished by friction between
the test piece and the grip faces.
6.2.2 Passive grip interfaces
Passive grip interfaces transmit the force applied by the test machine to the test piece through a direct mechanical
link. These mechanical links transmit the test forces to the test piece via geometrical features of the test pieces
such as shank shoulders or holes in the gripped head. See Figure 2.
NOTE Generally, the uniaxial force is transmitted to the test piece through uniform contact along the entire test piece/grip
interface thus minimizing eccentric forces.
6.2.3 Test train couplers
Various types of device (test-train couplers) may be used to attach the active or passive grip interface assemblies
to the testing machine. The test-train couplers in conjunction with the type of gripping device play major roles in the
alignment of the test train and subsequent bending imposed in the test piece. The efficacy of the test train couplers
and grip interfaces is verified through the procedure discussed in 8.1 and Annex A.
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ISO 15733:2001(E)
Key
1Testpiece
2 Wedge grip
3 Grip body
4 Grip mechanism
Figure 1 — Example of an active grip interface
Key
1 Retaining plate
2Testpiece
3 Inserts for lateral centring of test piece
4 Grip attachment
Figure 2 — Example of a passive grip interface
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ISO 15733:2001(E)
6.3 Strain measurement
Strain measurement is required for tensile testing of CFRCMC test pieces in accordance with this International
Standard.
Extensometers shall be of class 1 in accordance with ISO 9513. The extensometer gauge length shall be not less
than 10 mm (25 mm preferred) and shall be centrally located in the mid region of the parallel length of the gauge
section of the test piece.
Extensometers which are in mechanical contact with the test piece shall not cause damage to the test piece
surface such that a detrimental effect on tensile behavour is produced. Ensure that the extensometer does not
introduce bending greater than that allowed in 8.1. Extensometers shall preferably be of a type that is capable of
measuring elongation on both sides of a test piece (for averaging of strain and/or determination of in-situ percent
bending).
Strain gauges may also be used to measure strain in tensile tests of CFRCMCs. Unless it can be shown that strain
gauge readings are not unduly influenced by localized strain events such as fiber crossovers, strain gauges should
be not less than 9 mm to 12 mm in length for the longitudinal direction and not less than 6 mm in length for the
transverse direction. The strain gauges, surface preparation and bonding agents should be chosen to provide
adequate performance on the subject materials and suitable strain-recording equipment should be used.
6.4 Data acquisition
Obtain at least an autographic record of applied force and gauge section elongation or strain versus time using
either analogue chart recorders or digital data acquisition systems. Recording devices shall be accurate to within
1 % of the selected range for the testing system including readout unit and should have a minimum data acquisition
rate of 10 Hz with a response of 50 Hz deemed more than sufficient.
6.5 Dimension measurement
Micrometers and other devices used for measuring linear dimensions shall be accurate and precise to at least one
half the smallest unit to which the individual dimension is required to be measured and shall be in accordance with
ISO 3611. To obtain consistent measurements of cross sectional dimensions, use a flat, anvil-type micrometer.
Ball-tipped or sharp anvil micrometers are not recommended for woven CFRCMCs because the resulting
measurements may be affected by the peaks and troughs of the weave. Measure cross-sectional dimensions to
within 0,02 mm using dimension-measuring devices with accuracies of 0,01 mm.
7 Test piece
7.1 Test piece geometry
The choice of geometry of a tensile test piece is dependent on the ultimate use of the tensile behaviour data. For
example, if the tensile strength of an as-fabricated component is required, the dimensions of the resulting test piece
may reflect the thickness, width and length restrictions of the component. If it is desired to evaluate the effects of
interactions of various constituent materials for a particular CFRCMC manufactured via a particular processing
route, then the size of the test piece and resulting gauge section will reflect the desired volume or surface area to
be sampled.
Therefore, no single test piece geometry can be recommended or prescribed to meet all the requirements of a
particular testing programme or apparatus. Annex B contains further information on test piece geometries including
a figure showing examples of successful test piece geometries used for CFRCMCs.
Certain dimensional requirements are contained in Tables 2 and 3 depending on whether contoured (Figure 3) or
straight-sided geometries (Figure 4) are used, respectively.
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ISO 15733:2001(E)
Table 2 — Minimum dimensions of contoured test piece geometries (see Figure 3)
Minimum value Tolerance
Dimension
mm mm
Total length, L
W 100 � 0,5
2
Gauge Length, L
W 30 � 0,2
1
Thickness, d
W 2 and at least a) three plies for simply woven materials or b) � 0,2
one unit cell width for complex woven materials
Gauge width, W
W 6 and at least a) three fibre bundles for simply woven materials � 0,2
1
or b) one unit cell width for complex woven materials
Grip width, W
W 10 and at least 1,4� W � 0,2
2
1
Blend radius, R
W 35 � 2
Parallelism of 0,05
machined part
a
Smooth and blend at intersection with width, W , of gauge section.
1
b
Simple intersection (no steps of jogs) with width, W , of grip section.
2
Figure 3 — "Generic" countered test piece geometry (see Table 2)
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ISO 15733:2001(E)
Table 3 — Minimum dimensions of straight-sided test piece geometries (see Figure 4)
Minimum value Tolerance
Dimension
mm mm
Length, L
W 100 � 0,5
Thickness, d
W 2 and at least a) three plies for simply woven materials or b) � 0,2
one unit cell width for complex woven materials
Width, W
W 6 and at least a) three fibre bundles for simply woven materials � 0,2
or b) one unit cell width for complex woven materials
Parallelism of machine part 0,05
Figure 4 — "Generic" straight-sided test piece geometry (see Table 3)
7.2 Test piece preparation
Any test piece preparation route, including those discussed here, may be used as long as the preparation
procedure is reported in sufficient detail so as to allow replication.
7.2.1 As-fabricated
The test piece shall simulate the surface/edge conditions and processing route of an application where no
machining is used; e.g., as-cast, sintered or injection molded part. No additional machining specifications are
relevant. As-processed test pieces may possess rough surface textures and non-parallel edges and as such may
cause excessive misalignment and/or be prone to non-gauge section fractures.
7.2.2 Application-matched machining
Finish the test piece as close to the same surface/edge preparation as that applied to the component. Unless the
process is proprietary, report specifics about the stages of material removal, wheel grits, wheel bonding, amount of
material removed per pass and type of coolant used.
7.2.3 Customary practices
In instances where a customary machining procedure has been developed that is completely satisfactory for a class
of materials (i.e., it induces no unwanted surface/subsurface damage or residual stresses), use this procedure.
7.2.4 Recommended procedure
Perform all grinding or cutting with an ample supply of appropriate filtered coolant to keep the workpiece and
grinding wheel constantly flooded and particle flushed. Grind in at least two stages, ranging from coarse to fine rate
of material removal. Cut in one stage appropriate for the depth of cut. Remove stock in the order of 0,03 mm per
pass using diamond tools that have between 320 and 600 grit. Remove equal quantities of stock from each face
where applicable.
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ISO 15733:2001(E)
7.3 Number of test pieces
A minimum of five valid tests is required for the purpose of estimating a mean. A greater number of tests may be
necessary if estimates regarding the form of the strength distribution are required. If material cost or test piece
availability limit the number of tests to be conducted, fewer tests can be conducted to determine an indication of
material properties.
7.4 Valid test
A valid individual test is one which meets the following requirements:
a) all the testing requirements of this International Standard;
b) failure occurs in the uniformily-stressed gauge section unless those tests failing outside the gauge section are
interpreted as interrupted tests for the purpose of censored test analyses.
7.5 End tabs
End tabs may be required to provide a compliant layer for gripping for active grip interfaces. Balanced 0/90° cross-
ply E-glass fiber-reinforced epoxy, PM, and carbon fiber-reinforced resins are satisfactory tab materials. Each
bevelled tab (bevel angleu 15°) should be a minimum of 30 mm long, the same width of the test piece with the
total thickness of the tabs in the order of the thickness of the test piece. Any high-elongation (tough) adhesive
system may be used with the length of the tabs determined by the shear strength of the adhesive, size of the test
piece, and estimated strength of the composite. In any case, a significant fraction (e.g.,W10 % to 20 %) of fractures
within one test piece width of the tab shall be cause to re-examine the tab materials and configuration, gripping
method and adhesive, and to make necessary adjustments to promote fracture within the gauge section. Figure 5
shows an example of a successful tab design.
Dimensions in millimetres
a
Width of specimen
b
Toward longitudinal midpoint of spe
...