ENV 14186:2002
(Main)Advanced technical ceramics - Ceramic composites - Mechanical properties at room temperature, determination of elastic properties by an ultrasonic technique
Advanced technical ceramics - Ceramic composites - Mechanical properties at room temperature, determination of elastic properties by an ultrasonic technique
Migrated from Progress Sheet (TC Comment) (2000-07-10): Stage 41/51=ENV ++ Selected for 'comparison' in the experiment in one language (type B in BT N 4927
Céramiques techniques avancées - Céramiques composites - Propriétés mécaniques à température ambiante, détermination des propriétés élastiques par une méthode ultrasonore
La présente ENV spécifie une méthode ultrasonore pour déterminer les composants du tenseur d'élasticité des composites à matrice céramique à température ambiante. Les modules de Young, les modules de cisaillement et les coefficients de Poisson peuvent être déterminés à partir des composants du tenseur d'élasticité.
Cette norme s'applique aux composites à matrice céramique à renfort fibreux continu unidirectionnels (1D), bidirectionnels (2D) et tridirectionnels (xD, avec 2 x 3), qui ont au minimum une symétrie orthotrope et dont les axes de symétrie sont connus.
Cette méthode est applicable uniquement lorsque la longueur d'onde ultrasonore utilisée est supérieure à l'épaisseur du volume élémentaire représentatif, ce qui impose une limite supérieure à la gamme de fréquences des transducteurs utilisés.
NOTE Les propriétés obtenues au moyen de cette méthode peuvent ne pas être comparables avec les modules obtenus par les méthodes décrites dans l'EN 658-1, l'EN 658-2 et l'ENV 12289.
Sodobna tehnična keramika - Keramični kompoziti - Mehanske lastnosti pri sobni temperaturi, določanje upogibnih lastnosti z ultrazvočno tehniko
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST ENV 14186:2007
01-januar-2007
6RGREQDWHKQLþQDNHUDPLND.HUDPLþQLNRPSR]LWL0HKDQVNHODVWQRVWLSULVREQL
WHPSHUDWXULGRORþDQMHXSRJLEQLKODVWQRVWL]XOWUD]YRþQRWHKQLNR
Advanced technical ceramics - Ceramic composites - Mechanical properties at room
temperature, determination of elastic properties by an ultrasonic technique
Céramiques techniques avancées - Céramiques composites - Propriétés mécaniques a
température ambiante, détermination des propriétés élastiques par une méthode
ultrasonore
Ta slovenski standard je istoveten z: ENV 14186:2002
ICS:
81.060.30 Sodobna keramika Advanced ceramics
SIST ENV 14186:2007 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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EUROPEAN PRESTANDARD
ENV 14186
PRÉNORME EUROPÉENNE
EUROPÄISCHE VORNORM
August 2002
ICS 81.060.30
English version
Advanced technical ceramics - Ceramic composites -
Mechanical properties at room temperature, determination of
elastic properties by an ultrasonic technique
Hochleistungskeramik - Keramische Verbundwerkstoffe -
Mechanische Eigenschaften bei Raumtemperatur,
Bestimmung von elastischen Eigenschaften mittels
Ultraschallwellen
This European Prestandard (ENV) was approved by CEN on 13 July 2001 as a prospective standard for provisional application.
The period of validity of this ENV is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the ENV can be converted into a European Standard.
CEN members are required to announce the existence of this ENV in the same way as for an EN and to make the ENV available promptly
at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the ENV) until the final
decision about the possible conversion of the ENV into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. ENV 14186:2002 E
worldwide for CEN national Members.
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ENV 14186:2002 (E)
Contents
Foreword.3
1 Scope .4
2 Normative references .4
3 Principle.4
4 Significance and use .7
5 Terms and definitions and symbol.7
6 Apparatus .10
6.1 Ultrasonic tank with thermostatic control.10
6.2 Temperature measurement device .10
6.3 Test specimen holder .10
6.4 Transducers.10
6.5 Transducer holders .10
6.6 Pulse generator.10
6.7 Signal recording system .11
7 Test specimens .11
8 Test Specimen preparation.11
9 Test procedure .11
9.1 Choice of frequency .11
9.2 Establishment of the test temperature. .12
9.3 Reference test without test specimen .12
9.4 Measurement with the specimen.12
9.4.1 Measurement of the bulk density and of the thickness.12
9.4.2 Mounting of the specimen .12
9.4.3 Acquisition of different angles of incidence.12
10 Calculation.13
10.1 Delay.13
10.2 Calculation of the propagation velocities .13
10.3 Calculation of the refracted angle qq.14
r
10.4 Identification of the elastic constants C .14
ij
10.4.1 Basic considerations.14
C
10.4.2 Calculation of .15
33
10.4.3 Calculation of C , C and C .15
22 23 44
10.4.4 Calculation of C , C and C .16
11 13 55
10.4.5 Calculation of C and C .16
12 66
10.5 Back calculation of the phase velocities.17
10.6 Polar plots of the velocity curves.17
10.7 Calculation of the quadratic deviation.17
10.8 Calculation of the engineering constants .18
11 Test validity .18
11.1 Measurements.18
11.2 Criterion of validity for the reliability of the C components .18
ij
12 Test report .19
(informative)
Annex A Example of a presentation of the results for a material with orthothropic
symmetry .20
Bibliography .22
2
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ENV 14186:2002 (E)
Foreword
This document (ENV 14186:2002) has been prepared by Technical Committee CEN/TC 184 "Advanced technical
ceramics", the secretariat of which is held by BSI.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this European Prestandard: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain,
Sweden, Switzerland and the United Kingdom.
3
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ENV 14186:2002 (E)
1 Scope
This ENV specifies an ultrasonic method to determine the components of the elasticity tensor of ceramic matrix
composite materials at room temperature. Young moduli, shear moduli and Poisson coefficients, can be
determined from the components of the elasticity tensor.
This standard applies to ceramic matrix composites with a continuous fibre reinforcement: unidirectional (1D),
bidirectional (2D), and tridirectional (xD, with 2< x £ 3) which have at least orthotropic symmetry, and whose
material symmetry axes are known.
This method is applicable only when the ultrasonic wave length used is larger than the thickness of the
representative elementary volume, thus imposing an upper limit to the frequency range of the transducers used.
NOTE Properties obtained by this method may not be comparable with moduli obtained by EN 658-1, ENV 658-2 and
ENV 12289.
2 Normative references
This European Prestandard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Prestandard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies.
ENV 1389, Advanced technical ceramics – Composite ceramics – Physical properties – Determination of density
and of apparent porosity.
ENV 13233:1998, Advanced technical ceramics – Composite ceramics – Notations and symbols.
ISO 3611, Micrometer callipers for external measurements.
ISO 653, Long-solid-stem thermometers for precision use.
3 Principle
The determination of the elastic properties consists of calculating the coefficients of the propagation equation of an
elastic plane wave, from a set of properly chosen velocity measurements along known directions.
A thin specimen with planparallel faces is immersed in an acoustically coupling fluid (e.g. water) – see Figure 1.
The specimen is placed between an emitter (E) and a receiver (R) which are rigidly connected to each other and
have two rotational degrees of freedom. Using appropriate signal processing, the propagation velocities of each
wave in the specimen are calculated.
4
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ENV 14186:2002 (E)
Key
1 Rotation drive
2 Test specimen
3 Pulse generator
4 Digital Oscilloscope
5 Micro-computer
Figure 1 — Ultrasonic test assembly
Depending on the angle of incidence, the pulse sent by the emitter E is refracted within the material in one, two or
three bulk waves (one quasi longitudinal wave QL, one quasi transverse wave QT, or two quasi transverse waves
QT , QT ) that propagate in the solid at different velocities and in different directions. The receiver R collects one,
1 2
two or three pulses, corresponding to each of these waves. The difference in propagation time of each of the
waves and the propagation time of the emitted pulse in the coupling fluid without the specimen, is measured. The
evaluation procedure is based on the measurement of the time difference of the quasilongitudinal and one or both
quasitransverse waves, and is only valid when the QL and the QT waves are appropriately separated
(see Figure 2).
5
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ENV 14186:2002 (E)
Key
1 Amplitude
2 Incidence angle
Figure 2a) — Amplitude of the QL and QT waves as a function of the incidence angle
Key
1 Amplitude
2Time
Figure 2b) — Temporal waveform of the overlapping QL and QT waves at an incidence angle qq
i
Figure 2 — Overlapping of QL and QT waves at an incidence angle qq
i
From the propagation velocities the components of the elasticity tensor are obtained through a least square
regression analysis which minimises the residuals of the wave propagation equations.
Young moduli, shear moduli and Poisson coefficients are determined from these components.
6
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ENV 14186:2002 (E)
4 Significance and use
Only two constants (Lamé's coefficients or Young modulus and Poisson coefficient) are sufficient in order to fully
describe the elastic behaviour of an isotropic body. When anisotropy, which is a specific feature of composite
materials, has to be taken into account, the use of an elasticity tensor with a larger number of independent
coefficients is needed. While conventional mechanical methods allow only a partial identification of the elasticity of
anisotropic bodies, ultrasonic techniques allow a more exhaustive evaluation of the elastic properties of these
materials particularly transverse elastic moduli and shear moduli for thin specimens.
Successful application of the method critically depends on an appropriate selection of the central frequency of the
transducers. Frequency has to be sufficiently low for the measurement to be representative of the elementary
volume response but at the same time high enough to achieve a separation between the QL and the QT waves.
Contrary to mechanical test methods, the determination of elastic properties by the ultrasonic method described
here is not based on the evaluation of the stress-strain response over a given deformation range obtained under
quasi static loading conditions, but is based on a non-destructive dynamic measurement of wave propagation
velocities. Therefore the values of Young moduli, shear moduli and Poisson ratios determined by the two methods
may not be comparable, particularly for ceramic matrix composites which exhibit non linear stress-strain behaviour.
NOTE Mechanical test methods are based on a measurement performed under isothermal conditions, whereas the
ultrasonic method assumes adiabatic conditions.
In addition to the ultrasonic method described here, there also exist other non destructive methods to determine the
elastic properties, for instance the resonant beam technique and the impulse excitation method. Each of these has
its relative merits and disadvantages; the selection of a particular non destructive method has to be considered on
a case by case basis.
5 Terms and definitions and symbol
For the purposes of this European Prestandard, the terms and definitions and symbols given in EN 13233 and the
following apply.
5.1
stress-strain relations for orthotropic material
the elastic anisotropic behaviour of a solid homogeneous body can be described by the elasticity tensor of fourth
order C , represented in the contracted notation by a symmetrical square matrix (6 · 6). If the material has at
ijkl
least orthotropic symmetry, its elastic behaviour is fully characterised by 9 independent stiffness components C , of
ij
the stiffness matrix (C ), which relates stresses to strains, or equivalently by 9 independent compliance
ij
components S of the compliance matrix (S ), which relates strains to stresses. The stiffness and compliance
ij ij
matrices are the inverse of each other
7
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ENV 14186:2002 (E)
If the reference coordinate system is chosen along the axes of symmetry, the stiffness matrix C and the
ij
compliance matrix S can be written as follows:
ij
ØsøØC C C 0 0 0øØeø1 11 12 13 1
ŒœŒœŒœ
sC C C 0 0 0e2 12 22 23 2ŒœŒœŒœ
ŒœŒœŒœsC C C 0 0 0e3 3
13 23 33
Œœ=ŒœŒœ
s0 0 0 C 0 0e
Œ4œŒ44œŒ4œ
ŒœŒœŒœ
se0 0 0 0 C 0
5 55 5
ŒœŒœŒœ
ŒsœŒ0 0 0 0 0 CœŒeœ6 66 6ºßºßºß
ØeøØS S S 0 0 0øØsø1 11 12 13 1
ŒœŒœŒœ
eS S S 0 0 0s2 12 22 23 2ŒœŒœŒœ
ŒœŒœŒœeS S S 0 0 0s3 3
13 23 33
Œœ=ŒœŒœ
e0 0 0 S 0 0s
Œ4œŒ44œŒ4œ
ŒœŒœŒœ
es0 0 0 0 S 0
5 55 5
ŒœŒœŒœ
ŒeœŒ0 0 0 0 0 SœŒsœ6 66 6ºßºßºß
NOTE For symmetries of higher level than the orthotropic symmetry, the C and S matrices have the same form as here
ij ij
above. Only the number of independent components reduces.
5.2
engineering constants
the compliance matrix components of an orthotropic material are in terms of the engineering constants:
vØ1 vø21 31
--0 0 0
Œœ
E E E
11 22 33Œœ
Œœv 1 v
12 32
--0 0 0Œœ
E E E
11 22 33Œœ
Œœ
v v 1
13 23
Œ--0 0 0œ
[]S =
E E E
ijŒœ11 22 33
Œœ
1
Œœ0 0 0 0 0
GŒœ13
Œœ
1
Œœ0 0 0 0 0
ŒœG
12
Œœ
ºß
where
E , E and E are the elastic moduli in directions 1, 2 and 3 respectively;
11 22 33
G , G and G are the shear moduli in the corresponding planes;
12 13 23
n, n, nare the respective Poisson coefficients.
12 13 23
5.3
angle of incidence, q
i
angle between the direction 3 normal to the test specimen front face and the direction n of the incident wave
i
(see Figures 3 and 4)
8
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ENV 14186:2002 (E)
5.4
refracted angle, q
i
angle between the direction 3 normal to the test specimen front face and the direction n of propagation of the wave
inside the test specimen (see Figures 3 and 4)
5.5
azimuthal angle, y
angle between the plane of incidence (3, n ) and plane (2,3) where n corresponds to the vector oriented along the
i i
incident plane wave and direction 2 corresponds to one of the axes of symmetry of the material (see Figure 3)
Figure 3 — Definition of the angles
Figure 4 — Propagation in the plane of incidence
5.6
unit vector, n
unit vector oriented along the propagation direction of the incident plane wave inside the specimen, with its
components n (k = 1, 2, 3); n = sinq siny, n = sinq cosy, n = cosq, (see Figures 3 and 4)
k 1 r 2 r 3 r
5.7
propagation velocity, V(n)
phase velocity of a plane wave inside the specimen in dependence on unit vector n (i.e. in dependence on y and
q)
i
V is the propagation velocity in the coupling fluid.
o
9
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ENV 14186:2002 (E)
5.8
delay, dt(n)
difference between the flight time of the wave when the test specimen is in place and the flight time of the wave in
the coupling fluid with the test specimen removed under the same configuration of the transducers in dependence
on unit vector n
5.9
thickness of the test specimen, h
thickness of the test specimen
5.10
bulk density, r
b
bulk density of the specimen
6 Apparatus
6.1 Ultrasonic tank with thermostatic control
The ultrasonic tank shall be capable of maintaining the temperature of the coupling fluid constant to within – 0,1 °C
for the full duration of the test.
NOTE This requirement is imposed because the wave propagation velocity in the coupling fluid is highly temperature
sensitive.
6.2 Temperature measurement device
A temperature measurement device capable of measuring the temperature to within 0,1 °C e.g. according to
ISO 653.
6.3 Test specimen holder
The test specimen holder will allow rotation of the test specimen around one axis to cover the range of angles of
incidence q between 0° and 90°. Additionally it will allow for discrete settings of the azimuthal angle Y of 0°, 45°
i
and 90°. The accuracy in the measurement of the angles q and Y shall be better than 0,01° and 1° respectively.
i
NOTE The accuracy required for the measurement of the angle of incidence q depends on the nature of the coupling fluid
i
and is higher when using air as the coupling fluid. Commercially available goniometers with automatic positioning are commonly
used for this purpose.
6.4 Transducers
Piezoelectric broad-band transducers adapted to the coupling fluid and able to generate longitudinal ultrasonic
waves. Two identical transducers are used as emitter and receiver.
6.5 Transducer holders
The transducer holders will allow the transducers to be oriented towards each other. The transducers are mounted
in such a way that their relative position remains fixed during the test.
6.6 Pulse generator
The pulse generator shall be selected in accordance with the characteristics of the transducers.
It shall be able to generate short-duration (< 1 ms) pulses of voltage sufficient to provide a mechanical pulse
through the transducer. The frequency of the exciting pulse shall be chosen such as described in 9.1.
10
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ENV 14186:2002 (E)
The interval between consecutive pulses shall be long compared with the travel time being recorded, typically
greater than 1 ms, so that all signals from the preceding pulse have been dissipated before initiating the next.
6.7 Signal recording system
Any system, for instance: digital oscilloscope or dynamic analogic/digital board, with a minimum sampling
frequency of 100 MHz that allows to record emitted and received signals. The signal recording system will be
designed in order to allow to see on the display the generated and the detected pulses on the same time base and
to determine the time gap separating these two events.
7 Test specimens
The choice of test specimen geometry depends on the nature of the material and the reinforcement structure. The
thickness shall be large enough to allow separation of the echoes of the quasi longitudinal QL and quasi transverse
QT waves, and shall be representative of the material. The largest possible thickness is recommended, at least
5 times the size of the representative volume element (RVE) in the direction of propagation of the wave. The other
dimensions of the test specimen will be at least twice the diameter of the transducer. A plate with parallel faces is
recommended. The planparallelism of the two faces shall be better than 0,05 mm.
8 Test Specimen preparation
The material symmetry axes shall be identified. If machining is required, it shall be performed in such a way that the
material symmetry axes remain known at all times.
Machining procedures that do not cause damage to the test specimens shall be clearly defined and recorded.
These procedures shall be followed during machining of the test specimens.
NOTE Usually, plate test specimens are cut with their longitudinal axis coinciding with one of the principal directions of the
reinforcement.
One test specimen is sufficient to perform the test. Multiple measurements can be done on a single test specimen.
Care shall be taken to avoid interaction between the coupling fluid and the test specimen (ingress into open
porosity, chemical instability, absorption phenomena, etc.).
NOTE This can for instance be achieved by sealing the test specimen in an evacuated plastic bag, or by applying an
appropriate coating.
9 Test procedure
9.1 Choice of frequency
The selection of the appropriate frequency is critical for the application of the method. The frequency shall be
sufficiently low to ensure representativeness of the measurement.
NOTE 1 An initial selection of f < 0,2 V / d, where d is the size of the RVE in the direction of normal incidence is proposed
(q= 0).
i
NOTE 2 Because of the inverse relationship between wavelength l and frequency f (f = V / l) this corresponds to a
wavelength l of at least 5 times d.
11
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ENV 14186:2002 (E)
For the selected frequency the following criteria have to be met additionally:
a) measurable amplitude of the Q wave under normal incidence q = 0. If the amplitude is too small, the
L i
frequency has to be decreased;
b) time separation of the waves Q and Q when varying the angle of incidence q (see Figure 2b)). This is
L T i
promoted by increasing the frequency.
NOTE 3 A minimum frequency of 3V / 2h is proposed.
Because the frequency requirements for meeting the three mentioned criteria may be conflicting, there are cases
where the method is not applicable. In these cases the only remaining solution is to increase the specimen
thickness beyond the minimum thickness mentioned in clause 7.
NOTE 4 For example for a 2D SiC/SiC with a RVE of 0,5 mm (requiring a minimum test specimen thickness of 2,5 mm
according to 7), the transducer frequency, in order for the measurement to be representative, has to be lower than 2,25 MHz
(corresponding to wave velocities of around 5000 m/s). On the other hand for obtaining mode separation, the frequency has to
be higher than 3V / 2h = 3 MHz. The method can hence not be applied for the given thickness of 2,5 mm. An increase in
thickness to 3,3 mm allows to achieve mode separation for a frequency of 2,25 MHz.
9.2 Establishment of the test temperature.
Switch on the thermostatic control to establish the required temperature of the coupling fluid. Measure the
temperature of the coupling fluid at a location between the transducers in the vicinity of the future position of the
test specimen. Perform the reference measurement in accordance with 9.3. Mount the test specimen in the test
specimen holder in accordance with 9.4.2. Measure the temperature in the vicinity of the test specimen. Make sure
the temperature falls within – 0,1 °C from that of the reference measurement. Perform the test in accordance with
9.4.
9.3 Reference test without test specimen
Record the signals from the emitter and from the receiver versus time without a test specimen mounted.
9.4 Measurement with the specimen
9.4.1 Measurement of the bulk density and of the thickness
9.4.1.1 Measurement of the bulk density
Measure the bulk density in accordance with EN 1389.
9.4.1.2 Measurement of the thickness
Measure the thickness in 3 positions on the test specimen with a micrometer with an accuracy of 0,01 mm in
accordance to ISO 3611.
9.4.2 Mounting of the specimen
The specimen shall be oriented perpendicularly to the incoming beam. The accuracy of the perpendicularity
between the beam and the specimen shall be 0,1°.
The test specimen shall be mounted in such a way that one of the symmetry axes coincides with Y = 0° to
within 1°.
9.4.3 Acquisition of different angles of incidence
Set acquisition plane by selecting azimuthal angle Y= 0,45 and 90°. For each acquisition plane measurements are
made of the QL and QT signals at given values of the angle of incidence q. The incidence angleqvaries from 0° up
i i
to a maximum defined by a decrease of the amplitude of the QL wave to approximately one third of its maximum.
12
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ENV 14186:2002 (E)
The number of incidence angles has to be selected to optimise coverage over the range in which both the QL and
QT waves appear.
NOTE 1 Over the total range of q usually a minimum of 20 measurements is performed.
i
In the angular range where QL and QT overlap the step in angle q has to be reduced.
i
NOTE 2 This range of q may be defined as – 5° from the incidence angle where QL and QT have the same amplitude. In this
i
range the step is set at 0,5°.
NOTE 3 Maximum q is also configuration limited.
i
Only signals recorded at values of q andY which meet the following conditions can be used for subsequent
i
calculation and evaluation of C :
ij
a) the bulk waves are clearly identified (i.e. they can unambiguously be separated from other propagating waves);
b) 2- the longitudinal QL and the transverse QT waves are clearly separated in time making it possible to clearly
separate QL from QT.
NOTE 4 This is usually verified by representing the experimental results by the velocity curves as shown in appendix A.
NOTE 5 Signal stability should be secured by repeating the experiment under given conditions (Y, q) at different time
i
periods.
10 Calculation
10.1 Delay
For each value of Y and q the delay dt(n) on the QL and the QT waves is determined by comparing the signal
i
received in the coupling fluid alone (reference signal), and the signal received when the specimen is in the coupling
fluid.
NOTE The delay dt(n) is usually obtained by computer assisted signal processing techniques.
10.2 Calculation of the propagation velocities
For each measurement of dt(n) the associated propagation velocity V(n) is determined by the following relation:
V
0
V (n) =
Vdt(n) Vdt(n)
0 0
1+ -2 cosq
i
h hŁł
where
-1
V(n) is the propagation velocity
...
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