New SonicByte Non-Destructive Acoustic System Family for

New SonicByte Non-Destructive Acoustic System Family for
Microstructure Characterization and Quality Control of both
Homogeneous and Heterogeneous Materials
Claude Allaire and Alain Carbonneau
MQC Technology Inc.
1207 Antonio Lemaire, Chicoutimi, Quebec, Canada, G7K 1J2
[email protected]
ABSTRACT
Knowing the elastic properties of materials is of prime importance. These properties not
only reflect the extent of bonding in the material, but also permit to characterize its
behavior under stress. The measurement of such properties in refractory and carbon
materials, such as anodes and cathodes in aluminum electrolysis cells, may be difficult
due to their heterogeneous nature.
This paper presents a new non-destructive acoustic system family for quality control and
microstructure characterization of both homogeneous and heterogeneous materials,
including the estimation of their strength and critical flaw size, based on the measurement
of their elastic properties, at room or high temperature.
INTRODUCTION
Refractory and carbon materials, such as anodes and cathodes in aluminum electrolytic
cells, are heterogeneous materials containing pores, cracks and multi-phases aggregates.
Such materials are generally exposed in service to thermo-mechanical abuses such as
thermal shock, mechanical impact, abrasion and erosion. Such abuses provoke
microstructural changes in the materials thereby affecting their properties and
consequently their behavior during operation.
Non-destructive acoustic testing is commonly used to characterize the microstructure of
materials such as fine ceramics and metals. However, it is usually difficult to apply such
technique to heterogeneous materials due to multiple acoustic wave and microstructure
interactions which favor high acoustic wave attenuation and multiples acoustic wave
propagation modes. In the literature, the use of different techniques for the
characterization of refratories has been reported [1 to 7]. However, none of these
techniques allows for high temperature measurements of the set of elastic properties, i.e.,
the Elastic Modulus (under both flexural and longitudinal conditions), the Shear Modulus
and the Poisson ratio. An example of a reported apparatus allowing such measurements at
room temperature is the Grindo-Sonic apparatus. According to Headrick et al. [8], this
apparatus has been used at high temperature with refractory, but only for the
measurement of their Elastic Modulus under flexural conditions. The new SonicByte
Acquisition System and Software family manufactured by MQC Technology Inc. can not
only obtain the set of elastic properties, both at room and at high temperature, but also
allows materials' strength and critical flaw size estimation with the use of specially
designed algorithms. Moreover, this new system allows testing large material units since
unlike most conventional commercial acoustic equipments, it is not limited to high
frequency range measurements.
ACOUSTIC TESTING PRINCIPLE
Sonic or acoustic testing is based on time-varying deformation or vibration in materials.
All materials are comprised of atoms, which may be forced into vibration motion about
their equilibrium positions. Many different patterns of vibration motion exist at the
atomic level, however, most are irrelevant to acoustic testing. Acoustic testing focuses on
particles that contain many atoms that move in unison to produce a mechanical wave.
Provided a material is not stressed in tension or compression beyond its elastic limit,
individual particles yield elastic oscillations.
In solids, sound waves can propagate under different modes that are based on the way the
particles oscillate. Sound can propagate as longitudinal waves, shear waves, surface
waves, and in thin materials as plate waves. Longitudinal and shear waves are the two
modes of propagation most widely used in sonic testing.
When an elastic material is impacted, it resonates at a given natural frequency, which is a
function of its elastic properties, i.e., E (Elastic or Young’s modulus), G (Shearing or
Coulomb’s modulus) and  (Poisson’s ratio). The relationship between these properties is
given by the following equation:
G
E
21  v 
(1)
The natural resonance frequency, f, is reached when a stationary acoustic wave, of
wavelength /2 and velocity V, is created in the material, where:
V    f  2 L f  2 L
T
(2)
In the above equations, L represents material dimension, such as the length of a thin
cylindrical section, and T is the resonance period.
The calculation of the elastic constants from measured resonance periods is achieved
according to Spinner and Tefft [9].
Knowing the elastic properties of material is of prime importance. These properties not
only reflect the extend of bonding in the material, but also permits to characterize its
behavior under stress, such as shown on figure 1 and according to the following
equations:
L
L0
u
  G  G
L0
  E  E
 r  L 
v    0 
 L  r0 
(3)
(4)
(5)
where  and  are the material's tensile and shear strains under the action of the applied
tensile, , and shear, , stresses, respectively.
Fig. 1: Deformation of a cylinder under both tensile and shear stresses.
SONICBYTE NON-DESTRUCTIVE ACOUSTIC SYSTEM FAMILY
The SonicByte non-destructive acoustic system family, manufactured by MQC
Technology Inc. lies on a technique which consists in determining the elastic constants of
a material by measuring its acoustic resonance periods under three different modes:
flexural, torsional and longitudinal. Under flexural mode and when applicable, the
measurements are made along two orthogonal directions with respect to the material's
length. The two resonance periods thus obtained under that mode allow distinguishing the
effect of the uniformly and non-uniformly distributed microstrutural defects in the
material on their elastic properties, as well as on its mechanical strength. This technique
also allows considering separately the effect of geometrical discontinuities within the
material.
The principle of the technique used lies in converting the tested material in the form of an
equivalent material having two distinct zones: the active zone and the dead zone (see Fig.
2). The active zone only contains the original uniformly distributed microstructural
defects conferring the flexural elastic modulus, E0F, to the tested material. The nonuniformly distributed microstructural defects originally contained in the tested material
are converted into N equivalent uniform and equidistant straight cracks of length "aeq"
extending form one side of the equivalent material. The location of these cracks delimits
the dead zone whose rigidity is vanished since N is such that the distance between the
cracks is no more than their length, which promotes cracks interaction.
From the values of E0F and "aeq", the strength, R, of the tested material may then be
estimated, as well as the size of the critical defects, ac, it contains, according to specially
designed algorithms.
The basic principle allowing the determination of "aeq" is shown on Fig. 3.
NON-DESTRUCTIVE ANALYSIS OF LABORATORY SAMPLES
For non-destructive analysis of laboratory samples, the main device to be used is the
SonicByte XB-1000 signal analyser (see Fig. 4 (a)). The XB-1000 uses high frequency
response microphones specially designed to capture fast audio impulses coming from
hammer impacts (see Fig. 4 (e)). The resonance frequencies collected by the microphones
are analysed by the XB-1000 using a technique similar to FFT (Fast Fourier Transform).
The signal is electronically processed with an ultra-fast analog to digital converter
featuring very accurate timing. Mathematical calculations are performed with carefully
built algorithms to quickly output (< 100mSec) the prominent resonance period, which
corresponds to the average value from up to 2000 consecutive periods collected by the
system during each impact.
The SonicByte Excelbased software then uses the period readings and presents the results
on the computer screen as well as storing repetitive results and maintaining a data bank
that can be consulted further (see Fig. 4 (d)). The software allows viewing of the raw
signal (see Fig. 4 (b)) and the period spectrum after each impact (see Fig. 4 (c)).
A serial RS232 computer port is used for communication with the XB-300 Hammer
Control Box (see Fig. 4 (f)). This provides computer controlled, single and repetitive
hammer impacts of the sample. Using a controlled hammer instead of a manual hammer
greatly increases chances of repetitive measurements, simply because a repetitive reading
is, amongst other things, sensitive to the hit location. Although the SonicByte system may
be used manually (see Fig. 5) it may more conveniently use a maximum of four specially
designed electric hammers to repetitively hit the sample at exactly the same spot every
time, at four distinct locations.
Fig. 2: Example of (a) - A cathode block containing geometrical discontinuities, as well
as uniformly distributed microstructural defects (such as pores and microcracks) and nonuniformly distributed microstructural defects (such as the crack shown in bold), and (b) The equivalent block without the geometrical discontinuities and containing in the "Dead
Zone" the equivalent equidistant and uniform cracks of length "aeq", and in the "Active
Zone" the uniformly distributed microstructural defects conferring to the material the
flexural elastic modulus E0F.
Parallel
1) f 
Vibration direction
b //
h //
3) I // 
h0
aeq
Perpendicular
Vibration direction
aeq
5)
b// h//
12
h0
EI
ml 4
2) I 
bh 3
12
3
4) I  
b / h
12
3
T h//

T// h
6)
b
h
1 

T 2
h  hO
7) h//
 hO  a

T
a eq  hO  1  
T //




Fig. 3: Example of a parallelelipedic solid containing equidistant and uniform cracks of
length "aeq" and submitted to flexural resonance period measurements along two
orthogonal directions (Note: For simplicity, the equations presented in this example do
not include the correction factors required to consider the solid boundary conditions)
(a)
(e)
(f)
(b)
(c)
(g)
(h)
(d)
Fig. 4: SonicByte series of electronic instruments and SonicByte Software designed for
non-destructive testing of material: (a) - The XB-1000 Signal Processor, (b) - Example of
raw signal graphic showing accepted and rejected points for period calculation from up to
2000 points, (c) - Example of Spectrum showing the detected multi-resonance periods
after one impact. Scroll bar position adjustments allow for the pre-selection of accepted
periods; (d) - SonicByte DATA sheet as the main control room for measurement
adjustments and commands; (e) - Mounting Table for the four coupled Hammers and
Microphones disposed around the sample for room temperature testing; (f) - The XB-300
Hammer Control Box for hammer excitation energy control and microphones electrical
signal collection; (g) and (h) - Specially designed furnace for high temperature testing
including four coupled High Temperature Single Electric Hammering and Short
Impacting Microphone systems.
Fig 5: Manual use of the SonicByte analysis system
For room temperature testing, the SonicByte system uses a Mounting Table for Hammers
and Microphone disposition around the sample, as shown in Fig.4 (e). For high
temperature testing, a specially designed furnace and set-up is used, as shown in Fig. 4
(g) et (h). For this latter case, ceramic waveguides are used to collect the audio signals
from the sample following impacts from specially designed electric hammers coupled
with ceramic wire. For both room and high temperature testing on parallelepipedic
samples, the relative position of the hammers and microphones is as shown on Fig. 6.
This allows the SonicByte software to calculate and report Elastic Modulus under
longitudinal and flexural (in two orthogonal directions) modes, Shear Modulus, and
Poisson's ratio. As mentioned previously, the measurement of the flexural resonance
period along two orthogonal directions is the basis of a novel technique used by the
SonicByte system to estimate the critical flaw size in a sample.
Y
Z
X
Fig. 6: Relative position of the hammers (arrows) and microphones for resonance period
measurements under longitudinal (L), flexural (F) and torsional conditions (T). Note that
a second set of hammers and microphones for flexural measurements (not shown on this
figure) is used by the SonicByte system along the "z" direction to estimate defect size in
the test sample
NON-DESTRUCTIVE QUALITY CONTROL OF INDUSTRIAL MATERIALS
For industrial materials' quality control, the SonicByte EP-1000 signal processor and
SonicByteEP ExelBased Software should be used (see Fig. 7 and 8). As compared to the
SonicByte XB-1000, the SonicByte EP-1000 is coupled to a digital filtering system unit
that allows testing materials with various shapes, dimensions and sizes, which generally
tend to generate undesirable vibrations under impacts, such as harmonics and surface
waves. With the SonicByte EP system family, industrial materials' quality control can be
conducted manually, with the use of manual hammers, or under fully automatic mode
when a robotic system controlling electric hammers and microphones is used. Examples
of industrial quality control applications with the SonicByte EP system family are:
refractory bricks, pre-cast fired and non-fired refractory shapes, refractory ramming
mixes, industrial ceramics, carbon materials, metals and composites. Among the pre-cast
fired and non-fired refractory shapes that could successfully be tested are: tap hole
blocks, straight and conic thermocouple shields, floor tiles, straight and curved launder
sections, spouts and grid plates (see Fig. 9). With regard to carbon materials, successful
results can also be obtained with both green and fired anodes and cathodes such as those
used in aluminum electrolytic cells.
EXAMPLES OF RESULTS
To illustrate how the SonicByte non-destructive system family works, the following
examples are presented.
Laboratory refractory castable samples:
Four sets of laboratory refractory monolithic samples were submitted to microstructure
characterization with the SonicByte system family: (1) - Castable samples containing
equidistant and interacting notches, (2) - Castable samples containing equidistant and
non-interacting macroscopic cracks, (3) - Unfired Castable samples and (4) - Unfired
Ramming Mix samples.
Castable samples containing equidistant and interacting notches
Refractory castable samples containing 15 equidistant and interacting notches, such as
shown in Fig. 10, were tested according to the MQC technique. These notches, whose
length, Lo, was varying between 0 to 20.74 mm, were produced using a 1mm thick
diamond saw. The samples dimensions were 6.0 x 1.0 x 1.0 inches.
The elastic constants EF// (Flexural Elastic Modulus under parallel direction),
EF(Flexural Elastic Modulus under perpendicular direction), and E0F (Flexural Elastic
Modulus of the material's active zone), as well as the equivalent equidistant and uniform
crack's length, "aeq", for these samples are given in table I.
Fig. 7: SonicByte EP-1000 signal processor
Fig. 8: SonicByteEP ExcellBased Software main control room for measurement
adjustments and commands
Spout
Grid Plate
Launders
Tap Hole Block
Conic
Thermocouple
Shield
Fig. 9: Examples of pre-cast fired and non-fired refractory shapes that could successfully
be tested with the SonicByte EP System

//
Fig 10: Example of a notched sample.
In theory, the E0F value for the five samples should be the same. This is almost what has
been obtained, as shown in Table I. Moreover, the notches' length and the "aeq" values for
these samples is very well correlated (R2 = 0.99), as shown in Fig. 11.
Table I
Elastic constants and equivalent equidistant and uniform crack's length
for the tested samples
Parameters
Lo = 0 mm
Lo = 4.23 mm
Lo = 8.47 mm
Lo = 12.7 mm
Lo = 20.74 mm
EF// (GPa)
11.76
±
0.99
8.27
±
0.69
4.44
±
0.37
1.79
±
0.15
0.22
±
0.02
EF (GPa)
11.76
±
0.99
11.87
±
1.00
9.46
±
0.79
7.01
±
0.58
3.19
±
0.26
12.22
0.94
±
±
1.95
1.22
13.30
-4.03
±
±
2.75
1.16
13.16
-8.21
±
±
2.68
1.01
13.48
-12.96
±
±
2.71
0.85
11.89
-18.99
±
±
2.36
0.67
0
E F (GPa)
aeq (mm)
Lo=Notches' length. Note: A negative value for the equivalent equidistant and uniform
crack's length "aeq" means that these cracks are oriented along the parallel direction.
Otherwise, these cracks are oriented along the perpendicular direction.
25.00
(R2 = 0.99)
aeq (mm)
20.00
15.00
10.00
5.00
0.00
0
5
10
15
20
25
-5.00
Lo (mm)
Fig. 11: Correlation between the calculated equivalent equidistant and uniform cracks
length, aeq, and the notches' length, Lo.
Castable samples containing equidistant and non-interacting macroscopic cracks
Refractory castable samples containing 0 to 5 equidistant and non-interacting
macroscopic cracks, such as shown in Fig. 12, were first tested according to the MQC
technique and then submitted to three-point bending test for the measurement of their
modulus of rupture, at room temperature. These cracks were produced by inserting 0.1
mm thick plastic sheets in the material, during the forming process, to achieve cracks
length, Lo, varying from 0 to 25.4 mm. The samples dimensions were 6.0 x 1.5 x 1.5
inches.
//
Fig. 12: Schematic representation of a sample containing one straight open edge
macroscopic crack.
As shown in table II, the sample with the shortest cracks' length was taken as the
reference for the calculation of the relative strength values, for each three sets of cracks
number (i.e, N = 1, 3 and 5, respectively). The relative strength, R(//) / R)ref(//), values
were calculated according to two methods.
The first method is based on the modulus of rupture (MOR) measured values, according
to the following equation:




R (//)
_____
R)
ref (//)
MOR
=
____________
(MOR)
(6)
ref
The second method is based on the values of E0F and "aeq", according to the specially
designed algorithm includes in the SonicByte Software.
As shown in Fig. 13, there is a perfect correlation between both measured (Eq. 6) and
estimated strength values (from E0F and "aeq"). Moreover, such very good correlation was
also observed between L0 (the real cracks' length) and the estimated critical flaw size
"ac", as shown in Table II.
Unfired castable samples
Unfired castable samples were submitted to flexural elastic modulus measurements
during sintering. The results are presented in Fig. 14.
Table II
Estimation of the relative strength of refractory castables containing straight open edge
macroscopic cracks along their width
N
Lo
H
=Heq
Lo/H
EF//
EF
E0F
aeq
ac
Relative
MOR
(MPa)

R/Rref
(MPa)
(mm)
(mm)
(GPa)
(GPa)
(GPa)
(mm)
(mm)
0
0.00
38.27
0.00
114.87
112.95
116.24
0.45
0.45
----
----
1
6.35
37.84
0.17
100.21
100.53
100.79
-0.09
-6.44
1.00
1.00
1
12.70
37.63
0.34
60.31
87.88
112.13
-8.14
-10.63
0.69
0.69
1
25.4
38.55
0.66
14.41
57.03
129.48
-21.55
-22.52
0.21
0.25
3
6.35
36.27
0.18
97.68
96.99
98.18
0.19
-7.62
1.00
1.00
3
12.70
37.61
0.34
49.41
86.70
123.80
-11.27
-13.38
0.61
0.62
3
25.4
38.51
0.66
10.12
49.71
126.58
-23.38
-24.14
0.19
0.20
5
6.35
37.46
0.17
81.98
99.01
112.21
-4.40
-7.36
1.00
1.00
5
12.70
37.64
0.34
39.23
78.11
120.18
-13.17
-15.05
0.65
0.58
5
25.4
38.92
0.65
8.75
46.55
124.01
-24.31
-24.99
0.21
0.20
Relative Strength (Estimated)
N=Number of cracks; Lo=Cracks' length; H=Samples' height; R/Rref = Relative strength
calculated from E0F and "aeq". Note: A negative value for the equivalent equidistant and
uniform crack's length "aeq" as well as for the critical flaw size "ac" means that these
cracks are oriented along the parallel direction. Otherwise, these cracks are oriented along
the perpendicular direction
1.0
(Lo = 6.35 mm)
0.8
0.6
0.4
(Lo = 25.4 mm)
N=1
N=3
N=5
(Lo = 12.7 mm)
0.2
0.0
0.0
0.2
0.4
0.6
Relative Strength (Measured)
Fig. 13: Measured .vs. Estimated Relative Strength
0.8
1.0
Fig. 14: Flexural elastic modulus variation during sintering of a refractory castable (after
drying at 110 oC)
Unfired ramming mix samples
Seven unfired cylindrical ramming mix samples having different sizes were submitted to
longitudinal and flexural elastic modulus measurements at room temperature. Although
the acoustic wave attenuation in such materials is very high, the SonicByte system was
able to produced relevant results, as shown in Fig. 15.
Fig. 15: Results obtained with a refractory ramming mix
Other examples of laboratory applications of the SonicByte system can be found in
reference 10.
Aluminum cast-house industrial spouts:
Four aluminum cast-house industrial spouts having the geometry, sizes and dimensions
shown on Fig. 16 were submitted to quality control with the SonicByte EP system family.
These spouts were made from amorphous silica-based refractory castables. They were
shaped in two-section molds creating geometrical defects such as shown in Fig. 17 after
mold removal. Among those spouts, two were originals (SA and SB) and two others were
had already been used in an aluminum cast-house (SC) and (SD).
By referring to Fig. 16 and 18, these spouts were tested for the quality of their different
zones with the use of the following hammer and microphone positions:




Zone 1 (Conic Extremity): Hammer P3 and Microphone M3
Zone 2 (Cylindrical Core): Hammer P4 and Microphone M4
Zone 3 (Cylindrical Extremity): Hammer P2 and Microphone M2
Zones 1 and 2 and 3 (Overall spout): Hammer P1 and Microphone M1
The time required for testing each spout in these different positions was less than 30
seconds.
Moreover, the spouts were rotated during the tests along their central axis to detect any
sign of anisotropy.
The results obtained are presented in Table III.
Table III
Relative resonance frequencies of the spouts associated to their different zones
Spouts
SA (unused)
SB (unused)
SC (used)
SD (used)
Zone 1
(P3, M3)
1
- 1.036
- 1.059
-1.096
Zone 2
(P4, M4)
1
-1.027
-1.040
-1.173
Zone 3
(P2, M2)
1
-1.044
-1.059
-1.168
Zones 1 + 2 + 3
(P1, M1)
1
-1.03
-1.042
-1.052
According to Table III, the original spout SA demonstrates the highest quality. The
lowest quality is observed for the used spout SD. The quality of the latter provides
evidence of more deterioration in service in zones 2 (Cylindrical Core) and 3 (Cylindrical
Extremity).
Moreover, as shown in Fig. 19, the geometrical defects that were introduced during the
forming process of the tested spouts confer them lower elastic properties along the Yaxis.
Conic
Extremity
Cylindrical
core
Cylindrical
Extremity
Fig. 16: Dimensions of the tested aluminum cast-house spouts (in mm)
Geometrical defect
Fig. 17: Geometrical defect introduced during the spouts forming process
Fig. 18: Schematic representation of a spout submitted to quality control with the use of
the SonicByte EP system
Fig. 19: Spout anisotropy resulting from geometrical defects
CONCLUSION
The new SonicByte non-destructive acoustic system family for quality control and
microstructure characterization of both homogeneous and heterogeneous materials, based
on the measurement of their elastic properties, at room or high temperature, was
presented. This new system which operates both under manual or fully automatic mode
allows materials' strength and critical flaw size estimation for each manufactured material
unit or laboratory tested samples. More information about this new system which is
manufactured by MQC Technology Inc., can be found at the following web site:
"www.mqctechnologies.com".
REFERENCES
1. Allaire, C. and Talbot. L., “Methods and apparatus for non destructive testing of
materials using longitudinal compression waves”, United States Patent, No. 5, 040,419
(1991).
2. Ratle, A., Lagacé, M., Pandolfelli, V., Allaire, C., and Rigaud, M., “A Simple Method
for Evaluating Elastic Modulus of Refractories at High Temperatures”, J. of the Canadian
Ceram. Soc., Vol. 65, No. 3 (1996), 202-204.
3. "Standard Test Method for Dynamic Young's Modulus, Shear Modulus, and Poisson's
Ratio by Impulse Excitation of Vibration", ASTM E1876-99.
4. "Standard Test Method for Dynamic Young's Modulus, Shear Modulus, and Poisson's
Ratio by Sonic Resonance", ASTM E1875-97.
5. "Standard Test Method for Moduli of Elasticity and fundamental Frequencies of
carbon and graphite materials by sonic resonance", ANSI/ASTM C 747-93.
6. "Standard Test Method for young's Modulus of Refractory Shapes by Sonic
Resonance" ASTM C885-87 (1997).
7. Heritage, K., Frisby, C. and Wolfenden, A., "Impulse excitation technique for
dynamic flexural measurements at moderate temperature", Rev. Sci. Instrum., 59 [6]
(1988), 973-974.
8. Headrick, W. L. Jr., Moore, R. E. and Leuven, A. V., "Measuring Refractory MOE at
High Temperatures",
http://www.ceramicindustry.com/ci/cda/articleinformation/features/bnp_features_item/0,
2710,13644,00.html, 2000.
9. Spinner, S. and Tefft, W. E., ''A Method for Determining Mechanical Resonnance
Frequencies and for Calculating Elastic Moduli From These Frequencies'', Proceeding
ASTM, Vol. 61 (1961), 1221-1238, 1961.
10. Allaire, C, Allaire, J. and Carbonneau, A., “Room and High Temperature
Measurement of the Elastic Properties of Refractories Using a New Apparatus and Setup”, Light Metals 2004, pp. 629-636, 2004.