ASTM E1106-12(2021)
(Test Method)Standard Test Method for Primary Calibration of Acoustic Emission Sensors
Standard Test Method for Primary Calibration of Acoustic Emission Sensors
SIGNIFICANCE AND USE
4.1 Transfer Standards—One purpose of this test method is for the direct calibration of displacement transducers for use as secondary standards for the calibration of AE sensors for use in nondestructive evaluation. For this purpose, the transfer standard should be high fidelity and very well behaved and understood. If this can be established, the stated accuracy should apply over the full frequency range up to 1 MHz.
Note 1: The stated accuracy applies only if the transfer standard returns to quiescence, following the transient input, before any wave reflected from the boundary of the calibration block returns to the transfer standard (∼100 μs). For low frequencies with periods on the order of the time window, this condition is problematical to prove.
4.2 Applications Sensors—This test method may also be used for the calibration of AE sensors for use in nondestructive evaluation. Some of these sensors are less well behaved than devices suitable for a transfer standard. The stated accuracy for such devices applies in the range of 100 kHz to 1 MHz and with less accuracy below 100 kHz.
SCOPE
1.1 This test method covers the requirements for the absolute calibration of acoustic emission (AE) sensors. The calibration yields the frequency response of a transducer to waves, at a surface, of the type normally encountered in acoustic emission work. The transducer voltage response is determined at discrete frequency intervals of approximately 10 kHz up to 1 MHz. The input is a given well-established dynamic displacement normal to the mounting surface. The units of the calibration are output voltage per unit mechanical input (displacement, velocity, or acceleration).
1.2 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1106 − 12 (Reapproved 2021)
Standard Test Method for
Primary Calibration of Acoustic Emission Sensors
This standard is issued under the fixed designation E1106; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E1316 Terminology for Nondestructive Examinations
1.1 This test method covers the requirements for the abso-
3. Terminology
lute calibration of acoustic emission (AE) sensors. The cali-
bration yields the frequency response of a transducer to waves, 3.1 Refer to Terminology E1316 for terminology used in
at a surface, of the type normally encountered in acoustic this test method.
emission work. The transducer voltage response is determined
4. Significance and Use
at discrete frequency intervals of approximately 10 kHz up to
1 MHz. The input is a given well-established dynamic dis-
4.1 Transfer Standards—One purpose of this test method is
placement normal to the mounting surface. The units of the
for the direct calibration of displacement transducers for use as
calibration are output voltage per unit mechanical input
secondary standards for the calibration of AE sensors for use in
(displacement, velocity, or acceleration).
nondestructive evaluation. For this purpose, the transfer stan-
1.2 Units—The values stated in SI units are to be regarded dard should be high fidelity and very well behaved and
understood. If this can be established, the stated accuracy
as standard. No other units of measurement are included in this
standard. should apply over the full frequency range up to 1 MHz.
1.3 This standard does not purport to address all of the
NOTE 1—The stated accuracy applies only if the transfer standard
safety concerns, if any, associated with its use. It is the returns to quiescence, following the transient input, before any wave
reflected from the boundary of the calibration block returns to the transfer
responsibility of the user of this standard to establish appro-
standard (;100 μs). For low frequencies with periods on the order of the
priate safety, health, and environmental practices and deter-
time window, this condition is problematical to prove.
mine the applicability of regulatory limitations prior to use.
4.2 Applications Sensors—This test method may also be
1.4 This international standard was developed in accor-
used for the calibration of AE sensors for use in nondestructive
dance with internationally recognized principles on standard-
evaluation. Some of these sensors are less well behaved than
ization established in the Decision on Principles for the
devices suitable for a transfer standard. The stated accuracy for
Development of International Standards, Guides and Recom-
such devices applies in the range of 100 kHz to 1 MHz and
mendations issued by the World Trade Organization Technical
with less accuracy below 100 kHz.
Barriers to Trade (TBT) Committee.
2. Referenced Documents 5. General Requirements
2.1 ASTM Standards: 5.1 A primary difficulty in any calibration of a mechanical/
E114 Practice for Ultrasonic Pulse-Echo Straight-Beam electrical transduction device is the determination of the
Contact Testing mechanical-motion input to the device. To address this
E494 Practice for Measuring Ultrasonic Velocity in Materi- difficulty, this calibration procedure uses (i) a standard trans-
als by Comparative Pulse-Echo Method ducer whose absolute sensitivity is known from its design and
physical characteristics; and also (ii) a source that produces
E650 Guide for Mounting Piezoelectric Acoustic Emission
Sensors motion that approximates a waveform calculable from theory.
The use of two independent sources of information confers a
degree of redundancy that is employed to confirm the validity
This test method is under the jurisdiction of ASTM Committee E07 on
of the measurements and quantify the experimental errors.
Nondestructive Testing and is the direct responsibility of Subcommittee E07.04 on
Acoustic Emission Method.
Briefly stated, the sensitivity of the transfer standard (or other
Current edition approved June 1, 2021. Published June 2021. Originally
sensor under test) is determined by comparison with the
approved in 1986. Last previous edition approved in 2017 as E1106 – 12(2017).
standard transducer, while knowledge of a part of the theoreti-
DOI: 10.1520/E1106-12R21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or cal waveform is used as a check.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.2 Test Block and Mechanical Input—The mechanical
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. input to the sensors is obtained by pressing a glass capillary
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1106 − 12 (2021)
down onto the surface of a large test block until it breaks. The istics amenable to theoretical calculation. It should also present
reasons for selecting this approach are: (a) capillary breaks are no appreciable dynamic loading to the surface it is measuring.
localized and short in duration, like natural acoustic emission
5.3.1 For a calibration, the standard transducer and the
events; and (b) use of a large block simplifies wave propaga-
device to be calibrated are both placed on the same surface of
tion and makes sensor output less dependent on arbitrary
the block as the mechanical input and equidistant in opposite
features of block geometry.
directions from it. This guarantees that both experience the
5.2.1 Prior to the fracture of the glass capillary, the force it
same displacement-time history. Comparison of the output of
exerts on the surface is distributed over an area on the order of
the transfer standard or AE sensor with the output of the
2 mm × 0.3 mm. When the glass capillary breaks, the force it
standard transducer yields a calibration of the device under
was applying to the surface is abruptly relieved, within a time
test.
on the order of 0.2 to 0.3 μs. Within the limitations arising from
5.3.2 Other relative geometries for the input and transducers
these finite dimensions, the breaking of the capillary approxi-
are possible, but results from other geometries should only be
mates a step force function at a point on the surface of the
used to supplement results from the “same surface” geometry.
block. Theoretical solutions for the idealized response of a
AE waves in structures are most frequently dominated by
half-space to a normal point-force step function in time applied
4,5 surface wave phenomena, and the calibration should be based
to the surface are available. The outputs of flat-response
on the transducer’s response to such waves.
transducers have been found to be a good match (except for the
infinite amplitude part) to the theoretical waveforms, support-
5.4 Units for the Calibration—An AE sensor may be con-
ing the use of this theory as a check on the primary calibration
sidered to respond to either stress or strain at its front face. The
of sensors. An example with a flat response transducer is
actual stress and strain at the front face of a mounted sensor
shown in Figure 9. The vertical component of the theoretical
depend on the interaction between the mechanical impedance
waveform comprises three parts: (a) a low-amplitude response
of the sensor (load) and that of the mounting block (driver).
beginning at time d/c , where d is the distance from the source
L
Neither the stress nor the strain is amenable to direct measure-
and c is the longitudinal wave velocity; (b) a short impulsive
L
ment at this location. However, the free displacement that
response between times d/c and d/c , where c is the shear
S R S
would occur at the surface of the block in the absence of the
wave velocity and c the Rayleigh wave velocity; (c) a step
R
sensor can be inferred from measurements made elsewhere on
function beginning at d/c . It is the last of these that is salient
R
the surface. Also, the ideal displacement (except at the point
for checking the sensor calibration. The theoretical height
where the displacement becomes infinite) for an ideal source is
(shelf value [see Figure 9 for determination of the shelf value],
known from theory. Since AE sensors are used to monitor
relative to zero displacement) of this displacement step u is:
motion at a free surface of a structure and interactive effects
u 5 F A/4πμd~A 2 1!
3 0 between sensor and structure are generally of no interest, the
free surface motion is the appropriate input variable. It is,
where F is the applied force (which is measured), μ is the
therefore, recommended that the units of calibration should be
shear modulus (calculated by use of the shear wave velocity) of
voltage per unit of free motion; for example, volts per metre.
the test block, A = (c /c ) and d is the distance from the source
L S
to the transducer.
5.5 Block Material:
5.3 Absolute Displacement Measurement—An absolute 5.5.1 Since the calibration depends on the interaction of the
measurement of the dynamic normal surface displacement of
mechanical impedance of the block and that of the AE sensor,
the block is required for this calibration test method. The a calibration procedure must specify the material of the block.
transducer used for this measurement is a standard transducer
Calibrations performed on blocks of different materials will
against which the device under test is compared. The standard
yield transducer sensitivity versus frequency curves that are
transducer should meet or exceed the performance of the
different in shape and in average magnitude. The amount by
capacitive transducer described by Breckenridge and Greens-
which such averages differ may be very large. A transducer
pan. The important characteristics of the standard transducer
calibrated on a glass or aluminum block will have an average
include high fidelity, high sensitivity, and operating character-
sensitivity that may be from 50 to 100 % of the value obtained
on steel, and will have an average sensitivity that may be as
little as 3 % of the value obtained on steel if calibrated on a
3 polymethyl methacrylate block. In general, the sensitivity will
Burks, Brian, “Re-Examination of NIST Acoustic Emission Sensor Calibration:
Part I – Modeling the Loading from Glass Capillary Fracture,” Journal of Acoustic
be less if the block is made of a less rigid or less dense
Emission, Vol. 29, pp. 167–174.
material.
Breckenridge, F. R., “Acoustic Emission Transducer Calibration by Means of
5.5.2 The Rayleigh speed in the material of the block affects
the Seismic Surface Pulse,” Journal of Acoustic Emission Vol 1, pp. 87–94.
Hsu, N. N., and Breckenridge, F. R., “Characterization and Calibration of
surface wave calibrations. For a sensor having a circular
Acoustic Emission Sensors,” Materials Evaluation, Vol 39, 1981, pp. 60–68.
aperture (mounting face) with uniform sensitivity over the
Paul G. Richards, “Elementary Solutions to Lamb’s Problem for a Point Source
face, the aperture effect predicts nulls at the zeroes of J (ka),
and their Relevance to Three- Dimensional Studies of Spontaneous Crack
Propagation,” Bull. of the Seismological Society of America, Vol 69, No. 4, 1979, pp.
where k = 2πf ⁄c , and f = frequency, c = Rayleigh speed, and
R R
947–956.
a = radius of the sensor face (active element). Hence, the
Breckenridge, F. R., and Greenspan, M., “Surface-Wave Displacement: Abso-
frequencies at which the nulls occur are dependent upon the
lute Measurements Using a Capacitive Transducer,” Journal, Acoustic Society of
America, Vol 69, pp 1177–1185. Rayleigh speed.
E1106 − 12 (2021)
6. Apparatus 6.1.3 As a check, the shelf value (see section 5.2.1) deter-
mined from the standard transducer output is compared with
6.1 A typical basic scheme for the calibration is shown in
the value determined from the measured capillary break force
Fig. 1. A glass capillary, B, of diameter about 0.2 mm, is
using the equation in 5.2.1. This comparison should provide
squeezed between the tip of the loading screw, C, and the upper
supporting evidence that the precision stated in 8.5 has been
face of the large steel transfer block, A. When the capillary
attained. This check should be made at least one time for each
breaks, the sudden release of force is nearly a step function
calibration performed.
whose risetime is of the order of 0.2 μs to 0.3 μs. The
magnitude of the force step is measured by the combination of
6.2 The Transfer Block—The transfer block must be made
the PZT disc, D, in the loading screw and a charge amplifier, E,
from specially chosen material. It should be as defect-free as
connected to a waveform recorder, F. Alternatively, the force
possible and should undergo an ultrasonic longitudinal exami-
step can be measured by a strain-gage load cell within the
nation at 2.25 MHz. The method described in Practice E114
loading screw with standard electronic conditioning for the
should be used. The block should contain no flaws which give
strain gages. The standard capacitive transducer, G, and the
a reflection larger than 10 % of the first back wall reflection.
device under test, H, are placed equally distant (usually 100
The material should also be highly uniform as determined by
mm) from the source and in opposite directions from it. It is
pulse-echo time of flight measurements through the block at a
obvious from the symmetry that the surface displacements
minimum of 15 locations regularly spaced over the surface (see
would be the same at the two transducer locations if it were not
Practice E494). The individual values of the longitudinal and
for the loading effects of the transducers. The loading effect of
shear wave speed should differ from the average by no more
the standard capacitive transducer is negligible and the loading 4
than 61 part and 63 parts in 10 , respectively. A transfer block
effect of the unknown sensor is part of its calibration.
and calibration apparatus is shown in Fig. 2.
6.1.1 Voltage transients from the two transducers are re-
corded simultaneously by digital recorders, I, and the informa- 6.3 The Source—The source events, which are a useful
approximation to force step functions, are to be made by
tion is stored for processing by the computer, J.
6.1.2 With such a system, it is possible
...
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