1、Designation: E1106 12Standard Test Method forPrimary Calibration of Acoustic Emission Sensors1This standard is issued under the fixed designation E1106; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the requirements for the abso-lute calibration of acoustic emission (AE) sensors. The cali-bration yields the f
3、requency response of a transducer to waves,at a surface, of the type normally encountered in acousticemission work. The transducer voltage response is determinedat discrete frequency intervals of approximately 10 kHz up to1 MHz. The input is a given well-established dynamic dis-placement normal to t
4、he mounting surface. The units of thecalibration are output voltage per unit mechanical input (dis-placement, velocity, or acceleration).1.2 UnitsThe values stated in SI units are to be regardedas standard. No other units of measurement are included in thisstandard.1.3 This standard does not purport
5、 to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E114 P
6、ractice for Ultrasonic Pulse-Echo Straight-BeamContact TestingE494 Practice for Measuring Ultrasonic Velocity in Mate-rialsE650 Guide for Mounting Piezoelectric Acoustic EmissionSensorsE1316 Terminology for Nondestructive Examinations3. Terminology3.1 Refer to Terminology E1316 for terminology used
7、inthis test method.4. Significance and Use4.1 Transfer StandardsOne purpose of this test method isfor the direct calibration of displacement transducers for use assecondary standards for the calibration ofAE sensors for use innondestructive evaluation. For this purpose, the transfer stan-dard should
8、 be high fidelity and very well behaved andunderstood. If this can be established, the stated accuracyshould apply over the full frequency range up to 1 MHz.NOTE 1The stated accuracy applies only if the transfer standardreturns to quiescence, following the transient input, before any wavereflected f
9、rom the boundary of the calibration block returns to the transferstandard (;100 s). For low frequencies with periods on the order of thetime window, this condition is problematical to prove.4.2 Applications SensorsThis test method may also beused for the calibration ofAE sensors for use in nondestru
10、ctiveevaluation. Some of these sensors are less well behaved thandevices suitable for a transfer standard. The stated accuracy forsuch devices applies in the range of 100 kHz to 1 MHz andwith less accuracy below 100 kHz.5. General Requirements5.1 A primary difficulty in any calibration of a mechanic
11、al/electrical transduction device is the determination of themechanical-motion input to the device. To address this diffi-culty, this calibration procedure uses (i) a standard transducerwhose absolute sensitivity is known from its design andphysical characteristics; and also (ii) a source that produ
12、cesmotion that approximates a waveform calculable from theory.The use of two independent sources of information confers adegree of redundancy that is employed to confirm the validityof the measurements and quantify the experimental errors.Briefly stated, the sensitivity of the transfer standard (or
13、othersensor under test) is determined by comparison with thestandard transducer, while knowledge of a part of the theoreti-cal waveform is used as a check.1This test method is under the jurisdiction of ASTM Committee E07 onNondestructive Testing and is the direct responsibility of Subcommittee E07.0
14、4 onAcoustic Emission Method.Current edition approved June 15, 2012. Published September 2012. Originallyapproved in 1986. Last previous edition approved in 2007 as E1106 - 07. DOI:10.1520/E1106-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service
15、at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-29
16、59, United States.5.2 Test Block and Mechanical InputThe mechanicalinput to the sensors is obtained by pressing a glass capillarydown onto the surface of a large test block until it breaks. Thereasons for selecting this approach are: (a) capillary breaks arelocalized and short in duration, like natu
17、ral acoustic emissionevents; and (b) use of a large block simplifies wave propaga-tion and makes sensor output less dependent on arbitraryfeatures of block geometry.5.2.1 Prior to the fracture of the glass capillary, the force itexerts on the surface is distributed over an area on the order of2mm3 0
18、.3 mm.3When the glass capillary breaks, the forceit was applying to the surface is abruptly relieved, within a timeon the order of 0.2 to 0.3 s. Within the limitations arising fromthese finite dimensions, the breaking of the capillary approxi-mates a step force function at a point on the surface of
19、theblock. Theoretical solutions for the idealized response of ahalf-space to a normal point-force step function in time appliedto the surface are available.4,5The outputs of flat-responsetransducers have been found to be a good match (except for theinfinite amplitude part) to the theoretical wavefor
20、ms, support-ing the use of this theory as a check on the primary calibrationof sensors. An example with a flat response transducer isshown in Figure 9. The vertical component of the theoreticalwaveform comprises three parts: (a) a low-amplitude responsebeginning at time d/cL, where d is the distance
21、 from the sourceand cLis the longitudinal wave velocity; (b) a short impulsiveresponse between times d/cSand d/cR, where cSis the shearwave velocity and cRthe Rayleigh wave velocity; (c) a stepfunction beginning at d/cR. It is the last of these that is salientfor checking the sensor calibration. The
22、 theoretical height6(shelf value see Figure 9 for determination of the shelf value,relative to zero displacement) of this displacement step u3is:u35 F0A/4pdA21!where F0is the applied force (which is measured), is theshear modulus (calculated by use of the shear wave velocity) ofthe test block, A =(c
23、L/cS)2and d is the distance from the sourceto the transducer.5.3 Absolute Displacement MeasurementAn absolutemeasurement of the dynamic normal surface displacement ofthe block is required for this calibration test method. Thetransducer used for this measurement is a standard transduceragainst which
24、the device under test is compared. The standardtransducer should meet or exceed the performance of thecapacitive transducer described by Breckenridge and Greens-pan.7The important characteristics of the standard transducerinclude high fidelity, high sensitivity, and operating character-istics amenab
25、le to theoretical calculation. It should also presentno appreciable dynamic loading to the surface it is measuring.5.3.1 For a calibration, the standard transducer and thedevice to be calibrated are both placed on the same surface ofthe block as the mechanical input and equidistant in oppositedirect
26、ions from it. This guarantees that both experience thesame displacement-time history. Comparison of the output ofthe transfer standard or AE sensor with the output of thestandard transducer yields a calibration of the device undertest.5.3.2 Other relative geometries for the input and transducersare
27、possible, but results from other geometries should only beused to supplement results from the “same surface” geometry.AE waves in structures are most frequently dominated bysurface wave phenomena, and the calibration should be basedon the transducers response to such waves.5.4 Units for the Calibrat
28、ionAn AE sensor may beconsidered to respond to either stress or strain at its front face.The actual stress and strain at the front face of a mountedsensor depend on the interaction between the mechanicalimpedance of the sensor (load) and that of the mounting block(driver). Neither the stress nor the
29、 strain is amenable to directmeasurement at this location. However, the free displacementthat would occur at the surface of the block in the absence ofthe sensor can be inferred from measurements made elsewhereon the surface.Also, the ideal displacement (except at the pointwhere the displacement bec
30、omes infinite) for an ideal source isknown from theory. Since AE sensors are used to monitormotion at a free surface of a structure and interactive effectsbetween sensor and structure are generally of no interest, thefree surface motion is the appropriate input variable. It is,therefore, recommended
31、 that the units of calibration should bevoltage per unit of free motion; for example, volts per metre.5.5 Block Material:5.5.1 Since the calibration depends on the interaction of themechanical impedance of the block and that of the AE sensor,a calibration procedure must specify the material of the b
32、lock.Calibrations performed on blocks of different materials willyield transducer sensitivity versus frequency curves that aredifferent in shape and in average magnitude. The amount bywhich such averages differ may be very large. A transducercalibrated on a glass or aluminum block will have an avera
33、gesensitivity that may be from 50 to 100 % of the value obtainedon steel, and will have an average sensitivity that may be aslittle as 3 % of the value obtained on steel if calibrated on apolymethyl methacrylate block. In general, the sensitivity willbe less if the block is made of a less rigid or l
34、ess densematerial.5.5.2 The Rayleigh speed in the material of the block affectssurface wave calibrations. For a sensor having a circularaperture (mounting face) with uniform sensitivity over theface, the aperture effect predicts nulls at the zeroes of J1(ka),where k=2pf/cR, and f = frequency, cR= Ra
35、yleigh speed, anda = radius of the sensor face (active element). Hence, thefrequencies at which the nulls occur are dependent upon theRayleigh speed.3Burks, Brian, “Re-Examination of NISTAcoustic Emission Sensor Calibration:Part I Modeling the Loading from Glass Capillary Fracture,” Journal of Acous
36、ticEmission, Vol. 29, pp. 167174.4Breckenridge, F. R., “Acoustic Emission Transducer Calibration by Means ofthe Seismic Surface Pulse,” Journal of Acoustic Emission Vol 1, pp. 8794.5Hsu, N. N., and Breckenridge, F. R., “Characterization and Calibration ofAcoustic Emission Sensors,” Materials Evaluat
37、ion, Vol 39, 1981, pp. 6068.6Paul G. Richards, “Elementary Solutions to Lambs Problem for a Point Sourceand their Relevance to Three- Dimensional Studies of Spontaneous Crack Propa-gation,” Bull. of the Seismological Society of America, Vol 69, No. 4, 1979, pp.947956.7Breckenridge, F. R., and Greens
38、pan, M., “Surface-Wave Displacement: Abso-lute Measurements Using a Capacitive Transducer,” Journal, Acoustic Society ofAmerica, Vol 69, pp 11771185.E1106 1226. Apparatus6.1 A typical basic scheme for the calibration is shown inFig. 1. A glass capillary, B, of diameter about 0.2 mm, issqueezed betwe
39、en the tip of the loading screw, C, and the upperface of the large steel transfer block, A. When the capillarybreaks, the sudden release of force is nearly a step functionwhose risetime is of the order of 0.2 s to 0.3 s. Themagnitude of the force step is measured by the combination ofthe PZT disc, D
40、, in the loading screw and a charge amplifier, E,connected to a waveform recorder, F. Alternatively, the forcestep can be measured by a strain-gage load cell within theloading screw with standard electronic conditioning for thestrain gages. The standard capacitive transducer, G, and thedevice under
41、test, H, are placed equally distant (usually 100mm) from the source and in opposite directions from it. It isobvious from the symmetry that the surface displacementswould be the same at the two transducer locations if it were notfor the loading effects of the transducers. The loading effect ofthe st
42、andard capacitive transducer is negligible and the loadingeffect of the unknown sensor is part of its calibration.6.1.1 Voltage transients from the two transducers are re-corded simultaneously by digital recorders, I, and the informa-tion is stored for processing by the computer, J.6.1.2 With such a
43、 system, it is possible to do the necessarycomparison between the signal from the unknown sensor andthat from the standard transducer.6.1.3 As a check, the shelf value (see section 5.2.1) deter-mined from the standard transducer output is compared withthe value determined from the measured capillary
44、 break forceusing the equation in 5.2.1. This comparison should providesupporting evidence that the precision stated in 8.5 has beenattained. This check should be made at least one time for eachcalibration performed.6.2 The Transfer BlockThe transfer block must be madefrom specially chosen material.
45、 It should be as defect-free aspossible and should undergo an ultrasonic longitudinal exami-nation at 2.25 MHz. The method described in Practice E114should be used. The block should contain no flaws which givea reflection larger than 10 % of the first back wall reflection.The material should also be
46、 highly uniform as determined bypulse-echo time of flight measurements through the block at aminimum of 15 locations regularly spaced over the surface (seePractice E494). The individual values of the longitudinal andshear wave speed should differ from the average by no morethan 61 part and 63 parts
47、in 104, respectively.Atransfer blockand calibration apparatus is shown in Fig. 2.6.3 The SourceThe source events, which are a usefulapproximation to force step functions, are to be made bybreaking glass capillary tubing (Fig. 3). The capillaries aredrawn down from ordinary laboratory glass tubing ma
48、de ofborosilicate glass. Sizes of the capillary may range from about0.1 mm to 0.3 mm outside diameter, with 0.2 mm being typical.A bore size equal to the wall thickness gives the best results.The force obtained is usually between 10 N and 20 N.6.3.1 The capillary is to be laid horizontally (perpendi
49、cularto the propagation direction to the transducers) on a piece ofmicroscope cover glass (0.08 mm by 1.5 mm by 1.5 mm)which has been cemented to the top face of the steel block withAsteel transfer blockBcapillary sourceCloading screwDPZT disc or strain-gage load cellEcharge amplifier or strain gage conditioning electronicsFtransient recorderGstandard transducerHtransducer under testItransient recordersJcomputerFIG. 1 Schematic Diagram of the ApparatusE1106 123salol (phenyl salicylate) or cyanoacrylate cement. The force isapplied to the capillar
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