1、Designation: E1106 12 (Reapproved 2017)Standard 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
2、last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the requirements for the abso-lute calibration of acoustic emission (AE) sensors. The cali-bra
3、tion yields the frequency 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-plac
4、ement normal to the mounting surface. The units of thecalibration are output voltage per unit mechanical input(displacement, 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 d
5、oes not purport 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.1.4 This international standard wa
6、s developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenc
7、ed Documents2.1 ASTM Standards:2E114 Practice for Ultrasonic Pulse-Echo Straight-BeamContact TestingE494 Practice for Measuring Ultrasonic Velocity in Materi-alsE650 Guide for Mounting Piezoelectric Acoustic EmissionSensorsE1316 Terminology for Nondestructive Examinations3. Terminology3.1 Refer to T
8、erminology E1316 for terminology used 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
9、purpose, the transfer stan-dard should 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 trans
10、ient input, before any wavereflected from 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 calibra
11、tion ofAE sensors for use in nondestructiveevaluation. 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 diffi
12、culty in any calibration of a mechanical/electrical transduction device is the determination of themechanical-motion input to the device. To address thisdifficulty, this calibration procedure uses (i) a standard trans-ducer whose absolute sensitivity is known from its design andphysical characterist
13、ics; and also (ii) a source that producesmotion 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 sen
14、sitivity of the transfer standard (or 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.5.2 Test Block and Mechanical InputThe mechanicalinput to the sensors is obtained by pressing a glass capil
15、lary1This test method is under the jurisdiction of ASTM Committee E07 onNondestructive Testing and is the direct responsibility of Subcommittee E07.04 onAcoustic Emission Method.Current edition approved June 1, 2017. Published July 2017. Originally approvedin 1986. Last previous edition approved in
16、2012 as E1106 - 12. DOI: 10.1520/E1106-12R17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM I
17、nternational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standar
18、ds, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1down 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 natural acoustic e
19、missionevents; 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 of2 mm 0.3 mm.3When th
20、e glass capillary breaks, the force itwas 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 theblock. Theo
21、retical 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 waveforms, support-in
22、g 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 from the sour
23、ceand 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 theoretical h
24、eight6(shelf value see Figure 9 for determination of the shelf value,relative to zero displacement) of this displacement step u3is:u35 F0A/4dA 2 1!where F0is the applied force (which is measured), is theshear modulus (calculated by use of the shear wave velocity) ofthe test block, A =(cL/cS)2and d i
25、s 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 the device un
26、der 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 amenable to theoret
27、ical 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 oppositedirections from it.
28、 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 possible, but
29、 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 CalibrationAn AE sens
30、or may be con-sidered to respond to either stress or strain at its front face. Theactual stress and strain at the front face of a mounted sensordepend on the interaction between the mechanical impedanceof the sensor (load) and that of the mounting block (driver).Neither the stress nor the strain is
31、amenable to direct measure-ment at this location. However, the free displacement thatwould occur at the surface of the block in the absence of thesensor can be inferred from measurements made elsewhere onthe surface. Also, the ideal displacement (except at the pointwhere the displacement becomes inf
32、inite) 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 that th
33、e 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 block.Cal
34、ibrations 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 averagesensit
35、ivity 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 less dens
36、ematerial.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=2fcR, and f = frequency, cR= Rayleigh spe
37、ed, 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 AcousticEmissio
38、n, 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 Evaluation, Vol 3
39、9, 1981, pp. 6068.6Paul G. Richards, “Elementary Solutions to Lambs Problem for a Point Sourceand their Relevance to Three- Dimensional Studies of Spontaneous CrackPropagation,” Bull. of the Seismological Society of America, Vol 69, No. 4, 1979, pp.947956.7Breckenridge, F. R., and Greenspan, M., “Su
40、rface-Wave Displacement: Abso-lute Measurements Using a Capacitive Transducer,” Journal, Acoustic Society ofAmerica, Vol 69, pp 11771185.E1106 12 (2017)26. Apparatus6.1 A typical basic scheme for the calibration is shown inFig. 1. A glass capillary, B, of diameter about 0.2 mm, issqueezed between th
41、e 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, in
42、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 test,
43、 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 standar
44、d 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 syst
45、em, 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 brea
46、k 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. It s
47、hould 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 high
48、ly 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 in 10
49、4, 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 made ofborosilicate glass. Sizes of the capillary may range from aboutAsteel transfer blockBcapillary sourceCloading screwDPZT disc or strain-gage load cellEcharge amplifier or strain gage conditioning electronicsFtransient recorderGstandard transducerHtran
