1、Designation: E2374 16Standard Guide forAcoustic Emission System Performance Verification1This standard is issued under the fixed designation E2374; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 System performance verification methods launch stresswaves into the examination article on which the sensor ismounted. The resulting stress
3、wave travels in the examinationarticle and is detected by the sensor(s) in a manner similar toacoustic emission.1.2 This guide describes methods which can be used toverify the response of an Acoustic Emission system includingsensors, couplant, sensor mounting devices, cables and systemelectronic com
4、ponents.1.3 Acoustic emission system performance characteristics,which may be evaluated using this document, include somewaveform parameters, and source location accuracy.1.4 Performance verification is usually conducted prior tobeginning the examination.1.5 Performance verification can be conducted
5、 during theexamination if there is any suspicion that the system perfor-mance may have changed.1.6 Performance verification may be conducted after theexamination has been completed.1.7 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstan
6、dard.1.8 This standard does 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.2. Referen
7、ced Documents2.1 ASTM Standards:2E750 Practice for Characterizing Acoustic Emission Instru-mentationE976 Guide for Determining the Reproducibility ofAcousticEmission Sensor ResponseE1316 Terminology for Nondestructive ExaminationsE1419 Practice for Examination of Seamless, Gas-Filled,Pressure Vessel
8、s Using Acoustic EmissionE1781 Practice for Secondary Calibration of Acoustic Emis-sion Sensors3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 examination articlethe item which is being exam-ined with AE and to which AE sensors are attached.3.1.2 velocitythe measured velocity
9、of a stress wave,traveling in the examination article, using specified AE systemparameters and components. Velocity is often used in triangu-lation calculations to determine the position of the AE source.3.1.3 auto sensor test (AST)an electronic means by whicha sensor can be fed an electronic pulse
10、to excite the examina-tion article. The resulting stress wave in the examination articlecan be measured by the same sensor or by other sensors that areon the same examination article. See 3.1.4 and 3.1.5.3.1.4 auto sensor test-self test modea means by which anAST sensor may be used to check its own
11、performance.3.1.5 auto sensor test-near neighbor modea means bywhich an AST sensor may be used to determine the sensitivityof one or more neighboring sensors on the same examinationarticle.4. Significance and Use4.1 Acoustic Emission data acquisition can be affected bynumerous factors associated wit
12、h the electronicinstrumentation, cables, sensors, sensor holders, couplant, theexamination article on which the sensor is mounted, back-ground noise, and the users settings of the acquisition param-eters (for example, threshold).4.2 This guide is not intended to replace annual (or semi-annual) instr
13、umentation calibration (see Practice E750)orsensor recertification (see Practice E1781).4.3 This guide is not intended to replace routine electronicevaluation of AE instrumentation or routine reproducibilityverification of AE sensors (see Guide E976).1This guide is under the jurisdiction of ASTM Com
14、mittee E07 on Nondestruc-tive Testing and is the direct responsibility of Subcommittee E07.04 on AcousticEmission Method.Current edition approved June 15, 2016. Published July 2016. Originallyapproved in 2004. Last previous edition approved in 2015 as E2374 - 15. DOI:10.1520/E2374-16.2For referenced
15、 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.*A Summary of Changes section appears at the end of this standardCopyright A
16、STM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.4 This guide is not intended to verify the maximumprocessing capacity or speed of an AE system.4.5 This guide does not purport to address all of the safetyconcerns, if any associated with its use
17、. It is the responsibilityof the user of this guide to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.5. Apparatus5.1 To determine system performance a sensor must besubjected to a stress wave traveling in the examination articl
18、e.Transient stress waves are launched by mechanical or electro-mechanical devices that produce a waveform with fast rise-time, short duration and repeatable peak amplitude. Steadystate (continuous) stress waves are launched by mechanical orelectromechanical devices that produce a waveform with longd
19、uration constant amplitude. Various apparatus can be used asverification sources including the following:5.1.1 Pencil Lead Break (PLB)A mechanical pencil tech-nique whereby lead is pushed against the examination articlessurface with sufficient force to break the lead. When the leadbreaks, there is a
20、 sudden release of stress on the surface. (SeeGuide E976, subsection 4.3.3 and Fig. 5.)5.1.1.1 The distance between the PLB and the sensor mustbe specified and kept consistent.5.1.1.2 The “Hsu pencil source” uses a mechanical pencilwith a 2.5 mm lead extension, 2H hardness and 0.3 mm or 0.5mm diamet
21、er (0.3 mm is preferred).5.1.1.3 The “Nielsen shoe” can aid in breaking the leadconsistently.5.1.1.4 The pencil should be held at an angle of 30 degreesto the surface.5.1.1.5 Three to five lead breaks are generally conducted toshow a consistent result.5.1.1.6 Application standards (for example, Test
22、 MethodE1419, Table X1.2) specify the minimum signal amplitude thatmust be measured by the AE instrumentation.5.1.1.7 Channels which are found to have unacceptably lowor high sensitivity can be re-coupled (that is, replace couplant),repaired (that is, replace sensor, or cable, or both), or replacedt
23、o the examination article (that is, exchanged for anotherchannel), or both.5.1.1.8 PLB can be used to determine the apparent velocityin the examination article (apparent velocity = sensor spacing/time-of-flight). “Time-of-flight” is the time required for a stresswave to travel the sensor-spacing dis
24、tance5.1.2 Independent Piezoelectric PulserAn electrome-chanical device held against the examination article and used inconjunction with an electronic signal or pulse generator. Theelectrical signal from the signal/pulse generator is convertedinto a mechanical displacement by the transducers crystal
25、.(See Guide E976, subsection 4.3.1.) One significant advantageof this technique is that the output of the electronic signal/pulsegenerator can be adjusted in numerous ways (for example,amplitude and repetition rate).5.1.2.1 The independent pulser can be used to excite thereceiving AE sensor before,
26、during and after an examination asverification that there were no changes in coupling or sensorresponse. The independent pulser technique is particularlyuseful when there is limited access to the examination articlethat would preclude the use of manual techniques (for example,PLB).5.1.2.2 The indepe
27、ndent pulser technique is particularlyuseful in continuous monitoring situations where sensors willbe on the examination article for a long period of time. In thissituation the independent pulser is left in place and usedperiodically to assure system performance.5.1.3 AST Capable Integrated Pulser/S
28、ensorAn AE sen-sor that has been designed to accept an electronic signal/pulseinto its crystal. The mechanical displacement of the crystalexcites the examination article. The stress wave generated inthe examination article can be detected by other sensors on thesame examination article. With certain
29、 realizations of the ASTfunction (self test mode), it can also be detected by the excitingsensor.5.1.3.1 Auto Sensor Test: Near Neighbor ModeAn inte-grated pulser/sensor can be used to measure sensitivity andtime-of-flight (that is, the time required for a stress wave totravel the sensor-spacing dis
30、tance) for neighboring sensors onthe same examination article. The time-of-flight can be used tocalculate the apparent velocity of the stress wave (apparentvelocity = sensor spacing/time-of-flight).5.1.3.2 Auto Sensor Test: Self Test ModeAn integratedpulser/sensor can be used to verify the performan
31、ce of thesensor coupling and the sensor and channel electronics towhich it is attached by establishing a baseline duration (orenergy) measured from the AST pulse using a sensor that isknown to be operating properly and mounted optimally on theexamination article. The baseline duration number (forexa
32、mple, 10 000 s) can then be compared with the ASTduration measurements from each channel on the examinationarticle. Channels, which produce AST duration measurementsthat are low compared to the baseline, should be recoupled,repaired or replaced as necessary.5.1.4 Spring Loaded Center PunchA spring l
33、oaded devicethat imparts a mechanical impact force, creating a very largestress wave on the examination article. The spring assures aconsistent and repeatable force.5.1.4.1 The spring-loaded center punch is of particularadvantage whenAE sensors are distributed over large distanceson an examination a
34、rticle, as the imparted force is so strong itcan be detected easily.5.1.4.2 The spring-loaded center punch is readily availableand easy to apply anywhere on the examination article, at anytime.5.1.4.3 To avoid damage to the surface, it is desirable toapply the center punch through an intermediate in
35、terface suchas a thin sheet of metal.5.1.5 ProjectileAn object which is launched or projectedto impact the surface of the examination article. Examplesinclude a steel ball dropped onto the surface, a BB gun fired atthe surface or a mass at the end of a pendulum. In most casesthe energy being imparte
36、d onto the surface can be determined.5.1.6 Gas JetA gas jet forces a gas through a nozzle athigh pressure onto the surface of the examination article beinginstrumented. The gas jet is controlled by an electronic valveE2374 162with the ability of being turned on momentarily to create atransient surfa
37、ce wave or kept on to create a continuous surfacewave.5.1.6.1 The gas jet is usually used in an industrial environ-ment where compressed air or gas is readily available.5.1.6.2 The gas jet is usually used in places that areinaccessible so that system verification can be carried outremotely from the
38、sensor.5.1.6.3 The gas jet is a good device for creating a simulated,continuous leak-type, AE signal.5.1.7 Electrical Spark DischargeA spark struck betweentwo electrodes near the surface of the examination articlegenerates stress waves that propagate in a manner similar toacoustic emission. The tech
39、nique can be used in a similarmanner to a pencil lead break or independent piezoelectricpulser. The advantage of an electrical spark discharge is itsshort duration and impulse type response, providing a wide-band frequency response.5.1.8 Mechanical CrackerA mechanically loaded devicewhich is embritt
40、led or subjected to chemical attack (whichcauses it to crack at a rate controlled by the applied mechanicalload). When coupled to the surface of the examination article,the device produces true AE signals of varying amplitude. Thismethod truly generates acoustic emission and is useful incharacterizi
41、ng the AE system response to a brittle crack.5.1.9 Laser SourceA pulsed laser, (such as a “Nd-YAG”laser), can be used to create a high energy, short duration pulsethat impinges on the surface of the test object, creatingmechanical waves that travel through the test object to theneighboring sensors.
42、The pulse energy needs to be adjusted lowenough to avoid surface ablation (melting or vaporization)damage. Surface damage can be eliminated by using aluminumtape at the target site. This allows for multiple laser pulses atthe same target site.6. Procedure6.1 The procedure for accomplishing system pe
43、rformanceverification utilizes one of the devices listed in Section 5 toproduce a stress wave on the examination article. Thesensor(s), mounted a specified distance from the verificationdevice detects the stress wave and the acoustic emission systemprocesses the information for display and storage.
44、The operatorof the acoustic emission system examines the data to determineif they are within the limits specified in the written testprocedure. Note that two operators may be required: one tooperate the verification device (for example, PLB) and asecond to read the data and record the results.6.1.1
45、Verification of Acoustic Emission transient signalparameters (or AE features)Waveform parameters/featuresthat are necessary for achieving the desired examination resultsare typically required to be measured, within a specified degreeof accuracy, during system performance verification. Theseparameter
46、s and the required degree of accuracy are specified inthe written test procedure.6.1.1.1 An example of this process is provided in Table 1and Fig. 1 where peak amplitude from each sensor is used toverify system performance. The accuracy requirements used inthis example are found in Test Method E1419
47、, Table X1.2.TABLE 1 Example of Peak Amplitude Performance VerificationNOTE 1Specific values are found in Test Method E1419, AppendixX1.2. At a specified distance of greater than 100 mm from each sensor aPLB verification device is used. The acoustic emission system mustrespond with a specified peak
48、amplitude reading of greater than 70 dBAE.Waveform parameter to be verified Peak amplitudeSpecified acceptable range 70 dBAEVerification device PLBLead diameter 0.3 mmLead hardness 2HLead length 2.5 mmPLB distance 100 mm, specifyNOTE 1Specific values are found in Test Method E1419, Appendix X1.FIG.
49、1 Illustration of Peak Amplitude Performance VerificationE2374 1636.1.2 Verification of Source Location AccuracySourcelocation accuracy that is necessary for achieving the desiredexamination results are typically required to be measured,within a specified degree of accuracy, during system perfor-mance verification. The means of determining source locationand the required degree of accuracy are specified in the writtentest procedure.6.1.2.1 An example of this process is provided in Table 2and Fig. 2 where linear source location accuracy is measured toverify sy
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