ASTM E650-1997(2007) Standard Guide for Mounting Piezoelectric Acoustic Emission Sensors《安装压电声发射传感器》.pdf

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1、Designation: E 650 97 (Reapproved 2007)Standard Guide forMounting Piezoelectric Acoustic Emission Sensors1This standard is issued under the fixed designation E 650; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r

2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This document provides guidelines for mounting piezo-electric acoustic emission (AE) sensors.1.2 This standard does not pur

3、port 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:2E

4、976 Guide for Determining the Reproducibility of Acous-tic Emission Sensor ResponseE 1316 Terminology for Nondestructive Examinations3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 bonding agenta couplant that physically attachesthe sensor to the structure.3.1.2 couplanta mate

5、rial used at the structure-to-sensorinterface to improve the transfer of acoustic energy across theinterface.3.1.3 mounting fixturea device that holds the sensor inplace on the structure to be monitored.3.1.4 sensora detection device that transforms the particlemotion produced by an elastic wave int

6、o an electrical signal.3.1.5 waveguide, acoustica device that couples acousticenergy from a structure to a remotely mounted sensor. Forexample, a solid wire or rod, coupled to a sensor at one end andto the structure at the other.3.2 Definitions:3.2.1 For definitions of additional terms relating to a

7、cousticemission, refer to Terminology E 1316.4. Significance and Use4.1 The methods and procedures used in mounting AEsensors can have significant effects upon the performance ofthose sensors. Optimum and reproducible detection of AErequires both appropriate sensor-mounting fixtures and consis-tent

8、sensor-mounting procedures.5. Mounting Methods5.1 The purpose of the mounting method is to hold thesensor in a fixed position on a structure and to ensure that theacoustic coupling between the sensor and the structure is bothadequate and constant. Mounting methods will generally fallinto one of the

9、following categories:5.1.1 Compression MountsThe compression mount holdsthe sensor in intimate contact with the surface of the structurethrough the use of force. This force is generally supplied bysprings, torqued-screw threads, magnets, tape, or elastic bands.The use of a couplant is strongly advis

10、ed with a compressionmount to maximize the transmission of acoustic energythrough the sensor-structure interface.5.1.2 BondingThe sensor may be attached directly to thestructure with a suitable adhesive. In this method, the adhesiveacts as the couplant. The adhesive must be compatible with thestruct

11、ure, the sensor, the environment, and the examinationprocedure.6. Mounting Requirements6.1 Sensor SelectionThe correct sensors should be chosento optimally accomplish the acoustic-emission examinationobjective. Sensor parameters to be considered are as follows:size, sensitivity, frequency response,

12、surface-motion response,and environmental and material compatibility. When a multi-channel acoustic-emission examination is being conducted, asubset of sensors with characteristics similar to each othershould be selected. See Guide E 976 for methods of comparingsensor characteristics.6.2 Structure P

13、reparationThe contacting surfaces shouldbe cleaned and mechanically prepared. This will enhance thedetection of the desired acoustic waves by assuring reliablecoupling of the acoustic energy from the structure to the sensor.Preparation of these surfaces must be compatible with theconstruction materi

14、als used in both the sensor and the structure.1This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-tive Testing and is the direct responsibility of Subcommittee E07.04 on AcousticEmission Method.Current edition approved July 1, 2007. Published July 2007. Originally approvedin 19

15、85. Last previous edition approved in 2002 as E 650 - 97(2002)e1.2For 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 webs

16、ite.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Possible losses in acoustic energy transmission caused bycoatings such as paint, encapsulants, loose-mill scale, weldspatter, and oxides as well as losses due to surface curvature a

17、tthe contact area must be considered.6.3 Couplant or Bonding Agent Selection:6.3.1 The type of couplant or bonding agent should beselected with appropriate consideration for the effects of theenvironment (for example, temperature, pressure, compositionof gas, or liquid environment) on the couplant a

18、nd theconstraints of the application. It should be chemically compat-ible with the structure and not be a possible cause of corrosion.In some cases, it may be a requirement that the couplant becompletely removable from the surface after examination. Ingeneral, the selection of the couplant is as imp

19、ortant from anenvironmental standpoint as it is from the acoustical stand-point.6.3.2 For sensors that are primarily sensitive to particlemotion perpendicular to their face, the viscosity of the couplantis not an important factor. Most liquids or greases will work asa couplant if they wet the surfac

20、es of both the structure and thesensor. For those few sensors which are sensitive primarily tomotion in the plane of their face, very high-viscosity couplantor a rigid bond is recommended.6.3.3 The thickness of the couplant may alter the effectivesensitivity of the sensor. The thinnest practical lay

21、er ofcontinuous couplant is usually the best. Care should be takenthat there are no entrapped voids in the couplant. Unevenness,such as a taper from one side of the sensor to the other, can alsoreduce sensitivity or produce an unwanted directionality in thesensor response.6.3.4 A useful method for a

22、pplying a couplant is to place asmall amount of the material in the center of the sensor face,then carefully press the sensor on to the structure surface,spreading the couplant uniformly from the center to the outsideof the sensor face.6.3.5 In some applications, it may be impractical to use acoupla

23、nt because of the nature of the environment (for ex-ample, very high temperatures or extreme cleanliness require-ments). In these situations, a dry contact may be used, providedsufficient mechanical force is applied to hold the sensor againstthe structure. The necessary contact pressure must be dete

24、r-mined experimentally. As a rough guide, this pressure shouldexceed 0.7 MPa (100 psi).6.3.6 Great care must be taken when bonding a sensor to astructure. Surface deformation, that can be produced by eithermechanical loading or thermal expansion, may cause a bond tocrack, peel off, or, occasionally,

25、 destroy the sensor. Bondcracking is a source of acoustic emission.Acompliant adhesivemay work in some cases. If differential expansion between thesensor, the bond, and the surface is a possibility, a suitablebonding agent should be confirmed by experiment.6.3.7 When bonds are used, the possibility

26、of damagingeither the sensor or the surface of the structure during sensorremoval must be considered.6.3.8 The use of double-sided adhesive tape as a bondingagent is not recommended.6.4 Mounting Fixture Selection:6.4.1 Mounting fixtures must be constructed so that they donot create extraneous acoust

27、ic emission or mask valid acousticemission generated in the structure being monitored.6.4.1.1 The mount must not contain any loose parts ofparticles.6.4.1.2 Permanent mounting may require special techniquesto prevent sensor movement caused by environmental changes.6.4.1.3 Detection of surface waves

28、may be suppressed if thesensor is enclosed by a welded-on fixture or located at thebottom of a threaded hole. The mounting fixture should alwaysbe designed so that it does not block out a significant amountof acoustic energy from any direction of interest.6.4.2 The mounting fixture should provide su

29、pport for thesignal cable to prevent the cable from stressing the sensor orthe electrical connectors. In the absence of a mounting fixture,some form of cable support should be provided. Care should betaken to ensure that the cable can neither vibrate nor be movedeasily. False signals may be generate

30、d by the cable striking thestructure and by triboelectric effects produced by cable move-ment.6.4.3 Where necessary, protection from the environmentshould be provided for the sensor or sensor and mountingfixture.6.4.4 The mounting fixture should not affect the integrity ofthe structure being monitor

31、ed.6.4.4.1 Permanently installed mounting fixtures must beconstructed of a material compatible with the structure. Pos-sible electrolytic effects or other forms of corrosion must beconsidered when designing the mounting fixture.6.4.4.2 Alterations of the local environment by the mount,such as remova

32、l of the insulation, must be carefully evaluatedand corrected if necessary.6.4.5 The mounting fixture should be designed to have aminimal effect on the response characteristics of the sensor.6.5 WaveguidesWhen adverse environments make directcontact between the sensor and the structure undesirable,

33、anacoustic waveguide may be used to convey the acoustic signalfrom the structure to the sensor. The use of a waveguide insertsanother interface with its associated losses between the struc-ture and the sensor and will distort, to some degree, thecharacteristics of the acoustic wave.6.5.1 An acoustic

34、 waveguide should be mounted so as toensure that its surface will not contact any materials that willcause signal damping in the waveguide.6.5.2 If acoustic waveguides are used when acoustic-emission source location is being performed, the extra timedelay in the waveguides must be accounted for in t

35、he sourcelocation program.7. Verification of Response7.1 After the sensor(s) are mounted on a structure, adequateresponse should be verified by injecting acoustic signals intothe structure and examining the detected signal either on anoscilloscope or with the AE system to be used in the exami-nation

36、. If there is any doubt as to the sensor response, thesensor should be remounted.7.1.1 The test signal may be injected by an external sourcesuch as the Hsu-pencil source, or a gas jet (helium or othersuitable gas), or by applying an electrical pulse to anotherE 650 97 (2007)2sensor mounted on the st

37、ructure. For a description of thesemethods see Guide E 976.7.2 Periodic VerificationOn an extended acoustic emis-sion examination, it may be desirable to verify the response ofthe sensors during the examination. Verification should beperformed whenever circumstances indicate the possibility of achan

38、ge in the coupling efficiency.7.3 Post VerificationAt the end of an acoustic emissionexamination, it is good practice to verify that all sensors arestill working and that there have been no dramatic changes incoupling efficiencies.8. Report8.1 Any report of the mounting practice should includedetail

39、s of the sensor mounting fixture(s), surface preparationmethod, and the couplant that was used.9. Keywords9.1 acoustic emission; acoustic emission sensors; acousticemission transducers; AE; bonding agent; couplant; mountingfixture; waveguideASTM International takes no position respecting the validit

40、y of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject

41、 to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarter

42、s. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard i

43、s copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E 650 97 (2007)3