1、Designation: E650/E650M 12E650/E650M 17Standard Guide forMounting Piezoelectric Acoustic Emission Sensors1This standard is issued under the fixed designation E650/E650M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of l
2、ast 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*1.1 This document provides guidelines for mounting piezoelectric acoustic emission (AE) sensors.1.2 UnitsThe values stated
3、 in either SI units or inch-pound units are to be regarded separately as standard. The values statedin each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining valuesfrom the two systems may result in non-conformance with the standard.1.3 T
4、his standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1.4 This international
5、 standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2.
6、 Referenced Documents2.1 ASTM Standards:2E976 Guide for Determining the Reproducibility of Acoustic Emission Sensor ResponseE1316 Terminology for Nondestructive Examinations3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 bonding agenta couplant that physically attaches the sen
7、sor to the structure.3.1.2 couplanta material used at the structure-to-sensor interface to improve the transfer of acoustic energy across theinterface.3.1.3 mounting fixturea device that holds the sensor in place on the structure to be monitored.3.1.4 sensora detection device that transforms the par
8、ticle motion produced by an elastic wave into an electrical signal.3.1.5 waveguide, acoustica device that couples acoustic energy from a structure to a remotely mounted sensor. For example,a solid wire or rod, coupled to a sensor at one end and to the structure at the other.3.2 Definitions:3.2.1 For
9、 definitions of additional terms relating to acoustic emission, refer to Terminology E1316.4. Significance and Use4.1 The methods and procedures used in mounting AE sensors can have significant effects upon the performance of thosesensors. Optimum and reproducible detection of AE requires both appro
10、priate sensor-mounting fixtures and consistentsensor-mounting procedures.5. Mounting Methods5.1 The purpose of the mounting method is to hold the sensor in a fixed position on a structure and to ensure that the acousticcoupling between the sensor and the structure is both adequate and constant. Moun
11、ting methods will generally fall into one of thefollowing categories:1 This guide is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.04 on Acoustic EmissionMethod.Current edition approved June 15, 2012June 1, 2017. Published
12、 July 2012June 2017. Originally approved in 1985. Last previous edition approved in 20072012 asE650 - 97E650 - 12.(2007). DOI: 10.1520/E0650-12.10.1520/E0650-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of
13、 ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technicall
14、y possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this stand
15、ardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.1.1 Compression MountsThe compression mount holds the sensor in intimate contact with the surface of the structurethrough the use of force. This force is generally supplied by sprin
16、gs, torqued-screw threads, magnets, tape, or elastic bands. Theuse of a couplant is strongly advised with a compression mount to maximize the transmission of acoustic energy through thesensor-structure interface.5.1.2 BondingThe sensor may be attached directly to the structure with a suitable adhesi
17、ve. In this method, the adhesive actsas the couplant. The adhesive must be compatible with the structure, the sensor, the environment, and the examination procedure.6. Mounting Requirements6.1 Sensor SelectionThe correct sensors should be chosen to optimally accomplish the acoustic-emissionAE examin
18、ationobjective. SensorSelection parameters to be considered are as follows: size, sensitivity, frequency response, surface-motionresponse, and environmental and material compatibility. environmental compatibility, background noise, source locationrequirements, and material properties of the structur
19、e under examination. When a multichannel acoustic-emission examination isbeing conducted, a subset of sensors with characteristics similar to each other should be selected. See Guide E976 for methods ofcomparing sensor characteristics.6.1.1 If the examination objective is to includeAE source locatio
20、n, sensor selection may be governed by the material propertiesof the structure and may affect subsequent sensor spacing due to attenuation. It may be necessary to evaluate attenuation effectsas part of the pre-examination procedure. If performed, the attenuation data shall be retained as part of the
21、 experimental record.6.1.2 When a multichannel acoustic-emission examination is being conducted, a subset of sensors with characteristics similarto each other should be selected. See Guide E976 for methods of comparing sensor characteristics.6.2 Structure PreparationThe contacting surfaces should be
22、 cleaned and mechanically prepared. This will enhance thedetection of the desired acoustic waves by assuring reliable coupling of the acoustic energy from the structure to the sensor.Preparation of these surfaces must be compatible with the construction materials used in both the sensor and the stru
23、cture. Possiblelosses in acoustic energy transmission caused by coatings such as paint, encapsulants, loose-mill scale, weld spatter, and oxidesas well as losses due to surface curvature at the contact area must be considered.6.2.1 The location of each sensor should be measured and marked accordingl
24、y on the structure and recorded as part of theexamination record.6.2.2 If surface preparation requires removing paint from a metal surface, the paint may be removed with a grinder or othermechanical means, down to bare metal. The area of paint removal should be slightly larger than the diameter of t
25、he sensor. If themetal surface is smooth, sandpaper may be used to roughen the surface prior to bonding.6.2.2.1 After paint removal, the surface should be cleaned with a degreaser and wiped clean with a cloth.6.2.2.2 If corrosion is present on the structure, additional cleaning may include using a c
26、onditioner (mild acid) and neutralizerto minimize potential corrosion beneath the sensor after mounting.6.2.2.3 If the structure is located in a marine environment, soluble salts (e.g. chlorides, nitrates, sulfates) may still reside onthe steel surface even after cleaning. These types of salts attra
27、ct moisture from the air, and may result in additional corrosionbeneath the sensor and failure of the bond. As such, a liquid soluble salt remover is recommended as an additional step in surfacepreparation prior to sensor mounting.6.3 Couplant or Bonding Agent Selection:6.3.1 The type of couplant or
28、 bonding agent should be selected with appropriate consideration for the effects of the environment(for example, temperature, pressure, composition of gas, or liquid environment) on the couplant and the constraints of theapplication. It should be chemically compatible with the structure and not be a
29、 possible cause of corrosion. In some cases, it maybe a requirement that the couplant be completely removable from the surface after examination. In general, the selection of thecouplant is as important from an environmental standpoint as it is from the acoustical standpoint.6.3.2 For sensors that a
30、re primarily sensitive to particle motion perpendicular to their face, the viscosity of the couplant is notan important factor. Most liquids or greases will work as a couplant if they wet the surfaces of both the structure and the sensor.For those few sensors which are sensitive primarily to motion
31、in the plane of their face, very high-viscosity couplant or a rigidbond is recommended.6.3.2.1 Testing has shown that in most cases, when working at frequencies below 500 kHz, most couplants will suffice.However, due to potential loss of high frequency (HF) spectra when working above 500 kHz, a low
32、viscosity couplant or rigidbond, relative to sensor motion response, is recommended. Additionally, when spectral response above 500 kHz is needed, it isrecommended that FFT be performed to verify adequacy of HF response.6.3.3 The thickness of the couplant may alter the effective sensitivity of the s
33、ensor. The thinnest practical layer of continuouscouplant is usually the best. Care should be taken that there are no entrapped voids in the couplant. Unevenness, such as a taperfrom one side of the sensor to the other, can also reduce sensitivity or produce an unwanted directionality in the sensor
34、response.6.3.4 A useful method for applying a couplant is to place a small amount of the material in the center of the sensor face, thencarefully press the sensor on to the structure surface, spreading the couplant uniformly from the center to the outside of the sensorface. Typically, this will resu
35、lt in a small band (fillet) of couplant around the outside circumference of the sensor.6.3.5 In some applications, it may be impractical to use a couplant because of the nature of the environment (for example, veryhigh temperatures or extreme cleanliness requirements). In these situations, a dry con
36、tact may be used, provided sufficientE650/E650M 172mechanical force is applied to hold the sensor against the structure. The necessary contact pressure must be determinedexperimentally. As a rough guide, this pressure should exceed 0.7 MPa 100 psi.6.3.6 Great care must be taken when bonding a sensor
37、 to a structure. Surface deformation, that can be produced by eithermechanical loading or thermal expansion, may cause a bond to crack, peel off, or, occasionally, destroy the sensor. Bond crackingis a source of acoustic emission.Acompliantpliant adhesive may work in some cases. If differential expa
38、nsion between the sensor,the bond, and the surface is a possibility, a suitable bonding agent should be confirmed by experiment.6.3.7 When bonds bonding agent are used, the possibility of damaging either the sensor or the surface of the structure duringsensor removal must be considered.6.3.7.1 To mi
39、nimize damage to the sensor during removal, any excess bonding agent may be gently removed from around thebase of the sensor using a small chisel and hammer or mallet. Place a small block of wood, or the handle of the chisel, at the baseof the sensor. Using a hammer or mallet gently tap the side of
40、the block or handle to generate a shear force at the base of the sensorto break the bond. Attempting to pry or twist off the sensor by hand, or striking the side of the sensor at the top will often causethe ceramic face or wear plate of the sensor to debond from the sensor housing and destroy the se
41、nsor.6.3.7.2 Any bonding agent remaining on the face of the sensor after removal may be gently chipped off or removed with agrinder at low speed to avoid damage to the wear plate.6.3.8 The use of double-sided adhesive tape as a bonding agent is not recommended.6.4 Mounting Fixture Selection:6.4.1 Mo
42、unting fixtures must be constructed so that they do not create extraneous acoustic emission or mask valid acousticemission generated in the structure being monitored.6.4.1.1 The mount must not contain any loose parts of particles.6.4.1.2 Permanent mounting may require special techniques to prevent s
43、ensor movement caused by environmental changes.6.4.1.3 Detection of surface waves may be suppressed if the sensor is enclosed by a welded-on fixture or located at the bottomof a threaded hole. The mounting fixture should always be designed so that it does not block out a significant amount of acoust
44、icenergy from any direction of interest.6.4.2 The mounting fixture should provide support for the signal cable to prevent the cable from stressing the sensor or theelectrical connectors. In the absence of a mounting fixture, some form of cable support should be provided. Care should be takento ensur
45、e that the cable can neither vibrate nor be moved easily. False signals may be generated by the cable striking the structureand by triboelectric effects produced by cable movement.6.4.3 Where necessary, protection from the environment environment, such as encapsulation, should be provided for the se
46、nsoror sensor and mounting fixture.6.4.4 The mounting fixture should not affect the integrity of the structure being monitored.6.4.4.1 Permanently installed mounting fixtures must be constructed of a material compatible with the structure. Possibleelectrolytic effects or other forms of corrosion mus
47、t be considered when designing the mounting fixture.6.4.4.2 Alterations of the local environment by the mount, such as removal of the insulation, must be carefully evaluated andcorrected if necessary.6.4.5 The mounting fixture should be designed to have a minimal effect on the response characteristi
48、cs of the sensor.6.4.6 Mounting fixtures and waveguides should be designed to provide isolation of the sensor case from the fixture orwaveguide that is in contact with the structure to avoid grounding the sensor to the structure ground, especially those sensors thatuse an isolated sensor face (e.g e
49、poxy or ceramic face). Failure to isolate the sensor will result in a ground loop and will createa significant amount of electrical noise in the AE system and may mask detection of the AE activity of interest.6.5 WaveguidesWhen adverse environments make direct contact between the sensor and the structure undesirable, an acousticwaveguide may be used to conveytransmit the acoustic signal from the structure to the sensor. The use of a waveguide insertsaddsanother interface boundary transition with its associated losses between the structure and the sensor, and will distor
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