1、Designation: E 664 93 (Reapproved 2005)Standard Practice for theMeasurement of the Apparent Attenuation of LongitudinalUltrasonic Waves by Immersion Method1This standard is issued under the fixed designation E 664; the number immediately following the designation indicates the year oforiginal adopti
2、on or, in the case of revision, the year of last revision. 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 practice describes a procedure for measuring theapparent attenuation
3、 of ultrasound in materials or componentswith flat, parallel surfaces using conventional pulse-echoultrasonic flaw detection equipment in which reflected indica-tions are displayed in an A-scan presentation.1.2 The measurement procedure is readily adaptable for thedetermination of relative attenuati
4、on between materials. Forabsolute (true) attenuation measurements, indicative of theintrinsic nature of the material, it is necessary to correct forspecimen geometry, sound beam divergence, instrumentation,and procedural effects. These results can be obtained with morespecialized ultrasonic equipmen
5、t and techniques.1.3 The values stated in inch-pound units are to be regardedas the standard.1.4 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 prac
6、tices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 214 Practice for Immersed Ultrasonic Examination by theReflection Method Using Pulsed Longitudinal WavesE 317 Practice for Evaluating Performance Characteristicsof Ultrasonic Pu
7、lse-Echo Testing Systems Without the Useof Electronic Measurement InstrumentsE 1316 Terminology for Nondestructive Examinations3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, seeTerminology E 1316.3.2 Definitions of Terms Specific to This Standard:3.2.1 apparent a
8、ttenuationthe observed ultrasound en-ergy loss. In addition to the true loss, the apparent attenuationmay also include losses attributable to instrumentation, speci-men configuration, beam divergence, interface reflections, andmeasurement procedure.3.2.2 attenuationa factor that describes the decrea
9、se inultrasound intensity with distance. Normally expressed indecibels per unit length.NOTE 1The attenuation parameter is sometimes expressed in nepers(Np) per unit length. The value in decibels (dB) is 8.68 times the value innepers. If the loss over a path is 1 Np, then the amplitude has fallen to
10、1/eof its initial value (e = 2.7183. . .).3.2.3 decibel (dB)twenty times the logarithmic expres-sion of the ratio of two amplitudes.dB 5 20 log10amplitude ratio!3.2.4 true attenuationthat portion of the observed ultra-sound energy loss which is intrinsic to the medium throughwhich the ultrasound pro
11、pagates. True attenuation losses maybe attributed to the basic mechanisms of absorption andscattering.4. Summary of Practice4.1 This practice describes a procedure for determiningapparent attenuation by measuring the decay of multiple backreflections of longitudinal ultrasonic waves introduced intos
12、pecimens with flat, parallel surfaces by the immersion tech-nique.5. Significance and Use5.1 The measurement of apparent attenuation in materials isuseful in applications such as the comparison of heat treat-ments of different lots of material or the assessment of thedegradation of materials due to
13、environment.5.2 Several different modes of wave vibration can bepropagated in solids. This practice is concerned with theattenuation associated with longitudinal waves introduced intothe specimen by the immersion method.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structiv
14、e Testing and is the direct responsibility of Subcommittee E07.06 onUltrasonic Method.Current edition approved January 1, 2005. Published January 2005. Originallyapproved in 1978. Last previous edition approved in 2000 as E 664 - 93 (2000).2For referenced ASTM standards, visit the ASTM website, www.
15、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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.3 Th
16、is practice allows for the comparison of the apparentattenuations of geometrically similar specimens.5.4 For the determination of apparent attenuation, the pro-cedures described herein are valid only for measurements inthe far field of the ultrasonic beam.6. Apparatus6.1 Ultrasonic Flaw Detection Sy
17、stem A system capableof generating, receiving, and displaying electrical pulses at thefrequency of interest. Display shall be an A-scan presentation.6.1.1 Performance CharacteristicsThe vertical linearitylimits shall be determined as specified in Practice E 317. Allmeasurements shall be made only wi
18、thin the linear ranges ofthe system.6.2 Search UnitThe size and frequency should be deter-mined to suit the application, and only non-focused searchunits may be used.6.3 CouplantNormally water. See Practice E 214 for al-ternatives.6.4 Reference BlockThe use of a reference block issuggested to evalua
19、te the stability of the measurement systemif measurements will be made over a period of time. Thereference block should have acoustic properties similar to thoseof the examined material in the frequency range of interest.7. Specimen7.1 Geometric SimilarityWhen comparing the apparentattenuations of t
20、wo or more materials or components, thespecimens used must be geometrically similar. They must beflat and parallel within 0.008 in. 0.20 mm/in. 25.4 mm ofdiameter or cross section and differ in thickness by no morethan a factor of 2. The cross section of each specimen mustmeet the requirements of 7.
21、2.7.2 Minimum DimensionsThe thickness of the specimen(parallel to the ultrasonic beam) shall be of a dimension so thatat least two back surface reflections can be resolved at thefrequency of interest. The dimensions normal to the ultrasonicbeam shall be much greater than the beam width and wave-leng
22、th (at least three times the transducer dimension) so thatside wall echoes do not interfere with the measurements.NOTE 2For the determination of true attenuation, careful consider-ation must be made of parameters such as front surface and back surfaceparallelism, surface finish, etc. However, useful
23、 apparent attenuationinformation can be obtained if the requirements of 7.1 and 7.2 aresatisfied.8. Procedure8.1 Measure the thickness of the specimen to an accuracy of60.001 in. 60.03 mm or 60.1 %, whichever is greater.8.2 Place the sample in a suitable immersion tank.8.3 Place the search unit in a
24、 fixture suitable for manipulat-ing the sound entry angle and lateral position. Position thesearch unit over the sample, and angulate the beam to obtainthe maximum number of back reflections. See Fig. 1. The waterpath should be such that the entry surface is in the far field ofthe ultrasonic beam.NO
25、TE 3If the frequency and dimensions of the transducers availabledo not readily permit the top surface of sample to be in the far field, thismethod may be used provided the back reflections measured and recordedare in the far field of the sound beam.8.3.1 With the reject level set at zero, measure an
26、d recordthe amplitudes of any two back reflections that show decreas-ing amplitude with increase in back reflection number.NOTE 4If the apparent attenuation of two or more materials orcomponents are to be compared, the same two back reflections should beselected for each sample.8.3.2 Determine the a
27、pparent attenuation by the relationshipindicated below. The apparent attenuation will be in terms ofdecibels per unit length as defined by the units of thickness.Apparent attenuation 520 log10AmAn2 n 2 m! Twhere:Amand An= amplitudes of the mth and nth back reflec-tions (n m), andT = specimen thickne
28、ss.NOTE 5When instruments are used that have dB calibrated gaincontrol, the measurements in decibels may be used instead of amplitudemeasurements. The dB control is used to bring the amplitude of the nthFIG. 1 Typical A-Scan Presentation Showing Multiple Back Reflections for Evaluation of Apparent A
29、ttenuation.E 664 93 (2005)2reflection up to the amplitude of the mth reflection and the gain in decibelsis substituted for the numerator in the attenuation formula. The formulathen becomes:dB2 n 2 m! T9. Report9.1 The report should include the following:9.1.1 Instrument make, model, and serial numbe
30、r,9.1.2 Pertinent equipment settings such as gain, pulselength, damping, etc.,9.1.3 Search unit type, frequency, serial number and trans-ducer size,9.1.4 Specimen dimensions,9.1.5 Amplitudes and numbers of each of the back reflec-tions used to calculate the attenuation parameter,9.1.6 Attenuation pa
31、rameter, and9.1.7 Water path length.10. Precision and Bias10.1 PrecisionMeasurements of apparent attenuation arereproducible to within 615 %.NOTE 6Many characteristics of ultrasonic systems affect the measure-ments described herein. These include the pulse shape and frequencyspectrum of the driving
32、pulse, the frequency spectrum, damping, etc., ofthe search unit, and others. Since these characteristics are not specifiedhere, the reproducibility of measurements on different systems is uncer-tain. Caution should be exercised when comparing data gathered ondifferent, although nominally identical,
33、systems.10.2 BiasAs mentioned throughout, this procedure isconcerned only with comparative values between specimens.Therefore, there is no correct value for comparison.11. Keywords11.1 apparent attenuation; attenuation; immersion method;nondestructive examination; ultrasonic examinationASTM Internat
34、ional takes no position respecting the validity 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 the
35、ir own responsibility.This standard is subject 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
36、be addressed to ASTM International Headquarters. 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 Standar
37、ds, at the address shown below.This standard is 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 664 93 (2005)3
