1、Designation: E2985/E2985M 14Standard Practice forDetermination of Metal Purity Based on Elastic ConstantMeasurements Derived from Resonant UltrasoundSpectroscopy1This standard is issued under the fixed designation E2985/E2985M; the number immediately following the designation indicates the yearof or
2、iginal adoption or, in the case of revision, the year of last 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. Scope1.1 This practice is intended for use with resonant ultra-sound s
3、pectrometers capable of exciting, measuring, recordingand analyzing multiple whole body mechanical vibrationresonant frequencies within parts exhibiting acoustical ringingin the acoustic or ultrasonic, or both, resonant frequencyranges.1.2 This practice uses Resonant Ultrasound Spectroscopy(RUS) to
4、distinguish conforming parts, as determined fromqualified training sets, from those containing significantanomalies in their elastic properties.1.3 The basic functions of a RUS monitoring system are todetect and classify resonance phenomena. Solid structureresonances are governed by the parts dimens
5、ions, density andelastic properties. When a material substitution occurs in aprecious metal, the chosen metals have almost identical den-sities and unchanged dimensions, leaving only the elasticproperties to affect the resonances.1.4 This practice can be used to replace destructivemethods, which dam
6、age the test object through drilling ormelting, or both.1.5 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues
7、 from the two systems may result in non-conformancewith the standard.1.6 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
8、applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E543 Specification for Agencies Performing NondestructiveTestingE1316 Terminology for Nondestructive ExaminationsE2001 Guide for Resonant Ultrasound Spectroscopy forDefect Detection in Both Metallic and
9、Non-metallic Parts2.2 Other Referenced DocumentsANSI/ASNT CP-189 Standard for Qualification and Certifi-cation of Nondestructive Testing Personnel3NAS-410 NDT Certification4SNT-TC-1A Personnel Qualification and Certification inNondestructive Testing53. Terminology3.1 DefinitionsThe definitions of te
10、rms relating to conven-tional ultrasonic examination can be found in TerminologyE1316.3.2 Resonant ultrasound spectroscopy (RUS)Basic RUSwas originally applied in fundamental research applications inphysics and materials science. A few other recognizable namesinclude acoustic resonance spectroscopy,
11、 acoustic resonantinspection, and resonant inspection. Guide E2001 documentsRUS extensively. A nondestructive examination method whichemploys the measurement and analysis of acoustic or ultra-sound resonance patterns, or both, for the identification ofacceptable variations in the physical characteri
12、stics of test partsin production environments. In this procedure an isolated, rigidpart is caused to resonate. Certain resonances are measured andcompared to a previously defined acceptable pattern combina-tion of resonances. Based on this comparison the part is judged1This test method is under the
13、jurisdiction of ASTM Committee E07 onNondestructive Testing and is the direct responsibility of Subcommittee E07.06 onUltrasonic Method.Current edition approved Oct. 1, 2014. Published October 2014. DOI: 10.1520/E2985_E2985M-142For referenced ASTM standards, visit the ASTM website, www.astm.org, orc
14、ontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Availa
15、ble from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.5Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.Copyri
16、ght ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1to be acceptable or, if it does not conform to the establishedpattern, to be unacceptable.4. Summary of Practice4.1 Reports indicating that gold bullion is being physicallyhollowed and replace
17、d with similar density metals, such astungsten, are surfacing. While not a huge concern for theoriginal manufacturer, the secondary exchange market canexperience disruption if the integrity of the asset comes intoquestion. Verifying the sample purity is critical and must beperformed quickly and nond
18、estructively. Several potential testmethods are applicable, but most are not good solutions forexpense and technical reasons.4.2 In physics, resonance is the tendency of a system tooscillate at a greater amplitude at some frequencies than atothers. These are known as the systems resonance frequencie
19、sand are generally functions of the square root of the stiffnessover the mass. Since each unique metal has a set of definedelastic constants, the stiffness of any two metals will always bedifferent, meaning that the resonances produced from anydriving forces will be different and easily measured. Re
20、so-nances can be produced from any swept sine spectrometer(preferred) or with an impulse function (striking with ahammer). Independent of how the resonance spectrum iscreated, it can be measured and compared with known goodsamples to observe whether or not it has been altered asdescribed in 4.4.4.3
21、RUS, as defined in Guide E2001, describes a samplebeing excited by an exciting mechanical input (transducer) at aplurality of ultrasonic frequencies (the swept sine method), andsensing the resonant mechanical responses with the inverseprocess (one or two mechanical receiving transducers). Adynamic s
22、ignal analyzer is connected to receive the response ofthe sample and to output the resonance spectrum. Either acomputer, or visual observation, then determines the relevantresonances that adequately describe the conforming spectrum.4.4 Training sets of acceptable bullion are readily available,and se
23、veral mints have intentionally created doped samples tobe used for comparison. This “training set“ procedure has beenused with multiple NDT methods to establish selection criteria.To manufacture training sets, metals of similar density areemployed. For example, the density of gold is 19.30 g/cm3andt
24、ungsten is 19.25 g/cm3, almost indistinguishable. Moreover,since bullion is cast into a form, the dimensions of a billet arenot exact due to production variations. All of the worldstandard gold bars are defined as being 400 Troy ounces(12,441 g 27.43lb). Any bar weighing from 380 to 420 Troyounces (
25、11,819 to 13,063 g) satisfy this requirement. Ofcourse, the real value depends only on an accurate weight,which is stamped on the sample. RUS spectra are measured formany different samples to observe the differences from differ-ent mints and geometries. A RUS examination of dopedsamples is then used
26、 to illustrate spectral differences andestablish detection limits.5. Significance and Use5.1 Since the beginning of human history, currency hasexisted in the form of metal coins and bullion. Thieves learnedthat shaving some precious metal provided a method to changeits value. Substitution of common
27、metals for precious metals ofhigher value was commonplace until weighing methods be-came so accurate, that it became easily detected. Alloys werealso used as substitutes until inexpensive spectrometers be-came available which ended the counterfeiting practice. Therapid rise in the value of gold insp
28、ired the unscrupulous to finda new method. Tungsten was widely used for light bulbfilaments until regulations changed that market. The greatabundance of tungsten now available, coupled with the almostidentical density of gold, presented a new opportunity.5.2 RUS provides a method to create an unique
29、 electronicsignature for each piece tested which is operator independent.6. Basis of Application6.1 The following items are subject to contractual agree-ment between the parties using or referencing this practice.6.2 Personnel Qualification6.2.1 If specified in the contractual agreement, personnelpe
30、rforming examinations to this standard shall be qualified inaccordance with a nationally and internationally recognizedNDT personnel qualification practice or standard such asANSI/ASNT CP-189, SNT-TC-1A, NAS-410, or similar asapplicable. The practice or standard used and its applicablerevision shall
31、 be identified in the contractual agreement be-tween the using parties.6.3 Qualification of Nondestructive Testing AgenciesIfspecified in the contractual agreement, NDT agencies shall bequalified and evaluated as described in Practice E543. Theapplicable edition of Practice E543 shall be specified i
32、n thecontractual agreement.6.4 Timing of ExaminationThe timing of the examinationshall be in accordance with a contractual agreement or with anestablished internal procedure.6.5 Extent of ExaminationThis application requires sen-sor(s) placement such that the location where pipe movementoccurs can b
33、e reliably detected.6.6 Reporting Criteria/AcceptanceReporting criteria forthe examination results shall be in accordance with Sections 1113.6.7 Reexamination of Repaired or Reworked ItemsReexamination of repaired or reworked items is not addressedin this standard and if required shall be specified
34、in acontractual agreement.7. Examination Preparation7.1 Before the examination begins, make the followingpreparations for RUS monitoring:7.1.1 Determine the type, number, and placement of sen-sors. Two or three sensors are adequate for RUS testing withonly a single part under examination;7.1.2 The t
35、est stand shall be flexible to provide three pointsupport, as this will ensure equal weight loading on eachcontact surface;E2985/E2985M 1427.1.3 Appropriate resonant piezoelectric sensors with fre-quency range from 1 to 50 kHz shall be employed to providethe requisite excitation and receiving vibrat
36、ions;7.1.4 Establish communications between the control pointfor the application of the stimulus and responses to theexamination control center;7.1.5 Provide a means for continuously recording a measureof the resonances; and7.1.6 A training set of parts should be assembled andexamined by this method
37、, from known “good“ and “defective“pieces as previously determined by controlled castings. Thesedata establish a baseline for future comparisons to defineacceptable/reject parts, as this method is applicable to therepetitive examination of large sets of parts on a periodic basis,and not for one time
38、 testing of unique structures.8. Safety Precautions8.1 No specific safety hazards have been identified for thismethod, except for the physical handling of heavy parts (400Troy ounce 27.43 lb billets), which should be approachedwith caution9. Calibration and Standardization9.1 Annual calibration and
39、verification of RUS sensors,preamplifiers (if applicable), signal processor (particularly thesignal processor time reference), and RUS swept sine generatorshould be performed. Equipment should be adjusted so that itconforms to equipment manufacturers specifications. A stan-dard rectangular parallele
40、piped measuring 12.7 cm x 6.35 cmx 3.175 cm 5 in. x 2.5 in. x 1.25 in. made from A36 lowcarbon steel plate shall accompany each system, and a baselinespectra shall be taken and stored for comparison. Thesedimensions were selected because they produce spectra in thesame ranges of interest as the stan
41、dard gold and silver billets.9.2 A system performance verification must be conductedonce per week whereby selected resonances shall be measuredand compared with the baseline to ensure proper operation.Performance verifications can also be conducted during theexamination if there is any suspicion tha
42、t the system perfor-mance may have changed. Routine electronic evaluations(verification) must be performed any time there is a concernabout signal generation or receiving performance. Each signalprocessor channel must respond within 6 3 when comparedwith the baseline sample.10. Examination Procedure
43、10.1 RUS data shall be accumulated during the excitation ofthe structure, as specified in the written procedure.10.1.1 The part to be examined shall be placed on a threepoint fixture such that the weight is equally distributed.10.1.2 The part shall be examined according to the fre-quency range(s) es
44、tablished from an appropriate training setwhere the acceptable parts reliably indicate differences fromknown doped parts.10.1.3 This procedure is followed for multiple parts and alldata shall be archived to create a permanent record.10.1.4 Following the examination of all parts within aseries, repea
45、t the performance verification in accordance with9.2.11. Examination Records11.1 All system performance verification data and instru-ment adjustments, including equipment description and perfor-mance data, shall be included in the records of the examinationwith all pertinent qualification/certificat
46、ion records and besigned by the responsible RUS examiner. The informationrecorded should be sufficient to permit complete reanalysis ofthe results. This information should include, but not be limitedto:11.1.1 Serial number, dimensions of structure, purity ofsample and, if possible, origin data,11.1.
47、2 Sensor specifications, frequency response and con-figuration of mounting stage,11.1.3 Sensor locations,11.1.4 Frequency ranges evaluated, and11.1.5 Permanent data record of the measured RUS spectrain analog or digital form.12. Interpretation of Results12.1 All results shall be summarized on an app
48、ropriatedisplay, or tabulated, or both, for ready reference and interpre-tation. This display or tabulation shall indicate the interpreta-tion with respect to conforming, or nonconforming withpertinent comments.13. Report13.1 Areport should contain at least the examination record,the interpretation
49、of results and a diagram of the setup showingthe sensor location(s). The report shall catalog all partsexamined by type, serial number, weight and disposition(conforming/nonconforming)14. Keywords14.1 elastic properties; nondestructive examination; nonde-structive inspection; production variation; quality control;resonance inspection; resonances and vibration characteristics;resonant frequency; resonant mode; resonant ultrasound spec-troscopyE2985/E2985M 143ASTM International takes no position respecting the validity of any patent rights asserted in connection
