1、Designation: E1685 13Standard Practice forMeasuring the Change in Length of Fasteners Using theUltrasonic Pulse-Echo Technique1This standard is issued under the fixed designation E1685; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers a procedure for measuring changesin length of threaded fasteners using convention
3、al ultrasonicpulse-echo bolt-measuring instrumentation which has beenproperly calibrated.1.2 This procedure is normally intended for metal bolting6.3 mm or more in nominal diameter with effective length-to-diameter ratios of 2:1 or greater.1.3 The values stated in SI units are to be regarded asstand
4、ard. No other units of measurement are included in thisstandard.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 practices and determine the appli
5、ca-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E6 Terminology Relating to Methods of Mechanical TestingE1316 Terminology for Nondestructive ExaminationsE1544 Practice for Construction of a Stepped Block and ItsUse to Estimate Errors Produced by Speed-of-S
6、oundMeasurement Systems for Use on Solids (Withdrawn2012)32.2 ASME Standards:4ASME B46.12009 Surface Texture (Surface Roughness,Waviness, and Lay)3. Terminology3.1 The definitions in this practice are in accordance withTerminology E6 and Section I of Terminology E1316.3.2 Definitions of Terms Specif
7、ic to This Standard:3.2.1 change in length L, nphysical change in length ofa threaded fastener due to a change in tension within thefastener.3.2.2 effective length L, nthe length of a bolt that isresponsive to stress.3.2.2.1 DiscussionThis quantity lies somewhere betweenthe overall length of the bol
8、t and the grip length. It is usuallyestimated as the grip length plus one half the thickness of thehead and one half the thickness of the nut.3.2.3 longitudinal wave, nthose waves in which the par-ticle motion of the material is in the same direction as the wavepropagation.3.2.4 pulse-echo bolt-meas
9、uring instrumentan assemblyof ultrasonic instruments designed specifically to measurechanges in the lengths of bolts. See Appendix X1.3.2.5 reference length L, nthe ultrasonic time of flight inthe test specimen multiplied by a reference propagation veloc-ity.3.2.6 reference propagation velocity, LT-
10、1, nthe veloc-ity of propagation of the ultrasonic wavefront in a calibrationtest block or in the bolts whose changes of length are beingmeasured.3.2.7 time of flight, T, nthe measured time intervalbetween the launching of an ultrasonic pulse at the start of apath of travel and the reception of the
11、pulse at the end of thepath.4. Summary of Practice4.1 This practice describes a procedure for determining thechange in length of a threaded fastener due to a change intension in the fastener. Measurements of the ultrasonic time offlight are made before and after the fastener tension is changed,and a
12、 calculation of the change in length is made from thechange in the time of flight.4.1.1 Brief bursts of ultrasound (pulses) are generated byapplying high-voltage electrical signals to an electroacoustic1This practice is under the jurisdiction of ASTM Committee E28 on MechanicalTesting and is the dir
13、ect responsibility of Subcommittee E28.13 on Residual StressMeasurement.Current edition approved Nov. 1, 2013. Published January 2014. Originallyapproved in 1995. Last previous edition approved in 2006 as E168500(2006). DOI:10.1520/E1685-13.2For referenced ASTM standards, visit the ASTM website, www
14、.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.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from American Society of
15、Mechanical Engineers (ASME), ASMEInternational Headquarters, Two Park Ave., New York, NY 10016-5990, http:/www.asme.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1t
16、ransducer having a resonant frequency in the 5 to 10-MHzrange. The pulses enter the bolt through the transducer/boltinterface, travel to the far end of the bolt, and reflect back(echo) to the transducer. The time of flight required for thesignal to make its round-trip is measured electronically. Bym
17、easuring the change in the time of flight due to a change intension within the bolt, the equipment can determine thechange in the length of the bolt due to the change in tension.Compensation for the direct effect of stress on the propagationvelocity in the bolt is automatically done by a computer or
18、microprocessor within the equipment.4.2 This procedure is used on fasteners as they are tightenedwithin their elastic limits; or on previously tightened fastenersas they are loosened. The latter can have been tightened pastyield.5. Significance and Use5.1 The techniques described provide for the ind
19、irect mea-surement of change in length of a fastener. Such measurementsare made from one end of the specimen without requiringaccess to the rear surface.5.2 The equipment is field portable and should be used inthe manner prescribed by the manufacturer. Common usesinclude monitoring changes in length
20、 of fasteners and as a toolfor industrial quality control. Current applications includefasteners used in turbines, petrochemical pressure vessels,aircraft, automotive manufacturing, general bolting within thenuclear industry, structural steel connections, laboratorytesting, and so forth.6. Apparatus
21、6.1 Pulse-echo bolt-measuring instrumentFor ultrasonicmeasurementsof the change in length of bolts, anylongitudinal-wave pulse-echo ultrasonic instrument capable ofreporting calculated changes in length is acceptable providedthat its accuracy and precision satisfy the requirements set forthin Annex
22、A1. The major components of suitable instrumentsare as follows:6.1.1 Pulser/transmitter, a means of generating electricalpulses to excite an acoustic transducer.6.1.2 Receiver/detector, a means of amplifying and detect-ing the returning back-wall echo.6.1.3 Time-base Controller, a means of measuring
23、 changesin ultrasonic time of flight.6.1.4 Acoustic Transducer, a means of sending and receiv-ing ultrasonic waves. Experience has shown that transducerswith resonances in the 5 to 10-MHz frequency range areusually satisfactory. In general, select an acoustic transducerhaving an element of the large
24、st diameter available while notexceeding the minimum body diameter of the bolt.6.2 Other Apparatus:6.2.1 CouplantFor longitudinal pulse-echomeasurements, a liquid is required to couple ultrasound be-tween the transducer and the fastener. Of the couplantscommonly used, where applicable a 50/50 glycer
25、ine/water mixoften provides optimal results. Light oil or standard commer-cially available ultrasonic couplants are also satisfactory.6.2.2 OscilloscopeFor optimal adjustment of theapparatus, the use of an oscilloscope is necessary. The oscil-loscope must have two input channels, two traces, externa
26、ltriggering, and a dual time base with delayed sweep capability.Its bandwidth should be at least 35 MHz or its equivalent.6.2.2.1 Pulse-echo bolt-measuring instruments with built-inoscilloscope display capabilities must have sampling speedsequivalent to at least ten times the transducer frequency fo
27、rsatisfactory signal display.6.2.3 Standard Reference Blocks, for periodic recalibrationof the pulse-echo bolt-measuring instrument.6.2.3.1 A glass or metallic reference block of known lengthand appropriate surface roughness, shape, thickness, and par-allelism is recommended. Acceptable standards in
28、clude a glassblock, two metal bars of unequal length, and single bars ofknown acoustic velocity. The path length of the standard mustbe determined by a technique of higher accuracy. See PracticeE1544. The calibration of instruments and standards should betraceable to national standards, where system
29、s of traceabilityexist.7. Procedure7.1 The performance of the pulse-echo bolt-measuring in-strument should be verified or adjusted to a reference standardin accordance with the manufacturers specifications. SeeAnnex A2.7.1.1 In noncritical applications, where uncertaintiessmaller than 615 % of the c
30、hange in length are not required, aninstrument calibrated on one bolt of a given material may usedon other bolts of the same material but having different shapes.7.1.2 In critical, safety-related applications or where uncer-tainties of less than 3 % are required, or both, the pulse-echobolt-measurin
31、g instrument should be recalibrated on a statisti-cally significant sample of each new lot of bolts.7.2 Fastener PreparationTo ensure reliable ultrasonicmeasurements the finish and geometry of the fastener shall besuitable. One end shall be accessible for transducer placement.This end shall, for at
32、least the diameter of the transducer, be flatand perpendicular to the axis of the bolt. A machined surfacewith a finish of Ra=3.2m or better is recommended, exclusiveof indented grade markings. Remove raised grade markings. Ifthe end is recessed it shall have a flat spot face. The surface ofthe refl
33、ector end of the fastener shall be flat and parallel to theother end. The amount of axial runout on the end depends onfastener size and the accuracy requirement. An area as small as3 mm in diameter may be sufficient. The ends of bolts withthrough center holes may be prepared adjacent to the holes,wi
34、th the transducer locations marked.7.2.1 Do not remove grade markings indiscriminately.Document and maintain grade marking removals.7.3 Measure average fastener temperature within 1C, inaccordance with instructions in the instrument operatingmanual.7.4 Transducer Placement:7.4.1 Apply a suitable aco
35、ustic couplant to allow adequatesound transmission. Glycerine or some other high-viscosityE1685 132couplant is recommended if the fastener has indented grademarkings or if its surface has a few pits.7.4.2 Wipe the coupling surface clean each time couplant isapplied. The amount of couplant to be used
36、 should be sufficientto wet the transducer face but not excessive. Use consistentamounts for successive or repetitive readings.7.4.3 Place the transducer on the flat surface of the bolt to bemeasured. To minimize possible impact damage to the wear-plate portion of the transducer, set it down on its
37、edge and thencarefully rotate it into a flat position. Seat the transducer bylight, back-and-forth finger movements to squeeze out excesscouplant and to obtain the shortest, most stable, length display,or the largest echo signal on the oscilloscope. Repeat thisprocess several times to ensure repeata
38、bility.7.4.4 To ensure repeatable readings always return the trans-ducer to the same position during the measurement process.This location may be marked on the end of the fastener, and theidentification/serial number may be noted for a relative posi-tion. See Appendix X2.7.5 Obtain the reference len
39、gth of the fastener in either theuntensioned or tensioned condition. Record the referencelength for future comparisons. Ensure that the fastener in theuntensioned condition is physically loose.7.6 If the reference length was determined in the unten-sioned condition, tighten the fastener. If the refe
40、rence lengthwas determined in the tensioned condition, unload the fastener.7.7 Measure the change in length of the fastener and recordthe value.7.8 Additional measurements may be made at any time inthe future by following 7.1, 7.3, 7.4, and 7.7, and using thereference length as measured in accordanc
41、e with 7.5.8. Report8.1 If a report is required, the following data should beincluded:8.1.1 Type of material measured.8.1.2 The calibration factors in use by the test equipment.These must include the stress factor, the material velocity, andthe temperature factor. See Annex A2.8.1.3 Transducer size,
42、 frequency, and serial number.8.1.4 Model and serial numbers of the pulse-echo bolt-measuring instrument and reference blocks, if applicable.8.1.5 Initial reference length (in millimetres) and the tem-perature at the time of measurement.8.1.6 Change-in-length measurement (in millimetres) andthe temp
43、erature at the time of measurement.9. Keywords9.1 bolts; change-in-length measurements; clamping force;fasteners; residual stress measurements; ultrasonics.ANNEXES(Mandatory Information)A1. INSTRUMENT RESOLUTIONA1.1 Pulse-echo bolt-measuring instruments are designed tomeasure and report the change i
44、n a fasteners length to thenearest 0.0025 or 0.00025 mm. To do this it must be able toresolve 0.0012 or 0.00012 mm. This degree of precision isrequired because a typical bolt tightened to its yield point willstretch only about 0.003 mm/mm of grip length.A2. INSTRUMENT CALIBRATIONA2.1 Calibration is
45、essential for the correct use of a pulse-echo bolt-measuring instrument, and this involves a number ofsteps. First, determine the ability of the instrument to measuretimes of flight accurately by using it to measure severaldimensions on a reference block.A2.2 Next, a sample (one in routine applicati
46、ons, several forcritical applications) of the actual fasteners whose changes inlength are to be measured is loaded in a tensile testing machineor tightened in a load cell. Measure the resulting change inlength of the sample the pulse-echo bolt-measuring instrumentand with another calibrated instrume
47、nt such as the extensom-eter on the testing machine. If the pulse-echo bolt-measuringinstrument will be used on fasteners at various temperatures,conduct additional tests in an oven or cold chamber.A2.3 In order to calibrate a pulse-echo bolt-measuringinstrument, three factors must be used to change
48、 the actualmeasured time of flight to a bolt elongation measurement.These factors depend on the properties of the bolt material.E1685 133A2.3.1 Stress FactorThe elongation (or delta length) mustbe corrected for the effect of stress on sound velocity. (Soundspeed decreases through a metal bolt when i
49、t is elongated by anaxial load.) The correction factor is commonly termed thestress factor and may be expressed in units of m/s/Pa.A2.3.2 Material VelocityThe time of flight is converted toa length measurement using the longitudinal wave velocity inthe unstressed material. This is commonly called the materialvelocity and may be expressed in units of m/s.A2.3.3 Temperature FactorThe change in length of a boltis also affected by temperature, and this is accommodated byusing a ratio that corrects for both the physical and theultrasonic length changes. Th
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