1、Designation: E 1685 00 (Reapproved 2006)Standard Practice forMeasuring the Change in Length of Fasteners Using theUltrasonic Pulse-Echo Technique1This standard is issued under the fixed designation E 1685; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 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 covers a procedure for measuring changesin length of threaded fasten
3、ers using conventional ultrasonicpulse-echo bolt-measuring instrumentation which has beenproperly calibrated.1.2 This procedure is normally intended for metal bolting0.25 in. (6.4 mm) or more in nominal diameter with effectivelength-to-diameter ratios of 2:1 or greater.1.3 This standard does not pur
4、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:2E6
5、 Terminology Relating to Methods of Mechanical Test-ingE 1316 Terminology for Nondestructive ExaminationsE 1544 Practice for Construction of a Stepped Block and ItsUse to Estimate Errors Produced by Speed-of-SoundMeasurement Systems for Use on Solids3. Terminology3.1 The definitions in this practice
6、 are in accordance withTerminology E6and Section I of Terminology E 1316.3.2 Definitions of Terms Specific to This Standard:3.2.1 change in lengthphysical change in length of athreaded fastener due to a change in tension within the fastener.3.2.2 effective lengththe length of a bolt that is responsi
7、veto stress.3.2.2.1 DiscussionThis quantity lies somewhere betweenthe overall length of the bolt 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 wavethose waves in which the particlemotion
8、of the material is in the same direction as the wavepropagation.3.2.4 pulse-echo bolt-measuring equipmentan assemblyof ultrasonic instruments designed specifically to measurechanges in the lengths of bolts. See Appendix X1.3.2.5 reference lengththe ultrasonic time of flight in thetest specimen multi
9、plied by a reference propagation velocity.3.2.6 reference propagation velocitythe velocity of propa-gation of the ultrasonic wavefront in a calibration test block orin the bolts whose changes of length are being measured.3.2.7 time of flightthe measured time interval between thelaunching of an ultra
10、sonic pulse at the start of a path of traveland the reception of the pulse at the end of the path.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 of
11、flight are made before and after the fastener tension is changed,and a 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 electroacoustictransducer having a resonant
12、 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. Bymeasuring the change in the
13、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 propagation1This practice is under the jurisdiction of ASTM Committee E28 on MechanicalTesting an
14、d is the direct responsibility of Subcommittee E28.13 on Residual StressMeasurement.Current edition approved Dec. 1, 2006. Published January 2007. Originallyapproved in 1995. Last previous edition approved in 2000 as E 168500.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orco
15、ntact 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.velocity in the bolt
16、 is automatically done by a computer ormicroprocessor 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 t
17、echniques described provide for the indirect 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 u
18、sesinclude monitoring changes in length 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, labor
19、atory test-ing, and so forth.6. Apparatus6.1 Pulse-Echo InstrumentFor ultrasonic measurementsofthe change in length of bolts, any longitudinal-wave pulse-echoultrasonic instrument capable of reporting calculated changesin length is acceptable provided that its accuracy and precisionsatisfy the requi
20、rements set forth in Annex A1. The majorcomponents of suitable instruments are 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 Contr
21、oller, a means of measuring 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 transducerhav
22、ing an element of the largest diameter available while notexceeding the minimum body diameter of the bolt.6.2 Other Apparatus:6.2.1 CouplantFor longitudinal pulse-echo measure-ments, a liquid is required to couple ultrasound between thetransducer and the fastener. Of the couplants commonly used,wher
23、e applicable a 50/50 glycerine/water mix often providesoptimal results. Light oil or standard commercially availableultrasonic couplants are also satisfactory.6.2.2 OscilloscopeFor optimal adjustment of the appara-tus, the use of an oscilloscope is necessary. The oscilloscopemust have two input chan
24、nels, two traces, external triggering,and a dual time base with delayed sweep capability. Itsbandwidth should be at least 35 MHz or its equivalent.6.2.2.1 Pulse-echo instruments with built-in oscilloscopedisplay capabilities must have sampling speeds equivalent to atleast ten times the transducer fr
25、equency for satisfactory signaldisplay.6.2.3 Standard Reference Blocks, for periodic recalibrationof the pulse-echo 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 include
26、 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 PracticeE 1544. Calibration of standards should be traceable to NIST.7. Procedure7.1 The performance of the pulse-echo
27、instrument should beverified or adjusted to a reference standard in accordance withthe manufacturers specifications. See Annex A2.7.1.1 In noncritical applications, where uncertaintiessmaller than 615 % of the change in length are not required, aninstrument calibrated on one bolt of a given material
28、 can beused on other bolts of the same material but having differentshapes.7.1.2 At the other extreme, if the instrument is to be used onbolts in critical, safety-related applications or where uncertain-ties of 61 to 3 % are required, or both, consideration should begiven to recalibration on a stati
29、stically significant sample ofeach new lot of bolts.7.2 Fastener PreparationFor reliable ultrasonic measure-ments the fastener must have suitable finish and geometryrequirements. One end must be accessible for transducerplacement. This end must, for at least the diameter of thetransducer, be flat an
30、d perpendicular to the axis of the bolt. Amachined surface with a finish of 125 RMS or better isrecommended, exclusive of indented grade markings. Raisedgrade markings must be removed. (See Note 1.) If the end isrecessed it must have a flat spot face. The reflector end of thefastener must have a fla
31、t surface parallel to the other end. Theamount of axial runout on the end is dependent on fastener sizeand the accuracy requirement. An area as small as18 in. (3mm) in diameter may be sufficient. The ends of bolts withthrough center holes may be prepared adjacent to the holes,with the transducer loc
32、ations marked.NOTE 1Grade markings should not be moved indiscriminately. Docu-mentation of grade marking removals should be created and maintained.7.3 Measure average fastener temperature within 1C, inaccordance with instructions in the instrument operatingmanual.7.4 Transducer Placement:7.4.1 Apply
33、 a suitable acoustic couplant to allow adequatesound transmission. Glycerine or some other high-viscositycouplant is recommended if the fastener has indented grademarkings or if its surface has a few pits.NOTE 2The coupling surface must be wiped clean each time couplantis applied. The amount of coup
34、lant to be used should be sufficient to wetthe transducer face but not excessive. Consistent amounts must be used forsuccessive or repetitive readings.7.4.2 Place the transducer on the flat surface of the bolt to bemeasured. To minimize possible impact damage to the wear-plate portion of the transdu
35、cer, it should be set down on itsedge and then carefully rotated to a flat position. The trans-ducer is seated by light, back-and-forth finger movements tosqueeze out excess couplant and to obtain the shortest, mostE 1685 00 (2006)2stable, length display, or the largest echo signal on theoscilloscop
36、e. Repeat this process several times to ensurerepeatability.7.4.3 For repeatable readings the transducer must always bereturned to the same position during the measurement process.This location may be marked on the end of the fastener, and theidentification/serial number can be noted for a relative
37、position.See Appendix X2.7.5 Obtain the reference length of the fastener in either theuntensioned or tensioned condition. Record the referencelength for future comparisons.NOTE 3The untensioned condition must be physically loose.7.6 If the reference length was determined in the unten-sioned conditio
38、n, tighten the fastener. If the reference 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 therefer
39、ence length as measured in accordance 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.
40、 See Annex A2.8.1.3 Transducer size, frequency, and serial number.8.1.4 Model and serial numbers of the pulse-echo instru-ment and reference blocks, if applicable.8.1.5 Initial reference length (in inches or millimetres) andthe temperature at the time of measurement.8.1.6 Change-in-length measuremen
41、t (in inches or millime-tres) and the temperature 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
42、designedto measure and report the change in a fasteners length to thenearest 0.0001 or 0.00001 in. (0.0025 or 0.00025 mm). To dothis it must be able to resolve 0.00005 or 0.000005 in. (0.0012or 0.00012 mm). This degree of precision is required becausea typical bolt tightened to its yield point will
43、stretch only about0.003 in./in. (0.003 mm/mm) of grip length.A2. INSTRUMENT CALIBRATIONA2.1 Calibration is essential for the correct use of apulse-echo bolt-measuring instrument, and this involves anumber of steps. First, the ability of the instrument to measuretimes of flight accurately must be det
44、ermined by using it tomeasure several dimensions on a reference block.A2.2 Next, a sample (one in routine applications, severalfor critical applications) of the actual fasteners whose changesin length are to be measured is loaded in a tensile testingmachine or tightened in a load cell. The resulting
45、 change inlength of the sample is measured with the pulse-echo instru-ment and with another calibrated instrument such as theextensometer on the testing machine. If the bolt-measuringinstrument is to be used on fasteners at various temperatures,additional tests involving an oven or cold chamber are
46、alsorequired.A2.3 In order to calibrate a pulse-echo bolt-measuringinstrument, factors must be used to change the actual measuredtime of flight to a bolt elongation measurement. These factorsare dependent on the properties of the bolt material.A2.3.1 Stress FactorThe elongation (or delta length)must
47、 be corrected for the effect of stress on sound velocity.(Sound speed decreases through a metal bolt when it iselongated by an axial load.) The correction factor is commonlytermed the stress factor and may be expressed in units ofin./s/psi or m/s/Pa.A2.3.2 Material VelocityThe time of flight is conv
48、erted toa length measurement using the longitudinal wave velocity inthe unstressed material. This is commonly called the materialvelocity and may be expressed in units of in./s or m/s.A2.3.3 Temperature FactorThe change in length of a boltis also affected by temperature, and this is accommodated byu
49、sing a ratio which corrects for both the physical and theultrasonic length changes. This ratio is commonly called thetemperature factor and may be expressed in units of in./s/ F orm/s/ C.A2.3.3.1 Different commercial pulse-echo bolt-measuringinstruments use different techniques to compensate for theseeffects. The manufacturers calibration procedures should beused. Once the calibration factors have been established for aE 1685 00 (2006)3given fastener material and shape the instrument may berecalibrated for that fastener using reference blocks only.APPENDIXES
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