ASTM E1685-20

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1685 − 13 E1685 − 20
Standard Practice for
Measuring the Change in Length of FastenersBolts Using
the Ultrasonic Pulse-Echo Technique
This standard is issued under the fixed designation E1685; the number immediately following the designation indicates the year of
original 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. Scope*
1.1 This practice covers a procedure for measuring changes in length of threaded fastenersbolts using conventional ultrasonic
pulse-echo bolt-measuring instrumentation which has been properly calibrated.the ultrasonic pulse-echo technique.
1.2 This procedure is normally intended for metal bolting 6.3 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 as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E6 Terminology Relating to Methods of Mechanical Testing
E111 Test Method for Young’s Modulus, Tangent Modulus, and Chord Modulus
E1316 Terminology for Nondestructive Examinations
E1544 Practice for Construction of a Stepped Block and Its Use to Estimate Errors Produced by Speed-of-Sound Measurement
Systems for Use on Solids (Withdrawn 2012)
2.2 ASME Standards:
ASME B46.1–2009 Surface Texture (Surface Roughness, Waviness, and Lay)
3. Terminology
3.1 The definitions of calibration, extensometer system, metrological traceability, reference standard, testing machine, and
verification, in this practice are in accordance with used as defined in Terminology E6 and Section I of Terminology E1316.
This practice is under the jurisdiction of ASTM Committee E28 on Mechanical Testing and is the direct responsibility of Subcommittee E28.13 on Residual Stress
Measurement.
Current edition approved Nov. 1, 2013Oct. 1, 2020. Published January 2014December 2020. Originally approved in 1995. Last previous edition approved in 20062013
as E1685–00(2006).E1685–13. DOI: 10.1520/E1685-13.10.1520/E1685-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1685 − 20
3.2 The definitions of attenuation, couplant, echo, longitudinal wave, pulse, pulse echo method, reference block, reflector,
resolution, time-of-flight, transducer, and ultrasonic are used as defined in Section I of Terminology E1316.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 change in length [L], n—physical change in length of a threaded fastener due to a change in tension within the fastener.
3.3.2 effective length [L], n—the length of a bolt that is responsive to stress. stress, defined here as the bolt length between head
and nut plus half the thickness of the head plus half the thickness of the nut.
3.2.2.1 Discussion—
This quantity lies somewhere between the overall length of the bolt and the grip length. It is usually estimated as the grip length
plus one half the thickness of the head and one half the thickness of the nut.
3.2.3 longitudinal wave, n—those waves in which the particle motion of the material is in the same direction as the wave
propagation.
3.3.3 pulse-echo bolt-measuring instrument—an assembly of ultrasonic instruments designed specifically to measure changes in
the lengths of bolts. See Appendix X1.
3.2.5 reference length [L], n—the ultrasonic time of flight in the test specimen multiplied by a reference propagation velocity.
-1
3.3.4 reference propagation velocity, [LT length [L], ], n—the velocity of propagation of the ultrasonic wavefront in a calibration
test block or in the bolts whose changes of length are being measured.ultrasonic time-of-flight in the test specimen multiplied by
a reference propagation velocity.
3.3.4.1 Discussion—
The reference propagation velocity is the velocity of propagation of the ultrasonic wavefront in a calibration test block or in the
bolts whose changes of length are being measured.
3.2.7 time of flight, [T], n—the measured time interval between the launching of an ultrasonic pulse at the start of a path of travel
and the reception of the pulse at the end of the path.
4. Summary of Practice
4.1 This practice describes a procedure for determining the change in length of a threaded fastener due to a change in tension in
the fastener. Measurements of the ultrasonic time of flight time-of-flight are made before and after the fastener tension is changed,
and a calculation of the change in length is made from the change in the time of flight.time-of-flight.
4.1.1 Brief bursts of ultrasound (pulses) are generated by applying high-voltage electrical signals to an electroacoustic transducer
having a resonant frequency in the 5 1 MHz to 10-MHz range. range (typical). The pulses enter the bolt through the transducer/bolt
interface, travel to the far end of the bolt, and reflect back (echo) to the transducer. The time of flight time-of-flight required for
the signal to make its round-trip is measured electronically. By measuring the change in the time of flight time-of-flight due to a
change in tension within the bolt, the equipment can determine the change in the length of the bolt due to the change in tension.
Compensation bolt and compensating for the direct effect of stress on the propagation velocity in the bolt is automatically done
by a computer or microprocessor within the equipment.the change in length of the bolt due to the change in tension can be
determined.
4.2 This procedure is used on fasteners as they are tightened within their elastic limits; or on previously tightened fasteners as they
are loosened. The latter can have been tightened past yield.
5. Significance and Use
5.1 The techniques described provide for the indirect measurement of change in length of a fastener. Such measurements are made
from one end of the specimen without requiring access to the rear surface.
5.2 The equipment is field portable and should be used in the manner prescribed by the manufacturer. Common uses include
monitoring Ultrasonic Pulse Echo technique is used to monitor changes in length of fasteners and as a tool for industrial quality
E1685 − 20
control. Current applications Applications include fasteners used in turbines, petrochemical pressure vessels, aircraft, automotive
manufacturing, general bolting within the nuclear industry, structural steel connections, laboratory testing, and so forth.and
laboratory testing.
6. Apparatus
6.1 Pulse-echo bolt-measuring instrument—For ultrasonic measurementsof measurements of the change in length of bolts, any
longitudinal-wave the pulse-echo ultrasonicbolt-measuring instrument shall be capable of reporting determining the calculated
changeschange in length is acceptable provided that its to the accuracy and precision satisfy the requirements set forth in Annex
A1. The major components of suitable instruments are as follows:
6.1.1 Pulser/transmitter, a means of generating electrical pulses to excite an acousticultrasonic transducer.
6.1.2 Receiver/detector,Receiver, a means of amplifying and detecting the returning back-wall echo.
6.1.3 Time-base Controller, a means of measuring changes in ultrasonic time of flight.time-of-flight.
6.1.4 Data analysis computer, a computer or microprocessor for processing the ultrasonic data for determination of the material
stress level from the measured fastener strain.
6.1.4.1 The pulser/transmitter, receiver/detector, time-base controller, and computer may be integrated into a unified system or
instrumented together from separate components.
6.1.5 AcousticUltrasonic Transducer, a means of sending and receiving ultrasonic waves. Experience has shown that transducers
with resonances in the 5 to 10-MHz frequency range are usually satisfactory. In general, select an acoustic transducer having an
element of the largest diameter available while not exceeding the minimum body diameter of the bolt.The resonance of the
transducer should be in the range 1MHz to 10 MHz.
NOTE 1—The choice of transducer frequency is determined by the length of fastener under investigation and dependent on two primary factors: signal
clarity and attenuation.
6.1.5.1 The ultrasonic frequency should be high enough to produce an ultrasonic pulse that is sufficiently short so that the
ultrasonic reflections from the far end of the fastener occurs after the ultrasonic reflection from entry surface has ended.
6.1.5.2 Conversely, the frequency should be low enough so that the signal reflected from the far end of the fastener is large enough
for successful detection.
NOTE 2— In general, short fasteners require higher frequency, whereas long fasteners require low frequencies.
6.1.5.3 The diameter of the ultrasonic transducer should be as large as possible, but shall not be larger than the minimum body
diameter of the bolt.
6.1.6 Pulse-echo bolt-measuring instruments are designed to measure and report the change in length of a bolt to the nearest
0.0025 mm or 0.00025 mm. To do this the instrument resolution shall be 0.0012 mm or 0.00012 mm.
NOTE 3—This degree of precision is required because a typical bolt tightened to yield will stretch only about 0.003 mm/mm of grip length.
6.2 Other Apparatus:
6.2.1 Couplant—For longitudinal pulse-echo measurements, a liquid is required to couplea liquid or glue that couples ultrasound
between the transducer and the fastener. Of the couplants commonly used, where applicable a 50/50 glycerine/water mix often
provides optimal results. Light oil or standard commercially available ultrasonic couplants are also satisfactory.
NOTE 4—A 50/50 glycerine/water mix, light oil or standard commerically available couplants and glues can provide satisfactory results.
E1685 − 20
6.2.2 Oscilloscope—For optimal adjustment of the apparatus, the use of an oscilloscope is necessary. The oscilloscope must have
two input channels, two traces, external triggering, 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-in oscilloscope display capabilities must have sampling speeds
equivalent to at least ten times the transducer frequency for satisfactory signal display.
6.2.3 Standard Reference Blocks, for periodic recalibration of the pulse-echo bolt-measuring instrument.
6.2.3.1 A glass or metallic reference block of known length and appropriate surface roughness, shape, thickness, and parallelism
is recommended. Acceptable standards include a glass block, two metal bars of unequal length, and single bars of known acoustic
velocity. The path length of the standard must be determined by a technique of higher accuracy. See Practice E1544. The calibration
of instruments and standards should be traceable to national standards, where systems of traceability exist.
7. Procedure
7.1 The performance of the pulse-echo bolt-measuring instrument should be verified or adjusted calibrated to a reference standard
in accordance with the manufacturer’s specifications. See Annex A2A1.
7.1.1 In noncritical applications, where uncertainties smallergreater than 615 %63 % of the change in length are not required,
acceptable, an instrument calibrated on one bolt of a given material may used on other bolts of the same material but having
different shapes.
7.1.2 In critical, safety-related applications or where uncertainties of less than 3 % are required, or both, the pulse-echo
bolt-measuring instrument should be recalibrated on a statistically significant sample of each new lot of bolts.
7.2 Fastener Preparation—To ensure reliable ultrasonic measurements the The finish and geometry of the fastener shall be
suitable. prepared to ensure reliable ultrasonic measurements. One end shall be acc
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