ASTM E1685-00
(Practice)Standard Practice for Measuring the Change in Length of Fasteners Using the Ultrasonic Pulse-Echo Technique
Standard Practice for Measuring the Change in Length of Fasteners Using the Ultrasonic Pulse-Echo Technique
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1.1 This practice covers a procedure for measuring changes in length of threaded fasteners using conventional ultrasonic, pulse-echo bolt-measuring instrumentation which has been properly calibrated.
1.2 This procedure is normally intended for metal bolting 0.25 in. (6.4 mm) or more in nominal diameter with effective length-to-diameter ratios of 2:1 or greater.
1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E1685–00
Standard Practice for
Measuring the Change in Length of Fasteners Using the
Ultrasonic Pulse-Echo Technique
This standard is issued under the fixed designation E 1685; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2.2.1 Discussion—This quantity lies somewhere between
the overall length of the bolt and the grip length. It is usually
1.1 This practice covers a procedure for measuring changes
estimated as the grip length plus one half the thickness of the
in length of threaded fasteners using conventional ultrasonic
head and one half the thickness of the nut.
pulse-echo bolt-measuring instrumentation which has been
3.2.3 longitudinal wave—those waves in which the particle
properly calibrated.
motion of the material is in the same direction as the wave
1.2 This procedure is normally intended for metal bolting
propagation.
0.25 in. (6.4 mm) or more in nominal diameter with effective
3.2.4 pulse-echo bolt-measuring equipment—an assembly
length-to-diameter ratios of 2:1 or greater.
of ultrasonic instruments designed specifically to measure
1.3 This standard does not purport to address all of the
changes in the lengths of bolts. See Appendix X1.
safety concerns, if any, associated with its use. It is the
3.2.5 reference length—the ultrasonic time of flight in the
responsibility of the user of this standard to establish appro-
test specimen multiplied by a reference propagation velocity.
priate safety and health practices and determine the applica-
3.2.6 reference propagation velocity—thevelocityofpropa-
bility of regulatory limitations prior to use.
gation of the ultrasonic wavefront in a calibration test block or
2. Referenced Documents
in the bolts whose changes of length are being measured.
3.2.7 time of flight—the measured time interval between the
2.1 ASTM Standards:
launching of an ultrasonic pulse at the start of a path of travel
E 6 Terminology Relating to Methods of Mechanical Test-
and the reception of the pulse at the end of the path.
ing
E 1316 Terminology for Nondestructive Examinations
4. Summary of Practice
E 1544 Practice for Construction of a Stepped Block and Its
4.1 This practice describes a procedure for determining the
Use to Estimate Errors Produced by Speed-of-Sound
2 change in length of a threaded fastener due to a change in
Measurement Systems for Use on Solids
tension in the fastener. Measurements of the ultrasonic time of
3. Terminology flight are made before and after the fastener tension is changed,
and a calculation of the change in length is made from the
3.1 The definitions in this practice are in accordance with
change in the time of flight.
Terminology E 6 and Section I of Terminology E 1316.
4.1.1 Brief bursts of ultrasound (pulses) are generated by
3.2 Definitions of Terms Specific to This Standard:
applying high-voltage electrical signals to an electroacoustic
3.2.1 change in length—physical change in length of a
transducer having a resonant frequency in the 5 to 10-MHz
threadedfastenerduetoachangeintensionwithinthefastener.
range. The pulses enter the bolt through the transducer/bolt
3.2.2 effective length—the length of a bolt that is responsive
interface, travel to the far end of the bolt, and reflect back
to stress.
(echo) to the transducer. The time of flight required for the
signal to make its round-trip is measured electronically. By
measuring the change in the time of flight due to a change in
This practice is under the jurisdiction ofASTM Committee E28 on Mechanical
tension within the bolt, the equipment can determine the
Testing and is the direct responsibility of Subcommittee E28.13 on Residual Stress
Measurement.
change in the length of the bolt due to the change in tension.
Current edition approved Oct. 10, 2000. Published January 2001. Originally
Compensation for the direct effect of stress on the propagation
published as E 1685–95. Last previous edition E 1685–95.
2 velocity in the bolt is automatically done by a computer or
Annual Book of ASTM Standards, Vol 03.01.
Annual Book of ASTM Standards, Vol 03.03. microprocessor within the equipment.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1685
4.2 This procedure is used on fasteners as they are tightened block, two metal bars of unequal length, and single bars of
within their elastic limits; or on previously tightened fasteners known acoustic velocity. The path length of the standard must
as they are loosened. The latter can have been tightened past be determined by a technique of higher accuracy. See Practice
yield. E 1544. Calibration of standards should be traceable to NIST.
5. Significance and Use
7. Procedure
5.1 The techniques described provide for the indirect mea-
7.1 Theperformanceofthepulse-echoinstrumentshouldbe
surement of change in length of a fastener. Such measurements
verified or adjusted to a reference standard in accordance with
are made from one end of the specimen without requiring
the manufacturer’s specifications. See Annex A2.
access to the rear surface.
7.1.1 In noncritical applications, where uncertainties
5.2 The equipment is field portable and should be used in
smallerthan 615 %ofthechangeinlengtharenotrequired,an
the manner prescribed by the manufacturer. Common uses
instrument calibrated on one bolt of a given material can be
include monitoring changes in length of fasteners and as a tool
used on other bolts of the same material but having different
for industrial quality control. Current applications include
shapes.
fasteners used in turbines, petrochemical pressure vessels,
7.1.2 At the other extreme, if the instrument is to be used on
aircraft, automotive manufacturing, general bolting within the
bolts in critical, safety-related applications or where uncertain-
nuclear industry, structural steel connections, laboratory test-
ties of 61 to 3 % are required, or both, consideration should be
ing, and so forth.
given to recalibration on a statistically significant sample of
each new lot of bolts.
6. Apparatus
7.2 Fastener Preparation—For reliable ultrasonic measure-
6.1 Pulse-Echo Instrument—Forultrasonicmeasurementsof
ments the fastener must have suitable finish and geometry
thechangeinlengthofbolts,anylongitudinal-wavepulse-echo
requirements. One end must be accessible for transducer
ultrasonic instrument capable of reporting calculated changes
placement. This end must, for at least the diameter of the
in length is acceptable provided that its accuracy and precision
transducer, be flat and perpendicular to the axis of the bolt. A
satisfy the requirements set forth in Annex A1. The major
machined surface with a finish of 125 RMS or better is
components of suitable instruments are as follows:
recommended, exclusive of indented grade markings. Raised
6.1.1 Pulser/transmitter, a means of generating electrical
grade markings must be removed. (See Note 1.) If the end is
pulses to excite an acoustic transducer.
recessed it must have a flat spot face. The reflector end of the
6.1.2 Receiver/detector, a means of amplifying and detect-
fastener must have a flat surface parallel to the other end. The
ing the returning back-wall echo.
amount of axial runout on the end is dependent on fastener size
6.1.3 Time-base Controller, a means of measuring changes
and the accuracy requirement. An area as small as ⁄8 in. (3
in ultrasonic time of flight.
mm) in diameter may be sufficient. The ends of bolts with
6.1.4 Acoustic Transducer, a means of sending and receiv-
through center holes may be prepared adjacent to the holes,
ing ultrasonic waves. Experience has shown that transducers
with the transducer locations marked.
with resonances in the 5 to 10-MHz frequency range are
usually satisfactory. In general, select an acoustic transducer
NOTE 1—Grade markings should not be moved indiscriminately. Docu-
mentation of grade marking removals should be created and maintained.
having an element of the largest diameter available while not
exceeding the minimum body diameter of the bolt.
7.3 Measure average fastener temperature within 1°C, in
6.2 Other Apparatus:
accordance with instructions in the instrument operating
6.2.1 Couplant—For longitudinal pulse-echo measure-
manual.
ments, a liquid is required to couple ultrasound between the
7.4 Transducer Placement:
transducer and the fastener. Of the couplants commonly used,
7.4.1 Apply a suitable acoustic couplant to allow adequate
where applicable a 50/50 glycerine/water mix often provides
sound transmission. Glycerine or some other high-viscosity
optimal results. Light oil or standard commercially available
couplant is recommended if the fastener has indented grade
ultrasonic couplants are also satisfactory.
markings or if its surface has a few pits.
6.2.2 Oscilloscope—For optimal adjustment of the appara-
NOTE 2—The coupling surface must be wiped clean each time couplant
tus, the use of an oscilloscope is necessary. The oscilloscope
is applied. The amount of couplant to be used should be sufficient to wet
must have two input channels, two traces, external triggering,
thetransd
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