DAKOTA ULTRASONICS MAX II Operation Manual page 86

Following steps determine the Sonic Stress Factor for bolts of a specific bolt material
and specific geometry by measurement of the actual change in bolt length.
Required Equipment:
NOTES:
 The Dakota Ultrasonics MAX II must be calibrated, or zeroed, as described in the
Zero Calibration procedure section Error! Reference source not found..
 The Velocity Calibration should be performed prior to determining the Stress
Factor. Refer to section 10.2.
 The sample bolts must be left to soak in the controlled temperature environment
for a period of not less than 24 hours. Care must be taken through out the
measurement process to avoid significant change in the bolt temperature due to
handling of the sample bolts, or the process of applying load.
 The mechanical apparatus for measurement of length must be calibrated in
accord with governing QA procedures. The device should be configured so that
minimum handling of the sample bolts will be required during the measurement
process.
Determination of the Sonic Stress Factor is accomplished by solving the equation:
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 A laboratory or room in which the temperature can be maintained at
between 66 to 70 F.
 A means of applying load to the bolt. Ideally this would be a tensile load
machine, capable of measuring the applied load to within 100 lbs.
However, since the actual value of the applied load is not used in
calculating the stress factor, any means of applying an approximate load
to the bolt will suffice. This includes tightening the bolt against a fixture
that simulates the actual joint. A mechanical means of traceable
measurement of the physical length of the sample fasteners at various
tensile loads to an accuracy of plus or minus 0.0001 inch. Examples of
such devices include the following
 Length measurement function of sophisticated tensile test machine
 Mechanical or electronic height gages
 Averaged values of length measurement with mechanical and
electric micrometers.
 A Dakota Ultrasonics MAX II Ultrasonic Bolt Tension Monitor.
 A minimum of three sample bolts which are representative of the bolt type
and geometry for which the Sonic Stress Factor is to be determined.
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