Operating Manual

Chapter 7: Material Constants
Page 26 Guide to Ultrasonic Inspection of Fasteners
the CUSTOM material mode is activated, you edit the
material name and any material property to match those
of your non-standard material type.
Even if you are able to obtain published constants for a
non-standard material type, it is best to perform some
amount of testing to determine the accuracy of the re-
sulting measurements.
Another way to determine the bolt type is to measure a
group of bolts and use the built in calibration function to
determine which material type gives the minimum error.
In this approach a calibration group is formed (using fas-
teners that are the same or similar to the ones being
tested). The fasteners are inserted in a fixture that loads
them at the same effective length with a known quantity
of load.
7.4 Material Variations
Many materials exhibit very uniform material constants.
However, material constants in samples of some materi-
als will vary widely.
A material’s elastic modulus has a direct effect on that
material’s acoustic velocity (Vo) and stress factor (K).
Hardening or heat treatment of the material or relaxation
of the hardening will affect the accuracy of the standard
values of these constants. In fact, the constants in some
materials can vary dramatically as a result of work hard-
ening of the material. Therefore, it is strongly suggested
that a sample of the bolts be tested to confirm the accu-
racy of the material properties you’ve chosen under ac-
tual loading conditions.