Operating Manual

Chapter 6: Fastener Geometry
Page 22 Guide to Ultrasonic Inspection of Fasteners
The effective length is calculated differently depending
on the fastener application. The directions for calculat-
ing the effective length in four different cases are out-
lined in Figures 6-2 through 6-5. Note that the resulting
values for effective length are approximate and may vary
due to certain other factors. For example, consider an
application using a bolt in a blind hole. Suppose the
material strength of the bolt is greater than the threaded
hole. The weaker threads in the hole will flex more than
the threads of the bolt, and the effective length will be
longer than if the materials were of the same material.
For the best accuracy of load or stress readings, cali-
brate the BoltMike for the specific application. This will
cancel errors due to effective length uncertainty. In this
approach a calibration group is formed (using fasteners
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.
Refer to Figures 6-2 through 6-5 to identify the fasten-
ing system closest to the one you are evaluating. Then
follow the instructions in the applicable figure to calcu-
late effective loading. The figures show:
• Stud fastening system (Figure 6-2)
• Through bolt fastening system (Figure 6-3)
• Bolt (screw) turned into a threaded hole
(Figure 6-4)
• Stud turned into a threaded hole (Figure 6-5)
FIGURE 6-2—This is a typical stud configuration. The effective length of a stud with nuts on each end is found by
adding the stud diameter to the clamp length.
FIGURE 6-3—This is a typical through bolt configuration. The effective length of a bolt with a single nut is found by
adding half the diameter to one-third the diameter (5/6 of the diameter total) to the clamp length.