TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
which, in conjunction with the pathlength, gives a
pulse velocity as described previously. The simplest
simple indication of pulse velocity. The pulse
way to utilize mechanical wave transmission data is
velocity can, to various degrees of accuracy, be
to simply record the arrival time and the pathlength
correlated with material properties. In addition,
and calculate an average velocity for the pulse. The
sonic techniques can be used to locate material
recorded data should then be plotted in some
flaws, however, the long wave length that makes a
understandable format. Two dimensional contours
sonic pulse appropriate for testing long expanses of
or three dimensional surface plots are
brick work also increases the minimum size flaw
recommended for direct tests, and x-y plots are
that can be detected.
recommended for indirect tests. Figure 10-8 plots
(1) Equipment. The basic equipment used
the pulse path length against the arrival time for an
for conducting mechanical pulse tests includes a 3
indirect mechanical pulse test. The presence of a
pound modally tuned hammer and an accelerome-
distinct flaw causes a noticeable break in the
ter. Unlike the ultrasonic test equipment, there is
velocity line.
(3) Application. The mechanical pulse tech-
no digital readout of travel time with this equip-
ment, so the signal must be recorded or displayed
nique is best suited to the task of locating flaws and
on an external device. A digital transient recorder
discontinuities such as missing mortar joints and
can be used to record both the hammer input signal
large cracks and establishing relative quality of
and the accelerometer output signals. The signals
masonry from one location to another. Indirect
can then be saved on floppy disks through a
tests are useful for determining the average velocity
portable computer. The testing apparatus is shown
through a single outer wythe of masonry, and for
in figure 10-7. Alternatively, an oscilloscope may
locating flaws in the outer wythes. Direct tests are
be used to measure travel time.
able to locate flaws and voids in interior wythes
(2) Use. Test results for mechanical pulse
and collar joints. The mechanical pulse technique is
tests are much the same as those for ultrasonic
superior to the ultrasonic system for flaw detection
10-9
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