TM 1-1500-204-23-11
tanks, normal safety precautions apply. Personnel who
irst approaches to damage assessment of bonded
perform visual inspections should have good eyesight
structures. Tap testing is widely used to evaluate the
and should be familiar with the appearance of the
condition of laminated and bonded structures. The
defects they are expected to ind. Also, surfaces to be
method consists of lightly tapping the surface of the
inspected should be clean and free of all conditions
part with a coin or other suitable object and listening for
that mask or obscure defects (e.g., dirt, paint, or
variations in the sound. Acoustic impact NDI is useful
other coatings).
only when the part being investigated produces distinct
differences in sound when laws are present. It has
relatively poor resolution capability and is affected by
ambient conditions (temperature, humidity, background
noise, etc.), changes in material density or thickness,
Sandwich structures with low density cores
and the presence of structural discontinuities (cutouts,
are particularly sensitive to impact damage.
reinforcements, fasteners, etc.). Figure 5-1 shows the
typical dimensions of a tap hammer.
b. Tap Testing. Judicious tapping of suspected
locations, along with careful observation, are the
5-2
