2. NDT- UT
• Ultrasonic testing uses pulses of high-frequency sound energy
to detect surface and subsurface cracks and other defects. These
pulses come from a transducer or probe, which a technician
manually moves over the surface of the component under
inspection. The probe emits ultrasonic waves into the material
at precise intervals and a set angle; when a sound wave
encounters a defect, some of that energy is reflected like an
echo.
• A probe sends a sound wave into a test material. There are two
indications, one from the initial pulse of the probe, and the
second due to the back-wall echo. A defect creates the third
indication and simultaneously reduces the amplitude of the
back-wall indication. The depth of the defect is determined by
the ratio D/Ep
3. UT methods used in aircraft inspections
• A conventional or standard UT probe is capable of generating and receiving
a single ultrasonic sound wave. The focal point and angle of the beam are
fixed, which can make it more difficult to locate and visualize flaws especially
in components with complex geometries like engine fan blades. The use of a
custom-shaped probe can help ensure the accuracy of such inspections.
• Phased-array UT is an advanced inspection method that uses multiple
individual elements (typically from 16 to 64) in a single probe. By exciting
each element in a controlled manner, a phased-array UT instrument can
produce a precise beam shape and generate two and three-dimensional views
of a flaw with greater speed and accuracy. This is a significant advantage for
inspection of complex geometries in order to improve probability of detection
(POD) and to better characterize potential indications.
