|
Ultrasonic Testing
Ultrasonic (high frequency) waves are
emitted from a transducer into an object and the returning waves are
analyzed. If an impurity or a crack is present, the sound will
bounce off of them and be seen in the returned signal. In order to
create ultrasonic waves, the transducer contains a thin disk made of a
crystalline material with piezoelectric properties, such as quartz.
When electricity is applied to piezoelectric materials, they begin to
vibrate, using the electrical energy to create movement. Since waves
travel in every direction from the source, an absorptive material is
layered behind the crystal to keep the waves from going backwards into the
transducer and interfering with its reception of returning waves.
One type of ultrasonic testing places the transducer in contact
with the test object. If the transducer is placed flat on a surface to locate defects,
the waves will go straight into the material, bounce off a flat back wall and return
straight to the transducer. The animation on the right, developed by NDTA,
Wellington, New Zealand, illustrates that sound waves propagate into a object
being tested and reflected waves return from discontinuities along the sonic
path. Some of the energy will be absorbed by the material, but some of it will
return to the transducer. When the
mechanical sound energy comes back to the transducer, it is converted into
electrical energy. Just as the piezoelectric crystal converted electrical
energy into sound energy, it can also do the reverse. The mechanical
vibrations in the material couple to the piezoelectric crystal which, in
turn, generates electrical current.
Ultrasonics can be used to
characterize flaws, cracks, delaminations, voids and inclusions. We
can inspect welds for voids, cracks, porosity, missed seams or lack of
penetration. Epoxy curing or ceramic sintering can be monitored.
Cracks, inclusions and voids can be detected in various materials.
We can measure the thickness of metal, ceramic, or polymer parts.
Applications:
- Find Hidden Defects; voids, cracks, inclusions
- Analyze Failures
This image is an example of using ultrasonic testng to detect weld
defects. the image on the left is the defect standard with four flat
bottom holes (blue). The image on the right is the sample tested;
blue indicates a defect.
|
