Through
a Small Business Innovative Research Project sponsored by the U.S. Army
Tank Armament and Automotive Command (TACOM), NDTA has developed the Acousto-Ultrasonic
(AU) technology as an inspection technique for use in the government and
industry.
The AU technology consists of sending low frequency acoustic pulses at a predetermined angle of incidence into a material under inspection. These acoustic pulses travel through the material and are reflected by the different interfaces inside the sample. If a discontinuity (delamination, debond etc.) is present inside the material, the reflected acoustic energy changes, revealing the presence of the discontinuity.
Originally intended for the inspection of multifunctional composite armor, NDTA has been using the AU technology extensively in the inspection of other critical composite structures such as:
- Graphite/epoxy, foam-core composite centrifugal arms for simulators
- Offshore platforms Fiber Reinforced Polymers fire system piping
- LAU 7 composite nitrogen receivers
- Type III Navy diving bottles
- Small Arms Protective Inserts (SAPI) for personal armor.
In order to determine the optimal inspection parameters for a particular composite structure (incidence angle,
frequency, and pulse length), a wave propagation model for multi-layered structures is used. This model is based on a plane wave propagation model using the
Thomson-Haskell transfer matrix for multilayered media. The characteristics of the composite material such as layout and material properties, are used as input data
to the model.
NDTA’s AU laboratory system is capable of generating C-scan images of amplitude and Time Of Flight (TOF), as well as A-scans of different areas of the composite
structure using a high-precision computer controlled scanning bridge. The system can be used with traditional wedge sensors or adapted for use with rolling sensors,
which eliminate the need for extra coupling between the sensor and the piece under inspection. The system can also be used with a free-motion, wireless position
tracking manual scanner.
