Simulation of laser-generated ultrasonic wave propagation in solid media and air with application to NDE |
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Authors: | A Pantano D Cerniglia |
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Institution: | (1) National Center for Physical Acoustics, University of Mississippi, 027 NCPA Bldg., 38677 University, MS, USA;(2) Department of Physics and Astronomy, The University of Mississippi, 123 Lewis Hall P. O. Box 1848, 38677 University, MS, USA |
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Abstract: | Ultrasonic methods are well known as powerful and reliable tool for defect detection. In the previous decades focus and interest
have been directed to non-contact sensors and methods, showing many advantages over contact techniques where inspection depends
on contact conditions (pressure, coupling medium, contact area). The non-contact hybrid ultrasonic method described here is
of interest for many applications, requiring periodic inspection in service or after manufacturing. Despite the potential
impact of laser-generated ultrasound in many areas of industry, robust tools for studying the phenomenon are lacking and thus
limit the design and optimization of non-destructive testing and evaluation techniques. Here a specific numerical method is
presented to efficiently and accurately solve ultrasound wave propagation problems with frequencies in the MHz range traveling
in relatively large bodies and through air. This work improves a previous numerical model where propagation of the acoustic
waves through air had not been considered, allowing us to simulate the presence of a non-contact transducer in reception in
order to simulate numerically the complete experimental setup. It is very important to limit the amount of air to be considered
in the FE analyses; otherwise the computational cost would often exceed the resources available. A way to solve the problem
is to implement non-reflecting boundary conditions. A non-reflecting boundary condition allows all outgoing waves to exit
the domain at the boundary where they have been imposed without reflection; thus, it is possible to model only the portion
of air between the non-contact transducer and the solid under testing. Several numerical and experimental analyses were conducted
on a 136 lb AREMA rail; here we study in detail two fully non-contact testing configurations for the rail head and web. The
information that can be acquired is very valuable for choosing the right setup and configuration when performing non-contact
hybrid ultrasonic inspection. |
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