Simulation of laser-generated ultrasonic wave propagation in solid media and air with application to NDE

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2010-02, Vol.98 (2), p.327-336
• Main Authors: Pantano, A., Cerniglia, D.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Computer simulation; Condensed Matter Physics; Condensed matter: structure, mechanical and thermal properties; Contact; Contact pressure; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Inspection; Machines; Manufacturing; Materials science; Materials testing; Mathematical models; Mechanical and acoustical properties of condensed matter; Mechanical properties of nanoscale materials; Nanotechnology; Optical and Electronic Materials; Physics; Physics and Astronomy; Processes; Surfaces and Interfaces; Thin Films; Transducers; Ultrasonic testing; Wave propagation
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-009-5402-0

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.