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

Abstract

Ultrasonic methods are well known as powerful and reliable tool for defect detection. In the last 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 in service inspection 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 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

Inspection of additive-manufactured layered components

“…Previous works [17][18][19] demonstrate that an explicit dynamic analysis together with the use of diagonal element mass matrices is computationally very efficient for the analysis of models with relatively short dynamic response times, as is the case for wave propagation with frequencies in the MHz range in relatively large bodies. The same method was implemented here.…”

Non-Contact Ultrasonic Guided Wave Inspection of Rails: Next Generation Approach

“…The degree of freedom of the finite elements used to model air is the acoustic pressure, which is the local pressure deviation from the ambient pressure caused by an ultrasonic wave [91].…”

Experiment and FEM study of one-way mixing of elastic waves with quadratic nonlinearity

“…Finite element methods (FEMs) are preferred in most studies of ultrasound wave propagation [7][8][9][10][11][12]. Finite element modeling requires strict rules for spatial and temporal discretization to study the interaction of waves, which can cause numerical problems at high frequencies and large dimensions.…”