We describe characterization of digital signals using analogs of thermodynamic quantities: the topological entropy, Shannon entropy, thermodynamic energy, partition function, specific heat at constant volume, and an idealized version of Shannon entropy in the limit of digitizing with infinite dynamic range and sampling rate. We show that analysis based on these quantities is capable of detecting differences between digital signals that are undetectable by conventional methods of characterization based on peak-to-peak amplitude or signal energy. We report the results of applying thermodynamic quantities to a problem from nondestructive materials evaluation: detection of foreign objects (FO) embedded near the surface of thin graphite/epoxy laminates using backscattered waveforms obtained by C-scanning the laminate. The characterization problem was to distinguish waveforms acquired from the region containing the FO from those acquired outside. In all cases the thermodynamic analogs exhibit significant increases (up to 20-fold) in contrast and for certain types of FO materials permit detection when energy or amplitude methods fail altogether.

Characterization of digital waveforms using thermodynamic analogs: applications to detection of materials defects

1) Departamento de Metalurgia, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brasil, LAMEF Laboratorio de Metalurgia Fisica, Av. Osvaldo Aranha, 99, sala 610, CEP: 90035190 Porto Alegre-RS-Brasil. 2) Departamento de Processos Metalurgicos, Instituto Federal do Rio Grande do Sul, Caxias do Sul, Brasil, Instituto Federal de Educacao, Ciencia e Tecnologia do Rio Grande do Sul Câmpus Caxias do Sul, Rua Mario de Boni, 2250, Bairro Floresta, CEP: 95012-580 Caxias do Sul-RS-Brasil.

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Evaluation of Discontinuities in A36 Steel Repairs with Friction Hydro Pillar Processing Using Different Axial Forces

The rail defect detection is vital to the rapid development of high-speed rail. A new, easily available nondestructive testing method which applies the photoacoustic detection technology is proposed here for the rail defect detection. Based on the ultrasonic sensor, a real-time photoacoustic imaging system for the rail non-destructive testing is established. The model of the system and its numerical solution are built first, and then the corresponding experiments and analysis are conducted. The photoacoustic image with damage characteristics can be reconstructed through the photoacoustic signals which excited by pulsed laser and then reflected back from the rail surface. According to the reconstructed image, the damage information such as the appearance, extension trend, and the depth of the rail defect can be effectively identified. It has been proved that the established photoacoustic detecting method for high-speed rail surface detection is an effective and non-destructive detecting technology.

Non-destructive photoacoustic detecting method for high-speed rail surface defects

: This report presents a broad overview of mathematical modeling in nondestructive evaluation (NDE). The primary emphasis is to expand the review of NDE modeling literature covered by previous general works. To provide a starting point for researchers and engineers, the discussions and references include multiple modeling approaches (analytical, asymptotic, and numerical) for a variety of NDE techniques. A second emphasis for this report is to present the pertinent modeling software packages for a variety of NDE techniques. Overviews of modeling for four NDE techniques, ultrasonic testing, eddy current testing, radiography, and thermography are presented. In order to present the broad subject of NDE modeling for this report, the discussions of modeling research and software packages are limited in scope; however, numerous references are provided in each section for further study by the reader. Given the inherent depth and importance of the field, special emphasis is given to ultrasonic NDE. Discussions are presented on the generation of ultrasound, wave propagation in elastic solids, scattering from cracks, and waves in guides and at interfaces.

Overview of Mathematical Modeling in Nondestructive Evaluation (NDE)

A noninvasive technique capable of characterizing material properties of the heart would be highly beneficial in clinical settings. Our group has been investigating the feasibility of using the Shearwave Dispersion Ultrasound Vibrometry (SDUV) method to estimate tissue viscoelasticity. Dispersion equations for the anti-symmetric Lamb and Rayleigh waves were derived and fitted to the experimental data to solve for elasticity and viscosity of the excised myocardium. The viscoelastic parameters obtained using the two methods agree within one standard deviation. The results suggest that the material properties of the myocardium can be obtained using both Lamb and Rayleigh wave excitation methods.

Ex vivo measurements of mechanical properties of myocardium using Lamb and Rayleigh wave dispersion velocities

The solid-state bonding of metals, e.g. diffusion bonding, friction welding, and inertial welding, is finding increasing use in the fabrication of structural components. A summary is presented of recent progress toward the development of nondestructive techniques to monitor the quality of such bonds. Emphasis is placed on the characterization of a particular microstructural origin of bond weakness, a distributed array of microcracks in the bond plane. Included is a discussion of theories for the interaction of ultrasound with such distributed defects, results of model experiments designed to validate the theories, and applications of techniques based on the resulting understanding to fracture studies of bonded surfaces and to inspection of aircraft engine turbine rotors. >

O. Buck

Papers

Ultrasonic nondestructive evaluation of solid-solid bonds