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We extend the applications of photothermal radiometric diagnostics to continuously curved cylindrical surface solids using lock-in thermography (LIT) imaging, in which both the photothermally induced surface temperature and the angularly dependent infrared radiation emitted by the curved surface are not constant. Specifically, a theoretical photothermal model is established based on the Green Function method from which the thermal-wave field distribution at different azimuthal angles on the curved surface is obtained and characteristics of the thermal-wave field with different material and measurement parameters/schemes are discussed. A laser-infrared photothermal lock-in imaging system for solid cylindrical samples is established, and the thermal diffusivity of AISI 304 cylindrical steel samples is measured directly based on the LIT images combined with empirically obtained infrared radiation angular distributions over the curved surfaces. The experimental results are in excellent agreement with the theory, which provides a fast and non-destructive quantitative tool for thermophysical evaluation of curved surface solids. [ABSTRACT FROM AUTHOR]

In this study, we established a theoretical photothermal model and its experimental validation for an infinitely long solid with an inner corner of arbitrary opening angle, with the solid being irradiated photothermally by a modulated laser beam of arbitrary spatial intensity distribution directed to the corner. The thermal-wave field distribution on the flat surfaces of the solid centered at the corner was obtained using the Green function method. Experimental results based on quantitative thermographic imaging were obtained and used to validate the theoretical model in which thermal diffusivity of an inner cornered stainless steel was measured. The thermal-wave theory based lock-in thermography imaging technique provides a quantitative tool for thermal property measurement and/or non-destructive evaluation of non-flat structures. It also generates valuable physical insights into the spatial distribution of the thermal-wave field in the neighborhood of geometric discontinuities such as inner corners in solids. [ABSTRACT FROM AUTHOR]

The influence of the photothermal laser source beam size on the measurement sensitivity of layered systems using photothermal radiometry (PTR) is presented. Based on an appropriate theoretical model, widely different behaviors of the photothermal amplitude and phase in terms of combinations of thermophysical properties (i.e., thermal conductivity and thermal diffusivity) between a thin coating and the substrate are observed. The beam size effect on PTR measurement sensitivity is theoretically examined and experimentally demonstrated using a carbonitrided C1018 steel sample. The experimental results of using a variable size laser beam for the carbonitrided C1018 sample validate the theoretical prediction, in which an expanded beam exhibits a much larger magnitude change in both amplitude and phase as a function of frequency than measurements with a focused beam. The fitted thermal conductivity and thermal diffusivity based on the assumed industrially relevant range of effective hardness case depth gives the approximate range of the change in thermal conductivity and thermal diffusivity of C1018 steels after the carbonitriding process. [ABSTRACT FROM AUTHOR]

Motivated by increasing practical and industrial applications of photothermal techniques in the measurement of materials of various shapes with curvature, we extend the applications of photothermal diagnostics to solid spheres, in which both theoretical and experimental photothermal radiometry studies on spherical geometries and thermal diffusivity of the sample are discussed. Based on the Green function method, a full thermal-wave field distribution of a spherical solid is obtained. The characteristics of the thermal-wave field with respect to thermophysical properties of the material, the diameter of the solid, the size of the incident laser beam, and the measurement angle are discussed. Experimental results with steel spheres of different diameters exhibit good agreement between the theory and the experiments. [ABSTRACT FROM AUTHOR]

We extend the applications of the photothermal diagnostics by means of laser-infrared photothermal radiometry (PTR) to samples with curved surfaces. Specifically, we present both the theoretical and experimental PTR studies on solid cylindrical samples (surfaces). Based on the Green function method, the thermal-wave field distribution of a cylindrical surface that is under the excitation of a periodically modulated uniform beam is obtained. The laser beam, which is of a cylindrical symmetry, impinges uniformly, partially or fully, on the cylindrical surface, which is practically infinitely long along the axial direction. The characteristics of the thermal-wave field with respect to the thermal diffusivity of the material, the diameter of the sample, the size of the incident beam, and the measurement of the angle are discussed. Experimental results are in good agreement with the theory. [ABSTRACT FROM AUTHOR]

Examines a photopyroelectric method for measuring the thermal diffusivity of ambient gases with optimal precision. Sensor design; Improvement in the signal-to-noise ratio; Cavity-length scanning employed; Comparisons of measurement precision.