Exact analytical solutions of the heat-diffusion problem encountered in the pulsed photothermal evaluation of layered materials are presented. The analysis relates to the long-time decay of the front face temperature following the absorption of a surface heat pulse. The configuration of a coating on a substrate is analyzed, and the parameters governing the temperature evolution are identified with a particular emphasis on the thermal contact resistance term. This model provides a new method of measuring the quality of the interface. Previously published data and new experiments with laminated materials and living tissues are analyzed using the proposed analytical solutions.

Abstract:Thermography was performed on stainless steel 316L and aluminium alloy 7010 samples as they were submitted to a sinusoïdal mechanical stress (traction/compression). For each stress amplitude value the temperature data were recorded in 5 s. A specific signal demodulation procedure was used to extract the first two Fourier components and the mean temperature rise. From their particular dependence on the stress amplitude, characteristic stress values could be derived. In some instances, these values are very close to the fatigue limit of the considered material.

No abstract

We present a new method for building sequences of solvable profiles of the electromagnetic (EM) admittance in lossless isotropic materials with 1D graded permittivity and permeability (in particular profiles of the optical refractive-index). These solvable profiles lead to analytical closed-form expressions of the EM fields, for both TE and TM modes. The Property-and-Field Darboux Transformations method, initially developed for heat diffusion modelling, is here transposed to the Maxwell equations in the optical-depth space. Several examples are provided, all stemming from a constant seed-potential, which makes them based on elementary functions only. Solvable profiles of increasingly complex shape can be obtained by iterating the process or by assembling highly flexible canonical profiles. Their implementation for modelling optical devices like matching layers, rugate filters, Bragg gratings, chirped mirrors or 1D photonic crystals, offers an exact and cost-effective alternative to the classical approaches.

Pulsed stimulated infrared thermography is a .powerful technique for the detection of thermally resistive defects in materials. Time-resolved analysis of the surface temperature field can then be used for the identification of· the defect characteristics (mainly its depth, its lateral size and its thermal resistance). Several such inversion procedures were proposed in the past. They are based either on a 1-0 or on a 2-to-30 modelling of thermal transfer in the inspected material. In this paper we describe a new 1-0 procedure for the defect geometry characterization (depth and lateral size). Compared to previous 1-0 methods, it is less sensitive to lateral diffusion. It however retains their high speed. NomenclatureGr, a z Cr = lOO(l-T lI'rep Crl = TrejI'