Jan Sermeus

Determination of thermoelastic material properties by differential heterodyne detection of impulsive stimulated thermal scattering

The underlying working principle of detecting impulsive stimulated scattering signals in a differential configuration of heterodyne diffraction detection is unraveled by involving optical scattering theory. The feasibility of the method for the thermoelastic characterization of coating-substrate systems is demonstrated on the basis of simulated data containing typical levels of noise. Besides the classical analysis of the photoacoustic part of the signals, which involves fitting surface acoustic wave dispersion curves, the photothermal part of the signals is analyzed by introducing thermal wave dispersion curves to represent and interpret their grating wavelength dependence. The intrinsic possibilities and limitations of both inverse problems are quantified by making use of least and most squares analysis.

Texture in steel plates revealed by laser ultrasonic surface acoustic waves velocity dispersion analysis

HIGHLIGHTSA laser‐ultrasonic approach for texture measurement was proposed.A clear SAW angular dependence which was strongly connected with texture was found.SAW velocity angular dispersion within single grains was numerically determined.SAW velocities and variation in {1 1 1} texture were smaller than in {1 1 0} texture. ABSTRACT A photoacoustic, laser ultrasonics based approach in an Impulsive Stimulated Scattering (ISS) implementation was used to investigate the texture in polycrystalline metal plates. The angular dependence of the ‘polycrystalline’ surface acoustic wave (SAW) velocity measured along regions containing many grains was experimentally determined and compared with simulated results that were based on the angular dependence of the ‘single grain’ SAW velocity within single grains and the grain orientation distribution. The polycrystalline SAW velocities turn out to vary with texture. The SAW velocities and their angular variations for {1 1 0} texture were found to be larger than that the ones for {1 1 1} texture or the strong &ggr; fiber texture. The SAW velocities for {0 0 1} texture were larger than for {1 1 1} texture, but with almost the same angular dependence. The results infer the feasibility to apply angular SAW angular dispersion measurements by laser ultrasonics for on‐line texture monitoring.

Temperature Dependent Elasticity of a Ni2MnGa Film as Measured by Impulsive Stimulated Scattering

We report the results of an impulsive stimulated scattering measurement conducted on a 550 nm film of Ni2MnGa on a MgO substrate, aiming at the direct experimental observation of the highly temperature dependent elasticity. The phase velocity of the surface acoustic waves excited on the surface of the coating-substrate shows an anomaly around the phase transition temperature of Ni2MnGa, showing that it is possible to use impulsive stimulated scattering as a characterization tool to determine temperature dependent elasticity of a thin film.

Thermomechanical properties of single crystals evaluated by impulsive stimulated thermal scattering technique

This paper describes the application of Impulse Stimulated Thermal Scattering (ISTS) for measurement of surface acoustic wave (SAW) velocity and thermal diffusion along a free surface of a strongly anisotropic material. The motivation for this work stems from the study of thermoelastic properties of individual phases of ferroelastics; experimental results were obtained on a single crystal in the austenitic phase a Cu-Al-Ni alloy (bcc single crystal having elastic anisotropy factor of about 12). The measured SAW velocities in specific directions are in a good agreement with the values calculated for the elastic constants obtained by other ultrasonic methods. Similarly, the evaluated thermal diffusivity coefficient (22 ± 2).10−6 m2/s of the austenite is consistent with the data in the literature. The proposed approach has also a potential for characterization of thin films grown on anisotropic substrates.