K. L. Muratikov

Photodeflection and photoacoustic microscopy of cracks and residual stresses induced by Vickers indentation in silicon nitride ceramic

The feasibility of using photodeflection and photoacoustic microscopy to detect subsurface lateral and vertical cracks, as well as residual internal stresses induced by Vickers indentation in silicon nitride ceramic has been investigated. It is shown that the normal component of the photodeflection signal can be used to detect lateral subsurface cracks and the tangential component to detect vertical cracks. It is established that the sensitivity of the photoacoustic method to residual internal stresses arises from the dependence of the elastic parameters or the coefficient of thermal expansion of the silicon nitride ceramic on the internal stresses.

Investigation of the influence of residual stresses on the thermophysical and thermoelastic properties of silicon nitride ceramic by photothermal and photoacoustic methods

Photodeflection and photoreflection microscopy have been used to show that residual stresses do not influence the thermophysical parameters of silicon nitride ceramic. It was demonstrated that photoreflection microscopy can provide information on the thermophysical properties of ceramics at the level of individual grains. It was established that the theory of photoacoustic signal formation with a piezoelectric recording method based on the Murnaghan model with allowance for the stress dependence of the thermoelastic coupling coefficient can qualitatively explain these experimental data and can be used to estimate the thermoelastic parameters of the ceramic.

Laser thermowave diagnostics of heat transfer through bonded interfaces in multielement semiconductor opening switches

Laser thermowave photodeflection methods have been used to study the process of heat transfer in bonded interfaces of semiconductor diode structures of high-voltage opening switches fabricated according to the stack technology. A theoretical model is proposed for the description of thermal wave propagation in these structures with allowance for technological features of the preparation of semiconductor surfaces, brazing layers, and welds. It is shown that laser thermowave photodeflection methods can be used for diagnostics of the quality of bonded interfaces between elements of high-voltage opening switches fabricated by means of various technologies.

Theory of the thermoelastic generation of mechanical vibrations in internally stressed solids by laser radiation

An investigation was made of the behavior of transient deformations in solids with internal stresses exposed to time-modulated laser radiation. The nonlinear theory of thermoelasticity is used to propose a model for the excitation of mechanical stresses which takes account of the stress dependence of the thermoelastic coupling parameter. An expression is derived for the electric signal recorded by a piezoelement when mechanical vibrations are generated in a uniformly deformed sample. The results are compared with existing experimental data and show qualitative agreement.

Diagnostics of heat removal from semiconductor solar cells by laser thermowave methods

Methods of laser thermowave diagnostics have been used to study the process of heat transfer between a semiconductor solar cell and heat-removal ceramics. A theoretical model is proposed that describes the propagation of thermal waves in these systems with allowance for a layer of solder present between the semiconductor and ceramics. It is shown that, using laser thermowave methods, it is possible to evaluate the thermal properties of solder joint layers and the character of their degradation under the action of working temperature variations.

Solving nonstationary thermoelasticity problems for solids in quasi-static approximation

A general approach to solving nonstationary thermoelasticity problems for solid objects in a quasi-static approximation is proposed. Analytical expressions describing thermoelastic strains in an object with a plane boundary under the action of nonstationary heat fluxes are obtained within the framework of a three-dimensional model. These results are used to derive formulas for the normal component of the thermoelastic strain vector in an object exposed to nonstationary laser radiation. Characteristics of an inteferometric signal observed during the measurement of such deformations are analyzed.

The effect of annealing on the photoacoustic and photothermal response of Al2O3-SiC-TiC ceramics with internal stresses

The Vickers indentation zones in Al2O3-SiC-TiC ceramics were studied by scanning laser photo-deflection and photoacoustic microscopy. The method of photoacoustic microscopy with piezoelectric detector (PAMPD) is sensitive to the internal stress distribution in the material. The effect of annealing on the PAMPD signal of the Al2O3-SiC-TiC ceramics was studied. An increase in the annealing time is accompanied by decrease in the PAMPD response from the vertices of radial cracks.

The effect of external stresses on the behavior of photoacoustic signals inside vickers indenter marks on a steel surface

It is experimentally established that the characteristics of photoacoustic signals inside Vickers indenter marks in metals significantly change under the action of external stresses. Relative changes in the signal amplitude are estimated in the framework of a quasi-static approximation based on the temperature dependence of the elastic modulus of the metal.

Photoacoustic thermoelastic effect near vickers indentations in nanocrystalline nickel

The character of the photoacoustic (PA) signal variations in the vicinity of Vickers indentation zones in nanocrystalline nickel has been studied. PA images revealing the response signal features inside and outside these zones have been obtained. The character of the PA signal variation is compared to that predicted by the existing model relating the PA response to stress-induced changes in the thermoelastic coupling coefficient of the material. It is shown that the existing model adequately describes the observed character of internal stress variations near the indentations sites only in the absence of additional stresses related to the sample preparation technology.

Laser Photoacoustic Imaging of Inhomogeneous Objects

The process of photoacoustic response formation in inhomogeneous objects is analyzed. In a quasi-static case, the photoacoustic image is formed predominantly due to inhomogeneities in the thermoelastic coupling coefficient. Expressions describing thermoelastic strains in an inhomogeneous object with allowance for the inhomogeneous thermoelastic coupling coefficient in the general form are obtained within the framework of a three-dimensional model using the perturbation theory. A comparative analysis is performed for the process of photoacoustic image formation in various regimes of piezoelectric sensor operation. The results are used to explain the behavior of a photoacoustic signal at the ends of vertical cracks.