Origin of laser damage in transparent dielectrics of the plexiglas type

A gasification mechanism is proposed. This mechanism is based on multiphoton photodegradation of the polymer molecules and the resulting formation of free radicals which trigger a chain reaction and the subsequent formation of gas molecules. The kinetics of this process, in which an important part is played by the microstructure of the material, are examined.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 232–238, March–April, 1973.     

Destruction of transparent polymers by laser beams

The action of laser beams of PS and PMM is considered. Changes in the microstructure of the irradiated polymer-expanded micropores-have been detected. The amount of gas in the disk-shaped cracks has been measured and the pressure determined. The amount of gas is sufficient to cleave the polymer. The experimental data confirm the photolysis postulate and the idea of crack formation as a result of splitting of the polymer by the action of the gas.Mekhanika Polimerov, Vol. 4, No. 1, pp. 188–189, 1968     

Destructive effect of free-running neodymium and ruby lasers on certain transparent dielectrics

The mechanism of the destructive effect of focused laser beams (wavelength 1.06 and 0.69 ) on certain optically transparent dielectrics has been experimentally investigated. It has been found that numerous cracks ("disks"), inclined at angles up to 90°, are formed around the focal point, and the material is severely charred.Tadzhik Lenin State University, Dushanbe. Translated from Mekhanika Polimerov, No. 2, pp. 359–360, March–April, 1972.     

Experimental study of steady-state localization in coupled beams with active nonlinearities

Summary Steady-state nonlinear motion confinement is experimentally studied in a system of weakly coupled cantilever beams with active stiffness nonlinearities. Quasistatic swept-sine tests are performed by periodically forcing one of the beams at frequencies close to the first two closely spaced modes of the system, and experimental nonlinear frequency response curves for certain nonlinearity levels are generated. Of particular interest is the detection of strongly localized steady-state motions, wherein vibrational energy becomes spatially confined mainly to the directly excited beam. Such motions exist in neighborhoods of strongly localized antiphase nonlinear normal modes (NNMs) which bifurcate from a spatially extended NNM of the system. Steady-state nonlinear motion confinement is an essentially nonlinear phenomenon with no counterpart in linear theory, and can be implemented in vibration and shock isolation designs of mechanical systems.Presently Assistant Professor of Aerospace and Mechanical Engineering, Boston University (from January 1995).     

Causes of the damage created by laser pulses in transparent polymers

The characteristics of the damage created in PMM, PS, and PC specimens by multiple irradiation are discussed. It is shown that, in addition to the growth of the damage zone, the processes of crack development that determine this zone are also important. The damage created in PMM when the laser beam is interrupted by a cylindrical cavity is considered. In this case, the cavity acts as a diverging lens and the damage beyond it is determined by the scattered flux. The damage produced in specimens of different shapes is investigated. A model is proposed for crack development in a polymer irradiated by a powerful flux. The model is consistent with most of the known experimental facts.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1035–1042, 1967     

Freezing-in and relaxation of the elastooptical effect in transparent polymers

The behavior of typical transparent plastics, characterized by the birefringence under load, has been investigated experimentally on the interval of transition from the high-elastic to the glassy state during cooling. The optical effect, thus frozen-in, relaxes on heating above a certain temperature which is characteristic of a given material.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1110–1116, 1967     

The effect of focusing on the parametric interaction of Gaussian sound beams

Using the method of quasi-optical approximation we study the parametric interaction of Gaussian sound beams with wave fronts having different radii of curvature on the boundary. We give a numerical and analytic analysis of the behavior of the amplitudes of a wave at the difference frequency in the cases when: 1) the focal length of one of the primary waves varies and the other is fixed (large or small in comparison with the length of the diffraction zone); 2) the focal lengths of both primary high-frequency waves are equal in absolute value.Translated fromMatematichni Metodi ta Fiziko-Mekhanichni Polya, Vol. 40, No. 3, 1997, pp. 82–86.     

Experimental study of the effect of technological parameters on the residual stresses in thin-walled coiled parts

The effect of the parameters of heat treatment and programmed winding under tension on the residual stresses in thin-walled coiled parts made from glass plastic by the "dry" winding of a heated glass strip on an unheated mandrel is studied experimentally. The effect of the thickness of the parts on the maximum radial residual stresses is considered. A method is proposed for regulating the residual stresses in parts with very thick walls.Translated from Mekhanika Polimerov, No. 1, pp. 75–80, January–February, 1972.     

Experimental investigation of the deflection of beams made of fiberglass plastics,resting on an elastic base

Results obtained in the testing of beams made of LSB-F fiberglass plastic are compared with those calculated on the basis of shear between layers.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 946–949, September–October, 1972.     

Experimental study of the effect of the technological factor of rolling-in (packing) on the physicomechanical properties of glass plastic

Conclusions 1. The rolling-in (packing) of wound glass-plastic objects is a favorable technological factor, improving the homogeneity of the material, increasing the elastic and strength characteristics of the glass plastic, and reducing the thermal expansion coefficients and macroscopic residual stresses due to the thermal shrinkage of the objects.2. However, extremely large packing forces may reduce certain of the mechanical characteristics of the material, chiefly the strength and modulus relating to interlayer shear.Moscow Power Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1043–1047, November–December, 1976.     

Experimental investigation of the effect of aircraft trailing vortices on roofs

Roofs of buildings in the vicinity of airports can be damaged by trailing vortices of aircraft during take-off and landing. Preliminary experimental investigations have been conducted in a water towing tank in order to examine a discrepancy between damage probability assumptions and actual roof damage frequency. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling of the microwave drying process of aqueous dielectrics

We propose a thermodynamic framework for describing the microwave drying process of aqueous dielectrics based on Maxwell-Lorentz Field equations and mixture theory. Several issues are discussed such as the form of entropy equation; the constitutive relations for the macroscopic electric polarization vectors, Cauchy stresses, heat fluxes, internal momentum supplies, etc., for each component of the mixture: porous solid, water and gas in different regions; and the interfacial jump conditions between different regions in the mixture. A brief examination of the status of material frame indifference within the context of our framework is presented.     

Experimental verification of damage detection methods based on mode shape measurements for beams and plates.

This paper presents experimental verification and comparison of damage detection methods based on changes in mode shapes such as: mode shape curvature (MSC), damage index (DI), strain energy (SE), modified Laplacian operator (MLO), generalized fractal dimension (GFD) and Wavelets Transform (WT). The object of the investigation is to determine benefits and drawbacks of the aforementioned methods and to develop data preprocessing algorithms for increasing damage assessment effectiveness by using signal processing techniques such as interpolation and extrapolation of measured points. Noise reduction algorithms are also tested. The experiments were performed on a steel cantilever beam and on an aluminium plate with riveted stiffeners. Damage was introduced in a form of open crack for beam object and damaged rivets and a saw cut in the angle bar for plate structure. Measurements were made using non-contact Scanning Laser Doppler Vibrometer (SLDV) at 125 points along beam length and 101 points in two rows, distributed on over the plate height and positioned along two reinforcing ribs. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On a variational analysis of finite deformations of prismatical beams and on the effect of warping stiffness on buckling loads

Summary An earlier approximate consideration of the finite-deformation problem of prismatical beams is modified through the inclusion of non-linear displacement derivative terms in the expressions for transverse shearing strains. The general system of equations is specialized so as to describe the problems of lateral buckling of doubly symmetric cross section cantilever beams including warping stiffness effects. While the present results agree with the earlier results for the case of a combination of end bending moment and axial end force, this is not so for the case of a transverse end force. For this latter problem we now have the classical Timoshenko result as a special case, in contrast to what followed from the earlier consideration.

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Zusammenfassung Eine frühere approximative Betrachtung des Problems der endlichen Formänderungen von prismatischen Balken wird abgeändert durch Einschluß von nichtlinearen Verschiebungsableitungsgliedern in den Ausdrücken für transverse Schubdehnungen. Das allgemeine Gleichungssystem wird spezialisiert auf das Problem der Kippstabilität eines Kragträgers mit doppelt symmetrischen Querschnitt, einschließlich des Effektes der Wölbsteifigkeit. Während die jetzigen Resultate mit den früheren übereinstimmen für den Fall einer Kombination von Endbiegemoment und Endaxialkraft, so ist dies nicht der Fall für die Endschubkraft. Für das letztere Problem haben wir jetzt das klassische Timoshenko Ergebnis als einen Spezialfall, im Gegensatz zu dem Ergebnis der vorhergehenden Betrachtung.