General algorithm of integrated photoelasticity is complicated and leads to nonlinear relationships between the stress components and measurement data. It is shown that effective algorithms for determining completely the axisymmetric state of stress and for measuring normal stress distribution in an arbitrary 3-D model, can be constructed if birefringence is weak. In the case of strong birefringence stresses can be determined only if rotation of the principal stress axes is absent or weak. In the general case of strong birefringence curious optical phenomena take place and integrated fringe pattern becomes ambiguous.

The development of a technique is connected to the working out of new more exact methods of calculation of construction strength. The basis of such calculation is the analysis of the stress-strain state of the investigated object. The role of experimental methods in this process is invariably high. This experiment is applied not only to check out numerical or analytical investigations but it is also independent, and a unique approach to the solution of most complex strength problems. Necessity of experimental valuation of results which basically depend on choice of the account scheme and division of the research object into elements has increased in connection with wide application of numerical methods of stress-strain account (MFE, MFD, MBE). The phenomenon of photoelasticity which is peculiar in greater or in a smaller degree to all transparent materials is used in polarized- optical investigations at modeling of a wide circle of the experimental mechanics problems. The appearance of gas lasers as the sources of monochromatic polarized light has become the reason of further development of a polarized- optical method based on measurements of scattered light intensities (SLI) -- scattered-light method. Scattered-light method is the most perspective but poorly developed among the polarized-optical approaches of the stress-strain analysis. The practical application of the given method is constrained because of several objective reasons: (1) complexity and insufficient accuracy of approaches of characteristic parameters determination of the photoelastic model; (2) complexity of stress-optic dependencies connecting optical characteristics with stress in common cases of investigated objects loading; (3) absence of reliable approaches of stress division in three-dimensional problems of photomechanics. Therefore, the development and practical application of a scattered-light method used in solving three-dimensional problems of strained body mechanics is an important problem.

The present work presents using scattered light technique for determination of 3D stress field. It is a generalization of the earlier introduced isodynes method, where by help of isodyne image and equilibrium equation stress field in the 2D case can be established. The 3D methods base on measurements of the intensity of the scattered light in some perpendicular to laser beam directions. It allow us to determine stress tensor but without hydrostatic component. However, this component can be obtained when two beams propagating in opposite directions interfere.

This original photoelasticity contribution is based on the combination of a modulation of the polarization vector of the light form to be measured with a signal processing of the light energy received by the phototransducer. By means of the described device one gets the equivalent of a special ellipsometer providing the coordinates of the polarization vector in Stokes space. The classical photoelastic parameters of either the analyzed light or the studied model can be derived directly by the microcomputer. The prototype on use is presented hereafter with the main setting to be carried on the first use. The very simplicity of mechanical set up associated with only two optical operators provides an accurate measurement of the ellipsis parameters of the light vector. The numerical treatment applied on the sampled signal relevant to the light energy avoids all the uncertainties that were previously involved by the analogical treatment of the electrical signal. Moreover control of any light operator is no more used. This automatic principle can be used in all the fields of photoelastic measurements such as plane or three dimensional applications.

Thanks to numerous investigations executed at the Laboratory of Stress Analysis (now Research Institute of Experimental Mechanics) of the MSUCE under the general direction of the recently deceased Prof. G. L. Khesin, the dynamic photoelasticity technique can be effectively used for solving some fundamental engineering problems of structures subjected to impact and blast action. The present paper comprises some examples of application of this method to solving solid elastic and plane visco-elastic problems of wave dynamics of structures.

The experimental-calculated method for determination of contact stresses is reported. The method is based on hybrid use of photoelasticity and finite element method (FEM). The results of contact pressure and contact angle determination in hinge joint as function of value and direction of load, clearance are presented. The contact stress distribution in three-dimensional hinge joint is shown which depend on elastic deformations of pin and lug.

The method of stress and strain determination in complex high-velocity rotors using three-dimensional photoelastic models is reported. The technique for modeling on scaled models with pressure inside rotor also is developed. The experimental setup developed for freezing of rotor models loaded by centrifugal force is considered. The examples of stress determination in rotor of the centrifugal pipe and separator are presented.

The new experimental method for determination of stresses inside of real rubber, rubber-cord and rubber-metal structures using frozen insets and photoelasticity is considered. This method is based on analogy between the elasticity and viscoelasticity problems for polymers during polymerization. The photoelastic materials of cold polymerization for insets making are developed and testing technology is reported. The results of stress analysis in automobile tires under interior pressure and radial loads are presented.

The stress-strain state and the stress concentration under the large elastic strains in the rubber specimens with the cracks or sharp notches subjected to uniaxial and biaxial tension were investigated. The cracks were placed horizontally or they were inclined. (Load direction is vertical). The investigation was carried out by means of the non-linear photoelastic method using the models made of a birefringent polyurethane resin. The nominal relative lengthening on the distance from the crack reached 55% and the maximum lengthening near the crack's tip were 120%. According to the results of the well-known theoretical solution large stresses at the cracks tip are infinite. It also concerns the large strains (V.V. Novozhilov, K.F. Chernikh). The goal of this research was to check out this statement. The experiment refutes it.

The paper deals with the photoelastic method of solving the problems of non-linear elasticity and plasticity under the large strains with the help of the birefringent materials, i.e. a polyurethane resin and a composition on the basis of epoxy. The transparent models and photoelastic coating method are used. The optical-mechanical dependencies of the non-linear photoelasticity under the strain in the range of 50 - 150% have been obtained. The interpretation of the optical patterns has been worked out when the object is under the large strains. There exist two ways of decoding. The first one uses Muny-Rilvin and Bartenev-Khazanovich's elastic potentials. The second one is much easier and describes the behavior of polyurethane in the whole range of the given strains, so it was used in the present investigation. It's worth mentioning that the processing of experimental data in non-linear problems is more complex than in classical photoelasticity, as it's necessary to take into account the change of the specimen's shape and geometry during the deformation. In this case the principle extent of lengthening lambda (a difference between the length of a deformed specimen and its initial length) was used as a strain value. The method of nonlinear photoelasticity gives the possibility to investigate the fundamental problems of the mechanics of solids. These problems have physical and geometrical non-linear properties, i.e. large elastic and plastic strains, mechanics of destruction. Siberian scientists have already investigated some problems of this kind. But they haven't reached the theoretical solution and solved it in the first approximation. So they need an experimental test. You'll find some of them below, i.e. the problem of thermal stresses in the multi-layered panels, determination of stresses in the reinforced beams with the naturally developing cracks, determination of forms and sizes of plastic zones near the sharp-notches tips in the metallic specimens, the problems of stress-strain condition in the necking of the plane steel specimens.

In a static problem of the deformed body mechanics, all the forces depending on their availability in the equation resolution system are classified as surface forces P_i, volume forces F_i and distortions or forced strains (xi) . It is known that there is partial equivalence of force which means an identify equality (analogy) of stresses or displacements under the action of different types of loads; in particular, between volume and surface force actions though under very strict limitations. It is easy to demonstrate that by introducing the third constituent -- a forced strain -- it appears to be possible to establish the necessary and sufficient conditions for the analogy. These conditions make it possible to present a forced strain action as the sum of volume and surface force actions; volume forces -- as the sum of surface force effects and forced strains; surface forces -- as the sum of forced strains and volume forces. The analogy in question is very important for the experimental solution of the problem because the realization of every force is limited by modeling technique's possibilities.

Issues connected with modeling of thermoelastic problem by photoelasticity method are considered in the report. Formula of similarity are given taking into account the influence of differences between mechanical characteristics of materials (E,v) from which models and real objects are made. An experimental method which allows us to model thermoelastics stresses and displacements without reproductions of temperature field in the model is described. The present method is used to solve piece wise-uniform problems of thermoelasticity.

With the purpose to apply the method of photoelasticity to educational process the 'photoelasticity' training system was developed. It embodies the latest achievements in experimental mechanics, optics and computerized data processing. This system is intended for conducting lectures and laboratory work during studying different mechanics courses.

Photoelasticity is the most promising experimental method of the mechanics of solids. In recent years this method has been used successfully on linear and nonlinear viscoelastic problems and on problems of lattice-nonhomogeneous medium. the further development of photoelasticity is concerned with nonlinear mechanics of nonelastic and composite materials, especially at finite and large deformations. The creation of the photoelastic methods is connected with choice or synthesis of birefringent material, having needed properties. It is necessary also to formulate basic stress-strain-optic relations, to work out procedures of model experimental studies, to develop methods of principal stresses and strains separation, to create similarity theories. In this paper the methods of orthotropic linear photoviscoelasticity, photoviscoplasticity, and some aspects of nonlinear photoelasticity are considered.

Photoelasticity method along with the numerical methods of equilibrium equation integration or with any other experimental methods makes it possible to determine stresses in structural members. To assess structural strength, it is necessary to apply the corresponding structural strength theories. If material properties are time dependent, then it is necessary to possess complete information on material behavior in time. But such a procedure for the solution of problems on structural strength and durability seems to be too complicated and not expedient from an engineering point of view. The paper in question suggests a direct method for structural strength and durability modeling by using the analogies of dimensions.

Designs of the borehole-type photoelastic gauges used in geomechanical measurements held at the Mining Institute, Novosibirsk, and tasks solved with the use of such gauges, some features of the optical pattern that form the basis for decrypting the readings of the gauges are considered.

The basic amount of known measurements of stressed state in front of development workings' faces was carried out with the use of hydraulic sensors, which give an information about principal stresses without their separation. Besides, the availability of pipe-line and cumbersome equipment make more complicated and sometimes impossible the process of stresses' measurements during works in mining process. In our opinion, the borehole and photoelastic sensors at high degree satisfy with the conditions of stresses' measurements in front of mining workings' faces. The principal idea of the method is in the usage of proper face advancing aiming the estimation of the field stresses in its neighborhood. Borehole and photoelastic sensors, fixed in the advanced boreholes, drilled from the active face react to the field change of stresses or deformation caused by working face advancing. While obtaining this information we may judge about the distribution of additional stresses in rock of face's neighborhood and concentration of stresses in front of face. The usage of cavity (because of face advancing) in the quality of disturbing influence in combination with the properties of ring photoelastic sensor to given an information about magnitude and direction of secondary principle stresses, permits us to obtain rather a simple and not labor consuming method of investigation of field additional stresses in the working's face neighborhood.

There is a great necessity for birefringent polymers characterized by regulated acoustic stiffness in solving wave process problems in continuous media by means of dynamic photoelasticity. This type of polymer is particularly significant for the investigation based on models of stress waves in composite constructions consisting of various materials. Special types of polymers are generally used as basic materials for creating models used in dynamic investigations. These are hard polymers based on epoxy oligomers cured by organic acid anhydrides. The speed of longitudinal wave spreading is 1,900 - 2,000 m.p.s. in such anhydrides. In the present survey, we consider the synthesis of birefringent polymers in accordance with two following directions: (1) synthesis of interpenetrating nets (IPN) through simultaneous curing of epoxymethyltetrahydrophthalic compound and bis(allylcarbonate) polypropylenglycol (BACPG); (2) polycyclotrimerization of carbofunctional silicon-organic macrodiisocyanates. The latter material -- carbofunctional silicon-organic macrodiisocyanates -- is synthesized by the interaction of oligomeric silicon-organic diols (M_n equals 282 - 3,500) with a double molar surplus of 2.4- tolylenediisocyanate. In both cases, the curing process is controlled with the help of the IR-spectroscopy method and through the gel-fraction accretion.

The characterization of materials used in civil constructions is needed and for this purpose many parameters can be obtained from experimental tests. In the last years optical interferometric techniques have acquired more and more importance in laboratory tests and can be proposed as alternative or complementary means to classical techniques. On the basis of previous calibration tests, in the paper the authors describe the application of ESPI method to the determination of the crack tip position and of the strain field surrounding the crack that propagates in a specimen of clay material.

The paper describes experimental-analytical methods developed to investigate local inhomogeneous fields of residual stresses on a basis of holographic interferometry and photo-elastic coatings. To solve the problems of such a kind the authors propose to use step-by-step advancing edge cracks as indicators of residual stresses. Procedures to perform the experiments including methods to create cracks- indicators are described.

The application of pulse holographic interferometry in investigating the stress state by dynamic photoelasticity is discussed. The polarized-holographic set-up with three pairs of reference beams having the orthogonal polarizations has been developed. The space-time control of reference beams allows us to record the interferograms of absolute retardations for three moments at a single hologram.

Displacement determinations inside three-dimensional transparent bodies by moire, holographic interferometry or speckle methods are based on the registering of the spatial frequencies' alterations of the light scattered in the investigated region of the object after its deformation. The main reason of these alterations is a light diffraction in the investigated section of the object. But there is another reason of these alterations -- the refraction in the whole nonhomogeneously stressed object. The effect of refraction depends of the stress gradient along the light ray and cannot be ignored when this ray cross's the high stress gradient regions. The mathematical model for investigating this effect is considered. This model is used for producing the calculating interferograms of interior sections of transparent objects. Only a phase model approximation is considered. The results obtained by this modeling are compared with the experimental results. It is shown that the effect of refraction may be compared with the diffraction effect and the phase model approximation may be used for their calculation or estimation.

The work considers a procedure for determining stress intensity factors of types I and II under combined loading on the basis of processing a two-dimensional normal displacement field, obtained by holographic interferometry. This procedure is based on obtaining the analytical idea of a stress field in a crack tip area which corresponds to the experimentally found pattern of isopahs. A case of crack edge loading by arbitrary distributed load is explained.

Research methods of axisymmetrical object's deformations by means of film holographic interferometer with the adaptive base are discussed.

Research methods of deformations of axisymmetrical objects by means of panoramic holographic interferometer and panoramic speckle interferometer are discussed. These methods allow us to analyze widely all the points of the surface with the same sensitivity and were subjected to experimental testing and metrological analysis.

A brief theoretical background and physical principles of superposed holographic interferometers are given. A practical procedure of surface displacements measurement is described. Examples of the interpretation process for the evaluation of the strain and stress fields, with illustrative experiments, are presented. The sensitivity and accuracy of the technique is also discussed.

The new equations, which describe the relation between the characteristics of optical scheme, sensibility and the depth of focus in moire topography, were obtained. Possibility of optimization of the registration scheme of fringe pattern was discussed. The examples of method application, in which the grating is projected on the investigated surface and this surface with image of that grating are projected to the reference grating, are presented. The examples show a good agreement between relief measured by the proposed methods and by independent means.

As it is known, any method has positive and negative sides. Hybrid methods based on combination of experimental and theoretical methods enable the usage of method's sides, which solve the task with the most efficiency. In this case physical and mathematical models, projections, photographs, televisions, lasers, measuring equipments and computers.

There are optical devices compatible with computers, which make it possible to decode the fringe patterns obtained by various optical techniques such as: holographic interferometry, the method of photoelasticity, the moire method, etc. in the semi-automatic regime. As it often happens in Russia such expensive equipment is not available at research and educational institutions but they possess quite a large number of computers and standard peripheral devices for them. Referring to the above mentioned the authors have developed a technique of fringe patterns decoding bases on the use of standard hardware and on the integrated system of automation of mathematical and engineering calculations MathCad 2.01. Applying the given technique the authors used the following devices: IBM PC AT 386SX CPU 33.3 MHz, ScanJet HP (Hewlett Packard Corp.). The errors of this technique have been investigated as well as the range of its application. The technique is illustrated by the examples of decoding of holographic interferograms, moire and photoelastic patterns.

Digital speckle-pattern interferometry systems for automatic measurement of in-plane deformation of a diffuse object are presented, based on phase shifting of a speckle interferogram. Before deformation, three digital speckle patterns are recorded as changing the phase of reference light such as 0,pi/4, pi/2. After deformation, three digital speckle patterns are recorded with phase shifts - pi/2, 3pi/4, pi, respectively. A calculation of the arctangent with phase-shifted speckle pattern gives the optical path difference which is proportional to the deformation.

An investigation was made of the dynamics of crater growth when a millisecond light pulse with a complicated temporal form interacted with the surface of a transparent dielectric. The characteristics of elastic waves generated in the course of this interaction were also studied. The effective growth of a crater consisted of two stages and lasted no more than 100 microseconds. In the first stage the area of the damage region increased while its depth remained practically constant, in the second stage the crater growth was three-dimensional. The generation of acoustic vibrations could be described satisfactorily by a model of loaded zone emitting waves into an elastic medium. The increasing use of laser processing of materials is responsible for the growing interest in the phenomena resulting from the interaction of high-power light pulses with the surface of a solid. The aim of our investigation was the dynamics of crater growth and of changes in the density of an inelastically deformed material and a study of generation of acoustic waves in the transparent insulator when its surface interacts with a millisecond laser pulse with a complex temporal profile.