This article discusses the possibility of improving technical means that enable the introduction of phase shifts into light beams in the interferometer paths. An optical–mechanical phase shift modulator in the form of a plane-parallel glass plate rotated around an axis lying in its plane was adopted as the initial version of these technical means. A differential method is proposed for the formation of relative phase shifts between beams in a two-arm interferometer. A variant of the modulator has been developed in the form of a pair of rigidly interconnected plates, with planes initially rotated at a given angle. In this case, each of the parallel light beams in the interferometer passes through its own plate, and it was revealed that a practically linear relationship is provided between the generated relative phase shift and the total angle of rotation of the plates. A variant of using a single plate as a modulator under the established conditions for the incidence on it of two beams that propagate in different arms of the interferometer is considered. The data of a test experiment confirms the operability of the proposed differential method for controlling the phase shift between light beams. The results obtained will be useful in developing special tools based on the method of digital speckle pattern interferometry for measurements of the displacement fields of deformable bodies.

The paper deals with applying the gradually growing fracture technique to study inhomogeneous high-gradient residual stress (RS) fields developing in areas of structural inhomogeneity of flat parts (specifically, in welded joints). The method of electronic speckle interferometry (ESI) is used to register the strain response in the form of surface field displacement of the object studied caused by generated and steadily growing incised fracture. It allows registering displacements directly without contact in digital form with high accuracy. The schematic diagrams of a specialized interferometer are described. The features are listed for recording displacement fields caused by the stepwise increase in the fracture length. The use of a return mechanism made it possible to take the test object out of the optical scheme and bring it back to the initial position as soon as the required mechanical operations are completed. A new method is outlined to determine the stress intensity factor (SIF) in fractures operating as RS indicators on the basis of mathematical processing of the tangential displacement fields. The potential of the interactive program operating in the semiautomated mode (in the MATLAB environment) to implement this approach is explained. The accuracy of the RS calculation procedure is estimated on the basis of the mathematical processing of the experimentally obtained RS indicator, i.e., the dependence of SIF on the fracture length. An example is given to apply techniques developed, equipment, and programs to study RS distribution in highly crack-resistant sheets made of 1163T aircraft alloy using the stir welding technique.

The novel non-destructive method for quantitative description of low-cycle fatigue damage accumulation is expanded to a case of contact interaction in the stress concentration area. Investigated objects are plane aluminium specimens with the centred hole filled by cylindrical steel inclusion. The specimen is subjected to cyclic pull-push loading. The key point, that defines scientific novelty and powerfulness of the developed approach, consists of involving local deformation parameters as current damage indicators. Required strain values follow from distributions of all three displacement components along the filled hole edge measured by reflection hologram interferometry. The data, which are derived at different stages of low-cycle fatigue for the single specimen, provide normalized dependencies of local strain values from number of loading cycle, which are a source of damage accumulation functions. These functions are constructed for the specimen with the filled hole and geometrically analogous specimen with the open hole. Obtained data quantitatively describe a difference in damage accumulation rates for two cases.

This paper addresses various methodological aspects of testing of composite laminates to determine elastic constants of materials. Electronic speckle pattern interferometry is used to measure deformation of specimens in the form of beams loaded with a bending moment. The optical compensation method allows determining directly of principal curvatures of deformed surface. To calculate the elastic constants of a material from the experimental data, the corresponding dependences of the theory of elasticity of an anisotropic body are used. Data are shown on the effect of moisture absorption on elastic properties of glass–epoxy laminate.

This article discusses the methodology for determining residual stresses in case-hardened material layers. It includes the joint use of the slitting method and the method of electronic pattern speckle interferometry. In the final part; experimental data are obtained from studies of samples with and without force strengthening effect.

The technologies and results of an experimental determination of residual stresses in the impeller blades of a hydraulic unit of the Krasnoyarsk hydroelectric power plant obtained through technical diagnostics beyond the projected periods of use are presented. The investigations of the residual stresses were performed by strain measurement with excision of templates and the optical method of speckle interferometry. Factual values of the components of the residual stresses in two zones of the blade with nonuniform stress fields were obtained.

Residual stress in layered composites significantly affects their mechanical properties. One of the most important tasks in the sphere of experimental mechanics is the development of effective methods for the accurate determination of residual stress values. This paper describes a modified destructive testing method implemented through layer-by-layer stitching. It differs from previous analogous methods by the use of electronic speckle pattern interferometry to measure the deformation response of a given sample. The interpretation of the initial experimental data in "stress terms" was carried out based on modeling through the use of the fmite element method (FEM).

The paper addresses some methodological aspects of the application of electronic speckle pattern interferometry to the study of the main vibration characteristics of solids in contact with liquid. The capacity of the method is demonstrated on an example of determination of resonance frequencies and modes of bending vibration of a thin plate in water.

An advanced experimental technique for determination of the stress intensity factor (SIF) and the T-stress is developed and carefully verified. The approach employs optical interferometric measurements of local deformation response to small crack length increment. Narrow notches are used for crack modeling. Initial experimental data represent in plane displacement component values measured by electronic speckle-pattern interferometry in the vicinity of the crack tip. Determination of the first four coefficients of Williams' series is the main feature of the developed technique. Relationships for transition from measured in-plane displacement components to required fracture mechanics parameters are presented. Availability of high-quality interference fringe patterns, which are free from rigid-body motion, serves as a reliable indicator of real strain state near the crack tip. Experimental verification of the proposed method is performed for non-symmetrical and symmetrical crack in thin rectangular plates subjected to uniaxial tension. The distributions of SIF and T-stress values for cracks of different length in residual stress fields near electronically welded joints of thin plates are presented as an example of practical implementing. (C) 2017 Elsevier Ltd. All rights reserved.

The paper presents an improved technique and the results of strength analysis for the aircraft structural elements with a structural defect like an arbitrary shape delamination.

Evolution of parameters of fracture mechanics at various stages of low-cycle damage is studied. The developed approach is based on elaboration of optical interference measurements of the deformation response to a small crack length increment. Three sequential symmetrical notches simulate the fatigue crack growth process across the cumulative fatigue damage zone caused by low-cycle fatigue. The values of tangential components of displacement that are measured at several points on cut edges by electronic speckle interferometry are initial experimental information. The coefficients of stress intensity (SIC) and T strains are determined on the basis of the Williams solution. Values of opening and coefficients of stress intensity (SIC) and T strains for cracks of different length with fixed values of preloading cycles N (c) equal 0, 100, 1000, 1800, 2500, and 3300 are obtained. The dependences of the parameters of fracture mechanics for cracks of the fixed length on N (c) are constructed.

Numerical evaluation of the reliable measurement range of residual stresses by probe-hole method is obtained using the finite element method. It is demonstrated that recovery of the ratio of components of the stress state when using the approach based on basis functions is performed with accuracy sufficient for practical application. Precise recovery of values of the components of the stress state is possible with the effective intensity of residual stresses in the range of 0–0.7 of the tensile yield of the studied material.

The paper presents an improved method of experimental and computational studies of vibratory condition of the composite constructions with structural defects such as local fibrations. With the proposed approach it is possible to determine the size of the defect and its influence on the inherent forms and structure vibration frequency. In our work we demonstrate practical application of the technique studying the vibration characteristics of the feathering propeller blades with defective structure of the material.

Evolution of the parameters of fracture mechanics at different stages of low cycle damage is analyzed. The developed approach is based on processing the results of optical interferometric measurements of the deformation response to a small increment of the crack length. Three consecutive symmetrical notches are used to simulate the process of fatigue crack propagation through the zone of accumulated damage induced by low cycle fatigue. The magnitude of tangential component of the displacement measured at several points on the edge of the notch using speckle-inter-ferometry is an input experimental data. The first four coefficients of the Williams series solution are used to determine the stress intensity factor (SIF) and T-stress values. The values of crack opening, SIF and T-stress for cracks of different lengths are obtained at a fixed number of preliminary loading cycles N c = 0, 100, 1000, 1800, 2500, and 3300. The dependences of the parameters of fracture mechanics for the cracks of fixed length on N c number which illustrate a process of fatigue damage accumulation are constructed.

The problems of the analysis of residual technological stresses (RS), the knowledge of which is one of the important conditions for the substantiation of strength, service life, and safety of machinery, are investigated. The methods of calculated estimation of the stress occurring during elastoplastic deformation of metals under varying temperature, as well as a modern approach to the experimental estimation of residual stresses, are set out. The experimental method used is based on the processing of large volumes of experimental data from the displacement fields in the area of the probe holes, which are registered by the interference-optical digital methods. An example of the study of residual stresses in a large-diameter pipeline is given, which is made using local induction heating using high-frequency mechanical loading.

The main questions related to increasing the accuracy of residual stress determination by combining the hole-drilling method and optical interferometric measurements of local deformation response are considered. All possible approaches of solving this problem have to be based on recording (of) high-quality interferograms with high fringe density at the local area of interest. For many cases such interference fringe patterns must be obtained on the opposite faces of thin-walled plane structures when a single probe hole is drilled. The required experimental procedure is illustrated for reflection hologram interferometry and for electronic speckle-pattern interferometry. The first of them and the most universal technique is implemented for a characterization of the residual stress field near the central cross section of the standard compact tension specimen with a transverse friction stir weld. A set of the interference fringe patterns, which are essential for deriving the required values of residual stress components within 5 percent accuracy proceeding from the general approach, is presented. The results obtained are illustrated by the distributions of the residual stress components in the weld vicinity. A specially designed optical system of electronic speckle-pattern interferometer is developed and tested. The main feature of this optical system resides in its capability of obtaining the interference fringe patterns near the probe hole, a quality which is comparable to analogous holographic interferograms. In this way a set of unique interference fringe patterns, which are related to a single probe hole drilled in the residual stress field and simultaneously obtained at the opposite faces of the thin plate, are recorded for the first time. The main feature of the developed optical setup resides in the fact that metrological parameters of the measurement system are substantiated and carefully verified by two different approaches. It is shown that the quality of the speckle-interferometric fringe patterns obtained is high enough to ensure determination of the residual stress component values within a 5 percent accuracy interval, as occurs in the case of reflection hologram interferometry implementation.