Inorganic Materials (v.53, #15)

This article discusses application of quantitative X-ray texture analysis (QTXA) based on measurement of direct pole figures and electron backscatter diffraction (EBSD) aimed at study of peculiarities of formation of texture and structure of MA2-1pch magnesium alloy after equal channel angular extrusion (ECAE) and subsequent annealing. Shear bands with the width of 60 μm oriented at 45°–50° to the extrusion direction are revealed, where an inclined scattered basis texture is detected, and outside of these bands, a prismatic texture. As a consequence, basic sliding is activated in the shear bands, which is confirmed by the distribution of Schmid factors. The influence of texture and orientation of shear bands on anisotropy of strength mechanical properties of alloy is discussed.
Keywords: direct pole figure; orientation distribution function; microstructure orientation map; shear bands; Schmid factor; basic and prismatic sliding; Taylor factor; anisotropy of strength mechanical properties; equal channel angular extrusion; MA2-1pch magnesium alloy

Characterization of Dielectric Properties in Liquid–Solid Phase Transition by A. N. Alekseev; M. M. Lazarenko; M. V. Lazarenko; K. N. Kovalev; S. Yu. Tkachev (1473-1477).
A method for determining the complex dielectric permeability of liquids based on the temperature changes in geometrical parameters (thickness) of samples and over the phase transition range is proposed. Allowing the measurements to be made in a wide temperature range (–190 to 60°C) at different frequencies (0.1–100 kHz), this technique is used for establishing the complex dielectric permeability of ethanol as a function of temperature. The accuracy of coincidence of the obtained values with the data reported in the literature is 3%.
Keywords: complex dielectric permeability; liquids; phase transitions

Determination of Particle Size Distribution of Zirconium Dioxide Powders by Static Laser Scattering and Optical Microscopy by R. A. Mironov; M. O. Zabezhailov; V. S. Yakushkina; M. Yu. Rusin (1478-1483).
Dispersing conditions of powdered zirconium dioxide with addition of 3 mol % yttrium oxide are determined. The particle size distribution of the powders is determined by static laser scattering and optical microscopy. The zeta potential of suspension of zirconium dioxide particles as a function of pH of medium is measured by electrophoresis with titration. The influence of acidity on suspension stability during measurements is studied. It is demonstrated that a stable suspension can be obtained by shift of pH to both the acid and alkaline regions as well as by addition of surfactants, such as Dolapix CE 64.
Keywords: static laser scattering; isoelectric point of zirconium dioxide; particle size distribution; stabilization of suspensions

Early Diagnostics of Damage and Fracture Zones in Composite Materials Using Brittle Strain Gauges and Acoustic Emission by Yu. G. Matvienko; I. E. Vasil’ev; A. V. Pankov; M. A. Trusevich (1484-1495).
The integrated use of the acoustic emission technique and brittle oxide strain gauges for testing the deformation of damage and fracture zones in samples of polymer composite materials (PCM) at the early phases is considered. For the realization of the proposed technique, integrated parameters were used and software including the cluster analysis and the classification of registered AE pulses was developed, which made it possible to differentiate crack formation signals in the brittle layer of a strain gauge from all the other signals that occur at the early phase of the deformation of PCM samples in the online mode. The use of acoustic emission testing and control video recording for the registration of cracks in a brittle oxide strain gauge with the threshold deformation value of 1000 μm/m provided the precise diagnostics of the forthcoming fracture zone in a sample at the early loading phase under the load level of 10–15% of the limiting one long before the beginning of the active PCM structural degradation phase and made it possible to determine the distribution fields of the highest main deformations in the region of a strain gauge and to perform their quantitative evaluation.
Keywords: brittle strain gauge; crack; acoustic emission; signal; descriptor; fracture

Estimation of Range of Reliable Measurements of Residual Stresses by Hole Drilling Method by A. A. Apal’kov; I. N. Odintsev; A. S. Plotnikov (1496-1501).
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.
Keywords: hole drilling method; finite element method; residual stress; reliable measurement range; plastic deformation

Numerical calculation data on the characteristics of linear and nonlinear fracture mechanics are presented. These characteristics help to predict the surface development of studied cracks before their initiation on the surface of a product. In addition, they provide the specified durability and strength evaluation of important elements of equipment with consideration of the kinetics of the local fracture processes along the contours of differently oriented semielliptical surface cracks with consideration of the local dimension of the stress state and their relative depth.
Keywords: relative deformation intensity factor; inclined semielliptical low-cycle cracks; elastic and elastoplastic deformations; stress-strain state dimension; durability and strength of structural elements

Technique for the Determination of the Critical Points under Acoustic Emission Tribological Tests by I. A. Rastegaev; D. L. Merson; A. Yu. Vinogradov; A. V. Danyuk (1506-1512).
The use of the acoustic emission technique for the determination of the critical points under tribological tests using standard friction machines is shown by citing a specific example. The distinctive feature of the proposed approach is the use of special techniques for the determination and presetting of the fracture load and the simulation of the predominant wear processes in a friction pair. This approach can also be used as a technique for the identification of the AE sources registered under the friction and wear of different friction units. It was shown that confocal laser microscopy can efficiently replace most of the well-known wear evaluation techniques.
Keywords: acoustic emission; hardware learning algorithm; tribological testing; experimental modeling of wear

Testing the Technique for the Cluster Analysis of Acoustic Emission Pulse Arrays under the Formation of a Conical Glass Granulate Pile by N. A. Makhutov; I. E. Vasil’ev; V. I. Ivanov; S. V. Elizarov; D. V. Chernov (1513-1524).
The technique for the cluster analysis and the classification of registered acoustic emission (AE) data arrays was used for the determination of the isolated phases upon the transition from the regular to the avalanche process of damage accumulation in a physical simulation model. The damage accumulation phases were modeled in the process of formation of a conical glass granulate pile. Their registration was performed by an AE control system synchronized with a high-speed video camera.
Keywords: acoustic emission; AE pulse; descriptor; registration; glass granulate

Effect of Low-Cycle Fatigue on Fracture Mechanics Parameters According to Speckle Interferometry by V. S. Pisarev; Yu. G. Matvienko; S. I. Eleonsky; I. N. Odintsev (1525-1537).
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.
Keywords: low-cycle fatigue; stress intensity coefficient; T strains; sequential crack length increment method; electronic speckle interferometry

Three variants of physical models of crack growth during corrosion fatigue destruction of steel are proposed: energy model, model of hydrogen embrittlement, and model of anodic dissolution of metal in crack tip. It is mentioned that the anodic model is more preferable for quantitative analysis. Using variant calculations, good agreement of this model with experimental results is demonstrated. The dominating role of local anodic dissolution is revealed as the main mechanism activating fatigue destruction of moderate strength carbon and low alloy steels in an aqueous corrosion medium.
Keywords: aqueous medium; metal; physical model; electrochemical reaction; activation energy; hydrogen embrittlement; anodic dissolution; fatigue; corrosion crack resistance; steel; destruction mechanism

The design and the algorithm for the use of an approved universal educational and research facility is described. The facility is designed to simulate a wide range of model controlled objects (vessels, pipelines, tube furnaces, reservoirs, etc.) and the main acoustic emission (AE) sources: cracks, leaks, corrosion damage, sites damaged by an aggressive medium, etc. The AE simulators installed at the facility are equipped with waveguides to provide the acoustic connection and protect the main elements of the facility in case of fracture of the simulators. The AE simulators are controlled using a loading device to preset the fracture initiation point and the simulator fracture rate. The facility is designed so as to provide low-cost repeated simulation of diverse situations that occur during the operation and examination of dangerous industrial objects. The facility can be used for research, education, and certification of personnel, techniques, and AE hardware; thus, it is useful for nondestructive testing laboratories.
Keywords: acoustic emission; signal simulator; educational facility; professional training; nondestructive testing

This article discusses analytical dependences of uniform elongation δp and ratios of yield strength to ultimate strength of metal on parameter of strain strengthening n in the Meyer equation. These dependences are verified experimentally for carbon and pearlitic steels upon determination of n using oblique illumination in a microscope for measurement of indentation diameter. The Meyer equation cannot be applied for some austenite steels because of structural phase transformations in deformed metal under indentation.
Keywords: spherical indenter; indentation; strengthening parameter; uniform elongation; yield strength; ultimate strength; diagnostics of metal

A mathematical processing technique and an algorithm for the numerical correction of experimental displacement fields on the specimen surface in the vicinity of a crack tip with consideration of the displacement of a body as a rigid whole under its loading and the actual position of a crack tip were proposed. The initial experimental displacement fields in the vicinity of a fatigue crack tip of a compact specimen were determined by digital image correlation. This approach was successfully used for a compact specimen and the possibility of its expansion to obtain the distributions of the stress intensity factors and the nonsingular T stresses along the spatial crack front was shown.
Keywords: compact specimen; stress intensity factor; T stresses; experimental–numerical technique; digital image correlation; mathematical data processing; minimization problem; finite element method

Measurement of Material Deformation with Fiber Bragg Gratings (Summarization) by V. V. Makhsidov; A. M. Shienok; D. V. Ioshin; V. A. Reznikov (1570-1577).
Fiber sensing elements based on Bragg gratings (FBG) are a prospective basis of sensors for detecting deformations in measuring systems, in particular, for integrated control of various structures. The possibility of their application in the structure of polymer composite material for aerospace construction elements is examined. The FBG operating principle is based on change in the period of the grating—the periodic structure of the refractive index of an optical fiber core. Change in the period can cause either thermal expansion or compression of an optical fiber. Therefore, to solve integrated control problems, one has to understand the cause of optical fiber deformation in the area of location of FBG—with change in mechanical loading applied to it or thermal operating conditions. Proposed approaches to the allowance for temperature change when measuring deformation with FBG are systemized and the results of works in this field are presented. Possible implementations of each approach are described. Measurement accuracy of deformation and temperature is determined. The structural scheme of sensing elements is described.
Keywords: fiber sensor element; fiber Bragg grating; deformation; polymer composite material; integrated control; FBG; PCM

The damaged zone (the inelastic deformation zone) near a crack tip is the region where the stress–strain state (SSS) cannot be described by fundamental functions in the solution of the elastic problem of a crack (the Williams solution). For the description of SSS outside the damaged zone, the Williams expansion is used, which requires a number of regular terms to be considered. It is proposed to use digital optical techniques for measuring the SSS parameters in the crack zone to provide a large amount of experimental information in the form of displacement fields on the surface of the studied object directly in digital form.
Keywords: crack; fracture mechanics; evaluation techniques for singular and nonsingular components of displacement fields; modeling errors; plasticity zone