Том 53, № 15 (2017)

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.

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.

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.

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.

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.

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.

This article discusses analytical dependences of uniform elongation δ_p 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.

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.