The strength of materials is determined by their atomic molecular structure and the process of decay of atomic molecular bonds, which must be taken into account when optimizing materials strength control technologies. The fracture photomicrograph of metal microdamage of welded joint at various moments of time, a multilevel model of flow of acoustic emission signals of materials are presented. The physical meaning, the scale level of parameters included in the model are revealed. The structure of the mathematical model of the flow of AE signals with components of its informative elements of different scale level by strength characteristics of structural materials and resource of technical objects is shown. The multilevel model of the AE signal flow is hierarchically structured, obtained by generalizing deterministic-statistical variability. It describes the process of randomly recording deterministic accumulated damages in the material both before and after the formation of a crack at the stage of waiting for its next leap. It is shown that the proposed nanotechnology of strength control of materials is reduced to non-destructive determination of parameters of prognostic homogeneous destruction, identification of which is based on multilevel modeling of time dependence of micro-crack formation, formulation of criterion of strength homogeneity, registration of AE parameters related to the model of a specific product, which can be automated processing of registration results and determination of universal strength nanoconstants from already published reference data of fatigue tests of standard material samples.
While manufacturing and exploitation of different materials, there could be observed complex physicochemical processes of interaction between their individual components and these components with the environment. Revealing such mechanisms helps to understand their distinct features and optimize technological processes of manufacturing materials with certain characteristics. The solution could be based on interpretation of results of acoustic emission (AE) tests from the perspective of multilevel kinetic model of AE of heterogeneous materials. The article describes the research, the essence of which was to identify systematic changes in the values of the parameters of the AE coefficients included in the model when changing various technological and operational factors on the basis of their operational assessment based on the results of acoustic emission tests.
The method of acoustic emission (AE) and the information-kinetic approach to AE diagnostics are identified as the most promising from the point of view of observing the process of growth of damage and optimization of production technologies. Based on a multi-level model of the time dependence of AE parameters, estimation of elastic homogeneous fracture intensity parameters of representative structural elements of a product and universal strength nanoconstants, the approach combines the traditional experimental way of resource estimation and kinetic representations of fracture. This allows to separate the effect of macro- and nano-factors on the AE of the material, variously related to the strength and acoustic emission activity of the material. A multilevel model and an informational-kinetic approach to acoustic emission diagnostics are described, combining nano-, micro- and macro-factors affecting acoustic emission activity, reliability of technical objects and methods for assessing their resource. On the example of a welded pressure vessel, the implementation of the method of its nano-diagnosis is considered. The possibility of effective resource estimation of various technical objects based on the information-kinetic approach to their acoustic emission diagnostics is shown. As a methodological basis, a multilevel model of the time dependences of the AE parameters is taken, which describes their behavior under conditions of strength and metrological heterogeneity.
Traditionally, the problem of monitoring the condition of rolling bearings can be solved based on registration of control signals that occur when the bearing performs a kinematic function due to contact of surface damage which is accumulated and caused by the processes of friction, impact, heat generation, contact electrical interaction, generation of elastic vibrations from them, etc. Relative to the bearing function of bearings, the diagnostic value of such signals is quite low, since they depend on many factors that are not related to resource-determining processes and play a destabilizing role in establishing the connection between control parameters and condition. The solution of the problem must be carried out based on a systematic approach linking the control of the object with the main criterion of its performance. Since the cause of bearing failures is fatigue processes occurring in the material of their elements, the most promising methods are those based on the registration of signals associated with the restructuring of the structure and the accumulation of damage of the material, and in particular, the method of acoustic emission (AE) based on recording the phenomenon of waves of elastic radiation at loading. The development of the acoustic emission method for monitoring the state of rolling bearings is based on a multi-level model of the time dependence of AE parameters, and the control is based on the assessment of the intensity parameters of the resource-determining stage of uniform elastic fracture of representative structural elements of the material of the test object. AE informative signals are selected, and diagnostic parameters are determined at the interlevel transition from macro- to micro- and nano-level. The idea of the transitions is to select representative informative parameters and to trace the connection between them through AE strength indicators that can highlight a useful signal in conditions of high instability and heterogeneity of the accompanying processes. The experimental stup and the results of experimental studies of AE of rolling bearings with an artificially created defect on the surface of the outer ring are described, the results of control are compared with the results of the analysis of the stress-strain state around the created defect, the informative value of the concentration and kinetic index and the possibility of evaluating the resource based on it are shown.
Geophysical methods for local rock burst prediction are currently being developed along two lines: improving recording equipment and improving data processing methods. Progress in developing processing methods is constrained by the lack of informative prognostic models that describe the condition of rock mass, the process of rock mass fracturing, and the phenomena that can substantiate the choice of both criteria and test parameters of the condition of rock mass and give an estimate of the time remaining until rock pressure manifestation. In particular, despite achievements in hardware design, researchers using the seismo-acoustic method to predict rock bursts measure the acoustical activity or energy capacity of elastic wave scattering after a man-made explosion and are faced with the dependence of forecast results on destabilizing factors. To solve this problem, we applied an information and kinetic approach to forecasting. In this article, we discuss the principles of selecting test parameters that are resistant to destabilizing factors. We propose a micromechanical model of fracture accumulation in a rock mass block that reflects the dependence of acoustic emission (AE) parameters on time, which makes it possible to detect the influence of various factors on forecast data and filter the signals. We also propose criteria and a methodology for rock burst risk assessment. The results were tested in analyzing the seismo-acoustic phenomena caused by man-made explosions at the Taimyrsky and Oktyabrsky mines in Norilsk. The article gives examples of using the proposed criteria. The effectiveness of their application is compared with traditional methods for assessing rock burst risks and evaluating the stress–strain parameters of rock mass in terms of their being informative, stable, and representative by means of statistical processing of experimental data.
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