This instrument is based on a new method for testing the quality of fitting the inner bearing race on a wheelset axle of a railway car. The operating principle of this instrument is described, and its performance characteristics are presented.One of the problems associated with the provision of railroad safety is the absence of both reliable methods and commercially produced instruments for testing the quality of fitting (i.e., tightness) of inner bearing races on the wheelset axles of railway cars [1][2][3][4][5][6][7]. The standard technique currently in use [8] is characterized by inadequate reliability, because it consists of measuring the diameters of a race and an axle before they are assembled. In this case, it ignores the fact that the procedure of heating the race and setting it on the axle, which is characterized by a great number of random parameters, has a very strong effect on the quality of the fit.Below we describe a èë -219 instrument based on a more reliable inspection method in which a race that has been fitted on an axle is subject to inspection. The function of the instrument consists in measuring the period of time it takes for a pendulum that collides with a race that has been fixed over an axle (Fig. 1) to perform a predetermined number of oscillations. The fit (tightness) is considered normal if the measured time interval is greater than a certain preset value.In a laboratory experiment carried out before designing the instrument, a 12-mm-diameter steel ball was suspended on a thread 70 mm long. The optical axis of a photon-coupled pair (an LED and a photodetector) was located 12 mm away from impact point A .Upon incidence and following recoil, the ball shut off the optical beam's path. As a result, a sequence of output pulses was formed by the photodetector. By processing these signals with a counter and a timer, it was possible to measure the time taken for a predetermined number of pendular oscillations. The first oscillation began when the pendulum was released at starting point B .When the ball collided with the race, a portion of its kinetic energy was transformed into the potential energy of elastic deformation, and the other portion was converted into the energy of a longitudinal acoustic wave propagating toward the axle. The coefficient of the wave's reflection from the race-axle interface varied according to the quality of the race's fit on the axle. As a result, the reflected wave (its front reached point A before the mechanical interaction between the ball and the race ended) changed in amplitude, which altered the kinetic energy of the ball after recoil.The external appearance of the instrument is shown in Fig. 2. There is a semicircular mounting seat at its bottom; its width is equal to that of the raceway in a bearing. When the instrument is placed on the race being tested, the mounting seat must register perfectly with the raceway. A liquid-crystal display, a control panel, and a level are all located on the upper panel of the instrument. The body of the instrument is prote...
The relationships between the sequence of deformational and fracture stages in solids and the integral parameters of an accompanying acoustic emission (AE) are analyzed. A method for reconstruction of the true (radiated) intensity of flow, the spectrum, and the duration and energy of an AE-act is described and the results obtained are presented. The S-shape of the curve of AE-act flow is physically interpreted. The possibility of identifying the fracture stages and, based on the positions of the break points in this curve, estimating the concentration of defects and their multiplication constants is shown. It is found that the lower break point in the curve corresponds to the transition point from the stage of plastic deformation to the stage of scattered accumulation of flaws. It is suggested that the appearance of this break point be used for the early detection of a material's destruction point. The upper break point is interpreted as the point of a change in the multiplication constant caused by the beginning of the localization of the defect generation process.The diagnostics and modeling of the early stages of a solid's fracture encounter considerable difficulties. Classic methods of continuum mechanics and fracture mechanics can be applied if the characteristic size of a single defect (crack) is at least 1 mm. This means that the presence of a single crack has a considerable effect on the strain-stress state (SSS) in the vicinity of a crack. In view of this, a new approach based on the study of the relationship between acoustic emission (AE) parameters and the kinetics of flaw accumulation in solids has actively been developed for over 30 years, along with conventional approaches.So far, the AE methods of diagnostics which find the widest practical use are based on such integral (in the general meaning of this term) parameters of the AE flow as intensity (activity), total number, and energy of detected AE signals. The high informativeness of these parameters follows directly from the nature of the AE phenomenon that involves radiation of elastic waves formed directly in the process of internal local restructuring (or damage) of a solid's structure.The relationship between AE and the stages of the defect generation processes, as well as the possibility of diagnosing the early fracture stages based on integral AE parameters, is studied in the present work.Each collective act of damaging (or restructuring) a structure (dislocation avalanche, merging of microcracks, merging of microcracks with a macrocrack, etc.) is accompanied by generation of an initial elastic pulse; the process of its radiation is known as an acoustic-emission act. Therefore, measurements of either flow intensity (flow rate) of AE acts or their total number N a makes it possible in principle to quantitatively study the kinetics of flaw accumulation and to diagnose the early fracture stages.From the formal point of view, it does not make any difference which parameter to detect, because it is easy to calculate ( t ) using the measured funct...
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