Switch rail is an important basic component of rail transportation. Due to its variable cross section structure, there are many guided wave modes that can propagate inside it. When the ultrasonic guided wave is used t...
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Switch rail is an important basic component of rail transportation. Due to its variable cross section structure, there are many guided wave modes that can propagate inside it. When the ultrasonic guided wave is used to detect the defect of switch rail, the defect echo is often superimposed with complex background signal, which is difficult to extract. To solve the problem that the time-domain baseline method needs complex temperature compensation algorithm and is difficult to be applied in engineering, this article explores a new method from the frequency domain. The Fourier transform is applied to the waveguide signal and the FFT result of a waveguide signal from a nondefective switch rail is selected as the baseline. The difference of the FFT result between the waveguide signal and the baseline is calculated by the algorithm designed, being defined as a frequency-domain operator. The results show that the frequency-domain baseline method has a comprehensive identification rate of 99.89% and that no temperature compensation is required for indoor switch rail detection. Based on this, this article proposes the wavelet baseline method that integrates time-domain and frequency-domain analysis. The 3-D waveform data of the guided wave is transformed by wavelet, the difference between the data to be recognized and the baseline data is calculated based on the corresponding segments by the algorithm designed, and the frequency-time operator is obtained. For indoor datasets, the comprehensive detection rate of the wavelet baseline method is 99.93%, and the defect discrimination is better than that of the frequency-domain baseline method. For outdoor test data collected within 28 days, the comprehensive detection rate of the wavelet baseline method is 99.2%. The defect detection experiment of the switch rail on the actual line with the accessory structure is also carried out. The results show that the wavelet baseline method can effectively identify the defects of the switc
The paper proposes a methodology for incorporating uncertainties of material behaviours in the microstructure evolution model for eutectoid steels. The stochastic model of phase transformations was developed. The mode...
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The paper proposes a methodology for incorporating uncertainties of material behaviours in the microstructure evolution model for eutectoid steels. The stochastic model of phase transformations was developed. The model accounts for a random character of the nucleation of pearlite and bainite and the differential growth equations for these structural components are solved for the stochastic variables. The coefficients in the model were identified using inverse analysis for the results of dilatometric tests. The model was applied to simulations of the cooling of rails by subsequent immersions of the rail head in the polymer solution. Johnson-Mehl-Avrami-Kolmogorow phase transformations model was used to design the optimal cooling cycle. Histograms of the microstructural parameters for this optimal cycle were calculated using the developed stochastic model. It was shown that the probability distributions of the pearlite colony size, the nodule size, the interlamellar spacing and the hardness are asymmetric. The model predicted deviations of microstructural parameters and hardness from the mean values.
This article proposes a practical auxiliary circuit for multiple voltage rails to improve dynamic response under significant load steps with an ultrafast slew rate. The proposed auxiliary circuit consists of a current...
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This article proposes a practical auxiliary circuit for multiple voltage rails to improve dynamic response under significant load steps with an ultrafast slew rate. The proposed auxiliary circuit consists of a current injection/absorption circuit with nonlinear control that can effectively reduce undershoot and overshoot during transients, a sampling mechanism supporting its independent operation, and a reconfigurable energy path supporting multiple voltage rails. The proposed auxiliary circuit is illustrated and verified in a high-power supply system for processors with two voltage rails at different voltage levels, which effectively improves the dynamic response of both voltage rails and demonstrates robustness in fast alternating load steps without affecting regular operation. The maximum load step of 250 A with the current slew rate of 1250 A/mu s is tested, and the overshoot and undershoot are reduced by 36% and 25%, respectively, with recovery times less than 9 mu s. Compared with existing research and solutions, the proposed auxiliary circuit has cost and space savings advantages, better versatility to support a wide range of power supply types, and is easy to implement.
Modern physical metallurgy methods are used to study the structure, phase composition, dislocation substructure, and carbon redistribution in differentially quenched 100-m rails after extremely long operation (passed ...
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Modern physical metallurgy methods are used to study the structure, phase composition, dislocation substructure, and carbon redistribution in differentially quenched 100-m rails after extremely long operation (passed gross tonnage 1770 mln t since 2013). The laws of changing the main parameters, namely, the relative content of various morphological varieties of a structure, the scalar and excess dislocation densities, the volume fraction of cementite, and the redistribution of carbon atoms, are revealed in the cross section of the rail head along the central axis of symmetry and the radius of rounding of the fillet at distances of 0, 2, and 10 mm from the surface. The decrease in the volume fraction of the carbide phase in the surface layer of the head is assumed to be associated with decarbonization and the motion of carbon atoms to defects in the steel structure. The transformations along the central axis are found to proceed much more slowly as compared to the change relative to the fillet radius.
The structural-phase sates and defect substructure are studied by the method of transmission electron microscopy using diffraction at different distances from the wheel-rail contact surface along the central axis of s...
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The structural-phase sates and defect substructure are studied by the method of transmission electron microscopy using diffraction at different distances from the wheel-rail contact surface along the central axis of symmetry of the top of rail (TOR) (rolling surface) and along the radius of rounding (fluting) of the differentially hardened rails of the DH400RK category made of hypereutectoid steel after their continuous service. Using the obtained structure parameters, the estimates are made of the hardening mechanisms (strengthening by pearlite component, incoherent cementite particles, grain- and subgrain boundaries, dislocation substructure and internal stress fields) controlling the yield stress in the steel under study. A comparison is performed of the quantitative fine structure parameters and the contributions into hardening on the rolling surface and fluting. It is found out that the prevailing morphological component near the wheel- rail contact surface is the subgrain structure, and in the fluting - strengthening by incoherent particles.
The structure, phase composition, and dislocation substructure in the head of long differentially quenched special-purpose rails made of E90KhAF steel after a passed gross tonnage of 187 mln t are analyzed. The format...
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The structure, phase composition, and dislocation substructure in the head of long differentially quenched special-purpose rails made of E90KhAF steel after a passed gross tonnage of 187 mln t are analyzed. The formation of flexural extinction contours is observed, which indicates an elastic-stressed state in the material. The sources of lattice curvature-torsion are found to be intra- and interphase boundaries, and the mechanisms of destruction of cementite lamellae are determined.
The studies of structural phase state and defect substructure of head surface of 100-meter differentially quenched rails after extreme long-term service (passed tonnage of 1770 million gross tons) on experimental ring...
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The studies of structural phase state and defect substructure of head surface of 100-meter differentially quenched rails after extreme long-term service (passed tonnage of 1770 million gross tons) on experimental ring of the Russian Railways are carried out by means of the methods of transmission electron diffraction microscopy (TEM). The quantitative comparative analysis of strengthening mechanisms of tread surface and surface of working fillet is performed. It is shown that steel strength is a multifactor value and is determined by combined action of a number of physical mechanisms. The contributions caused by matrix lattice friction, internal stress fields, solid solution strengthening and pearlite constituent of steel structure are estimated. It is detected that for tread surface the main strengthening is provided by long-range stress fields and for fillet the main mechanism is a substructural one. A comparison is made between dependences of combined yield point on a distance to head surface and steel data before operation and after passed tonnage of 691.8 and 1411 million gross tons. The detected decrease in yield point at passed tonnage of 1770 million tons can be related to formation of fragmentary structure in surface layers due to transformation of subgrain low angle boundaries in large angle boundaries in extremely long operation.
In previous studies, the armature-rail sliding contact interface is usually considered to be an ideal slide in which both rails are parallel and symmetric. However, due to the influence of structural deformation of th...
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In previous studies, the armature-rail sliding contact interface is usually considered to be an ideal slide in which both rails are parallel and symmetric. However, due to the influence of structural deformation of the barrel affected by boundary constraints and the manufacturing errors of rails and armature, it often leads to a variety of nonideal the armature-rail matching such as space curved or twisted rails, offset or deflected armature, and so on. This article focuses on the common vertical curved rail in electromagnetic railgun. By introducing centrifugal force effects and coupling electromagnetic force, the armature-rail contact pressure is analyzed theoretically. According to the 3-D finite-element simulation results, the effect of centrifugal force on sliding contact pressure should not be ignored. The effects of different curved radii, velocities, and densities of armature on the contact pressure are compared and analyzed. The influence law on the contact pressure is obtained, which provides a theoretical basis for the design of the railgun.
The inductance gradient is one of the most critical parameters in the electromagnetic rail launcher (ERL). It determines the electromagnetic force and efficiency in the ERL. In general, the inductance gradient in the ...
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The inductance gradient is one of the most critical parameters in the electromagnetic rail launcher (ERL). It determines the electromagnetic force and efficiency in the ERL. In general, the inductance gradient in the rails is treated as a constant. However, the inductance gradient in the rails changes dynamically during the launching process. It is very important for the electromagnetic driving force in the launching process to accurately solve the time-varying inductance gradient. For this reason, a method for establishing the analytical calculation of the time-varying inductance gradient is proposed in this article. The results show that the application conditions of the proposed method are (s/w > 2 and s/h > 1), and the shortest side length of the rail must be greater than 20 mm. At last, in order to verify the applicability of this method, the inductance gradients in five different ERLs injected with the pulse current are calculated and the results obtained are compared with the FEA. The research shows that the inductance gradient in the initial stage changes significantly due to the rapidly changing current frequency. After an interval, it tends to be a constant, which is the result of the stabilization of the current. It is consistent with the results reported in the literature. And if the rail dimensions meet the applicable conditions, the maximum error between the method in this article and the FEA is less than 5%.
Using the methods of transmission electron microscopy, the structure, phase composition and defect substructure of the surface fluting layers of special-purpose rails is studied after their long-term operation. It is ...
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Using the methods of transmission electron microscopy, the structure, phase composition and defect substructure of the surface fluting layers of special-purpose rails is studied after their long-term operation. It is shown that the ferrite and cementite plates contain defects and dislocations chaotically distributed in the material or forming a network substructure. The formation of regions with submicro- and nanocrystalline multiphase structure is observed, where the sizes of the & alpha;-phase and cementite crystallites are found to be 50-75 and 3-8 nm, respectively. There are regions with globular cementite inclusions measuring 150-200nm.
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