Fig 5 - uploaded by Vasiliy Krutikov
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Schematic representation of the inductor failure mechanisms for quenched steels (a) and after additional hardening by nitriding (b).
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... field pressure. Further this furrows, directed along the inductor channel (transversely to the current), result in straight cracks formation (Fig. 3a, III). Among the MFCs of quenched steel the ultimate number of pulses was about 60. Thus, two mechanisms of inductor failure attributed to the different steel toughness have been differentiated (Fig. ...
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Citations
... Механизм малоцикловой усталости будет запущен, если в ходе первого импульса материал дважды достигает порога текучести [15]: при омическом нагреве и при последующем охлаждении. В то же время в случае относительно хрупкого материала, не обладающего достаточным ресурсом пластичности, разрушительным мо-жет оказаться даже однократное достижение предела текучести при самом первом нагреве [16]. Именно такое (хрупкое) разрушение проводящего материала является предметом исследования в настоящей работе. ...
... В отличие от индивидуальных параметров, перечисленных в таблице, изменение которых для заданного материала труднореализуемо, удельное сопротивление материала ρ * e представляется более удобным параметром для варьирования в достаточно широких пределах. Во-первых, значения удельного сопротивления сильно отличаются для различных проводящих материалов, а во-вторых, даже для заданного материала достаточно широкое изменение величины ρ * e возможно за счет допирования, ионно-плазменной обработки, порошковых технологий, использования составных (например, биметаллических) проводящих материалов и т. д. [16,20,38,39]. В связи с этим проанализируем зависимость B th (ρ * e ) в диапазоне от сопротивления меди (ρ * e = 1.7 · 10 −8 · m) до сопротивления высокорезистивных сталей (ρ * e ≈ 100 · 10 −8 · m). ...
The main factors resulting in conductor failure under the action of a strong pulsed magnetic field are analyzed. The theoretical model describes the geometry of a cylindrical thick-walled solenoid and considers magnetic field diffusion, ohmic heating of the material and mechanical stresses arising in it. The magnetic field amplitude at which induced stresses in the material reach the von Mises yield criterion is used as the Bth threshold field separating the areas of safe (non-destructive) and dangerous fields. In the case of an initially uniform material, the maximum heating temperature corresponding to this limit, which predetermines the thermomechanical stress, has been derived analytically. In the general case, based on the analysis of the calculated threshold field, the influence of various parameters (magnetic pulse characteristics, elastic moduli of the material, etc.) on the conductor resistance in the pulsed magnetic field is studied and ways of increasing the threshold field are proposed, in particular, by using different spatial profiles of the initial resistivity. It is shown that in comparison with a uniform material, a modified layer with increased resistivity formed on the surface allows to significantly increase the amplitude of the magnetic pulse withstood by the material without fracture.
... The low-cycle fatigue mechanism will be triggered if the material reaches the yield threshold [15] twice during the first pulse: during ohmic heating and subsequent cooling. At the same time, even a single achievement of the yield strength at the very first heating can be destructive in the case of a relatively brittle material that does not have a sufficient plasticity resource [16]. This (brittle) destruction of the conductive material is the subject of study in this paper. ...
... In contrast to the individual parameters listed in the table, the change of which for a given material is difficult to implement, the resistivity of the material ρ * e seems to be a more convenient parameter for varying within a sufficiently wide range. Firstly-, the resistivity values are very different for different conductive materials, and -secondly, even for a given material, a sufficiently wide change in the value of ρ * e is possible due to doping, ionically-plasma processing, powder technologies, the use of composite (for example, bimetallic) conductive materials, etc., etc. [16,20,38,39]. In this regard, we will analyze the dependence of B th (ρ * e ) in the range from the resistance of copper (ρ * e = 1.7 · 10 −8 · m) to the resistance of highresistive steels (ρ * e ≈ 100 · 10 −8 · m). ...
The main factors resulting in conductor failure under the action of a strong pulsed magnetic field are analyzed. The theoretical model describes the geometry of a cylindrical thick-walled solenoid and considers magnetic field diffusion, ohmic heating of the material and mechanical stresses arising in it. The magnetic field amplitude at which induced stresses in the material reach the von Mises yield criterion is used as the Bth threshold field separating the areas of safe (non-destructive) and dangerous fields. In the case of an initially uniform material, the maximum heating temperature corresponding to this limit, which predetermines the thermomechanical stress, has been derived analytically. In the general case, based on the analysis of the calculated threshold field, the influence of various parameters (magnetic pulse characteristics, elastic moduli of the material, etc.) on the conductor resistance in the pulsed magnetic field is studied and ways of increasing the threshold field are proposed, in particular, by using different spatial profiles of the initial resistivity. It is shown that in comparison with a uniform material, a modified layer with increased resistivity formed on the surface allows to significantly increase the amplitude of the magnetic pulse withstood by the material without fracture. Keywords: Magnetic field diffusion, plastic deformation, thermomechanical stress, yield strength, von Mises yield criterion.
This work focuses on making and studying steel conductors with inhomogeneous surface conductivity. Employing such materials (structures) for engineering the high-field pulsed magnets can provide them with enhanced durability. In this work, monotonically changing resistivity was realized by pack chromizing the medium-carbon steels, 30KhGSA and 40Kh, which were treated at 1000 °C in argon for 150 h under the Cr-load of 20 mg/cm
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>
to obtain a diffuse layer with minimal carbides at the surface. An approach to investigate the resistivity distribution across a diffuse layer after steel chromizing is suggested and involves a stepwise surface grinding, resistance measurement, and analytical processing of experimental data. The resistivity profile obtained by this method is well described by the complementary error function. At the near-surface layer, 30KhGSA and 40Kh steels have almost the same values of resistivity, about 110–
$115 ~\mu $
Ohm
$\cdot $
cm, which is 2.9–4.3 times higher than that in the bulk depending on steel. A strong correlation, almost a linear dependence, of resistivity with the depth-derived chromium concentration in the material was found. The proposed method allows one to measure the depth-varied resistivity for ferrous alloys with proper accuracy, while it does not require complex measuring equipment compared with other ones.
The work concerns the realization of a conductor material with monotonically changing conductivity with depth and theoretical description of magnetic and thermal effects in such systems under high magnetic fields. Thick-walled cylindrical single-turn coil of steel was used as model inductor for theoretical and experimental studying. Surface modification of medium carbon steel 30KhGSA was made by pack chromizing. Characterization of modified surface layer depending on chromizing conditions has been made. The full-scale testing the inductors made of this steel with modified surface was carried out using an inductor system with magnetic flux concentrator as a test subject under generation a magnetic field of 50 T in amplitude and 15 µs in half-period. The results are discussed.
