HIGH-RISE TEMPERATURE DEPENDENCES FOR ISOTHERMAL SPACE OBJECT OF THE SPHERICAL FORM

Thermal balance of spherical space object in a near-earth space is investigated. Analytical description of stationary average temperature of such object in view of the existence of internal sources of thermal emissions and sunlight absorbed by its surface is received. Mathematical model, describing thermal balance of space object, is presented by the uniform equation combining two private models. One model considers heat irradiation from the object into space and radiation towards the Earth as well. The second one considers a shielding of a radiation stream into space by the Earth only. The choice of a model is defined by the direction of resultant radiation stream between object and the Earth. Functions describing high-rise dependences of temperature for space object of the spherical form are received. In the Earth shadow the choice of a model and the formulas, describing temperature for space object, is defined by the value of specific power of thermal emissions and its temperature level. On a solar site of a trajectory the choice of high-rise function type depends also on the ratio between coefficient of sunlight absorption and the degree of blackness for object surface. Criteria are offered making it possible to choose the function type, describing the relative change of object temperature with the height growth, prior to the beginning of calculations. Results of calculations carried out with the usage of high-rise functions, following from two models, are presented, and the limits of applicability for these functions are specified. Deduced analytical formulas give the possibility to calculate the temperature of spherical space object. Received conclusions are correct for convex form objects of standard configurations

The origin of fracture in the I-ECAP of AZ31B magnesium alloy

Magnesium alloys are very promising materials for weight-saving structural applications due to their low density, comparing to other metals and alloys currently used. However, they usually suffer from a limited formability at room temperature and low strength. In order to overcome those issues, processes of severe plastic deformation (SPD) can be utilized to improve mechanical properties, but processing parameters need to be selected with care to avoid fracture, very often observed for those alloys during forming. In the current work, the AZ31B magnesium alloy was subjected to SPD by incremental equal-channel angular pressing (I-ECAP) at temperatures varying from 398 K to 525 K (125 °C to 250 °C) to determine the window of allowable processing parameters. The effects of initial grain size and billet rotation scheme on the occurrence of fracture during I-ECAP were investigated. The initial grain size ranged from 1.5 to 40 µm and the I-ECAP routes tested were A, BC, and C. Microstructures of the processed billets were characterized before and after I-ECAP. It was found that a fine-grained and homogenous microstructure was required to avoid fracture at low temperatures. Strain localization arising from a stress relaxation within recrystallized regions, namely twins and fine-grained zones, was shown to be responsible for the generation of microcracks. Based on the I-ECAP experiments and available literature data for ECAP, a power law between the initial grain size and processing conditions, described by a Zener–Hollomon parameter, has been proposed. Finally, processing by various routes at 473 K (200 °C) revealed that route A was less prone to fracture than routes BC and C

Severe plastic deformation of TWIP steel

The severe plastic deformation of a Twinning Induced Plasticity (TWIP), 0.61C-22.3Mn-0.19Si-0.14Ni-0.27Cr (wt. %) steel by Equal Channel Angular Pressing (ECAP) at elevated temperatures was used to study the deformation mechanism as a function of accumulated strain and processing parameters. The relationship between the microstructures after different deformation schedules of ECAP at the temperatures of 200, 300 and 400oC, strain hardening behavior and mechanical properties was studied. The best balance between strength and ductility (1702 MPa and 24%) was found after 2 passes at 400oC and 300oC of ECAP. It was due to the formation of deformation microbands and twins in the microstructure. The twinning was observed after all deformation schedules except after 1 pass at 400oC. The important finding was the formation of twins in the ultrafine grains. Moreover, the stacking faults were observed in the subgrains with the size of 50nm. It is also worth mentioning the formation of nano- twins within the micro-twins at the same time. It was found that the deformation schedule affects the dislocation substructure with formation of deformation bands, cells, subgrains, two variants of twins that, in turn, influence the strain-hardening behavior and mechanical properties. Keywords: Twinning Induced Plasticity steels; Equal Channel Angular Pressing; mechanical properties; transmission electron microscopy; micro/nano twins; dislocation substructure

Modeling of the Earth’s Planetary Heat Balance with Electrical Circuit Analogy

The integral heat model for the system of the Earth’s surface—the atmosphere—the open space based on the electrical circuit analogy is presented. Mathematical models of the heat balance for this system are proposed. Heat circuit which is analog of the electrical circuit for investigating the temperature dependencies on the key parameters in the clear form is presented

The Influence of the Atmospheric Transmission for the Solar Radiation and Earth’s Surface Radiation on the Earth’s Climate

The physical and mathematical model of the planetary heat balance is developed to establish the influence of the atmospheric transmission for the solar radiation in the shortwave spectrum range and for the surface IR radiation in the longwave spectrum range on the Earth’s climate. It is shown the possibility of the decreasing of the atmospheric and surface temperatures with the decreasing of the atmospheric transmission for IR spectrum range, and this decreasing can’t be equilibrated with the change of the atmospheric transmission for the incoming solar radiation

Effect of counterpressure during equal-channel angular pressing on nanoporosity formation in ultrafine-grained copper

Results of small-angle X-ray scattering and high-precision density measurements showed that the application of counterpressure during the equal-channel angular pressing (ECAP) of ultrafine-grained copper leads to a decrease in nanoporosity and an increase in mechanical properties of the ECAP-processed metal

Asymmetric rolling of interstitial-free steel using one idle roll

The effect of additional shear on the asymmetric rolling (ASR) of an interstitial-free (IF) steel was studied by modeling and experiments. The asymmetry was introduced by making one roll idle. A 66 pct of total thickness reduction was performed in 6 passes with less than 16 pct reduction per pass. ASR was performed in two ways: monotonically and by rotating the sheet between passes by 180 deg around the rolling direction (RD). Better grain fragmentation was obtained in the near surface layers. The results of monotonic asymmetric rolling are similar to symmetric rolling in terms of misorientation and cell size with the difference that the volume fraction of grains containing shear bands (SB) is larger for monotonic ASR. ASR with the sheet rotated 180 deg around the RD direction between passes showed the most promising results in terms of grain refinement, depth of the highly deformed layer, texture, and properties. The grain fragmentation process was also simulated with a recent grain refinement polycrystal model for strain hardening, texture development, grain size distribution, and grain misorientation distribution. The obtained simulation results showed strong agreement with the experiments