The role of plotting of diagrams of isothermal and thermokinetic transformations of supercooled austenite in the development of heat treatment processes of steels is discussed. Specific examples of ...the necessity of plotting of thermokinetic diagrams of transformations in steels for solving critical production problems are considered.
We consider triple configurations of compression shocks in supersonic flows of an inviscid perfect gas. The boundaries of the domain of existence of shock-wave structures of a new type (triple ...configurations with a negative slope of the reflected shock or negative triple configurations) on a set of flow parameters have been theoretically investigated.
The problem of safe functioning of space vehicles is under investigation. Spacecraft safety is essentially affected by the impact of fragments of space debris and meteorites. Impact of small particle ...can lead to a perforation of the structure of a spacecraft or the Space station. The impact can cause formation of a perforation and gradual loss of atmosphere. Under these conditions, it is crucial detecting the point of perforation and take the measures of precaution for the loss of the internal atmosphere. Practically all known methods for testing the integrity of ground-based structures, aircrafts and other complex technogenic objects are inapplicable for solving similar problems of monitoring the spacecraft condition during a spaceflight. To solve this problem, the integrating fiber-optic sensors (IFOS)-based system for monitoring vibration deformation parameters of spacecraft housings’ surfaces is proposed, which can be developed and implemented in the shortest possible time. Mathematical modeling and laboratory studies have confirmed the possibility of using the Integrating fiber-optic sensors system for assessing the dynamic and static parameters of extended structures.
•The problem of safe functioning of space vehicles is under investigation.•Impact of small particle can lead to a perforation of the structure of a spacecraft or the Space station and gradual loss of atmosphere.•Practically all known methods for testing the integrity of ground-based structures, aircrafts and other complex technogenic objects are inapplicable for solving similar problems of monitoring the spacecraft condition during a spaceflight.•To solve this problem, the integrating fiber-optic sensors (IFOS)-based system for monitoring vibration deformation parameters of spacecraft housings’ surfaces is proposed.•Mathematical modeling and laboratory studies have confirmed the possibility of using the IFOS for assessing the dynamic and static parameters of extended structures.
A criterion for the selection of materials to protect against the mechanical dynamic loading is proposed and substantiated. The mechanisms of the fracture of brittle ceramic materials that are widely ...used in structures that prevent penetration and are very common in practice are discussed. Unlike other estimates, the proposed formula is based on the physical principle of comparing the total energies of loading and obstacles, and is in good agreement with the experimental data.
Highly porous aluminum alloys and honeycomb structures may be utilized as single-use shock absorbers in landing gear and other elements of spacecraft thus ensuring safety of the landing process. This ...paper presents the results of studies that make it possible to estimate mechanical properties and shock-absorbing characteristics of highly porous aluminum alloys and honeycomb aluminum alloy structures, the initial average densities of said alloys and structures ranging from 330 to 2250 kg/m³. We list analogs that correspond with different stages found on stress-strain curves of highly porous aluminum alloys and honeycomb structures. The paper also provides the foundations of calculating the specific and effective energies of shock absorption.
•The deformation diagrams of cellular aluminum are close to the idealized one.•Specific and effective impact absorption energy calculated by the deformation diagram.•Some honeycomb structures have a deformation diagram with hardening.•The presence of hardening worsens the shock-absorbing characteristics.•The deformation diagram depends on the porosity, matrix material and pore structure.
The paper is aimed at modeling results of hypervelocity impact of space debris fragments on shielding elements of space structures. For this purpose we developed numerical model based on a smoothed ...particle hydrodynamics method. Verification and validation of the model was made in simulation of a process of a hypervelocity impact of a spherical projectile with a thin plate and comparison with experimental data. The calculations were performed using Ls-Dyna explicit software. Both experimental and calculated debris clouds show practically identical characters of their development, their propagation velocity, shape and size. Collisions of the thin plate with other types of projectiles - cubes with various spatial orientations, cylindrical projectile were considered and their peculiarities analyzed. It was shown, that in case of the cube sharp edge impact, a debris cloud of a higher density, and therefore most dangerous for the considered systems of two plates, is formed.
A method is proposed for increasing the radiation resistance of semiconductor crystals (AlxGa1-x)2O3, which are promising for creating power electronics and optoelectronic devices for spacecraft ...performing tasks in near-earth orbits. The effect of the aluminum content on the bandgap in (AlxGa1-x)2O3 single crystals grown from a melt by the Czochralski method is investigated. The necessary conditions for the formation of a high-quality seed and subsequent growth of single crystals are achieved by setting temperature gradients at each successive stage of growth. The results of energy-dispersive X-ray spectroscopy analysis and optical transmission spectra of (AlxGa1-x)2O3 crystals with an aluminum content from 0 to 7.32% are presented. It is shown that an increase in the aluminum content leads to a monotonic increase in the bandgap from 4.7 eV to 5.0 eV, which provides an increase in radiation resistance.
•Aluminum content increase leads to the bandgap enlargement of (AlxGa1-x)2O3 crystals.•Bandgap enlargement of the semiconductor material enhances radiation resistance of the one.•Radiation robust wide-bandgap semiconductor materials can be utilized for space applications.•Czochralski method grown bulk (AlxGa1-x)2O3 crystals purity depends on temperature gradients at each successive growth stage.
Due to their capability to form high velocity elements, explosive launching devices are used for testing objects of rocket and space technology on anti-meteoric resistance. These devices include ...shaped charges with a combined hemisphere-cylinder liner. Currently used shaped charges with a hemisphere-cylinder liner can produce compact steel elements with velocities of 6 km/s. Based on numerical simulation in the framework of the two-dimensional axisymmetric problem of continuum mechanics, the possibilities of increasing the velocity of compact metal elements formed by shaped charges with a combined hemisphere-cylinder liner up to 9 … 10 km/s are considered. Simulation has been performed for a 100 mm diameter shaped charge with a copper liner. The stated goal has been achieved by giving the jet-forming hemispherical part of the liner a degressive (decreasing from the top to the base) thickness with a change in its shape from hemispherical to semi-ellipsoid. As a result of calculations, liners geometric parameters have been selected to form compact elements of maximum possible mass with velocities in the range from 5 to 9.5 km/s. For an element with a velocity of about 9.5 km/s, the mass was about 5 g.
•Combined hemisphere-cylinder liners can be used to produce high-speed elements.•Degressive thickness of the hemispherical liner allows you to increase the jet speed.•Semi-ellipsoid liner of degressive thickness allows controlling the jet parameters.•The kinetic energy of compact elements remains constant up to a speed of 8 km/s.•The element mass is about 5 g at a speed of 9.5 km/s for the 100 mm charge diameter.
The penetration of an aluminum jet into an aluminum alloy target with a speed of 8–11 km/s is investigated. An analysis of the kinetics and parameters of introduction, and the condition of the ...surface of the cavity after penetration suggests that the hydrodynamic nature of penetration is violated at speeds of more than 9 km/s because of fusion of interacting metals. The results of the study are intended to develop screen protection for spacecraft from the most dangerous fragments of space debris.
In this Letter, we study the destruction of a duralumin barrier when exposed to an aluminum jet (analogous to a fragment of industrial debris) at a velocity of 7–11 km/s in the presence of copper and ...aluminum metal shields. The effectiveness fraction of the shield protection, which is determined by the expansion of parts of the destroyed impactor between the shields, is distinguished. An increase in the efficiency of the shield protection due to the phase transitions of the interacting materials of the impactor and shield is determined.
PDF
