SPECIFIC FEATURES OF INELASTIC PROCESSES IN MATERIALS WITH NANOSCALE DEFECTS

Теоретически проанализирована высокоскоростная деформация сплавов, содержащих зоны Гинье-Престона, в условиях высокоэнергетических внешних воздействий. Анализ выполнен в рамках теории динамического взаимодействия структурных дефектов. Исследуемый механизм диссипации заключается в необратимом переходе энергии внешних воздействий в энергию дислокационных колебаний. Получено аналитическое выражение динамического предела текучести с учетом всех структурных дефектов, содержащихся в сплаве. Показано, что в условиях высокоэнергетических внешних воздействий наноразмерные дефекты влияют на характер зависимости механических свойств от концентрации атомов второго компонента. Зависимость динамического предела текучести от концентрации атомов второго компонента становится немонотонной и имеет минимум. Выполнены численные оценки концентрации, при которой предел текучести становится минимальным. При таком значении концентрации происходит переход от доминирования торможения дислокации зонами Гинье-Престона к доминированию торможения атомами второго компонента. The high strain rate deformation of alloys containing Guinier-Preston zones under high-energy external influences has been theoretically analyzed. The analysis was carried out within the framework of the theory of dynamic interaction of structural defects. The investigated dissipation mechanism consists in the irreversible transfer of energy of an external impact into the energy of dislocation vibrations. An analytical expression for the dynamic yield stress taking into account all structural defects of the alloy has been obtained. It is shown that, under high-energy external influences, nanoscale defects affect the nature of the dependence of mechanical properties on the concentration of atoms of the second component. The dependence of the dynamic yield stress on the atomic concentration of the second component becomes nonmonotonic and has a minimum. Numerical estimates of the concentration corresponding to the minimum yield stress has been made. At this concentration value, a transition occurs from the dominance of the dislocation drag by the Guinier-Preston zones to the dominance of the drag by the atoms of the second component.

In Situ Grafted Composite Nanoparticles-Reinforced Polyurethane Elastomer Composites with Excellent Continuous Anti-Impact Performance

Polyurethane elastomer (PUE) has attracted much attention in impact energy absorption due to its impressive toughness and easy processability. However, the lack of continuous impact resistance limits its wider application. Here, an amino-siloxane (APTES) grafted WS2-coated MWCNTs (A-WS2@MWCNTs) filler was synthesized, and A-WS2@MWCNTs/PUE was prepared by using the filler. Mechanical tests and impact damage characterization of pure PUE and composite PUE were carried out systematically. Compared with pure PUE, the static compressive strength and dynamic yield stress of A-WS2@MWCNTs/PUE are increased by 144.2% and 331.7%, respectively. A-WS2@MWCNTs/PUE remains intact after 10 consecutive impacts, while the pure PUE appears serious damage after only a one-time impact. The improvement of mechanical properties of A-WS2@MWCNTs/PUE lies in the interfacial interaction and synergy of composite fillers. Microscopic morphology observation and damage analysis show that the composite nanofiller has suitable interfacial compatibility with the PUE matrix and can inhibit crack growth and expansion. Therefore, this experiment provides an experimental and theoretical basis for the preparation of PUE with excellent impact resistance, which will help PUE to be more widely used in the protection field.

International Evidence on Extending Sovereign Debt Maturities

Portfolio diversification is as important to debt management as it is to asset management. In this paper, we focus on diversification of sovereign debt issuance by examining the extension of the maximum maturity of issued debt. In particular, we examine the potential costs to the U.S. Treasury of introducing 50-year bonds as a financing option. Based on evidence from foreign government bond markets with such long-term debt, our results suggest that a 50-year Treasury bond would likely trade at an average yield that is at most 20 basis points above that of a 30-year bond. Our results based on extrapolations from a dynamic yield curve model using just U.S. Treasury yields are similar.

Gelatine-Coated Carbonyl Iron Particles and Their Utilization in Magnetorheological Suspensions

This study demonstrates the formation of biocompatible magnetic particles into organized structures upon the application of an external magnetic field. The capability to create the structures was examined in silicone-oil suspensions and in a gelatine solution, which is commonly used as a blood plasma expander. Firstly, the carbonyl iron particles were successfully coated with gelatine, mixed with a liquid medium in order to form a magnetorheological suspension, and subsequently the possibility of controlling their rheological parameters via a magnetic field was observed using a rotational rheometer with an external magnetic cell. Scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis confirmed the successful coating process. The prepared magnetorheological suspensions exhibited a transition from pseudoplastic to Bingham behavior, which confirms their capability to create chain-like structures upon application of a magnetic field, which thus prevents the liquid medium from flowing. The observed dynamic yield stresses were calculated using Robertson–Stiff model, which fit the flow curves of the prepared magnetorheological suspensions well.

Study of methods for estimating the viscosity coefficient of metals

Problem setting. The coefficient of dynamic viscosity of metals is used in many branches of human life, but its search, for a more accurate assessment and interpretation, is currently insufficiently studied due to the variety of its application [1-4], as well as due to the uncertainty of the constant parameters of the environment in which it is applied or investigated. Target. Consider a number of known methods for estimating the viscosity coefficients of metals at different ranges of strain patterns. Results. The methods considered for estimating the viscosity coefficient of metals, during their scientific and theoretical study, did not give an unambiguous answer for determining the viscosity of metals. Practical significance. Further study of the dynamic yield strength and the dynamic viscosity coefficient of metals is necessary to achieve more complete results of the method of evaluating the viscosity coefficient of metals.

Влияние гигантской магнитострикции на динамический предел текучести в условиях высокоскоростной деформации

The high-strain rate deformation of crystals with giant magnetostriction is theoretically analyzed. It is shown that giant magnetostriction has a significant effect on the dynamic yield stress of crystals.