Stress-strain curves of polycrystals: Analysis of hardening and softening

The stress-plastic strain curve is regarded as a result of the simultaneous action of two processes: hardening occurring during instantaneous loading and softening which depends on temporal parameters. A physical interpretation of the piecewise-parabolic dependence for the stress—plastic strain curve is given. It was established experimentally that the instantaneous stress-plastic strain curve of a number of annealed polycrystals (copper, brass, duralumin, steel) regardless of the degree of plastic strain or type of deformation substructure can be described by a single parabolic function called the astructural stress-strain curve. The formation of the substructure provides realization of softening processes, the rate of which depends on the type of substructure. A criterion of transition from one parabolic segment of the stress-strain curve to another and, accordingly, change of the deformation substructures is formulated as the condition of maximum stress relaxation during deformation.Translated from Problemy Prochnosti, No. 10, pp. 18–33, October, 1995.     

On some criterial problems of fatigue crack initiation and growth in polycrystals

We address a relationship between mechanisms and direction of a fatigue crack growth at stages I and II. The criteria for the fatigue crack growth direction at those stages are substantiated based on a study of physical and mechanical features of the fatigue crack propagation in polycrystals. We discuss the conditions under which microcracks may initiate brittle fracture. __________ Translated from Problemy Prochnosti, No. 4, pp. 5–24, July–August, 2008.     

Effect of strain rate on the nature of failure in static and cyclic loading. Report 1. Formulation of general approaches

On the basis of the processes of initiation and growth of voids at grain boundaries, the authors develop a physicomechanical model of intergranular cavitation failure of polycrystalline materials. The model can be used to predict endurance in static and cyclic loading structural members in a multiaxial stress state and at a variable strain rate. An approach to describing the effect of this rate on the nature of failure of the material and transition from intragranular to intergranular failure is formulated.Translated from Problemy Prochnosti, No. 2, pp. 3–14, February, 1991.     

The Effects of Acidosis on eNOS in the Systemic Vasculature: A Focus on Early Postnatal Ontogenesis

The activity of many vasomotor signaling pathways strongly depends on extracellular/intracellular pH. Nitric oxide (NO) is one of the most important vasodilators produced by the endothelium. In this review, we present evidence that in most vascular beds of mature mammalian organisms metabolic or respiratory acidosis increases functional endothelial NO-synthase (eNOS) activity, despite the observation that direct effects of low pH on eNOS enzymatic activity are inhibitory. This can be explained by the fact that acidosis increases the activity of signaling pathways that positively regulate eNOS activity. The role of NO in the regulation of vascular tone is greater in early postnatal ontogenesis compared to adulthood. Importantly, in early postnatal ontogenesis acidosis also augments functional eNOS activity and its contribution to the regulation of arterial contractility. Therefore, the effect of acidosis on total peripheral resistance in neonates may be stronger than in adults and can be one of the reasons for an undesirable decrease in blood pressure during neonatal asphyxia. The latter, however, should be proven in future studies.     

Protective properties of petroleum lubricating oils

Chemistry and Technology of Fuels and Oils -     

An ultrasonic method of mixing powders of refractory metal dichalcogenides with gallium-base low-melting-point alloys

Conclusions The investigation has shown that ultrasonic treatment is the only effective mechanical method of mixing the components of systems consisting of tungsten and molybdenum disulfides (or diselenides) and gallium-base low-melting-point alloys. Ultrasonic treatment results in the formation of homogeneous mixtures of MoS₂, WS₂, MoSe₂, and WSe₂ with gallium alloys in a wide range of concentrations of the latter component (from 5 to 50 wt.%).Translated from Poroshkovaya Metallurgiya, No. 11(179), pp. 42–45, November, 1977.