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.     

Protective properties of petroleum lubricating oils

Chemistry and Technology of Fuels and Oils -     

Remodeling of Arterial Tone Regulation in Postnatal Development: Focus on Smooth Muscle Cell Potassium Channels

Maturation of the cardiovascular system is associated with crucial structural and functional remodeling. Thickening of the arterial wall, maturation of the sympathetic innervation, and switching of the mechanisms of arterial contraction from calcium-independent to calcium-dependent occur during postnatal development. All these processes promote an almost doubling of blood pressure from the moment of birth to reaching adulthood. This review focuses on the developmental alterations of potassium channels functioning as key smooth muscle membrane potential determinants and, consequently, vascular tone regulators. We present evidence that the pattern of potassium channel contribution to vascular control changes from K_ir2, K_v1, K_v7 and TASK-1 channels to BK_Ca channels with maturation. The differences in the contribution of potassium channels to vasomotor tone at different stages of postnatal life should be considered in treatment strategies of cardiovascular diseases associated with potassium channel malfunction.     

Probabilistic prediction of the crack resistance of nuclear pressure-vessel steels on the basis of a local approach. Part 2

On the basis of a new local probabilistic criterion of brittle fracture, a local criterion of ductile fracture proposed by the authors earlier, and the obtained approximate solution of the problem of stress-strain state near the crack tip, we develop a probabilistic model for the prediction of the crack resistance of pressure-vessel steels. The model enables one to predict the dependence of K _Ic on temperature for any given probability of brittle fracture and the influence of the thickness of the specimen on K _Ic. Bu using this model, we can also describe the temperature range of the brittle-ductile transition. The results of numerical calculations are compared with the experimental data for 15Kh2MFA pressure-vessel steel. It is shown that the proposed model fairly well describes the spread in the experimental data on the crack resistance of this type of steel. TsNII KM “Prometei,” St. Petersburg, Russia. Translated from Problemy Prochnosti, No. 2, pp. 5–22, March–April, 1999.