Microplasticity behavior of porous nickel

We have used a physical and structural approach to study the mechanical behavior of monoporous И=5–45%) and biporous (И=45–70%) nickel powder at room temperature within the strain range 10^?5 to 5·10^?3. We have shown that for both low porosity and high porosity materials, the true microyield curves depend on the hardening provided by grain boundaries or interparticle boundaries. We found effects connected with the geometrical structure of the materials under investigation. The increase in the deforming stresses in the base metal material when the porosity is greater than 25% can be explained by the peculiarities of the stress states in the interparticle connections. The softening effect, which depends mainly on the porosity of the powder subsystem, is related to initiation of cracks in the initial phases of microyield.     

Energy saving for steelmaking in plasma-arc furnaces

A design for a plasma-arc steel-melting furnace with four plasma generators and a rational method for steelmaking, which can decrease the heat time and the electric energy consumption, are pro- posed. The rational arrangement of wall plasma generators in the liquid stages of a heat are determined by analytical investigations.     

Limiting state of two-phase composites under uniaxial tension

We propose a model based on the statistical analysis of fracture processes and a concept of effective medium when a system of structural elements of different kinds is regarded as a quasihomogeneous medium with certain effective properties. This approach enables one to compute parameters of the stable stage of fracture of composite materials. The suggested model is used for the prediction of critical values of the parameters corresponding to the transition to unstable fracture under uniaxial tension. We also compare two-phase composites with brittle and plastic phases with strong and weak interfaces between the structural elements, respectively.Frantsevich Institute for Problems in Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 6, pp. 51–58, November–December, 1995.     

Bistability and self-pulsing in Cerenkov-type optical parametric interactions

A Cerenkov-type optical parametric oscillator exhibiting optical bistability, hysteresis, self-pulsing, and other effects is discussed. Noteworthy are a low threshold intensity of the pumping beam and a short characteristic time of the relaxation to steady-state light oscillations in the oscillator.     

Principles of the design of highly porous layered composites working in the bending mode

A comparative analysis is made of the spesific mechanical characteristics of a sandwich-type laminated porous composite under bending. The external layers of the composite are compact while the internal layer consists of a highly porous material made by using a pore-forming agent. The specific stiffness, strength, and yield load as a function of the volume fraction of pores Θ and the porous/compact-layer thickness ratio λ are considered. The stiffness, strength, and yield load are shown to be affected by variations of Θ and λ when the weight of the composite is constant. Translated from Poroshkovaya Metallurgiya, Nos. 3/4(412), pp. 70–78, March–April, 2000.     

Anisotropy of destruction viscosity of hot-pressed silicon nitride

The paper discusses the study of destruction viscosity and hardness of silicon nitride samples produced by hot pressing from powder and rolled ribbons. Anisotropy of crack resistance and a crystallographic texture are identified in both types of samples. The studies establish that the destruction viscosity in the direction parallel to the hot pressing force is higher than in the perpendicular direction. Acomparative analysis of anisotropy reveals its weak dependence on preliminary rolling. __________ Translated from Novye Ogneupory, No. 7, pp. 56–62, July, 2006.