Fatigue failure mechanism of polycrystalline materials at the mesoscopic level

Systematic studies of the mesoscopic mechanisms of deformation of polycrystalline materials of lead and its alloys have been carried out under conditions of sign-alternating bending at room temperature. It has been shown that fatigue failure is due to the evolution of vortices of mesoscopic substructures. Multiple slip separated in adjacent grains is the basis for this kind of deformation. This causes extremely strong localization of the displacement in individual favorably oriented grains and self-organization of these grains in agreement with regular structural levels of deformation. In polycrystalline lead, the mesoscopic substructure has a block character, with each block containing several grains. The elements of such substructures are nucleated in stress mesoconcentrator zones which arise at the grain boundaries under conditions of intense grain boundary slippage. In the course of cycling they gradually propagate through the whole transverse cross section of the sample, which completes its failure. Alloying substantially changes the character of the mesoscopic substructures which are formed. We have considered the different types of vortex mesoscopic substructures and studied their connection with cyclical endurance of the alloy. Recommendations for increasing the fatigue endurance of plastic polycrystalline materials are given. Institute of the Physics of hardening and Materials Science, Siberian Section, Russian Academy of Sciences. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 40–57, June, 1996.     

Nonlinear dynamics of high-density electron-beam resonant instabilities. Analytical solution

We obtain an analytical solution of the nonlinear dynamics of a resonant instability in a dense electron beam. It is shown that the instability of a dense beam saturates because of a nonlinear frequency shift and a deviation from the resonance condition.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 31–35, January, 1984.The authors acknowledge useful discussions with A. A. Rukhadze.     

Self-consistent calculation of the electron energy spectrum of aluminum

The local density function approximation is used to construct a fundamental nonlocally soft pseudopotential for aluminum which satisfies the norm conservation condition. This pseudopotential is used to perform a self-consistent calculation of the aluminum electron energy spectrum, which proves to agree well with experimental data. The effect of various pseudopotentials (constructed with norm conservation) on the form of the energy spectrum is studied. It is shown that these various pseudopotentials lead to identical results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 56–62, September, 1984.     

Strengthening effect of short-range order esf ternary face-centered cubic substitutional solutions

The increase produced by short-range order in the resistance to the movement of dislocations _sro in ternary f. c. c. substitutional solid solutions was studied. A general expression for _sro was derived taking into account the correlation on the first three coordination spheres and the change in the entropy associated with the passage of dislocations. The expressions obtained were used for qualitative calculation of the concentration dependence of _sro for several ternary systems.