Macroscopic investigation of the radiation creep of metals

The creep of metals and alloys during irradiation is investigated. It is noted that radiation-induced defects are a cause of the acceleration of a material's creep and hardening. A variant of the theory of flow, which describes the phenomena of radiation hardening and radiation creep is proposed. A function characterizing the degree of a material's saturation with radiation defects is introduced in the equation of the theory of flow. The case of uniaxial tension is discussed as an example. Quantitative correspondence between computed and experimental data is achieved by the selection of parameters of the equations for each material. Curves of the theoretical and experimental strain values of the steady-state creep of aluminum for different temperatures and neutronflux intensities, and also the dependence of the radiation-creep rate on stress are given.Translated from Problemy Prochnosti, No. 3, pp. 43–45, March, 1990.     

Investigation of the mechanisms of heat conduction in dielectrics and metals on the basis of the molecular-radiation theory of transfer

The activation mechanisms of transfer of a substance in condensed media are described. Analytical expressions defining the dependences of the electron, photon, and diffusion heat conductivity on the temperature, density, and microscopic characteristics of these media are presented. The temperature dependence of the density of free electrons in conductors was obtained. The results of a comparison of theoretical and experimental data are presented.     

Coupled modeling of steady-state creep rate and creep rupture strength for metals

New methods of coupled mathematical modeling of steady-state creep rate and creep rupture strength of metals in tension have been devised. Two nonlinear fractional power functions with four material constants are used as basic dependences of the steady-state creep and creep rupture life on stress. Computation of the functions is based on optimally solving two nonlinear and inconsistent — in the conventional meaning — equations sets by the method of minimization of quadratic residuals. The authors outline the methods for calculating material constants, which were used to derive analytical expressions that optimally approximate the test results for 10Kh15N27T3MR steel at 600°C under various stresses. A method of piecewise-linear approximation of creep rupture strength test results, which involves the use of a two-segment broken line, is put forward. It implies that the locations of kinks as well as other numerical characteristics of the broken line are determined from the condition of the line’s optimal arrangement relative to the experimental data points. The method takes a more comprehensive account of various damage accumulation mechanisms in steel under various stress levels. __________ Translated from Problemy Prochnosti, No. 4, pp. 25–35, July–August, 2008.     

On the creep of some metals at the superconducting transition

The influence of the superconducting transition on the creep of lead, indium, tin, and thallium was studied. It is shown that the transition to the superconducting state was accompanied by the jump-like creep-rate increase (sharp jump of the deformation creep curve). The jump of the deformation creep curve is indirectly dependent on the stress at which the metal transition from the normal (N) into the superconducting (S) state occurs and is observed when reaching some threshold value of the flow stress which differs for various metals. The regularities of the above phenomenon were investigated at transient and constant-strain creep rate. The time law of the creep in the N and S states and the character of the temperature dependence of the observed effect were determined. It is demonstrated that previously known experimental data and those described in the present paper can be explained without contradiction if they are interpreted in terms of the dynamic drag of dislocations, from the viewpoint of the disappearance of the force of their interaction with the conduction electrons during the N S transition, as well as the increase of the number of movable dislocations in the course of this transition.     

Phenomenological theory of the effect of negative creep

On the basis of the macroexperimental facts of the behavior of materials with the effect of negative creep, the article suggests an applied theory of deformation of these materials. When a body is subjected to a thermomechanical effect, the increase of full deformation consists of the sum of the increases of thermoelastic mechanical, thermal, and phase deformations. The article suggests a method of describing phase deformation by Heaviside functions and introduces the concept of the modulus of transformation of the phase Poisson ratio. It deals with the problem of thermomechanical loading of a thick-walled cylinder made of material with shape memory.Translated from Problemy Prochnosti, No. 2, pp. 44–48, February, 1991.