Nanoporosity and magnetic performance of Fe58Ni20Si9B13 amorphous metallic alloy

The structure and magnetic properties of this amorphous alloy are studied. The structure was varied by applying a hydrostatic pressure of 10 kbar. By means of small-angle x-ray diffraction analysis, two fractions of nanopores (30 and 140 nm in size) are revealed. The pressure decreases the size of nanopores and raises their mean spacing. As a result of pressure application, the maximal magnetic induction grows, in contrast to the remanent induction. A correlation between the magnetic properties and nanoporosity of the alloy is discussed.     

Correlation between characteristics of thermal and stress reversible deformations in solids with different structures

The dependences of the coefficients of reversible thermal expansion on the tensile stress and the temperature dependences of the elastic modulus are measured for solids with different structures, such as a metal, rigid-chain oriented polymers, and a flexible-chain oriented polymer-poly(ethylene) in the devitrified state. For these materials, the elastic moduli differ by several orders of magnitude, whereas the thermal expansion coefficients can differ not only in magnitude but also in sign. It is found that, for a solid, the derivative of the thermal expansion coefficient with respect to the stress is close to the derivative of the reciprocal of the elastic modulus with respect to the temperature. The inference is made that these parameters do not depend on the specific features of the solids under investigation. Calculations are performed for several mechanisms of thermal and stress deformations of solids with different structures. The results of these calculations are in reasonable agreement with experimental data.     

Relation between fracture and deformation in oriented polymers

The development of submicroscopic cracking under load has been studied (by a small-angle X-ray scattering technique) in such oriented polymers as Kapron (Nylon 6), polypropylene, etc. The increase in crack density (N_cr) is compared with the variation of the tensile strain (). The observed correlation between and N_cr indicates that the processes of fracture and deformation of oriented polymers are closely connected. The presence of a similar correlation in loading-relaxation-repeat loading experiments establishes fracture as the primary process.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 43–47, January–February, 1970.     

Kinetic nature of polymer microhardness

The dependence of the microhardness of PMMA and PS on indenter penetration time and temperature has been studied. It is shown that the microindentation process is a kinetic process. A relation is established between the kinetic characteristics of the microindentation process and the corresponding characteristics of the fracture process.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 22–28, January–February, 1973.     

Energy features of a loaded quantum anharmonic oscillator

A quantum anharmonic oscillator in the ground state has been considered under the conditions of loading with an external force. The wave functions have been calculated for different forces, and the eigenvalues of the energy of the system have been determined as a function of the load. It has been established that the zero-point energy of the oscillator varies linearly with a variation in the force (decreases under tension and increases under compression) and that the average kinetic and potential components of the energy are also characterized by linear variations.     

Dynamical effects induced by static elastic loading of solid bodies

Experimental data on two known effects arising in response to an adiabatic elastic loading of solid bodies are presented. These are the thermoelastic effect, which consist in a change in temperature upon loading, and the frequency-elastic effect, which consists in a change in the frequency of vibrations of atoms upon loading. Similar and dissimilar features of these two effects are indicated. The mechanisms of the effects are discussed, and the degree of their interplay is revealed. The frequency-elastic effect is found to play a leading role. The temperature effect appears to be a quantum consequence of the change in the frequency of vibrations of atoms because of the anharmonicity of atom-atom interaction. Energy features of both effects are discussed.     

Phase-field modeling of domain structure of confined nanoferroelectrics

The results of phase-field simulation of domain structures (DSs) in ferroelectric nanorods of different shapes and sizes are presented. It is shown that equilibrium DSs consist of an electrostatically compatible circuit of 180 degrees and 90 degrees domains. A DS in a thin rod contains 90 degrees cubic elastic domains. The trend to minimize the residual stress and the stray field results in the formation of crater-shaped sets of closed circuits of 90 degrees domains, which can be mechanically incompatible but able to maintain electrostatic compatibility during the evolution under an applied electric field.     

Polymer breakdown and fatigue

Problems of the mechanical breakdown of polymer materials are discussed on the basis of kinetic considerations on such breakdown, viewed as a thermofluctuation-induced process of an accumulation of breaks in interatomic bonds (either break or damage). The present state of this problem is analyzed, both for static and for cyclic loads (fatigue). Some approaches for developing a theory of breakdown are reviewed. Theories related to the accumulation of damage in the volume of the sample receive particular attention. Recent studies on fatigue in polymer materials are listed.Paper presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.A. I. Ioffe Physicotechnical Institute, Academy of Sciences of the SSSR, Leningrad. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 597–611, July–August, 1972.     

Morphological heterogeneity of polymer fibers which do not reveal small-angle x-ray reflections

For many aliphatic and wholly aromatic polymer fibers, meridional small-angle x-ray reflections (SAXR's) are not observed. The morphological features which give rise to this effect have Received little attention in the literature. It is sometimes speculated that this is evidence of a morphological homogeneity along the fiber axis (no fluctuation of electron density–no long periods), ignoring other possible reasons (morphology is heterogeneous but very irregular or the maximum intensity of SAXR (I_max) is low and SAXR cannot be observed against the background of diffuse scattering.) Fibers with homogeneous crystalline morphology should have an elastic modulus E_f close to that of the crystallites E_cr along the polymer chains over a broad range of stresses. But, as was found in this work for the overwhelming majority of such nonreflection fibers (including Kevlar aramid fibers) there is a considerable difference between E_cr and E_f (for some nonreflection fibers the ratio E_cr/E_f is on the order of 10). This means that their morphology is heterogeneous along the fiber axis and contains “weaker” intercrystalline regions. This heterogeneity appeared to be regular enough to give rise to SAXR, as determined from the appearance of SAXR during elastic extension and after the beginning of pyrolysis in some nonreflection fibers. Thus, it was concluded that the lack of observable SAXR for these fibers is a result of the weakness of I_max relative to the diffuse scattering. Support for this statement is seen in the analysis of the decrease of I_max to zero with increasing draw ratio for poly(vinyl alcohol) fibers. The key factors influencing the decrease of I_max in this case were found to be the decrease of fibril diameter (fibril splitting), an increase of the dispersion of the long periods and some possible decrease in the density difference between crystalline and amorphous regions. The particular combinations of such factors can be different for each particular case of missing SAXR and are discussed in this paper.     

Broadening of relaxation and retardation spectra due to uniaxial orientational drawing of polyamide films

The initial and quasi-equilibrium values of relaxation modulus, the mean statistic retardation and relaxation times, and the parameters of retardation and relaxation time distributions have been estimated from the corresponding creep, elastic relaxation, and stress relaxation curves. Changes in the above characteristics with an increase in the draw ratio are analyzed.