Role of long-range shear stresses in the plastic deformation of epitaxial films

The dependence of elastic energy on relaxation parameters ρ _x and ρ _y varying in limits from 0 to 1 is analyzed for near-surface layers of an In_0.1Ga_0.9As epitaxial film on a GaAs (001) substrate whose thickness exceeds the distance between neighboring misfit dislocations.     

Characteristics of plastic deformation under the action of ultrasound

Conclusions The process of plastic deformation under the action of ultrasound differs in a number of ways from deformation under static loading; a computer simulation has shown that these differences are attributable to the specific characteristics of the operation of a source of dislocations for a periodic law of variation of the stresses. Among the most significant features of the ultimate dislocation structure are the saturation of the density of defects (attainment of limiting states) and the formation of stable dislocation clusters, which do not produce stress fields.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 118–128, June, 1982.     

The effect of plastic deformation on the transverse magnetoresistivity of potassium

A number of pure potassium samples have been plastically deformed under tension at low temperatures and the effect of this on the transverse magnetoresistivity at fields up to 6 T has been investigated. Although the influence of the dislocations so introduced is readily visible in the change of the zero field resistivity ?₀, there is no appreciable effect on the magnetoresistivity other than a shift by an amount equivalent to the change in ?₀.     

Dynamics of plastic deformation: Waves of localized plastic deformation in solids

Conclusions It has been shown here that a localized plastic deformation in structurally inhomogeneous media can be of a wave nature and can propagate in the form of nonlinear plastic waves, not only at the microscopic level but also at the mesoscopic level. It has been established that there is an interrelationship between this new effect and grain-boundary slippage (an effect which has been under study for a long time) and also with certain types of quasiviscous fracture in plastically deformable materials.We have discussed certain specific practical problems in the mechanics of plastic deformation, and for certain types of fracture. In the future, these problems will be discussed at a more profound level and in greater detail, because of experimental studies which are presently being carried out on the dynamics of deformation for various types of loading and fracture [17, 18, 31]. We hope that the approach proposed here for a theoretical study of the localization of deformation and fracture can be taken to study such effects as splitting off [31], the influence of defect fluxes on grain-boundary slippage [22], superplasticity [23], the behavior of tectonic faults and boundaries of various types [32], electroplastic and magnetoplastic effects, and high-temperature localization of deformation [25].The general nature of the approach proposed here results from the circumstance that a localization of deformation is present explicitly or implicitly during plastic deformation, and the behavior of this deformation plays a role of fundamental importance in the propagation of plastic deformation through a material.The author wishes to thank V. E. Panin for a constant discussion of this problem and I. O. Nedavnii for carrying out the numerical calculations.V. V. Kuibyshev Tomsk State University. Institute of Strength Physics and Materials Science. Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 19–41, April, 1992.     

Avalanches and scaling in plastic deformation

Plastic deformation of crystalline materials is a complex nonhomogeneous process characterized by avalanches in the motion of dislocations. We study the evolution of dislocation loops using an analytically solvable phase-field model of dislocations for ductile single crystals during monotonic loading. The distribution of dislocation loop sizes is given by P(A) approximately A-sigma, with sigma=1.8+/-0.1. The exponent is in agreement with those found in acoustic emission experiments. This model also predicts a range of macroscopic behaviors in agreement with observation, including hardening with monotonic loading, and a maximum in the acoustic emission signal at the onset of yielding.     

Off-diagonal long-range order and the Meissner effect

We provide a general, model-independent, derivation of the Meissner effect, on the basis of assumptions of off-diagonal long-range order (ODLRO) and gauge covariance of the second kind. This is an exact result that is independent of the microscopic mechanism responsible for the ordering, and so is applicable both to high- and low-T _c superconductors.     

The effect of hydrogen disorder on dislocation movement and plastic deformation of ice

In the structure of ice at low pressures (ice I-h) the oxygen atoms are crystallographically arranged but the hydrogen atoms are believed to be randomly arranged consistent with the so-called Bernal-Fowler rules. The effect of this randomness is to make it impossible for a dislocation to move through the ice lattice without creating point defects (breaches of the Bernal-Fowler rules). A calculation of the energy of the defects that would have to be created gives a value so large that it would require a stress of about one tenth of the shear modulus of ice to push the dislocation through. It therefore seems likely that dislocations could not move through ice unless the hydrogen atoms are reoriented by thermally activated point defects ahead of the dislocation. This necessity will greatly slow down dislocations in ice and provides an explanation for the observed behaviour of ice single crystals in creep and constant strain-rate tests, and of the softening of ice at low temperatures produced by small concentrations of dissolved fluoride ions.     

Anomalous plastic deformation in nichrome

The temperature dependences of the properties of Kh20N80 Nichrome under tension have been found. Decarbonization of the alloy showed that there are two regions of anomalous strengthening, at 400–450 and 600–700 °C. The first region is attributed to order in the binary system, while the second is attributed to carbide aging. Correlation analysis of the oscillograms of the tension diagrams showed no local relationship between the load discontinuities and the intervals between them. The inadequacies of existing models for discontinuous flow are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 12–17, November, 1970.     

Relaxation waves in plastic deformation

Conclusion Experimental study of distortion fields of plastically deformed solids performed on a wide range of materials including fine- and coarse-grain body- and face-centered polycrystals, as well as amorphous alloys reveals that in these materials plastic deformation develops in the form of waves having translational and rotational components. This fact is in accordance with the currently developed theory of a turbulent mechanical field, which also has translational and rotational components.The plastic deformation waves are observable at a macroscopic structural level, and their spatial period (wavelength) is determined by the dimensions of the deformed object and dimensions of the basic structural elements (for a polycrystal, the grain size). The propagation rate of these waves is significantly less than the characteristic propagation rate of an elastic excitation and the velocity of previously described plastic waves which are produced by shock deformation, which latter speed is determined by the hardening coefficient.The character of plasticity waves depends on the form of the material's deformation curve, and on the stage of the hardening curve. The distribution of plastic distortion components changes especially significantly in prefailure regions, which allows detection of the latter long before formation of a macroscopic crack. The role of rotations in forming the failure process has been established.A synergetic interpretation of plasticity wave formation has been proposed, based on synchronization of relaxation acts occurring at stress concentrators during the deformation process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 19–35, February, 1990.     

The effect of plastic deformation on positron lifetime spectra in alkali halides

Positron lifetime spectra have been measured in plastically deformed KCl and NaCl single crystals. The experiments indicate that a third component of the order of 2 nsec is produced by the deformation, and its relative intensity (2–4%) is only weakly dependent on the degree of deformation.     

The inhomogeneity of plastic deformation

Considerable local strain differences occur in single crystals as a consequence of slip bands. A significant contribution to this phenomenon is the effect of the deformation rate on the inhomogeneity of its distribution. In polycrystalline materials the plastic deformation is affected by grain boundaries and their vicinity as well as by various orientations of single grains in onephase metals and alloys, and by various component properties in multiphase materials. In some cases it has been possible to describe these phenomena by means of micromechanics. Valuable information has also been acquired by means of three-dimensional stereology.     

非晶塑性变形机理研究新进展

非晶合金的塑性变形机理一直是材料科学和凝聚态物理研究的热点问题之一.文章简单介绍了近来中国科学院物理研究所在非晶合金塑性机理研究方面的最新进展,介绍了玻璃转变和塑性变形机制之间的关联性及最新的实验证据,以及从非平衡态统计力学角度对非晶塑性变形机制的理解,指出非晶合金的塑性和剪切带的动力学状态密切相关,发现韧性非晶合金在变形过程中可以演化到自组织临界状态.这对认识非晶合金的形成本质,探索具有实际应用价值的非晶合金具有重要意义.     

Low-temperature instability of the plastic deformation of aluminum

The low-temperature instability of the plastic flow (step deformation) with a change in the state of the defect structure and geometric sizes of the polycrystalline aluminum specimen is investigated. It is demonstrated that the dependence of the magnitude of the step on the deforming stress exhibits an identical behavior for all the studied parameters of the specimens. A model is proposed for generating the step deformation of the metal, according to which there occurs a primary athermic overcoming of the potential barrier by a group of dislocations.     

非晶塑性变形机理研究新进展

非晶合金的塑性变形机理一直是材料科学和凝聚态物理研究的热点问题之一.文章简单介绍了近来中国科学院物理研究所在非晶合金塑性机理研究方面的最新进展,介绍了玻璃转变和塑性变形机制之间的关联性及最新的实验证据,以及从非平衡态统计力学角度对非晶塑性变形机制的理解,指出非晶合金的塑性和剪切带的动力学状态密切相关,发现韧性非晶合金在变形过程中可以演化到自组织临界状态.这对认识非晶合金的形成本质,探索具有实际应用价值的非晶合金具有重要意义.     

Mesoscale plastic deformation of aluminum polycrystals

A study is made of the mechanism of plastic deformation at the mesoscale level in flat specimens of aluminum polycrystals. The mechanism is examined with the use of high-resolution optical-television system TOMSC-1. It is shown that a multilevel mesoscale structure is formed in the specimen as it is deformed. The formation of this structure leads to the appearance of two types of stationary waves 120 μm and 4.8 mm long. The results are interpreted within the framework of a hierarchy of mesoscale levels of deformation and are linked with the decisive role of surface oxide films in the formation of the mesoband structure and stationary waves associated plastic flow. Institute of the Physics of Strength and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 31–39, January, 1997.