Plastic deformation of alpha-zirconium polycrystals

The effect of temperature on flow stresses of alpha zirconium deformed at temperatures between 77 and 900 K has been investigated. Strong temperature dependences of the yield stress and the maximum stress are discussed.     

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.     

Elastic and plastic deformation of NaCl and Ni3Al polycrystals during compression in a multi-anvil apparatus

Abstract

The compression behaviour in a multi-anvil apparatus of pure NaCl and of a foil of Ni₃Al embedded in a pressure medium of NaCl has been studied by energy-dispersive X-ray diffraction. At ambient temperature, the pressure and stresses, determined from line positions of NaCl, were constant throughout the sample chamber. Line positions and line widths of NaCl reflections were reversible on pressure release. A saturation of microstrains observed in NaCl at 2 GPa is thus attributed to brittle fracture setting in at uniaxial stresses of around 0.3 GPa. Ni₃Al polycrystals, in contrast, undergo extensive (ductile) plastic deformation above 4 GPa. The compression behaviour of both Ni₃Al and NaCl is identical to that previously determined in a diamond anvil cell. While a multi-anvil device thus has the advantage, compared with a diamond anvil cell, of constant pressure and stress throughout the sample chamber, microstrains in poly-crystalline samples arise in both devices. Samples in a multi-anvil apparatus thus need to be mixed with a pressure medium and to consist of essentially single crystals just as in a diamond anvil cell. Annealing experiments at high pressures confirm that the release of the uniaxial stress component in the pressure medium does not cause a release of microstrains in the embedded sample if the latter has been plastically deformed. Annealing for the purpose of attaining hydrostatic conditions in compression studies thus has to be carried out with care.     

Microplastic deformation of polycrystals during cyclic loading

A model of microplastic deformation of polycrystals during zero-start cyclic loading with tensions lower than the yield strength is proposed according to which during cycling, thermally activated movement of dislocations occurs under conditions of stress relaxation. Based on this model and the statistical theory of polycrystalline microdeformation, the accumulation of microplastic deformation is theoretically described as a function of the number of loading cycles and the stress amplitudes. It is theoretically proved that in the cycling process the microplastic deformation that accumulates over one cycle decreases as the number of cycles increases; up to the macroscopic elastic limit it is independent of the stress amplitude, and then sharply increases. Agreement of the theory with experimental data for spring alloys is observed in the density of mobile dislocations, which decreases during cycling.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 29–34, March, 1990.     

Thermally (non-)activated deformation of Zr-Sn polycrystals

A non-monotonic temperature dependence of the activation volume of alpha zirconium is observed in the temperature range between 500 and 750 K. In this temperature range polycrystals of Zr-Sn alloys (with concentrations of 0·8, 3·0, 4·5 and 6·0 wt. % of Sn) have been deformed in order to investigate the influence of tin on the thermally activated deformation. The activation volume has been determined using the stress relaxation test.     

Stress relaxation in the region of microplastic deformation of polycrystals

Stress relaxation equations are derived to predict the relaxation capacity of a material on the basis of studies of microplastic deformation under static loading. The approach was checked experimentally on spring steels LANKMts, ÉI702, ÉP637, and 50KhFA.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 37–41, July, 1987.     

Grain boundary role and behaviour during high-temperature deformation of polycrystals

Data concerning the phenomenology and nature of some grain boundary (GB) processes — dynamic recovery at GB and GB sliding during high temperature deformation of polycrystals are given. On the basis of these data a new model of superplasticity (SP) is discussed. The possibility of realization of SP at relatively low temperatures is shown.     

Structural deformation and fracture levels of polycrystals under different kinds of loading

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 69–88, February, 1990.     

Evolution of triple junction defect structure at plastic deformation of metallic polycrystals

A method for the determination of the components of the Frank vector of disclinations in triple junctions (TJ) of real polycrystalline aggregates has been proposed. Using this method we found that real polycrystals contain junction disclinations (JD), the nature of which is related to their thermo-mechanical history. One of the elements of the evolution of the network of initial junction disclinations is the formation of disclination dipole configurations in the adjacent TJ. The influence of the types of boundaries forming the junctions on JD Frank vector power is discussed.     

Relationships and macroscopic mechanism of cyclic deformation of polycrystals at elevated temperatures

Systematic investigation of the development of deformation and fracture under cyclic stresses is conducted on a sample of lead alloy as a function of the type of alloying. A macroscopic mechanism for fatigue failure at elevated temperature is formulated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 27–31, November, 1987.     

Contribution from dislocation to deformation resistance in polycrystals of copper-based solid solutions

The evolution of dislocation structure in solid solutions of Cu-Al and Cu-Mn systems with different grain sizes and at different test temperatures is studied by means of transmission electron diffraction microscopy. The scalar density of dislocations is measured and its relationship to the flow stress of alloys is determined. Changes in the contribution from dislocation hardening to deformation resistance upon variations in the contributions associated with changes in grain size, solid-solution hardening, and test temperature are analyzed.     

Elastic deformation of Ti films during alternating bending

The effect of the state of stress at a film-substrate interface on the elastic deformation of Ti films is studied during alternating bending. The Al substrate compliance is shown to cause coherent deformation of the film-substrate system, resulting in the corrugation of a Ti film and the appearance of a wavelike film-substrate interface. Fatigue tests lead to the formation of a periodic distribution of normal and tangential stresses along the interface, and this distribution favors periodic film corrugation. The corrugation of a Ti film on a Ti substrate occurs randomly in local film separation areas and is caused by defects accumulated at the interface.     

应用于移动平台的器官柔性形变仿真方法

研究了应用于移动平台的器官柔性形变仿真方法。提出了面向移动平台的碰撞检测方法,通过模型的外层包围盒迅速剔除场景中未发生碰撞的情况,进而对模型的几何面元进行相交检测,从而实现对器官的碰撞检测。研究了应用于虚拟器官的质点-弹簧模型,通过对形变区域的控制降低形变的计算量,通过对虚拟器械的运动控制避免形变过程中虚拟器官发生穿透或者脱离器械的现象。实验结果表明,器官柔性形变仿真与交互方法计算速度快、交互过程自然,可应用于移动平台的虚拟手术仿真系统中。