Instantaneous work hardening behaviour of two-phase tungsten heavy alloys: a phenomenological approach

ABSTRACT

The present work describes a phenomenological approach to explain the instantaneous behaviour of tungsten heavy alloys (WHAs) in heat-treated and swaged conditions. The strengths and elongation values of heat-treated materials are lower and higher than those of the swaged samples respectively. The heat-treated materials exhibit two slopes in true stress–true plastic strain curves and follow the Ludwigson constitutive equation. On the other hand, swaged materials display a single slope and adhere to typical Swift constitutive equation. The latter reflect the presence of pre-strain in the materials due to swaging deformation. The fracture surfaces in heat-treated materials consist of W-W decohesion along with matrix rupture and W-cleavage, while swaged samples consist of mainly W-cleavage. Both the materials display three typical stages (I, II and III) of work hardening. The second derivatives of true stress–true plastic strain curves of these alloys exhibit a perfect parabola although the nature of true stress–true strain as well as true stress–true plastic strain curves is quite different in heat-treated and swaged materials. This has been observed for the first time in WHAs consisting of matrix and W-grains. The shape of the parabola is simple and easy to fit. The fitting parameters of parabolas have been successfully employed to explain the flow behaviour of a large number of tungsten heavy alloys having two-phase microstructure in different processing conditions.     

THE CRYSTALLIZATION BEHAVIOR OF URETHANE SUBSTITUTED POLYDIACETYLENE

The crystalline behavior of urethane substitute polydiacetylene was studied by using pohrized light and electron microscopy. The lamellar morphological structure was observed in the crystallized films. The thickness of lamellae is about 300A, being independent of the crystalline temperature. But the size and density of lamellae were dependent on the crystallization temperature. If the molten film was sheared during the crystallzation process the oriented lamellae grew with their long axes perpendicular to the direction of shear and the chain direction was normal to the lamellar surface.     

On the thermal behaviour of acetylphenyl-hydroxyaceticacid-4-nitrobenzyl esters

The 4-nitrobenzyl ester of acetylphenylhydroxyacetic acid differs in its melting behaviour from other nitrobenzyl esters of phenylhydroxyacetic or acetylphenylhydroxyacetic acids, the racemate having a higher melting point than the enantiomers. By means of thermal analysis, IR spectroscopy and X-ray diffractometry the ester can be shown to occur in two crystalline modifications. In the process of solidification of the molten mass, at first a modification of higher energy is formed, obviously being caused by an excess of one enantiomer, which is then exothermally rearranged in the lattice of the racemate.     

Polarity and steric effect of the lateral substituent on the mesophase behaviour of some newly prepared liquid crystals

Eight homologous series of 2- (or 3-) substituted phenyl 4?-(4?-alkoxy phenylazo) benzoates (In_a–h) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 6, 8, 10 and 12 carbons, while the other substituent, X, is a laterally attached polar group that alternatively changed from CH₃, H, F, Br and CN. Compounds prepared were characterised by infrared and ¹H-NMR spectroscopy, and their mesophase behaviour investigated by differential scanning calorimetry and identified by polarised light microscopy. The results were discussed in terms of polarity and steric effects. The stability of the mesophase was correlated once with the dipolar anisotropy of the whole molecule and another with the dipolar anisotropy of the substituent, X. A comparative study was made between the investigated compounds and their previously prepared linear 4-substituted isomers, namely 4-substituted phenyl 4?-(4?-alkoxy phenylazo) benzoates (In_i–k).     

Interaction of trip decisions and traffic systems dynamics

A major difficulty in the study of large-scale complex systems involving human decision-making with non-linear collective effects is that of obtaining pertinent data at the desired level of detail. A controlled experiment involving real commuters in a hypothetical computer simulated traffic system is described as an alternative approach of conducting observational studies to support the modelling of such complex dynamic interactive decision systems. An overview of the principal characteristics of the traffic system's evolution obtained in this experiment is presented. Also illustrated are the features of a proposed behavioral framework where users are viewed as boundedly rational seekers of a satisfactory choice outcome.     

橡胶支座水平剪切弹塑性力学性能试验研究

通过对铅芯橡胶支座剪切弹塑性力学性能试验,发现铅芯橡胶支座的滞回曲线与加载时程密切相关,在同一水平应变下,水平剪切刚度随加载次数的增多有所减小,最后趋于稳定;在不同应变下,水平剪切刚度随应变的增大而减小.试验还表明铅芯橡胶支座不仅在大应变存在着小应变滞回特性,而且在小应变也存在着小应变滞回特性.     

Characterization of magnetic labels for bioassays

Magnetic nanoparticles differing by their size have been synthesized to use them for multiparametric testing, based on their differing magnetic properties. The nanoparticle has two essential roles: to act as a probe owing to its specific magnetic properties and to carry on its surface precursor groups for the covalent coupling of biological recognition molecules, such as antibodies, nucleic acids. A totally unique, newly patented, method has been used to characterize magnetic signatures using the MIAplex technology. The MIAplex reader, developed by Magnisense, measures the non-linear response of the magnetic labels when they are exposed to a multi-frequency alternating magnetic field. This specific signature based on d²B(H)/dH² was correlated to other more conventional magnetic detection methods (superconducting quantum interference devices (SQUID) and Mössbauer).     

带有强迫项的具分布型时滞的非线性系统的渐近性

研究了一类带有强迫项的具有连续型滞量的非线性微分方程组解的渐近性，进一步推广了文[6]中的主要结果，得到了系统的解趋于零的充分条件。     

An approach to constitutive modelling of elasto-plasticity via ensemble averaging of the dislocation transport

Using an averaging procedure for large ensembles of dislocations, a basic but mathematically non-trivial modelling framework is developed for the transport of dislocation densities in a macroscopically homogeneous and isotropic film of a crystalline solid subjected to uniform shear. It has the form of a system of nonlinear, non-local partial differential equations of the first order with a source-type right-hand side. The solution to this system is studied numerically, and the associated average stress is evaluated as a function of time. The resulting stress-strain relations exhibit a size effect similar to those that previously motivated strain-gradient plasticity theories.