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61.
In this article, a discrete effect in the thermal Lattice BGK two-speed model is studied. These effects are due to the non-equilibrium state in the particle distribution function, and the non-equilibrium occurs near walls. The mechanism of the LBM counterpart of the thermal creep flow, which appears due to the temperature gradient of the boundary in rarefied gases, is clarified analytically and numerical calculations are performed for some cases. A technique for eliminating this effect is also shown. 相似文献
62.
63.
An analytical version of the discrete-ordinates method (the ADO method) is used with recently established analytical expressions for the rigid-sphere scattering kernels to develop concise and particularly accurate solutions to the viscous-slip, the diffusion-slip, and the half-space thermal-creep problems for a binary gas mixture described by the linearized Boltzmann equation. In addition to a computation of the viscous-slip, the diffusion-slip, and the thermal-slip coefficients, for the case of Maxwell boundary conditions for each of the two species, the velocity, heat-flow, and shear-stress profiles are established for each species of particles. Numerical results are reported for two binary mixtures (Ne–Ar and He–Xe) with various molar concentrations. 相似文献
64.
Changes in the elastic and viscoelastic (creep) characteristics of polymer concrete and its structural components (polyester resin, unfilled or filled with diabase flour) during a long-term exposure to water at 20°C were studied. Modeling the structural changes in polymer concrete with time showed an increase in the relative volume content of pores filled with water and a decrease in that of unfilled pores. Based on the free-volume concept and the data on swelling due to moistening and shrinkage due to physical aging of the binder, a rather accurate estimate of the time-moisture reduction function for polymer concrete was obtained. The function was found to be nonmonotonic: the interval of increase was followed by an interval of decrease. 相似文献
65.
推导基于Murakami-Ohno(M-O)蠕变本构模型的三维有限元公式,并将损伤因素耦合进现有的有限元公式中,进行数值分析,数值结果表明损伤对蠕变有重要影响。 相似文献
66.
Dynamic mechanical measurements were conducted for several kinds of ultra–high-strength polyethylene fibers with different methyl branch contents. As is the case with conventional polyethylene materials, UHSPE fibers also exhibit α, β, and γ-relaxation dispersions. Each relaxation process is the function of both the tensile moduli and the branch contents of UHSPE fibers. It was also found that the γ-process of UHSPE fibers is dominated mainly by the localized molecular motion in the crystalline part, such as a dislocation mode of crystallite defects, which is very sensitive to the branching content. From the time and temperature superposition of the frequency dispersion experiments, it was found that activation energies for both the α2-process and α3-process increase proportionally to the methyl branch content, while the α1-process is not so affected by the branch content. This result shows that the incorporated branch sites in the crystalline part effectively hinder the chain-to-chain slippage; meanwhile, they have not hindered the slippage at the grain boundary so far, which also enables us to explain the creep improvement of UHSPE fibers through branch incorporation with the same mechanism. © 1994 John Wiley & Sons, Inc. 相似文献
67.
Studies have been made of the creep behavior of oriented (15:1) polyethylenes containing 0.4 and 1.3 butyl branches per 1000 C atoms. Increasing the branch concentration reduces significantly the creep strain and the equilibrium strain rate. The data have been fitted to an established model comprising two thermally activated processes in parallel, relating to the amorphous network at low stress, and the crystal phase at high stress. Analysis based on this model indicates the similarity between branching, entanglements, and crosslinks on the creep response. The creep behavior of electron-beam-irradiated materials shows that increasing the branch concentration makes the polyethylene more susceptible to mainchain scission, indicated by increased creep flow rates at higher stress, consistent with previous rubber elasticity studies. Irradiation in an acetylene atmosphere with low (< 1 Mrad) doses is shown to reduce the creep rates at all accessible stresses, and this attributed to an increase in crosslinking compared with scission. © 1994 John Wiley & Sons, Inc. 相似文献
68.
A method based on rational approximations is presented to interpolate the data from sinusoidal experiments in linear viscoelasticity. Bounds to the corresponding dynamical function and a discrete approximation to the spectrum are established. From this approximation the related viscoelastic functions can be computed. The method is checked by considering two theoretical models of physical interest and a satisfactory accuracy is achieved. 相似文献
69.
Abstract A review is presented of a very general aspect of the response of all metals subjected to displacive irradiation. This aspect is referred to as «persistence» and describes the tendency of both radiation-induced microstructural evolution and the associated changes in material properties or dimensional stability to evolve to saturation states that resist further change upon continued irradiation. It is shown that new persistent states can develop on a longer time frame associated with the late-term loss of existing microstructural components or the gain of new components, especially when transmutation and/or segregation occurs. The persistent states are often dependent on the irradiation conditions, and if these are changed, the material usually adjusts to form the persistent state characteristic of the new conditions, with the memory of the former state often lost, and sometimes leaving no visible record of the former state in the new microstructure. Depending on the microstructural components involved, the transition toward the new persistent state can occur quickly or very slowly. 相似文献
70.