共查询到20条相似文献,搜索用时 453 毫秒
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Fielding SM 《Physical review letters》2011,107(25):258301
We study the linear instability with respect to necking of a filament of polymeric fluid undergoing uniaxial extension. Contrary to the widely discussed Considère criterion, we find the onset of instability to relate closely to the onset of downward curvature in the time (and so strain) evolution of the zz component of the molecular strain, for extension along the z axis. In establishing this result numerically across five of the most widely used models of polymer rheology, and by analytical calculation, we argue it to apply generically. Particularly emphasized is the importance of polymer chain stretching in partially mitigating necking. We comment finally on the relationship between necking and the shape of the underlying steady state constitutive curve for homogeneous extension. 相似文献
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Necking is a widely observed instability phenomenon. Surface tension often plays a significant role in the deformation of soft materials, especially at the micro scale, but its influence on the necking behavior of soft structures remains unclear. In this paper, we use the energy method to explore surface effects on the necking of soft plates and cylindrical bars under uniaxial tension. Analytical solutions are derived for the critical conditions of necking instability in the two types of structural components with a power-law constitutive relation. It is found that surface energy shows different impacts on their necking behaviors – it tends to postpone the occurrence of necking in soft plates but promote that in soft cylinders. This work not only deepens our understanding of the instability of soft materials but also helps design soft devices and robots. 相似文献
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We have used both electronic speckle-pattern interferometry (ESPI) and whole-field Subtractive Moiré (WSM) to follow the thickness reduction of sheet metal specimens subjected to uniaxial tensile tests. By analyzing the out-of-plane displacements induced between close load stages, we evaluated nonlinear effects linked to the progression of the thickness necking or transverse reduction in area of the sample. We observed that, during the transition zone of the test, long before reaching instability, the samples were thinned mainly along a relatively broad band. Due to its remarkable degree of localization, we identified this band as the diffuse necking. This diffuse necking preceded the development of the local neck and indicated the beginning of shear band formation. 相似文献
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The behavior of localized plasticity macrodomains is experimentally studied at the final stage of the plastic flow in going
to necking and ductile fracture in fcc, bcc, and hcp materials. General features of the localization process at the stage
of prefracture are found. They are a constant velocity of domains and their tendency to consistently move toward the focus
of a bundle of straight lines in space-time diagrams. A correlation between the type of fracture and the kinetics of localized
plasticity domains is established. 相似文献
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G. A. Malygin 《Physics of the Solid State》2003,45(12):2342-2347
The mechanism for the Euler instability of the bidirectional shape memory effect in a titanium nickelide strip is discussed in terms of the diffuse martensitic transformations. The shape instability and a plastic jerk of a strip that are observed in the temperature range of a forward and the reverse martensitic transformation are due to the additional bending moment that arises in the case where the ends of the strip are fixed (with the use of hinges) and the strip can only rotate about them. 相似文献
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We report molecular dynamics simulations of the recently discovered superelongation of carbon nanotubes (CNTs) at high temperatures. The nearly simultaneous activation and wide distribution of a large number of defects near the elastic limit play a key role in impeding the formation of localized predominant instability and facilitating large tensile elongation. It suggests new and more complex mechanisms for CNT superelongation in contrast with the previously proposed ideal defect glide and pseudoclimb. Defect interaction and evolution generate multistage necking and kinking and new types of larger defects that dominate the tensile elongation and breaking process. Intricate interplay between CNT sizes and defect nucleation and motion determine the overall deformation pattern. 相似文献
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The evolution of a microstructure and Schmid factors during tension under necking conditions are analyzed by electron backscatter
diffraction. The oscillatory instability of the plastic flow in the deformation zone in the hardening-softening mode is found
to be related to geometrical hardening (softening) during the reorientation of easy slip planes in grains with respect to
the loading axis. A relation between the activities of various slip systems and the evolution of quantitative microstructure
parameters is revealed. 相似文献
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The evolution of a strip (one-dimensional) fundamental beam with propagation distance owing to spatial modulational instabilities was analyzed in a quadratic medium near type I phase matching. We obtained the gain coefficient for the modulational instability and showed that the wave evolves into a clean periodic sequence of solitary waves and does not reproduce the incident beam. 相似文献
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A simplified approximate analytical model for Rayleigh–Taylor instability in elastic–plastic solid and viscous fluid with thicknesses 下载免费PDF全文
《中国物理 B》2021,(4)
A simplified theoretical model for the linear Rayleigh-Taylor instability of finite thickness elastic-plastic solid constantly accelerated by finite thickness viscous fluid is performed.With the irrotational assumption,it is possible to consider viscosity,surface tension,elasticity or plasticity effects simultaneously.The model considers thicknesses at rigid wall boundary conditions with the velocity potentials,and deals with solid elastic-plastic transition and fluid viscosity based on the velocity continuity and force equilibrium at contact interface.The complete analytical expressions of the amplitude motion equation,the growth rate,and the instability boundary are obtained for arbitrary Atwood number,viscosity,thicknesses of solid and fluid.The thicknesses effects of two materials on the growth rate and the instability boundary are discussed. 相似文献
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The effect of a small modulation superimposed on a strip (1D) solitary wave propagating in a bulk quadratic medium was investigated both analytically and numerically near Type I phase matching. General, exact results were obtained. By using first order perturbation theory, we obtained the gain coefficient for the modulational instability and the modulation cut-off frequency and we investigated their dependence on various beam and material parameters. The wave evolves into a clean periodic sequence of solitary waves and does not reproduce the incident beam. We showed that the beam breakup observed experimentally is due entirely to noise induced modulational instability. 相似文献
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《Nuclear Physics B》2001,594(3):625-659
We consider the one-point functions of bulk and boundary fields in the scaling Lee–Yang model for various combinations of bulk and boundary perturbations. The one-point functions of the bulk fields are analysed using the truncated conformal space approach and the form-factor expansion. Good agreement is found between the results of the two methods, though we find that the expression for the general boundary state given by Ghoshal and Zamolodchikov has to be corrected slightly. For the boundary fields we use thermodynamic Bethe ansatz equations to find exact expressions for the strip and semi-infinite cylinder geometries. We also find a novel off-critical identity between the cylinder partition functions of models with differing boundary conditions, and use this to investigate the regions of boundary-induced instability exhibited by the model on a finite strip. 相似文献
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为了提高电磁被动装甲对聚能射流的防护能力,利用叠加原理和磁流体线性不稳定理论,在轴向脉冲电流作用下建立了射流运动线性扰动控制方程,并对射流箍缩和扭曲不稳定性增长率随粘性、时间的变化规律进行了分析,得到了射流不稳定增长率和射流的变形规律,并利用数值方法得到了射流变形的计算公式。最后通过直径39.2mm破甲弹进行静破甲试验,通过后效板射流入射孔的大小验证了脉冲电流对射流的箍缩作用;利用具有初始弯曲、直径为1.75mm铜丝模拟了脉冲电流对射流的扭曲作用,通过铜丝的变形验证了脉冲电流对射流的扭曲作用。实验结果证实了理论分析的正确性。 相似文献
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