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81.
This paper reports a comparative study of shear banding in BMGs resulting from thermal softening and free volume creation.
Firstly, the effects of thermal softening and free volume creation on shear instability are discussed. It is known that thermal
softening governs thermal shear banding, hence it is essentially energy related. However, compound free volume creation is
the key factor to the other instability, though void-induced softening seems to be the counterpart of thermal softening. So,
the driving force for shear instability owing to free volume creation is very different from the thermally assisted one. In
particular, long wave perturbations are always unstable owing to compound free volume creation. Therefore, the shear instability
resulting from coupled compound free volume creation and thermal softening may start more like that due to free volume creation.
Also, the compound free volume creation implies a specific and intrinsic characteristic growth time of shear instability.
Finally, the mature shear band width is governed by the corresponding diffusions (thermal or void diffusion) within the band.
As a rough guide, the dimensionless numbers: Thermal softening related number B, Deborah number (denoting the relation of instability growth rate owing to compound free volume and loading time) and Lewis
number (denoting the competition of different diffusions) show us their relative importance of thermal softening and free
volume creation in shear banding. All these results are of particular significance in understanding the mechanism of shear
banding in bulk metallic glasses (BMGs).
Supported by the Chinese Academy of Sciences under the project “Multi-Scale Complex System” (Grant No. KJCX-SW-L08), the National
Natural Science Foundation of China (Grant Nos. 10725211 and 10721202), and the Doctorial Start-up Fund of Hunan University
of Science and Technology (Grant No. E50840) 相似文献
82.
Iron Nanoparticles in Severe-plastic-deformed Copper 总被引:1,自引:0,他引:1
Superparamagnetic iron nanoparticles with a size of a few nanometers were produced in copper by severe plastic deformation. In a isochronal annealing experiment near a temperature of 450K, which corresponds to the temperature of structural relaxation and the first step of grain growth (from 128 to 150nm) of submicrocrystalline copper, an abrupt increase in the magnetic susceptibility is detected. This increase is shown to be due to iron nanoparticles increasing in size from 2.8 to 3.3nm. The vanishing of the ferromagnetic contribution by iron nanoparticles observed at 850K, well below the Curie temperature of iron, is due to the dissolution of nanoparticles in plastically deformed copper. 相似文献
83.
用低杂波的可的性条件,参量不稳定条件和功率耦合谱分析了低杂波电流驱动。由于波的可近性条件限制耦合谱中平行相速度较大的波进入等离子体中心,参量不稳定性使平行相速度较低的波与离子相互作用,随着等离子体密度的增中,这些作用越来越明显,最终导致低杂波不能在中心与电子相互作用,驱动电流消失,这就是所谓密度极限。在本文建立的模型基础上的计算结果与实验结果符合较好。 相似文献
84.
85.
本文在考虑外载和温度的缓慢变化下,提出了一个新的运动安定定理。同时,在此基础上,又导出了既简单又适用的增量破坏准则.文末也以实例说明了它的应用。 相似文献
86.
87.
Cerisier P Porterie B Kaiss A Cordonnier J 《The European physical journal. E, Soft matter》2005,18(1):85-93
The motion of particles moving under gravity in the velocity field of a liquid in a Bénard hexagonal cell is studied experimentally
and numerically for Stokes flow conditions. We then explain the settlement of particles in the centers of cells to form a
regular quincunx. It is found that sedimentation also occurs preferentially along the lines connecting the centers of adjacent
cells to form a triangle deposition tessellation. Finally, it is explained why particles occupy the central part of each convective
cell while the peripheral part of the cell quickly becomes limpid. Numerical results are in agreement with the experimental
observations of Bénard and those of the present study. 相似文献
88.
The paper studies the dynamic behavior of perfect rigid-plastic plates in the form of a sector with hinged or clamped sides under short-term intensive loads. Two dynamic deformation mechanisms are demonstrated. The dynamic equation is derived for each of the mechanisms. The realization conditions for the mechanisms are analyzed. Analytical expressions are derived for the ultimate (high) loads and the maximum residual deflection. Numerical examples are given 相似文献
89.
90.
Bohn S 《The European physical journal. E, Soft matter》2003,11(2):177-189
We present an experimental and theoretical investigation
of a system composed of two soap bubbles strained between two
parallel solid surfaces. The two-bubble cluster can be found in
several configurations. The existence and stability of each of
these states is studied as a function of the distance between
the two facing surfaces. The change of this distance can induce
a transition from one configuration to another; we observe that
most transitions are subcritical, showing that the system is
often trapped in states where the minimum of free energy is only
local. The hysteretic transitions are responsible for the
dissipation of elastic energy. The existence of more than one
stable states for given boundaries conditions combined with the
absence of thermalization means that the history of the system
has to be taken into account and that there is no unique
stress-strain relation. In the present system, because of its
simplicity, a complete quantitative analysis of these general
processes is obtained. The presented results may contribute to a
better understanding of the dynamics of more complex systems
such as foams or granular materials where similar processes are
at work. 相似文献