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1.
This paper investigates theoretically the influence of magnetization
on fatigue life by using non-equilibrium statistical theory of
fatigue fracture for metals. The fatigue microcrack growth rate is
obtained from the dynamic equation of microcrack growth, where the
influence of magnetization is described by an additional term in the
potential energy of microcrack. The statistical value of fatigue
life of metal under magnetic field is derived, which is expressed in
terms of magnetic field and macrophysical as well as microphysical
quantities. The fatigue life of AISI 4140 steel in static magnetic
field from this theory is basically consistent with the experimental
data. 相似文献
2.
本文试图从位错理论出发来探索晶体脆性断裂的统计理论。脆性断裂过程,实质上是微裂缝在极小的范性形变过程中形成长大和传播的随机过程。本文导出了描述这种随机过程的微分方程,利用微裂缝形成长大的位错机理,解出了微裂缝大小的统计分布函数。文中给出了范性形变、加工硬化和活动位错源数目与微裂缝数目和大小之间的函数关系。过去研究脆性断裂时,范性变形只是含糊地包括在有效表面能之内,而加工硬化和活动位错源数目则一向被略去。从微裂缝大小的统计分布函数和微裂缝的传播条件,导出了强度的统计分布函数,从而求得了脆性断裂判别式、脆性断裂强度及脆性-范性转变温度。 相似文献
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本文用非平衡统计的概念和方法探讨了各种断裂过程中的共同问题——微裂纹或微空洞的演化。文中从描述微裂纹演化过程的多元主方程出发,导出了微裂纹演化动力学方程,指出了微观机理与宏观过程相结合的途径,讨论了微裂纹分布函数应有的性质。
关键词: 相似文献
5.
Non-equilibrium statistical theory about microscopic fatigue cracks of metal in magnetic field
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This paper develops the non-equilibrium statistical fatigue damage theory to study the statistical behaviour of micro-crack for metals in magnetic field. The one-dimensional homogeneous crack system is chosen for study. To investigate the effect caused by magnetic field on the statistical distribution of micro-crack in the system, the theoretical analysis on microcrack evolution equation, the average length of micro-crack, density distribution function of micro-crack and fatigue fracture probability have been performed. The derived results relate the changes of some quantities, such as average length, density distribution function and fatigue fracture probability, to the applied magnetic field, the magnetic and mechanical properties of metals. It gives a theoretical explanation on the change of fatigue damage due to magnetic fields observed by experiments, and presents an analytic approach on studying the fatigue damage of metal in magnetic field. 相似文献
6.
Wei-Sheng Lei 《哲学杂志》2016,96(35):3586-3631
The well established consensus that cleavage fracture is preceded by plastic deformation in structural steels implies that plastic yielding is the threshold stress state for a volume element to incur cleavage fracture. An accurate compliance with this consensus underlies the normalisation of cumulative cleavage fracture probability and the justification of constraint effect on cleavage fracture. These understandings lead to the proposal of a framework for statistical modelling of cleavage fracture in structural steels. The framework takes the spatial microcrack distribution into account to formulate the cumulative failure probability model that allows for a pertinent physical interpretation of Weibull statistics, and derives the fracture probability of an elemental volume in conformity with the yielding condition from a set of commonly adopted microcrack size or strength distributions. Alternative approaches to calibrating model parameters are suggested based on frequency analysis of brittle particles as cleavage initiators and on statistical analysis of cleavage fracture stress. The strict adherence to plastic yielding as a prerequisite to cleavage fracture also reveals the probabilistic nature of notch brittleness and ductile-to-brittle transition behaviour. 相似文献
7.
Acoustic emission generated by the nucleation of a microcrack in the proximity of a macrocrack is discussed in this paper. On the basis of some simple approximations the acoustic emission from a crack-opening event is directly related to its crack-opening volume as a function of time. It is shown that the nucleation of a microcrack in the immediate vicinity of a macrocrack generates additional crack-opening volumes for both the macrocrack and the microcrack, whose signals tend to be much larger than those that would emanate from a nucleating solitary microcrack. 相似文献
8.
阐述了以表述信息演化规律的信息(熵)演化方程为核心的非平 衡统计信息理论.推导出了 Shannon信息(熵)的非线性演化方程,引入了统计物理信息并 推导出了它的非线性演化方程.这两种信息(熵)演化方程一致表明:统计信息(熵)密度 随时间的变化率是由其在坐标空间(和态变量空间)的漂移、扩散和减损(产生)三者引起 的.由此方程出发,给出了统计信息减损率和统计熵产生率的简明公式、漂移信息流和扩散 信息流的表达式,证明了非平衡系统内的统计信息减损(或增加)率等于它的统计熵产生( 或减少)率、信息扩散与信息减损同时
关键词:
统计信息(熵)演化方程
统计信息减损率
统计熵产 生率
信息(熵)流
信息(熵)扩散
动态互信息 相似文献
9.
L. K. Izraileva E. N. Rumanov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(2):296-297
The process of implanted atom gas release from a crystal into microcracks arising under implantation and annealing has been
theoretically studied. The rate of heat exchange with a substrate has been shown to affect the microcrack growth. 相似文献
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A microcrack in a silicon single crystal was experimentally investigated using high-resolution transmission electron microscopy (HRTEM). In particular, the numerical Moiré (NM) method was used to visualize the deformations and defects. The lattice structure of the microcrack was carefully observed at the nanoscale. HRTEM images of the microcrack demonstrated that the lattice structure of most of the microcrack regions is regular with good periodicity. In addition, the microcrack cleavage expands alternately along different crystal planes, where the principal cleavage plane is the (1 1 1) crystal plane. The NM maps showed no sharp plastic deformation around the microcrack, but discrete edge dislocations can be found only near the crack tip. 相似文献
13.
A theoretical model is proposed describing a new physical microscopic mechanism of increased fracture toughness of nanocrystalline ceramics. According to this model, when a ceramic with a microcrack is deformed, intensive grain boundary sliding occurs near the crack tip under certain conditions. This sliding is accompanied by the formation of an array of disclination dipoles (rotational defects) producing elastic stresses. These stresses partially compensate the high local stresses concentrated near the microcrack tip and thereby hamper the microcrack growth. The proposed model is used to theoretically estimate the increase in the critical microcrack length (the length above which the catastrophic growth of microcracks occurs) caused by the formation of disclination dipoles during grain boundary sliding in nanoceramics. The increase in the critical microcrack length is a quantitative characteristic of the increased fracture toughness of nanoceramics. 相似文献
14.
Joseph L. McCauley 《Physics letters. A》1979,73(1):26-28
We show that the idea of a boundary layer for discrete vortices arises naturally from the equation of motion for the probability distribution of an interacting vortex pair. In contrast with classical hydrodynamics, this boundary layer is of statistical origin, and the method leads to a scaling law for the exact dissociation rate of a bound vortex pair. 相似文献
15.
V. S. Kirchanov 《Russian Physics Journal》2006,49(12):1294-1300
A formalism for describing quantum dissipative systems in statistical mechanics is developed. A new equation of the Lindblad
type with a quadratic superoperator consisting of Hermitian dissipative operators is derived from the Bloch equation for temperature
density matrix using the Feynman integral over the trajectories with a modified Menskii weight functional. By way of example,
this equation is solved for a one-dimensional quantum harmonic oscillator with linear dissipation. Applying the projection
operator technique, an integral-differential equation for a reduced temperature statistical operator is obtained, which is
analogous to the Zwanzig equation in statistical mechanics, and its formal solution is found as a convergent series.
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Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 30–34, December, 2006. 相似文献
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V. K. Ignatjev A. V. Nikitin S. V. Yushanov 《Radiophysics and Quantum Electronics》2010,53(2):132-145
We propose an algorithm for estimating the parameters of a signal from its quasiharmonic representation and a method for estimation
of slowly varying coefficients of a second-order differential equation. The considered approach uses Tikhonov’s regularization
for the class of slowly varying functions. The results of statistical modeling for the Mathieu equation are presented. Solution
of the frequency comparison problem on the example of estimation of the frequency instability of a quartz resonator setting
a signal sampling rate is considered. Relations for determining the sampling rate are obtained and the results of numerical
simulation are reported. 相似文献
18.
J.S Langer 《Annals of Physics》1971,65(1):53-86
A statistical theory of the thermally driven composition fluctuations in a binary alloy is developed for the purpose of studying the phenomenon of spinodal decomposition. The theory can be stated in the form of a Fokker-Planck equation, which reduces, upon taking a suitable moment, to the nonlinear generalized diffusion equation which has been the basis of recent work in this field. Using the full Fokker-Planck equation, it is possible to compute the lifetime of the stationary solutions of the diffusion equation, and thus to study the rate at which the structure of the alloy coarsens during aging. 相似文献
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XING Xiusan 《中国科学G辑(英文版)》2006,49(1):1-37
In recent years we extended Shannon static statistical information theory to dynamic processes and established a Shannon dynamic
statistical information theory, whose core is the evolution law of dynamic entropy and dynamic information. We also proposed
a corresponding Boltzmman dynamic statistical information theory. Based on the fact that the state variable evolution equation
of respective dynamic systems, i.e. Fokker-Planck equation and Liouville diffusion equation can be regarded as their information
symbol evolution equation, we derived the nonlinear evolution equations of Shannon dynamic entropy density and dynamic information
density and the nonlinear evolution equations of Boltzmann dynamic entropy density and dynamic information density, that describe
respectively the evolution law of dynamic entropy and dynamic information. The evolution equations of these two kinds of dynamic
entropies and dynamic informations show in unison that the time rate of change of dynamic entropy densities is caused by their
drift, diffusion and production in state variable space inside the systems and coordinate space in the transmission processes;
and that the time rate of change of dynamic information densities originates from their drift, diffusion and dissipation in
state variable space inside the systems and coordinate space in the transmission processes. Entropy and information have been
combined with the state and its law of motion of the systems. Furthermore we presented the formulas of two kinds of entropy
production rates and information dissipation rates, the expressions of two kinds of drift information flows and diffusion
information flows. We proved that two kinds of information dissipation rates (or the decrease rates of the total information)
were equal to their corresponding entropy production rates (or the increase rates of the total entropy) in the same dynamic
system. We obtained the formulas of two kinds of dynamic mutual informations and dynamic channel capacities reflecting the
dynamic dissipation characteristics in the transmission processes, which change into their maximum—the present static mutual
information and static channel capacity under the limit case where the proportion of channel length to information transmission
rate approaches to zero. All these unified and rigorous theoretical formulas and results are derived from the evolution equations
of dynamic information and dynamic entropy without adding any extra assumption. In this review, we give an overview on the
above main ideas, methods and results, and discuss the similarity and difference between two kinds of dynamic statistical
information theories. 相似文献