共查询到13条相似文献,搜索用时 93 毫秒
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Numerous studies have shown that crack tip constraint has an important effect on the level of conservatism when crack extension is investigated in elastic-plastic fracture mechanics. Constraint effect has been explored extensively in the past but mainly for pure mode I problems. Very few researchers have dealt with the effects of crack tip constraint on mode II or mixed mode I/II fracture in metallic materials. In this paper, the evolution of mode II constraint parameter Q in terms of applied external load is determined numerically for a test specimen under pure mode II loading. The finite element method is utilized to model the specimen and to study the range of validity of mode II constraint parameter determined from a Q—T diagram. The parameter Q calculated from the finite element simulation (or from the full field solution) is compared with the values of Q determined from the Q—T diagram. For low levels of load, the results of full field solution are shown to be consistent well with the results obtained from the Q—T diagram. However, when the external load increases significantly, the results of Q—T diagram are no longer accurate and mode II constraint parameter Q should be calculated directly from finite element results. 相似文献
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O. V. Sosnin V. V. Tsellermaer Yu. F. Ivanov V. E. Gromov É. V. Kozlov 《Russian Physics Journal》2003,46(10):1047-1056
Structure and phase transformations in Fe–0.6C–1Mn–2Si steel subjected to multicyclic fatigue tests under normal conditions and with intermediate electrostimulation are investigated by the methods of metallography of etched microsections and scanning and transmission electron diffraction microscopy of thin foils and carbon replicas. It is demonstrated that fatigue failure under normal loading is preceded by complete dissolution of initial cementite particles with carbon localized on structural defects (dislocations, subboundaries, and boundaries), micropores, and microcracks. Electrostimulation, promoting the relaxation of stress concentrators through dissolution of particles localized on the grain boundaries and the state change of the interphase boundaries between the matrix and second-phase particle, causes the mean and maximum subcritical crack length to increase together with the thickness of the sample layer involved in the strain of the material and the zone of fatigue crack growth. This is accompanied by a significant increase in the operating lifetime of the material. 相似文献
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We derive the first four terms in a series for the order paramater (the stationary activity density ) in the supercritical regime of a one-dimensional stochastic sandpile; in the two-dimensional case the first three terms are reported. This is done by reorganizing the pertubation theory derived using a path-integral formalism [Dickman and Vidigal, J. Phys. A 35, 7269 (2002)], to obtain an expansion for stationary properties. Since the process has a strictly conserved particle density p, the Fourier mode N-1 k=0 p, when N , and so is not a random variable. Isolating this mode, we obtain a new effective action leading to an expansion for in the parameter 1/(1+4p). This requires enumeration and numerical evaluation of more than 200,000 diagrams, for which task we develop a computational algorithm. Predictions derived from this series are in good accord with simulation results. We also discuss the nature of correlation functions and one-site reduced distributions in the small- (high-density) limit. 相似文献
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《理论物理通讯》2015,(8)
In this paper, the Hopf bifurcation in a new hyperchaotic system is studied. Based on the first Lyapunov coefficient theory and symbolic computation, the conditions of supercritical and subcritical bifurcation in the new hyperchaotic system are obtained. Numerical simulations are used to illustrate some main results. 相似文献
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In this paper, the Hopf bifurcation in a new hyperchaotic system is studied. Based on the first Lya-punov coefficient theory and symbolic computation, the conditions of supercritical and subcritical bifurcation in the new hyperchaotic system are obtained. Numerical simulations are used to illustrate some main results. 相似文献
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卢道明 《原子与分子物理学报》2010,27(1):113-116
利用时间演化算符方法研究了K模相干光场与二能级原子相互作用系统中系统态矢的演化.利用数值计算方法研究了三模相干光场与二能级原子相互作用系统中场熵的演化,讨论了初始光场强度对场熵演化的影响.结果表明:当初始光场较强时,场熵随时间的演化呈现出规则的振荡,光场与原子之间的相互作用主要表现为双光子跃迁过程. 相似文献
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F. Berto 《Physical Mesomechanics》2015,18(4):273-282
The fictitious notch rounding concept has been recently applied for the first time to V-notches with root hole subjected to in-plane mixed mode loading. Out-of-bisector crack propagation is taken into account. The fictitious notch radius is determined as a function of the real notch radius (the microstructural support length) and the notch opening angle. Due to the complexity of the problem, a method based on the simple normal stress failure criterion has been used. It is combined with the maximum tangential stress criterion to determine the crack propagation angle. An analytical method based on Neuber’s procedure has been developed. The method provides the values of the microstructural support factor as a function of the mode ratio and the notch opening angle. The support factor is considered to be independent of the microstructural support length. Finally, for comparison, the support factor is determined on a purely numerical basis by iterative analysis of finite element models. The present paper is aimed to give a brief overview of the recent findings on this challenging topic making clear the state of the art. 相似文献
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The particle motion in a standing left circularly polarized wave is studied. For wave frequency lower than the ion cyclotron frequency ?ci, the slow varying trajectory is given by the ponderomotive force FNL=q2?|E|2/[m?(?-?ci)]. However, for ? close to ?ci, stochastic trajectories occur. These stochastic trajectories are due to the overlapping of closed orbits due to each of the propagating waves which form the standing wave. 相似文献
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In the stochastic limit the resonances play a fundamental role because they determine the generalized susceptivities which
are the building blocks of all the physical information which survives in this limit. There are two sources of possible divergences,
one related to the singularities of the form factor, another to the chaoticity of the spectrum. The situation will be illustrated
starting from the example of the discrete part of the hydrogen atom in interaction with the electromagnetic field. 相似文献