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51.
We consider one possible approach to the problem of describing the dependence of material plastic strain characteristics on
the stress hydrostatic component arising in many porous, fractured, and other inhomogeneous materials. The plastic strain
of the media under study is investigated under the plasticity assumption in the corresponding generalized form with the use
of the form parameter of the stress state. The plasticity constitutive relations are stated on the basis of the plastic flow
law associated with the accepted plasticity condition. For the conditions of plane stress state in the framework of the material
rigid-plastic model, a system of partial differential equations is obtained and conditions for its hyperbolicity are determined.
The relations for determining the stress fields and velocity fields in plastic domains are obtained, and their properties
are investigated. The problem of tension of a strip with symmetric angular notches is solved, where the stress fields are
determined and the continuous displacement rate field is constructed. The problem of uniform symmetric tension of a plane
with a circular hole is considered. The stress fields in a strip with symmetric circular notches are examined. A comparison
with solutions for plastically incompressible media whose properties are invariant with respect to the form of the stress
state is performed. 相似文献
52.
53.
Jun Meng Amir Boag Vitaliy Lomakin Eric Michielssen 《Journal of computational physics》2010,229(22):8430-8444
A multilevel Cartesian non-uniform grid time domain algorithm (CNGTDA) is introduced to rapidly compute transient wave fields radiated by time dependent three-dimensional source constellations. CNGTDA leverages the observation that transient wave fields generated by temporally bandlimited and spatially confined source constellations can be recovered via interpolation from appropriately delay- and amplitude-compensated field samples. This property is used in conjunction with a multilevel scheme, in which the computational domain is hierarchically decomposed into subdomains with sparse non-uniform grids used to obtain the fields. For both surface and volumetric source distributions, the computational cost of CNGTDA to compute the transient field at Ns observation locations from Ns collocated sources for Nt discrete time instances scales as O(NtNslogNs) and O(NtNslog2Ns) in the low- and high-frequency regimes, respectively. Coupled with marching-on-in-time (MOT) time domain integral equations, CNGTDA can facilitate efficient analysis of large scale time domain electromagnetic and acoustic problems. 相似文献
54.
S. V. Stovbun S. M. Lomakin A. I. Shchegolikhin A. A. Skoblin V. P. Mel’nikov 《Russian Journal of Physical Chemistry B, Focus on Physics》2018,12(1):36-45
Thermogravimetry is used to study the thermodestruction of nitrocellulose (NC) with various nitrogen contents at various heating rates. At high degrees of nitration and high heating rates of the sample, the reaction occurs in an explosion mode with a threshold of its weight loss depending on the temperature. To explain this behavior, it is assumed that the nitration of cellulose gives rise to structural stresses, which weaken the covalent bonds in it by ~37 kJ/mol (at a nitrogen content of ~13%). This process apparently involves two different mechanisms of weight loss during heating: (a) conventional thermal destruction of NC macromolecules through the rupture of covalent bonds (with k0 = 1013 s?1, E = 150.2 kJ/mol, and n = 1) at heating rates of up to 10 K/min and nitrogen content in NC of up to 9%; (b) Zhurkov’s thermofluctuational mechanism of the destruction of strained macromolecules, characterized by a sharp (threshold) dependence of the weight loss on the heating rate, which is operative at heating rates above ~4 K/min and high (>13%) nitrogen contents and at 20 K/min and a low (~9%) nitrogen content. Under conditions of rapid heating, ~10–20 K/min, the work done by stressed states to overcome the potential barrier to the rupture of covalent bonds causes an increase in the decomposition rate by a factor of 2000. The observed threshold pattern of weight loss during the thermodestruction of NC explains the long-known critical dependence of the properties of NC used to manufacture propellants on small changes in the nitrogen content. 相似文献
55.
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57.
The influence of a nonuniform field of internal stresses and the generation of a dislocation loop by a Frank-Read source operating under the action of an alternating load is investigated by computer simulation. It is shown that the field of a tilt boundary affects every stage of development of a dislocation loop until its closure. The influence of the boundary field is determined by the ratio between the length of the source and the space scale of the field nonuniformities. It is established that not only the value of the dynamic yield point but also the form of its dependence on the ultrasonic frequency can vary in an internal stress field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 35–39, February, 1985. 相似文献
58.
59.
Koverzanova E. V. Usachev S. V. Shilkina N. G. Lomakin S. M. Gumargalieva K. Z. Zaikov G. E. 《Russian Journal of Applied Chemistry》2004,77(3):445-448
Specific features of thermal oxidative degradation of polypropylene and its composite with Mg(OH)2 were studied by pyrolytic gas chromatography-mass spectrometry and thermal gravimetric analysis. 相似文献
60.
Problems of similarity and simulation of the processes of deformation of linear media with memory are investigated by the method of similarity for cases of different and identical materials. In the latter case coincidence of the body and surface forces in the natural object and the model, coincidence of the characteristic displacements at like points, and proportionality of the stresses are considered.Mekhanika Polimerov, Vol. 3, No. 1, pp. 54–59, 1967 相似文献