The paper is summarizing latest results connected with application of the incubation time approach to problems of dynamic fracture of rock materials. Incubation time based fracture criteria for intact media and media ...
详细信息
The paper is summarizing latest results connected with application of the incubation time approach to problems of dynamic fracture of rock materials. Incubation time based fracture criteria for intact media and media with cracks are discussed. Available experimental data on high rate fracture of different rock materials and incubation time based fracture criteria are used in order to evaluate critical parameters of causing fracture in these materials. Previously discovered possibility to optimize (minimize) energy input for fracture is discussed in connection to industrial rock fracture processes. It is shown that optimal value of momentum associated with critical load in order to initialize fracture in rock media does strongly depend on the incubation time and the impact duration. Existence of optimal load shapes minimizing momentum for a single fracturing impact or a sequence of periodic fracturing impacts is demonstrated.
A problem for a central crack in a plate subjected to plane strain conditions is investigated. Mode I crack loading is created by a dynamic pressure pulse applied at a large distance from the crack. It was found that ...
详细信息
A problem for a central crack in a plate subjected to plane strain conditions is investigated. Mode I crack loading is created by a dynamic pressure pulse applied at a large distance from the crack. It was found that for a certain combination of amplitude and duration of the pulse applied, the energy transmitted to the sample has a strongly marked minimum, meaning that with the pulse amplitude or duration moving away from the optimal values, minimum energy required for initiation of crack growth increases rapidly. The results obtained indicate a possibility to optimise energy consumption of different industrial processes connected with fracture. Much could be gained in, for example, drilling or rock pounding where energy input accounts for the largest part of the process cost. Presumably further investigation of the effect observed can make it possible to predict optimal energy saving parameters, i.e. frequency and amplitude of impacts, for industrial devices, e.g. bores, grinding machines, and hence significantly reduce the process cost. The pre- diction can be given based on the parameters of the media fractured (material parameters, prevalent crack length and orientation, etc.).
Transient effects of stress-strain fields in the vicinity of a stationary crack tip under high rate loads are *** analytical solutions to near tip stresses are compared to fields prescribed by leading terms(one or sev...
详细信息
Transient effects of stress-strain fields in the vicinity of a stationary crack tip under high rate loads are *** analytical solutions to near tip stresses are compared to fields prescribed by leading terms(one or several) of Williams asymptotic *** of load application mode,time(or,which is the same,distance from a crack tip) and Poisson's ratio on this discrepancy is extensively *** effects connected with crack tip propagation speed are also *** inconsistencies between real(or received in numerical solutions of state *** element computations) crack tip fields and stress intensity factor(SIF) singular field observed by numerous researchers are *** scope of problems where SIF field can be used for correct prediction of dynamic stress-strain fields in the crack tip region is *** to correctly approximate fields that are not SIF dominated,accounting additional terms of Williams expansion,is studied.
In this paper,a modified Rayleigh-Lamb equation is derived that takes into account the radial vibrations of a gas bubble coated with a viscoelastic shell and located in an elastic *** small oscillations of inclusion,t...
详细信息
In this paper,a modified Rayleigh-Lamb equation is derived that takes into account the radial vibrations of a gas bubble coated with a viscoelastic shell and located in an elastic *** small oscillations of inclusion,the problem of heat exchange between a gas,a liquid phase,a viscoelastic shell,and an elastic medium is *** energy integral is *** the case of small disturbances,the dispersion relation is found from the Rayleigh-Lamb equations,energy,and the known wave equation for the bubbly *** analytical expression of the equilibrium speed of sound is written out and its dependence on the size of the viscoelastic shell and the disturbance frequency is *** example of a mixture of polydimethylsiloxane with air bubbles coated with a rubber shell illustrates the influence of the elasticity of the carrier medium and the shell of the bubbles on the dependence of the phase velocity and attenuation coefficient on the perturbation *** a mixture of water with air bubbles coated with a rubber shell,the influence of the dependences of the shear modulus and viscosity of butyl rubber on the frequency of disturbances at different temperature on the dispersion curves is shown.A comparison of the theory with experimental data is given.
This paper outlines the results of experimental study of the dynamic rock failure based on the comparison of dry and saturated limestone samples obtained during the dynamic compression and split tests. The tests were ...
详细信息
This paper outlines the results of experimental study of the dynamic rock failure based on the comparison of dry and saturated limestone samples obtained during the dynamic compression and split tests. The tests were performed using the Kolsky method and its modifications for dynamic splitting. The mechanical data(e.g. strength, time and energy characteristics) of this material at high strain rates are obtained. It is shown that these characteristics are sensitive to the strain rate. A unified interpretation of these rate effects, based on the structuraletemporal approach, is hereby presented. It is demonstrated that the temporal dependence of the dynamic compressive and split tensile strengths of dry and saturated limestone samples can be predicted by the incubation time criterion. Previously discovered possibilities to optimize(minimize) the energy input for the failure process is discussed in connection with industrial rock failure processes. It is shown that the optimal energy input value associated with critical load, which is required to initialize failure in the rock media, strongly depends on the incubation time and the impact duration. The optimal load shapes, which minimize the momentum for a single failure impact, are demonstrated. Through this investigation, a possible approach to reduce the specific energy required for rock cutting by means of high-frequency vibrations is also discussed.
The authors worked out a simulation model of technological mineral dressing processes,in which two simulations of technological mineral dressing processes methods are used:transformed structural graph method and metho...
详细信息
The authors worked out a simulation model of technological mineral dressing processes,in which two simulations of technological mineral dressing processes methods are used:transformed structural graph method and method of separation *** first method makes it possible to simulate technological mineral dressing processes at the design stage in conditions of feedstock,equipment and control information *** second method is an effective instrument for operating plant simulation at the reengineering *** and economic efficiency evaluations of the mineral dressing plant are appended to the model.
Magnetic susceptibilities of flux-grown single crystals of LitnP4012 (Ln=Nd, Gd, Er) were measured in the temperature range of 2-300 K. The compounds were paramagnetic, and obeyed the Curie-Weiss law in the entire t...
详细信息
Magnetic susceptibilities of flux-grown single crystals of LitnP4012 (Ln=Nd, Gd, Er) were measured in the temperature range of 2-300 K. The compounds were paramagnetic, and obeyed the Curie-Weiss law in the entire temperature interval, without magnetic phase transitions, and with effective magnetic moments close to those of the corresponding free Ln3+ ions. X-ray photoelec- tron spectroscopy was applied to determine the positions of core-level electrons relative to the Fermi level: Li is; Ln 4f, 5p, 5s, 4d, 3d; P 2s, 2p; O 1s, 2s. The binding energies in these compounds were found slightly shifted compared to the respective values of the same elements.
Analytical solution for spherically symmetric nonstationary oscillations of acoustic and elastic solid sphere is *** dependence of potential,kinetic and internal energy of a solid sphere is *** received results are of...
详细信息
Analytical solution for spherically symmetric nonstationary oscillations of acoustic and elastic solid sphere is *** dependence of potential,kinetic and internal energy of a solid sphere is *** received results are of practical importance for a wide range of problems connected to testing of material dynamic strength parameters and to the problems of optimizing(minimizing)energy needed for fracture of solids.
A rotamak is one kind of compact spherically shaped magnetic-confinement device. In a rotamak the plasma current is driven by means of rotating magnetic field (RMF). The driven current can reverse the original equil...
详细信息
A rotamak is one kind of compact spherically shaped magnetic-confinement device. In a rotamak the plasma current is driven by means of rotating magnetic field (RMF). The driven current can reverse the original equilibrium field and generate a field-reversed-configuration. In a conventional rotamak, a toroidal field (TF) is not necessary for the RMF to drive plasma current, but it was found that the present of an additional TF can influence the RMF current drive. In this paper the effect of TF on the RMF current drive in a rotamak are investigated in some detail. The experimental results show that addition of TF increases the RMF driven current greatly and enhances the RMF penetration dramatically. Without TF, the RMF can only penetrate into plasma in the edge region. When a TF is added, the RMF can reach almost the whole plasma region. This is an optimal strength of toroidal magnetic field for getting maximum plasma current when Bv and radio frequency generator power are fixed. Besides driving current, the RMF generates high harmonic fields in rotamak plasma. The effect of TF on the harmonic field spectra are also reported.
Experiments on the dynamic fracture of solids,hquids,conductors,andinsulators that is caused by fast intense actions of environment or directed energy fluxesreveal a number of effects indicating a fundamental differen...
详细信息
Experiments on the dynamic fracture of solids,hquids,conductors,andinsulators that is caused by fast intense actions of environment or directed energy fluxesreveal a number of effects indicating a fundamental difference between the fast dynamicrupture(breakdown)of materials and a similar process under slow quasistatic *** example,one of the basic problems in testing the dynamic-strength properties of ma-terials is associated with the dependence of the limiting characteristics on the duration,amplitude,and growth rate of an external action,as well as on a number of other *** a critical value is a constant for a material in the static case,experimentallydetermined critical characteristics in dynamics are strongly unstable,and as a result,their behavior becomes *** indicated(and some other)features of thebehavior of materials subjected to pulsed actions are common for a number of seeminglyquite different paysical processes,such as dynamic fracture(starting cracks and scab-bing),cavitation in liquids,and electrical breakdown in *** this paper,we analyzeexamples illustrating typical dynamic effects inherent in these *** propose aunified interpretation for the fracture of solids and liquids and electrical breakdown ininsulators using the structural-time approach[1,2]based on the concept of the fractureincubation time.
暂无评论