Many engineering problems can be modeled within the framework of non-dissipative gasdynamic flows. However, some problems also involve large strains of various types of shells, and accounting for the elastoplastic properties of the materials becomes important if the characteristic pressures are too much greater than the yield point. By making such allowances, it is then possible to more accurately calculate the final strains and evaluate the heating of the shell due to dissipative forces. Also, dissipative losses due to viscous forces become important for high-speed flows characterized by high strain rates [1][2][3][4][5][6].Heating due to viscosity is usually characterized by large discontinuities in the dissipation of kinetic energy into heat. The greatest local heating is realized near various physical discontinuities in the material being deformed, i.e., near foreign inclusions and cavities, at grain boundaries and slip planes, etc. Nonuniform heating of the material due to viscosity will obviously lower its strength characteristics and can thereby facilitate deformation along certain planes and directions [6]. Typical examples of the latter are the piercing of a shell by a fragment or the deep penetration of a barrier by microscopic particles. Such penetration has recently been the subject of intensive research [7]. At the same time, these examples also serve to illustrate the present state of fracture mechanics, which has as yet been unable to quantitatively describe such experiments [8-101.It has long been known that dissipative processes are nontrivial in high-rate viscoplastic flows. For example, the authors of [1, 2] studied the dependence of the viscosity of several materials on compression and temperature behind a shock wave (compression range cr < 2, temperature T -104 ~ The viscoplastic properties of the materials were also studied in [3,11,12] in tests involving the inertial collision of cylindrical shells (compression a -1, temperature T -103 ~ The shells were accelerated and collided in these experiments as a result of energy supplied by an explosive. In this scheme, the parameters of the explosive charge and the shells can be chosen so that all of the initial kinetic energy of the shell is transformed into heat and the shells are left with a certain radius.It has been established that the main physical processes which occur in the shell material are characterized by nonuniform heating of the shell material through the thickness. The greatest degree of heating is reached on the internal boundary of the shell, and the degree of nonuniformity of the heating increases toward the shell's center [11,13]. This alters properties such as dynamic yield point and absolute viscosity.The phenomena mentioned above are likely to be seen to some extent in any high-rate viscoplastic flow. Progress in systematically accounting for dissipative losses during intensive viscoplastic flows in different problems involving high energy densities is being slowed by the lack of adequately developed phenomenological models ...
The problem of the incidence of a shock wave with a front-pressure amplitude of about 30 GPa at the profiled free surface of an aluminum sample is studied. It is shown that in the case of large perturbations (amplitude 1 mm and wavelength 10 mm), jet flows occur on the free surface. The data obtained are described using a kinetic fracture model that takes into account the damage initiation and growth in the material due to tensile stress and shear strain.The normal incidence of a shock wave (SW) on the free surface (FS) of a condensed material sample without macroscopic features can lead to a number of effects due to the deviation of the SW velocity from the doubling law, velocity dispersion, particle ejection (dusting) from the FS [1-3]. However, the FS can have macroscopic features in the form of defects, artificial conical or hemispherical cavities and attached masses or a certain profile of, for example, a sinusoidal shape, whose amplitude a and wavelength λ far exceed the parameters characteristic of the FS microrelief. The occurrence of microroughness is due to the surface finish (a R z and λ R z , where R z is the height of the surface microroughness). The incidence of a SW on a FS with defects, cavities, and attached masses is accompanied by ejection of cumulative flows of particles [4][5][6], which complicates the numerical modeling and prediction of the fragmentation and dispersion of structural materials under shock-wave loading. The processes occurring on a profiled FS upon incidence of a SW, especially for λ a R z , have been studied inadequately. The present paper reports new experimental and calculation results from studies of the generation and propagation of perturbations caused by the incidence of a SW of intensity 30 GPa on the FS of AMts aluminum samples of sinusoidal shape with an initial amplitude 2a = 1 mm and a wavelength λ = 10 mm. A diagram of the experiments is given in Fig. 1.A cylindrical charge of a high explosive (HE) 120 mm in diameter and 60 mm high was initiated by a plane SW generator, which provided for a time difference for SW arrival at the sample of not more than 50 nsec. The FS of the sample in the form of a 130 × 130 mm plate 10 mm thick had cavities of sinusoidal shape, which allowed the use of a soft x-ray radiographic technique. Figure 2 gives X-ray photographs obtained at various times in the experiments (the dashed curves are drawn over the convexities of the sample relief). An analysis of the X-ray photographs shows that the displacements of the FS of the sample by 5 and 12 mm relative to the initial position, which correspond to the times in the X-ray photographs t γ = 29 and 31 µsec from the moment of HE initiation, leading jet flows are formed in the sample regions located under the initial concavities, and in the region of the initial convexities, there is deceleration of the sample material of lower density. The decreased density of the sample material observed in the X-ray photographs in the regions of convexities (Fig. 2b and c) is apparently caused by particl...
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