Modeling jet flows caused by the incidence of a shock wave on a profiled free surface

Abstract

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...