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Ivanov et al. [1] examined problems involved in the development of determinate perturbations in cylindrical casings filled with air and accelerated by explosion products. They established that the shear strength of the material of the casing had a marked effect on the shape and amplitude of the perturbations at the stage of acceleration of the casing toward the axis of symmetry. Of interest is the case of a compressed casing cavity filled partially or, as, for example, in [2], fully by a medium more dense than air. In this case there is the possibility of studying deceleration processes and the subsequent disintegration of the casings, when the conditions for Rayleigh-Taylor (RT) gravitational instability of the interface between the casing and the compressed medium may arise.i. During accelerated motion of the interface between two mediums with different densities (in the presence of initial perturbation) they can be unstable, if the acceleration is directed from the light medium to the heavy one, and stable, if the acceleration is in the other direction. During the approach stage of motion of the casing toward the axis of symmetry, the acceleration is directed toward the axis and the conditions for RT instability can be realized only at the outer interface of the casing accelerated by the explosion products. The inner casing interface (ICB) will be stable. During deceleration of the casing at the disintegration stage of its motion, conditions for RT instability of the ICB can be realized with variation in the direction of acceleration.While investigation of RT instability in liquid and gases has been the subject of a large number of articles, the number of publications dealing with instability in solid mediums is limited. As a result of experimental [4-6] and computationaltheoretical investigations in the framework of an ideally elastic [7], an ideally plastic [8], and an elastoplastic [9, 10] model of a medium it has been possible to establish that the rheological characteristics of a medium (strength and viscosity) have a significant stabilizing effect on RT instability. As a function of the model of the medium used, the criteria defining the transition of the surface from the region of stability to the unstable region are taken to be: the critical wavelength X. [7, 9], the critical initial perturbation amplitude a, [8], or their combination [10]#:Here g is the acceleration; G is the shear modulus; and a s is the dynamic yield point. Three stages in the development of RT instability are usually distinguished. In the first stage, perturbation at the unstable interface grows exponentially and at the second its growth slows with the transition to the exponential law. The final tExpression (1.3) is a simplified variant of formula (31) from [10].Arzamas-16.

Predictive simulation of the long-term response of multilayer targets with ceramics layers to shock compression demands appropriate material models. Because ceramics are complex brittle materials, which tend to lose their strength under heavy loads, such simulation requires the failure models well-proven for a wide range of strains and strain rates. Standard plate impact experiments provide the main data utilized for developing and validating the mechanical models of material response to shock compression. However, apart from the fact that such experimental data are inherently one-dimensional, they can be insufficient to verify the failure model at relatively low strain rates typical for long unloading waves. Here, we present the experimental results for explosive compression of a spherical multilayer shell initiated by a single detonator. The explosive-coated shell consists of the nested spherical layers: the outer made of boron carbide and the inner of lead. X-ray images showing the evolution of those layers after detonation are then compared with simulation results. Propagation of the compression wave through the layers resulting in ceramics damage is analyzed in detail. We demonstrate that the failure model of boron carbide should be adjusted for compressions below 10 GPa to achieve a good agreement with our experimental images. Such an improved failure model provides the predictive simulation of long-term dynamics of targets after unloading, and it has almost no effect on wave profiles after plate impact.

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