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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. [ABSTRACT FROM AUTHOR]

Ceramic materials have a long-term industrial demand due to their high mechanical hardness and chemical and temperature resistance. They are brittle and tend to lose strength under heavy loads which complicates the development of a comprehensive material model for simulation of engineering prototypes containing ceramic parts. We developed an improved failure model of ceramics based on the well-known Johnson–Holmquist approach. This model redefines the damage rate equation using a consistent definition of the total plastic strain in the failed material. It reduces the number of free model parameters and enables the plastic strain to be explicitly accumulated during the failure process. The corresponding non-iterative algorithm utilizing this explicit failure model is developed. It is successfully validated by simulation of the wave profiles obtained in plate-impact experiments with boron carbide using the contact smoothed particle hydrodynamic method. [ABSTRACT FROM AUTHOR]

The magnetosphere response to the solar wind forcing at various values of the plasma resistivity is studied. The simulation is performed within a two-dimensional MHD resistive model; the meridional plane is considered. The incoming solar wind and southward interplanetary magnetic field are supposed to be stationary. The calculations were made for two plasma resistivity values η ={106; 104} m given by constants in the whole flow field. The plasma resistivity was specified on the basis of the spacecraft measurements of the bow shock width. At higher plasma resistivity steady magnetospheric convection takes place; at lower resistivity the sawtooth event is realized. The sequence of sawtooth cycle phases is analyzed in terms of the open magnetic flux and reconnection rates. The evolution of the magnetic force lines and velocity vector lines in every phase is described. In the (x, t) diagram, the movement of axial positions of boundaries between dipole, interplanetary and island magnetic fields is plotted. In the growth and expansion phases, a vortex train is generated in the tail dipole sector. The reconnection at the magnetosphere dayside occurs through two x-points positioned symmetrically at the top and bottom peaks of the magnetic island. [ABSTRACT FROM AUTHOR]