Vitaly Paris

ON THE COMPRESSIVE AND TENSILE STRENGTH OF MAGNESIUM ALUMINATE SPINEL

Magnesium aluminate spinel is a strong polycrystalline transparent ceramic. Spinel is an attractive material for armor applications and its behavior under shock wave loading is of obvious interest. The purpose of the present study was to determine the Hugoniot elastic limit (HEL) of this material, its Hugoniot response above the HEL, and its spall strength. Planar impact experiments were performed over the 2 to 40 GPa stress range using the Velocity Interferometer System for Any Reflector (VISAR) as a principal diagnostics tool. According to these tests, spinel has a HEL of about 11.3 GPa. The spall strength of the material was found to be close to zero at low, about 2 GPa, impact stress.

Study of Compressive Failure of Alumina in Impact Experiments with Divergent Flow

Axisymmetric divergent flow characterized by increasing (with propagation distance) difference between longitudinal and radial stress was produced in the plane‐parallel alumina samples by impact of spherical (R=200–600 mm) copper impactors having velocities 210 to 260 m/s. The velocity of the interface between the impacted 5‐mm alumina samples and 6‐mm sapphire windows was continuously monitored by VISAR. Preliminary AUTODYN simulations show that such impact is capable of producing in the sample the stress states which cannot be produced by planar impact loading and which may result in the brittle failure of alumina. Actually, the waveforms recorded in these experiments contain distinct signatures of the alumina failure. AUTODYN numerical simulations of the experiments allow one finding the alumina failure threshold, the path of the increasingly damaged alumina, the kinetics of this damaging and the locus of the states of comminuted material in the principal stress space. Possible applications of the deve...

STUDY OF COMPRESSIVE STRENGTH OF SIC IN IMPACT EXPERIMENTS WITH DIVERGENT FLOW

The axisymmetric divergent flow was generated in SiC samples by impact of convex copper flyer plates (radius of curvature ranging from 88 to 550 mm) having velocities from 550 to 700 m/s. The sample‐window (sapphire) interface velocities or the velocities of the free surface of the nickel witness plate were continuously monitored by VISAR. The maximum shear stress achieved under different confining stress just prior to the sample failure is associated with the compressive failure threshold of the SiC. Both the compressive failure threshold of SiC and the parameters of its inelastic deformation were found by matching the results of the AUTODYN‐2D numerical simulation with the experimentally obtained waveforms. The compressive failure threshold of SiC is characterized by a transition from brittle‐like behavior below the confining stress of 1.4–1.5 GPa to the ductile‐like one at higher confining stress.