Toshimori Sekine

Shock equation of state of basalt

Detailed wave profiles for Kinosaki basalt at pressures up to 25 GPa are measured using a laser velocity interferometer in order to determine the dynamic properties. The results indicate a Hugoniot elastic limit of ∼2 GPa and a relationship between shock velocity (Us) and particle velocity (Up) approximated by Us (km/s) = 3.5 + 1.3Up (km/s) in the low-pressure plastic region (Up below ∼4 km/s). These data are compared with the known data for rocks with basaltic compositions, and tensile strength of the basaltic rocks was found to be about one tenth of that of compression strength.

Emission Spectroscopy of Eu-Doped CaF2 under Static and Dynamic High Pressures

The time-resolved emission spectra of the CaF2(Eu) crystal subjected to impact-induced shock compression in the inelastic region have been measured up to 31.6 GPa and the effect of shock and release waves on the Eu emission spectrum has been recorded. The Eu2+ spectrum centered at ~425 nm shifts toward the longer wavelength with a shock pressure of up to ~15 GPa, but no further shift has been observed at higher pressures. Emission spectra under static pressure have also been measured up to 10.2 GPa and compared with those under shock compression. A blue Eu2+ emission at ~425 nm and a sharp orange Eu3+ emission at ~590 nm are observed under static pressure. A large pressure shift of ~2.2 nm/GPa is observed for the blue emission at pressures of up to ~10 GPa, but the orange emission spectrum hardly moves against pressure. The Hugoniot determined for the CaF2(Eu) single crystal is Us=5.15+1.18Up.

Shock compression of magnesium silicon nitride

Shock Hugoniot of magnesium silicon nitride MgSiN2 was measured up to pressures of 150 GPa by the inclined mirror method. Shock recovery experiments for the powder were carried out and the post‐shock samples were investigated by x‐ray diffraction method. There was no clear evidence for high‐pressure phase transition as suggested by the first‐principles calculations. The experimental results were compared with those of shocked AlN with a similar structure.

Measurement of dynamic tensile strength of nanocrystalline copper by laser irradiation

An approach is developed to investigate the dynamic tensile fracture of nanocrystalline copper by laser irradiation loading. A push-pull type velocity interferometer system for any reflector is used to measure the rear free surface velocity profiles. The dynamic tensile strength of nanocrystalline copper films is determined from these velocity profiles as a function of the tensile strain rate. Results show that the dynamic tensile strength of nanocrystalline copper film is about 3 GPa, which is much higher than that of polycrystalline bulk copper, but lower than that of single crystal copper. This dynamic tensile strength increase may be attributed to constraints on dislocation motion by more grain boundaries in nanocrystalline materials.

Hugoniot and impact-induced phase transition of magnesite

Abstract Hugoniot equation-of-state and release adiabat results are presented for magnesite to a pressure of ~140 GPa. A sharp change in the shock velocity and particle velocity relation suggests that a phase transition to a high-pressure phase occurs at 107±10 GPa. Decomposition of magnesite was observed by abrupt volume expansion during the pressure release from a pressure over the phase transition and by investigating post-shock magnesites recovered from hypervelocity impacts of mini-flyers performed using a laser-driven acceleration. Post-shock magnesites above 95 GPa contained MgO crystallites and the amount of MgO increased with increasing shock pressure.

Numerical Simulation of Carbon Simple Cubic by Dynamic Compression

An impact scheme of a slab target and flyer with a layered structure is proposed to achieve low-entropy dynamic compression of diamond. The thermodynamic state of diamond during compression is examined using one-dimensional Lagrangian hydrodynamic code and the tabulated equation of state library, SESAME. The use of a material with a small shock impedance for the impact interfaces markedly decreases the strength of the primary shock wave. It is found that a gradient of shock impedance across the thickness of the flyer generates small multiple shock waves into the diamond and is effective for low-entropy compression. The thermodynamic conditions required for carbon simple cubic and low-entropy dynamic compression is achieved.