[1] In order to reevaluate the scaling law on impact fragmentation, attenuation of shock waves induced by impact events is numerically simulated in two-dimensional axial symmetry using the cubic interpolation propagation method in wide stress regime: not only the regime where targets respond plastically, but also the regimes where shock stresses are comparable to the Hugoniot elastic limit (HEL) of target materials. As a constitutive equation of state for brittle materials that lose the strength, we newly propose a ''brittle model'' based on experimental data. Comparing our results with previous studies on shock attenuation, an ''elastic-plastic regime'' in the vicinity of HEL where the attenuation becomes rapid is newly found. We calculate the antipodal stresses normalized by the dynamic compressive strength through simulations for some previous impact experiment data using rocks and ices and reevaluate a scaling law of the impact fragmentation. The results suggest that the description of the fragmentation process that the largest fragment is mainly produced by the tensile waves emanated from the free surface at the antipodal point is plausible.
[1] Laser ablation experiments are carried out using a high intensity laser ($10 10 W/cm 2 ) and basalt targets. Using a high-speed camera and a spectrometer, the radius and the temperature of the silicate vapor clouds generated by laser ablation are observed as a function of time. Then a numerical simulation of vapor expansion is carried out, and the thermodynamic state of the silicate vapor is determined so as to reproduce the experimental results. The result of the analysis indicates that the impact velocity which would generate a vapor cloud with this thermodynamic state is $120 km/s for collisions between two basaltic bodies.
We present the experimental results of the measurement of fragment velocity in an impact disruption. Cylindrical projectiles impact on a side (edge) of thin glass plates, and the dispersed fragments were observed using a high-speed camera. The fragment velocity did not depend on the mass but rather on the initial position of the fragment; the velocity component parallel to the projectile direction increased with the distance from the impacted side, while the component perpendicular to the projectile direction increased with the distance from the central axis parallel to the projectile direction. It appears that there are two mechanisms for fragment ejection: one is "spallation," where the fragment velocities depend on the particle velocity induced by shock waves, and the other is "elastic ejection," where the velocities are controlled by the strain energy stored in targets and are at most a few tens of meters per second. We performed a one-dimensional numerical simulation of elastic ejection with a discrete element method and obtained the velocity distribution as a function of the initial position. The numerical results are qualitatively consistent with the experimental ones.
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