Sunao Hasegawa

Hypervelocity impact experiments were performed on transparent materials, SiO_2 glass and polycarbonate, to investigate the impact-induced damage process. Stress wave propagation and damage evolution associated with hypervelocity impact were visualized using a high-speed video camera. Recorded images clearly showed how stress waves propagate and interact each other, and how damages form and propagate during hypervelocity-impact event. For examples, the interaction of the transversal wave with the longitudinal wave reflected from rear surface initiated the drastic nucleation of damage points in SiO_2 glass. In the case of polycarbonate, delamination was initiated by the interaction of the reflected rarefaction waves from both side surfaces. Such information provides a valuable insight into the fundamental understanding of the hypervelocity-impact damage process on glass, ceramics, and polymer materials.

The effects of projectile impact velocity on ejecta fragment size were investigated by striking aluminum alloy 6061-T6 targets with 3.2-mm-diameter aluminum alloy 2017-T4 spheres at velocities ranging from 2 to 6 km/s. The two-stage light-gas gun at the Institute of Space and Astronautical Science (ISAS)/ Japan Aerospace Exploration Agency (JAXA), was used for the experiments. To examine the scattering angles of ejecta, a witness plate (150 mm × 150 mm, 2 mm in thickness) made of copper C1100P-1/4H, with a 30-mm hole in the center, was placed 50 mm in front of the target. The behavior of ejected fragments was observed using a high-speed video camera. The projected areas of ejecta collected from the test chamber after the impact experiments were measured....

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Lightcurves of 20 V-type asteroids and 13 asteroids are by-productions for V-type asteroid observations have been obtained. We have determined rotation periods of 18 V-type asteroids and 11 non V-type asteroids....

The effects of projectile material properties on crater shape and ejecta in thick aluminum alloy 6061-T6 targets were investigated at velocities ranging from approximately 0.5 to 6 km/s. The projectile density affected the crater depth, but the projectiles hardness did not affect it. At the impact velocity of 6 km/s, the density of projectiles clearly affected the mass and size of ejecta fragments. The impact velocity clearly affected the diameter of ejecta rings. The ejecta ring diameter of metal projectiles was almost the same.