Ceramic materials have been a promising candidate for structural materials under severe conditions. While metals are large components of spacecraft, ceramic materials are often significant components of optical and thermal protection systems of space structures. Because these ceramic materials are much more sensitive to hypervelocity impact than metals, it is important to verify their reliability against the impact of space debris and micrometeoroids. In this article, two studies which are conducted to investigate the damage behavior of ceramic materials subjected to hypervelocity impact are described. First one is the impact-damage evaluation on silicon nitride ceramics which is used for a new advanced ceramic thruster. Second one is the high-speed imaging of impact damage evolution in SiO2 glass which is the primal optical material of space structures.
In this article, recent studies on impact cratering and impact disruption of planetary bodies are reviewed. A widely accepted scaling law for impact cratering is introduced to discuss the effects of material strength and planetary gravity on the crater formation process. A sophisticated scaling law for impact disruption is also introduced and we notice that non-dimensional impact stress is useful parameter to describe the catastrophic disruption. The impact strength of icy bodies, meteorite parent bodies and primitive asteroids are studied by using various materials simulating them, and these results are explained briefly.
In this article, local damage of a concrete member subjected to high-velocity impact by a rigid projectile and an evaluation method for the local damage were presented. Characteristics of the local damage of concrete were examined by conducting high-velocity impact tests. Considering the strain rate effects and pressure dependency of concrete, numerical simulations were conducted and the failure mechanism of the local damage of concrete was investigated. An evaluation procedure based on the failure mechanism was introduced and applicability of the procedure to previous test data was examined.
In this article, ejecta size distribution was examined when polycarbonate spheres struck thick aluminum alloy targets at very high velocities. The size and mass of the ejecta fragments collected from the test chamber were also measured. The ejecta size distributions depended on the aluminum alloy types of targets. The ejecta fragment size was proportional to the cubic root of the impact energy.
After reviewing the history and mechanism of Whipple bumper shield to protect spacecrafts from the hypervelocity impact by micrometeoroids and orbital space debris, this paper proposes and demonstrates the methodology on the determination of ballistic limit curve of Whipple shield only by numerical analyses by using a hydrocode: AUTODYN. In the numerical method, fragmentations and phase changes of projectile and target materials are taken into account.
High-power laser irradiation creates extremely higher-pressure and density conditions in materials than conventional pulsed-power devices. Here we present new experimental results on ultrafast solid-solid phase transformation of silicon from semiconductor to metal and laboratory synthesis of a water-rich extrasolar planet. These interdisciplinary works motivate new experiments using an emerging, intense and coherent light source as observation tool in order to reveal new behavior and/or diversity of material under tera-Pascal pressures and femtosecond dynamics.
This paper described the cases where a high-pressure treatment of 200 MPa was found to be effective against the two typical heat-resistant spores, B. subtilis and B. cereus when conducted as a pretreatment step before heat sterilization at 90 to 100℃. In addition, when the B. cereus was used as the indicator, it took 36 minutes (D=3 min.) to complete the heat sterilization at 100℃, whereas the holding time of only 6 minutes (D=0.5 min.) was enough to achieve sterility by using the Hi-Pit (high-pressure induced transformation) effect.