Publications (3)1.18 Total impact
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ABSTRACT: Porous materials are believed to be common in the asteroids and satellites of the outer planets. In order to study the relationship between the structure of small bodies and their thermal and collisional evolution, we performed impact disruption experiments on porous sintered glass bead targets using a light-gas gun. The sintered glass bead targets were prepared to have various porosity and compressive strength. The compressive strength ranges over an order of magnitude according to the various sintering conditions. Both the compressive strength and the longitudinal wave velocity were found to have good correlations with the size of the necks developed between the bead particles.In our first low-velocity impact runs with these targets, we selected the targets with roughly the same porosity but different compressive strength. We shot the targets by cylindrical polycarbonate projectiles at velocities ranging from 10 to 120 m/s. The results showed that the targets of higher compressive strength have higher impact strength as could be expected. However, compared to previous results from the impact disruption of glass bead targets at velocity of 4.9–5.5 km/s [Love, S.G., Hörz, F., Donald, E.B. Target porosity effects in impact cratering and collisional disruption. Icarus 105, 216–224, 1993], the impact strength derived in our study was found to be lower by more than an order of magnitude [Setoh, M., Nakamura, A.M., Hiraoka, K., et al. Collisional disruption of weakly sintered porous targets at Low impact velocities. Earth Planet. Space (in press)]. The differences between the two experiments were the impact velocity, target-projectile size ratio, and the projectile material and shape.In our new low-velocity impact runs, we used projectiles of glass spheres that are similar to those of Love et al. The impact strength was again found to be much smaller than those found in high-velocity runs performed by Love et al. Therefore our previous and present results show that collisional outcomes of porous bodies are highly dependent upon impact velocity.Advances in Space Research 40(2):252-257. · 1.18 Impact Factor
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ABSTRACT: Porous structure is common in asteroids and satellites of outer planets In order to study the relation between structure of the small bodies and their thermal and collisional evolution we prepared porous sintered targets measured the compressive strength and determined their impact strength Previous studies showed using sintered glass beads Love et al 1993 the targets with higher compressive strength have higher impact strength and the targets with higher porosity have higher impact strength However in these experiments the porosity of the targets were changed according to the compressive strength Therefore we fixed the porosity while the compressive strength was varied Our experiments were performed with low impact velocity condition because low impact velocities are common among icy bodies far from the Earth We sintered soda lime glass beads of 50 micron diameter and 2 5g cm -3 nominal density at various temperatures and durations to produce targets with similar porosity sim 40 and different compressive strength 0 2 sim 7 8MPa We performed impact disruption experiments using a low velocity light-gas gun at Kobe University sim 100m s We used cylindrical polycarbonate projectiles 1 5 cm in height and 1 0 cm in diameter We determined the specific energy J kg of projectile kinetic energy per kilo gram initial target mass for the condition that the largest fragment mass being the half of the initial target mass is the threshold energy for collisional disruption Q Fujiwara et al 1989 Holsapple et al36:1214.
Article: High- and low-velocity impact experiments on porous sintered glass bead targets of different compressive strengths: Outcome sensitivity and scaling[show abstract] [hide abstract]
ABSTRACT: Impact experiments on porous targets consisting of sintered glass beads have been performed at different impact velocities in order to investigate the disruption impact energy threshold (also called Q∗) of these targets, the influence of the target compressive strength on this threshold and a scaling parameter of the degree of fragmentation that takes into account material strength. A large fraction of small bodies of our Solar System are expected to be composed of highly-porous material. Depending on their location and on the period considered during the Solar System history, these bodies collide with each other at velocities which cover a wide range of values from a few m/s to several km/s. Determining the impact response of porous bodies in both high- and low-velocity regimes is thus crucial to understand their collisional evolution over the entire Solar System history, from the early stages of planetary formation through collisional accretion at low impact velocities to the current and future stages during which impact velocities are much higher and lead to their disruption. While these problems at large scale can only be addressed directly by numerical simulations, small scale impact experiments are a necessary step which allows the understanding of the physical process itself and the determination of the small scale behavior of the material used as target. Moreover, they are crucial to validate numerical codes that can then be applied to larger scales.Sintered glass beads targets of different shapes and porosity have been built and their main material properties, in particular their compressive strength and their porosity, have been measured. The outcomes of their disruptions both at low and high impact velocities have then been analyzed.We then found that the value of Q∗ strongly depends on the target compressive strength. Measuring the particle velocities as a function of their distance to the impact point, we first found that the attenuation rate of the stress wave in our sintered glass bead targets does not depend on the impact velocity regime. Ejecta velocities as a function of the distance from the impact point can thus be well fitted by a power law with an exponent about −2 in both velocity regimes. We then looked for a scaling parameter that can apply to both regimes. We found that the scaling parameter PI, which is related to the initial peak pressure and to the stress wave attenuation can be used to represent the outcome in a general way. Future investigations will be performed to determine whether these results can be generalized to other kinds of porous materials.Icarus.