9:00 AM - 9:15 AM
[PPS07-01] Hypervelocity Impacts on granular materials: Temperature Distribution near the Impact Point
Keywords:Hypervelocity impacts, Granular materials, Shock recovery
Hypervelocity Impact on granular materials: Temperature Distribution near the Impact Point
K. Kurosawa, M. Sato, H. Ono, N. Tomioka, T. Niihara, and S. Hasegawa
Impacts between planetary bodies among the fundamental processes of in planetary sciences. The generation of shock waves irreversibly converts orbital energy around the Sun into thermal energy [e.g., Ahrens&O'Keefe72, Moon 4, 214-249]. Shock metamorphic features formed at high temperatures and pressures generated during impacts have been found in various meteorites and lunar samples, and have been used as probes to reconstruct the dynamical states of the early solar system [e.g., Marchi+13, Nature Geo. 6, 303-307]. The reconstruction requires a precise understanding of the momentum and energy partitioning during shock wave propagation. In most cases, the impact conditions required for producing metamorphic features have been estimated based on the assumption that a projectile and a target are homogeneous media. However, natural materials are mixtures of grains, which have a variety of density and size, and there are grain boundaries and voids in the media. Recent shock physics modeling in a mesoscale, which can handle multiple materials, have shown that in such complex systems, significant pressure and temperature heterogeneity occurs during shock wave propagation [Bland+14, Nature Comm. 5, 5451]. The previous interpretations of the results of analyses of shocked meteorites and lunar samples should be reviewed. Investigations of the momentum and energy distribution process around the impact point of hypervelocity impacts, which are exposed to the strongest shock waves, is indispensable for investigating the nature of shock wave propagation in actual rocky materials.
We have attempted to recover shocked materials around the impact epicenter in granular targets in a fully-open system and to measure the temperature distributions in the recovered samples. Thermal remanent magnetization was used for a temperature indicator. This measurement technique has been developed in the field of paleomagnetism and has recently been applied to impact experiments [Sato, M. (2021) Geophysical Research Letters 48, e2021GL092716., North, T. L. et al. (2022) LPI Contrib. No. 2695, 6394.]. A vertical two-stage light gas gun installed at ISAS/JAXA was used for the experiment. Granular targets containing demagnetized magnetite powder were placed in an artificially generated magnetic field and vertically impacted. The magnetite particles acquire thermal remanent magnetization corresponding to the peak temperature during the impacts. By optimizing the experimental conditions, a bowl-shaped structure is left at the center of the impact crater, and it is possible to recover a small amount of the shocked granular materials initially located immediately beneath the impact point.
The recovered bowl-shaped samples were hardened with a resin, cut into small pieces, and the thermal remanent magnetization was measured using a superconducting quantum interference device magnetometer at the University of Tokyo. The results show that (1) the temperature decreases with increasing distance even within a spatial scale shorter than the diameter of the projectile, and (2) the peak temperature at the region nearest the impact point is lower than the Hugoniot temperature calculated with a porosity compaction model, but rather close to that calculated for an ideal crystal without any porosities. In the presentation, we will discuss the shock wave propagation process in granular media, including the results of microscopic observations of polished thin sections.
Acknowledgments: This work was supported b yISAS/JAXA as a collaborative program with the Hypervelocity Impact Facility. This research was supported by JSPS KAKENHI Grant No. JP21K18660.
K. Kurosawa, M. Sato, H. Ono, N. Tomioka, T. Niihara, and S. Hasegawa
Impacts between planetary bodies among the fundamental processes of in planetary sciences. The generation of shock waves irreversibly converts orbital energy around the Sun into thermal energy [e.g., Ahrens&O'Keefe72, Moon 4, 214-249]. Shock metamorphic features formed at high temperatures and pressures generated during impacts have been found in various meteorites and lunar samples, and have been used as probes to reconstruct the dynamical states of the early solar system [e.g., Marchi+13, Nature Geo. 6, 303-307]. The reconstruction requires a precise understanding of the momentum and energy partitioning during shock wave propagation. In most cases, the impact conditions required for producing metamorphic features have been estimated based on the assumption that a projectile and a target are homogeneous media. However, natural materials are mixtures of grains, which have a variety of density and size, and there are grain boundaries and voids in the media. Recent shock physics modeling in a mesoscale, which can handle multiple materials, have shown that in such complex systems, significant pressure and temperature heterogeneity occurs during shock wave propagation [Bland+14, Nature Comm. 5, 5451]. The previous interpretations of the results of analyses of shocked meteorites and lunar samples should be reviewed. Investigations of the momentum and energy distribution process around the impact point of hypervelocity impacts, which are exposed to the strongest shock waves, is indispensable for investigating the nature of shock wave propagation in actual rocky materials.
We have attempted to recover shocked materials around the impact epicenter in granular targets in a fully-open system and to measure the temperature distributions in the recovered samples. Thermal remanent magnetization was used for a temperature indicator. This measurement technique has been developed in the field of paleomagnetism and has recently been applied to impact experiments [Sato, M. (2021) Geophysical Research Letters 48, e2021GL092716., North, T. L. et al. (2022) LPI Contrib. No. 2695, 6394.]. A vertical two-stage light gas gun installed at ISAS/JAXA was used for the experiment. Granular targets containing demagnetized magnetite powder were placed in an artificially generated magnetic field and vertically impacted. The magnetite particles acquire thermal remanent magnetization corresponding to the peak temperature during the impacts. By optimizing the experimental conditions, a bowl-shaped structure is left at the center of the impact crater, and it is possible to recover a small amount of the shocked granular materials initially located immediately beneath the impact point.
The recovered bowl-shaped samples were hardened with a resin, cut into small pieces, and the thermal remanent magnetization was measured using a superconducting quantum interference device magnetometer at the University of Tokyo. The results show that (1) the temperature decreases with increasing distance even within a spatial scale shorter than the diameter of the projectile, and (2) the peak temperature at the region nearest the impact point is lower than the Hugoniot temperature calculated with a porosity compaction model, but rather close to that calculated for an ideal crystal without any porosities. In the presentation, we will discuss the shock wave propagation process in granular media, including the results of microscopic observations of polished thin sections.
Acknowledgments: This work was supported b yISAS/JAXA as a collaborative program with the Hypervelocity Impact Facility. This research was supported by JSPS KAKENHI Grant No. JP21K18660.