Presentation Information
[PPS04-P04]Stress Propagation and Internal Behavier Analysis During Impact on Crushable Granular Material
*Kazuma Kita1, Hironori Sakata1, Satoshi Takada1 (1.Tokyo University of Agriculture and Technology)
Keywords:
Impact,Asteroid,Crater
In space collision phenomena, analyzing the propagation of internal stresses within an impacted body and their propagation speed after collision is crucial. By deepening our understanding of the temporal and spatial evolution of internal behavior, it becomes possible to predict the orbits of celestial bodies before and after impact. In recent years, research has explored artificially colliding with near-Earth objects to alter their orbits and prevent Earth impacts. NASA’s DART mission successfully demonstrated this approach by colliding a spacecraft with the asteroid Dimorphos, changing its orbital period and proving the effectiveness of artificial collisions for orbital modification. The importance of momentum transfer and orbital prediction for the target celestial body before and after collision is increasing. Understanding the overall behavior of the target and elucidating the factors related to these pre- and post-collision parameters are essential. Among these factors are the particle layer on the target’s surface at the time of collision, the parameters of the particles composing it, and the porosity. Porosity is considered to significantly influence stress propagation, stress pathways, and energy dissipation behavior.
This study aims to deepen understanding of the effects on parameters related to pre- and post-impact processes by constructing target body and impactor models, visualizing stress propagation and internal behavior within the target body, and analyzing momentum transport, constituent particle behavior, and crater formation. This research was conducted using LAMMPS, a discrete element method (DEM) simulator. By assuming the target body as a friable granular assembly and the impactor as either a friable granular assembly or a non-friable body, collision simulations were performed using granular materials composed of particle aggregates. In these simulations, the time evolution of the system was calculated by sequentially solving the equations of motion for each particle constituting the model, enabling more realistic dynamic behavior. For particle interactions, the JKR (Johnson–Kendall–Roberts) model was employed. Unlike the Hertz–Mindlin model, which considers elastic and frictional forces between particles, the JKR model incorporates adhesion due to surface energy, thereby reproducing the contact and separation behavior of constituent particles and representing behavior closer to that of actual surface regolith particles. For the simulation conditions, the porosity of the target body was set to three levels: 68%, 55%, and 48%. Additionally, the impact angle of the projectile relative to the target body was varied to 0°, 15°, 30°, 45°, and 60°.
As a result, visualization of stress propagation and momentum loss within the target body due to collision revealed that stress propagation is enhanced as porosity decreases, while momentum loss shows a decreasing trend. The increased speed of stress propagation promotes stress dissipation, suggesting that the target body exhibits a relatively soft mechanical response. Changes in stress propagation due to varying impact angles confirmed that stresses increase in the direction of propagation and near the circumference, accompanied by reduced stress dissipation and the occurrence of localized stress concentrations. Furthermore, simulations using a model focused solely on the surface were performed to conduct detailed analysis of the region near the local impact point in addition to the entire target body model. Surface particles were assigned interactions based on the Hertz–Mindlin model, the JKR model, and cohesion, respectively, to reproduce the strength and porosity of the surface layer. By investigating the mixing degree and density distribution of the impactor particles within the particle layer simulating the target body’s surface, particle behavior related to stress propagation and impact/crater formation was visualized. The behavior of the impactor after entering the surface particle layer varied depending on conditions such as impact velocity and porosity. These variations also affected the crater shape on the surface and the extent of impactor penetration and expansion within the target body’s near-surface region. This presentation reports on stress propagation before and after impact and the internal behavior of each model using these two simulation models of the impact phenomenon.
This study aims to deepen understanding of the effects on parameters related to pre- and post-impact processes by constructing target body and impactor models, visualizing stress propagation and internal behavior within the target body, and analyzing momentum transport, constituent particle behavior, and crater formation. This research was conducted using LAMMPS, a discrete element method (DEM) simulator. By assuming the target body as a friable granular assembly and the impactor as either a friable granular assembly or a non-friable body, collision simulations were performed using granular materials composed of particle aggregates. In these simulations, the time evolution of the system was calculated by sequentially solving the equations of motion for each particle constituting the model, enabling more realistic dynamic behavior. For particle interactions, the JKR (Johnson–Kendall–Roberts) model was employed. Unlike the Hertz–Mindlin model, which considers elastic and frictional forces between particles, the JKR model incorporates adhesion due to surface energy, thereby reproducing the contact and separation behavior of constituent particles and representing behavior closer to that of actual surface regolith particles. For the simulation conditions, the porosity of the target body was set to three levels: 68%, 55%, and 48%. Additionally, the impact angle of the projectile relative to the target body was varied to 0°, 15°, 30°, 45°, and 60°.
As a result, visualization of stress propagation and momentum loss within the target body due to collision revealed that stress propagation is enhanced as porosity decreases, while momentum loss shows a decreasing trend. The increased speed of stress propagation promotes stress dissipation, suggesting that the target body exhibits a relatively soft mechanical response. Changes in stress propagation due to varying impact angles confirmed that stresses increase in the direction of propagation and near the circumference, accompanied by reduced stress dissipation and the occurrence of localized stress concentrations. Furthermore, simulations using a model focused solely on the surface were performed to conduct detailed analysis of the region near the local impact point in addition to the entire target body model. Surface particles were assigned interactions based on the Hertz–Mindlin model, the JKR model, and cohesion, respectively, to reproduce the strength and porosity of the surface layer. By investigating the mixing degree and density distribution of the impactor particles within the particle layer simulating the target body’s surface, particle behavior related to stress propagation and impact/crater formation was visualized. The behavior of the impactor after entering the surface particle layer varied depending on conditions such as impact velocity and porosity. These variations also affected the crater shape on the surface and the extent of impactor penetration and expansion within the target body’s near-surface region. This presentation reports on stress propagation before and after impact and the internal behavior of each model using these two simulation models of the impact phenomenon.