Research And Modeling Of Debris Cloud Produced By Hypervelocity Impact Of Projectile With Thin Plate

With the increase of space debris, hypervelocity collisions between space debris and spacecrafts have became a more seriously hazard to space flights, espetially manned spacecrafts. The most useful shielding structure with one or multi-layer shielding walls in front the spacecraft bulkhead with a distant is used to break the space debris and disperse impact energy, in order to get effective protection effect. Generally, the material of shielding wall is aluminum alloy.The damage of rear wall (spacecraft bulkhead or inner shielding wall) impacted by debris cloud which generates from the hypervelocity impact process between space debris and shielding structures depends on the characteristics of debris cloud. So, research on fundamental theory and technologies of debris cloud under hypervelocity impact has an important significance on shilding structure design and development. Nowadays, the quantitative investigation on debris cloud formation is still very limit and most models presented before are only for debris cloud produced by impacts with relatively higher velocties.Based on the background mentioned above, within relatively lower velocity range, this paper mainly investigates the fragmentation process of hypervelocity impact for aluminum sphere and aluminum thin plate at normal angle, formation process of debris cloud, structure and morphology characteristics of debris cloud, velocity and mass characteristics of debris cloud, fragmentation properties of projectile and energy characteristics under hypervelocity impact phenomenon. Based on the individual results, a fresh analytical model of debris cloud is formed. In this paper the impact velocity (v0) is ranging from 2.00km/s and 5.00km/s, thickness of thin plate to projectile diameter ratio (t/D) is between 0.032and 0.315.First, experiments of aluminum spherical projectiles impacting on aluminum thin plates at normal angle were performed by two stage light gas gun loading technique. Debris cloud radiographs were captured by flash X-ray radiography device. Damage patterns were recorded by witness plate placed behind the thin plate. The projectile diameter is 6.35mm. The thickness of thin plate is between 0.50mm~2.00mm. Impact velocity is ranging from 2.23km/s to 5.26km/s. Quantity of numerical simulations using SPH method were performed to remedy inadequacy of experiment results and mechanism studies. Results in numerical simulations and expreriments were nearly same for the debris cloud morphology and velocities on measurement points. These comparisons deduced the validity of simulation results.Second, the stress wave propagation principle and marerial damage mechanism inside the projectile and thin plate under hypervelocity impact were discussed which are also verified by experimental and numerical results. According to experimental results, critical state problems are proposed on fragmentation of projectile material and debris cloud initial formation process. Critical impact conditions of projectile fragmentation and debris cloud formation are determined by numerical method. By analyzing the numerical simulation results, differences of material fragmentation and fragments ejection process on the front surface of thin plate are found. Possibly reasons are proposed and quantitative expressions are discussed. The composition and structure of debris cloud under different impact conditions are defined based on experimental and numerical results. Debris cloud morphological characteristics are described and summarized. By comparing the images of debris cloud with witness plate damage patterns, the corresponding relations are confirmed.Third, four measurement points on debris cloud are defined based on the debris cloud morphology. With simulation data, variations of velocities on measurement points with impact condition (v0, t/D) are analyzed. Quantitative relationships between measurement point velocities and impact condition are obtained. By a comprehensive consideration on theoretical, experimental and numerical results, a mass calculation model on different parts of debris cloud is raised. Quantitative relationship between energy dissipation and impact condition during hypervelocity impact is fitted based on simulation data. By analyzing witness plate experimental damage patterns, variations of physical quantities, such as the maximum fragment's dimension, characterizing the level of projectile fragmentation with impact condition are discussed. The relationship between major part of debris cloud mass distribution and damage degree of projectile is also discussed.Last, Based on the previous study and reasonable assumptions, a debris cloud model including cloud shape description, velocity distribution and mass distribution is deduced. All components of debris cloud are described in this model. Plane curve equations are determined to describe different component contours of debris cloud. Furthermore, velocity distribution models for debris cloud being freely expanding are derived. Based on the experimental and numerical results, mass distribution models for different parts of debris cloud are discussed respectively, especially for the major part which has a complicate mass distribution. By using mass, momentum and energy conservation equations, parameters introduced in debris cloud model are determined. Finally, two typical simulation examples are used to verify the usefulness of the model.The result of this paper is a basic technical knowledge for ballistic limit of shielding structure and design of spacecraft protection system. The mechanism of debris cloud formation is also explained in this paper. The results also can be the basic idea to develop the newly multi-layered shields. This paper has an effective and theoretical guidance values.