FRAGMENTATION MODELS FOR HYPERVELOCITY IMPACT

In order to support the development of engineering fragmentation model involved in orbital collision of space debris, the objective of this research is to better understand the physical fundamentals of hypervelocity impact fragmentation algorithm, and to develop a couple of semi-empirical fragmentation models for aluminum thin-plate impact at hypervelocity. Particularly, this research takes account of some typical effects influencing hypervelocity impact fragmentation, including projectile shape, impact inclination, target thickness and impact velocity. To this end, the works conducted in this research are generalized as follows: First, the morphology study of the projectile shape effect on debris cloud subjected a thin-plate impact has been performed by numerical simulations as well as experiments. On one hand, numerical simulations of aluminum projectiles impacting onto aluminum thin-plates or Whipple shields were performed by SPH simulation methodology. More than 160 simulation cases had been computed to provide a comprehensive database. On the other hand, a total of 20 hypervelocity impact tests were conducted on a two-stage-gas-gun, the debris cloud formation was imaged by a sequential laser shadow instrument. Based on the simulation and experimental database, the debris cloud geometries were compared and discussed, and the moving velocities were characterized on shape ratio. Second, a couple of semi-empirical models for debris-cloud velocities and perforation hole diameters have been developed. Models for the expanding velocity and the leading-edge velocity of debris cloud of spherical impact were proposed, and they are calibrated and validated with both simulation and experiment data. In additional, the perforation hole models were developed based on typical perforation hole model of spherical impact to incorporate the projectile shape effect. Third, the property and models for the large-central-fragment in debris cloud were studied qualitatively and quantitatively. The mass and velocity of the large-central-fragment have been characterized. By analyzing the characterization results, the issues of the projectile shape on geometrical scaling of large-central-fragment, optimum bumper thickness of spaced shield, and fragmentation threshold velocity have been studied. Finally, the models for the large-central-fragment mass and velocity have been proposed combining dimensional analysis. After calibration and extrapolation of the proposed models, the model has been validated. Fourth, the projectile shape and the inclined impact effect on the damage response on the backwall of Whipple shield was investigated based on experimental results. The damage morphology of different shaped projectiles on the backwall was observed and discussed. The critical inclination angle of cylindrical impact was studied by test results and extrapolated simulation results, and an analytic model was studied to calculate the critical inclined angle. Two typical ballistic-limit-equations were referred and compared to experimental results, and the availability and limits for each BLE was discussed. Lastly, the experimental study on fragments distributions for thin-plate impact was performed. A serials of fragments recovery test for aluminum thin-plate impact with varying shaped projectiles were conducted by using a special fragments recovery setup, and the fragments were collected and classified. The fragments distribution corresponding to each projectile shape was characterized and made a comparison. A new fragments distribution model was developed to take projectile shape ratio into account. The research results presented in this thesis are the fundamental knowledge for the development of an engineering fragmentation model, as well as the design of spacecraft shielding structure. This thesis provides effective reference value in simulation and experiment results for hypervelocity impact fragmentation.