Fragmentation-initiation threshold and debris cloud characteristics of Whipple Shield under hypervelocity impact

The fragmentation-initiation threshold and debris cloud characteristics in hypervelocity impacts are critically influenced by key impact parameters, including impact velocity (V₀) and the bumper-thickness-to-projectile-diameter ratio (t/D). However, their quantitative effects on the transition from intact to fragmented states and debris cloud evolution remain insufficiently understood. In this study, Finite element-smoothed particle hydrodynamics adaptive method (FE–SPH) was employed to systematically investigate these processes. The Johnson–Cook constitutive model, incorporating strain-rate dependence, and the Grüneisen equation of state were employed to describe the dynamic behavior of the projectile and bumper materials. A series of simulations were conducted with constant material parameters, with t/D ranging from 0.026 to 0.424 and V₀ ranging from 4 to 8 km/s. The results reveal that a higher t/D significantly lowers the fragmentation-initiation threshold and leads to wider debris cloud dispersion, with enhanced development of the ejecta veil. In contrast, increasing V₀ induces finer fragmentation; simultaneously, a larger portion of the initial kinetic energy is converted into internal energy, reducing the fraction of energy transferred to the ejecta veil at higher velocities. These findings provide quantitative insight into how impact parameters influence fragmentation behavior and offer theoretical guidance for optimizing shield configuration in spacecraft protection systems.