层状结构冰球的高速撞击特性实验

为研究冰雹在不同撞击速度下的破碎特性及致损能力，通过空气炮加载技术，开展了单一性状冰球和层状结构冰球高速撞击刚性靶实验，利用测力杆记录了两种类型冰球在不同撞击速度下的撞击力时程曲线，并结合高速摄影技术研究了两类冰球的高速撞击破碎特性。实验结果表明:两类冰球高速撞击刚性靶的宏观破碎特性相似，在碰撞初始阶段冰球已完全破碎，形成微颗粒团簇体，反向溅射角呈随撞击动能增大而增大的趋势；与单一性状冰球撞击力曲线相比，层状结构冰球撞击力曲线中出现二次上升信号，推测是由于破碎界面在层间界面发生偏折，小球未完全破碎再次撞击测力杆所导致；高速撞击下层状结构冰球的撞击力高于单一性状冰球，推测是由于层间结构的存在延缓了冰球的破碎进程，提升了其在冲击方向传递动量的能力，进而产生了更高的撞击力。研究结果有助于深化对冰雹在高速撞击下的破坏力学行为的认识，同时可为飞行器结构防护、冰雹撞击安全设计研究等提供参考。

Experimental investigation on characteristics of layered ice spheres under high-velocity impact

The hail impact has become a realistic threat for aerospace industries. Natural hail ice has a spherically-layered construction. In order to study the impact failure characteristics and damage ability of hail ice, spherically-layered ice spheres with two layers were created. A series of high- velocity impact experiments were conducted for the simulated hail ice spheres (both monolithic and spherically layered ice) through a smooth barrel gas gun. The dynamic failure properties of ice spheres were studied using high-speed video images during the impact event. Based on the experimental results, it is found that both the monolithic and layered ice spheres present the similar macroscopic crushing characteristics. The ice fragments are formed in the early impact stage. Fragments trajectories lie almost in the target plane. The angle between the fragment trajectories and the plane of the target increases with the increase of impact kinetic energy. A possible explanation for this phenomenon could be attributed to the release rate of projectile kinetic energy. The impact force histories of ice spheres under different velocities were recorded by a force measurement bar apparatus. The impact force curves of monolithic ice show a trend of a sudden increase of the force reaching a maximum, followed by a more gradually decreasing force versus time decay. However, the impact force curves of layered ice show a second rising signal at the last stage. The formation mechanism of the secondary rise signal is hypothesized that the internal small ball is not completely fragmented due to the deflection of failure front at the interlayer interface during impact process. The measured peak impact force is observed to increase with the increase of the projectile kinetic energy. The maximum peak force is reached at very early stage of the impact. Then the ice is actually fragmented, which can not transfer more momentum in the impact direction. In addition, there is a suggestion of higher impact forces for layered ice. This result is expected that the fragmentation process of layered-ice spheres is delayed by the interlayer interface, which is able to transfer much more momentum in the direction of the impact. The achievements of the study are helpful to better understand the dynamic mechanical behaviors of ice under impact loading, and can also provide reference for the safe design of aerocraft structure.