Understanding the dynamic behavior of nanomaterials under hypervelocity impact is of great importance to develop advanced materials or structures for protective applications. The present work gives insight into the damage characteristics of aluminum nanorod under hypervelocity impact based on atomistic simulations. First of all, the propagation of impact wave is found to experience a rapid decaying because of its release from the side surface, which leads to a complex three-dimensional stress wave and two tension regions inside the nanorod. The damage mode under this tension state is found to be very different from the classical spallation. Due to the interaction of two release waves from the side and end surfaces, a temporary spall damage is observed and its initial tensile strength is close to that of bulk material. However, that early spall damage does not develop into a complete spall fracture. More importantly, all generated voids are found to be closed eventually after their coalescence. Furthermore, the mass continues expanding outward from the impact plane and finally causes a radial annular fragmentation. The annular fragmentation shows a clear crystalline direction dependence for low impact velocities. The number and the size of final fragments are found to follow a power law relationship for all impact velocities.

中文翻译：

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超高速撞击下铝纳米棒的损伤特性

了解纳米材料在超高速冲击下的动态行为对于开发用于防护应用的先进材料或结构非常重要。目前的工作基于原子模拟，深入了解了铝纳米棒在超高速撞击下的损伤特性。首先，发现冲击波的传播由于从侧面释放而经历了快速衰减，这导致纳米棒内部产生复杂的三维应力波和两个张力区域。发现这种张力状态下的损伤模式与经典的散裂非常不同。由于来自侧面和端面的两个释放波的相互作用，观察到暂时的剥落损伤，其初始拉伸强度接近散装材料的拉伸强度。然而，早期的剥落损坏不会发展成完全的剥落断裂。更重要的是，发现所有产生的空隙在它们合并后最终都会闭合。此外，质量继续从撞击平面向外膨胀，最终导致径向环形碎片。对于低冲击速度，环形碎片显示出明显的结晶方向依赖性。发现最终碎片的数量和大小对于所有撞击速度都遵循幂律关系。对于低冲击速度，环形碎片显示出明显的结晶方向依赖性。发现最终碎片的数量和大小对于所有撞击速度都遵循幂律关系。对于低冲击速度，环形碎片显示出明显的结晶方向依赖性。发现最终碎片的数量和大小对于所有撞击速度都遵循幂律关系。