Damage characteristics of aluminum nanorod under hypervelocity impact

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.