The grain boundary effect on shock induced spallation of polycrystalline uranium

The shock-induced spallation mechanism of polycrystalline uranium is explored by molecular dynamics, and the role of grain boundaries in it is analysed. Present work reveals that the growth and fusion of voids are the main mechanism of uranium during spallation, and the grain boundaries have significant effects on nucleation and growth of voids. The spallation strength of polycrystalline uranium is lower than that of single crystal uranium, and the relative instability of the structure at the grain boundaries causes the conjunction point of multiple grains is the first nucleation position of voids. Besides, a mutual promotion relationship between the growth of voids and local thermal dissipation is verified, which greatly promotes the development of spallation. Furthermore, the grain boundary effect on the spallation is influenced by the shock intensity. Under lower shock intensity (0.3 km/s, 0.4 km/s, 0.5 km/s), the mechanical properties of the grain boundary are the major influence factor of the spalling strength of polycrystalline uranium. The lower the speed, the more obvious the grain boundary effect, and the larger the gap between the spallation strength of single crystal uranium and polycrystalline uranium. As the shock intensity gradually increases (0.6 km/s, 0.8 km/s), the grain boundary effect is gradually weakened. When the shock intensity approaches the melting intensity, the spallation behavior of single-crystalline and polycrystalline uranium tends to be consistent.