Microscopic and Macroscopic Fragmentation Characteristics under Hypervelocity Impact Based on MD and SPH Method

Abstract

This work investigates the difference in the fragmentation characteristics between the microscopic and macroscopic scales under hypervelocity impact, with the simulations of Molecular Dynamics (MD) and Smoothed Particle Hydrodynamics (SPH) method. Under low shock intensity, the model at microscopic scale exhibits good penetration resistance due to the constraint of strength and surface tension. The bullet is finally embedded into the target, rather than forming a typical debris cloud at macroscopic scale. Under high shock intensity, the occurrence of unloading melting of the sample reduces the strength of the material. The material at the microscopic scale has also been completely penetrated. However, the width of the ejecta veil and external bubble of the debris cloud are narrower. In addition, the residual velocity of bullet, crater diameter and expansion angle of the debris cloud at microscopic scale are all smaller than those at macroscopic scale, especially for low-velocity conditions. The difference can be as much as two times. These characteristics indicate that the degree of conversion of kinetic energy to internal energy at the microscopic scale is much higher than that of the macroscopic results. Furthermore, the MD simulation method can further provide details of the physical characteristics at the micro-scale. As the shock intensity increases, the local melting phenomenon becomes more pronounced, accompanied by a decrease in dislocation atoms and a corresponding increase in disordered atoms. In addition, the fraction of disordered atoms is found to increase exponentially with the increasing incident kinetic energy.

Atomistic assessment of structural evolution for magnesium during hypervelocity nanoprojectile penetration

“…Several Atomistic simulation studies are done on hypervelocity impact such as to study the ballistic behavior of multilayer graphene polymer composite (MGPC) Molecular Dynamics (MD) simulations were done [16]. Fragmentation characteristic studies were done for macro and micro scales at high and low shocks using MD and Smoothed Particle Hydrodynamics (SPH) method [17]. The investigation of the effects of spacing of interlayers and the degree of oxidation of graphene oxide nanochannels was performed using MD simulations [18].…”

Nanomechanics and Plasticity

“…Interestingly, Jiang et al [ 36 ] found that the presence of copper nanoparticle will trigger the formation of regular stacking fault in the single crystal aluminum under shock compression. Based on the smoothed particle hydrodynamics (SPH) method, Wu et al [ 37 ] discussed the differences in the fragmentation characteristics between the microscopic (atomic scale) and macroscopic scales under hypervelocity impact. In real applications, materials are usually exposed under a complex loading environment, e.g., electronics experience cyclic thermal and mechanical loadings during service [ 38 ].…”