Damage-fragmentation transition: Size effect and scaling behavior for impact fragmentation of slender projectiles

Abstract

The focus of the present article is on the size effect of a transition region from the damaged to the fragmented phase in impact-induced breakup of a slender projectile. Molecular dynamics simulations of the classic ballistic Taylor test are performed with a simple generic model to explore an extended low-energy range. In the simulation setup, flat-ended, monocrystalline, nanoscale projectiles, with a fixed aspect ratio but 10 different diameters, collide perpendicularly with a rough rigid wall. With gradually increasing impact energy, a non-negligible projectile disintegration eventually takes place and is identified with the damage-fragmentation phase transition. These atomistic simulations offer an indispensable tool to gain an insight into damage evolution in the neighborhood of the damage-fragmentation transition resulting in the occurrence of fragmentation at the critical point. A finite size scaling analysis of the average fragment mass is carried out to determine critical exponents and dependence of the critical striking velocity upon the slender projectile’s diameter.

Phenomenology of the Maximum Fragment Mass Dependence Upon Ballistic Impact Parameters

“…For example, the 2D-MD simulation results (Mastilovic, 2015a(Mastilovic, , 2016a(Mastilovic, , 2016b confirm that fragment mass distributions are generally of the Poisson hyper-exponential type as experimentally verified for ductile materials (e.g., Mayers, 1994). As far as the strain rate effect on the fragment mass is concerned, the MD simulation result presented by Eq.…”

“…It cannot be overstated that this robust MD model requires only three material input parameters (the atomic mass and diameter, and the strength of attraction); obviously, only a limited quantitative agreement with experimental data could be expected under such circumstances. The main limitations of the present model have been already discussed in the preceding article (Mastilovic, 2016b).…”

“…The impact fragmentation in confined spatial dimensions is expected to result in increased fragmentation thresholds due to the small-scale hardening of the material as indicated, for example, by Rinaldi (2011). Timar et al (2012) and Mastilovic (2016b) proposed recently scaling forms of the critical velocity v0 in terms of the system size and determined critical velocities of the infinite system.…”

“…The model is described in detail in preceding studies (Mastilovic, 2015a(Mastilovic, , 2016a(Mastilovic, , 2016b, thus, a succinct summary is deemed sufficient herein. A monatomic system is comprised of atoms of equal masses mi = m0 that form an ideal defect-free triangular lattice (without any quenched disorder) and interact with their nearest neighbors according to the LJ potential to mimic a monocrystalline, flat-nosed projectile.…”

“…The details of this sunflower-like petaling define mmax0 (under highly stochastic circumstances of the critical-impact-energy neighborhood). Based on the present 2D-MD simulation observations (Mastilovic, 2015a(Mastilovic, , 2016b, it is justi-…”