Shock-induced melting of honeycomb-shaped Cu nanofoams: Effects of porosity

Abstract

We investigate shock-induced melting in honeycomb-shaped Cu nanofoams with extensive molecular dynamics simulations. A total of ten porosities (/) are explored, ranging from 0 to 0.9 at an increment of 0.1. Upon shock compression, void collapse leads to local melting followed by supercooling at low shock strengths. Superheating occurs at / 0:1. Both supercooling of melts and superheating of solid remnants are transient, and the equilibrated shock states eventually fall on the equilibrium melting curve for partial melting. However, phase equilibrium has not been achieved on the time scale of simulations in supercooled Cu liquid (from completely melted nanofoams). The temperatures for incipient and complete melting are related to porosity via a power law, ð1 À /Þ k , and approach the melting temperature at zero pressure as / ! 1. V C 2015 AIP Publishing LLC.

Shock response of open-cell nanoporous Cu foams: Effects of porosity and specific surface area

“…Such simulations are compared against independent Hugoniostat simulations (a method to simulate Hugoniot states 34 ), and their results are in excellent agreement for strong shocks. 15,34 The agreement is likely because under strong shocks, the structures and states become "highly" homogenized even after different intermediate processes or paths, in sharp contrast to weak shocks.…”

“…Such porosity effect 5 is well observed for powders, 36,43 and nanofoams with drastically different microstructures. [12][13][14][15] Shock-induced collapse of voids or pores leads to marked increase in internal energy, likely internal jetting as well, and subsequently, drastic temperature rise and even melting. For given q r , shock temperature increases with increasing w at the same pressure [ Fig.…”

“…Equation (6) is a modification of the power law in Ref. 15 and also considers the effect of specific surface area on shock-induced melting, which was previously neglected. Herein, Equation (6) is a combination of a power-law function and a linear function [ Fig.…”

“…Previous MD simulations examined shock responses of regular-patterned nanofoams with different microstructures (pore shape, arrangement and size, and grain boundaries), including elastic-plastic deformation, Hugoniot states, void collapse, hot spot generation, jetting, melting, and vaporization. 4,[12][13][14][15] For convenience, these idealized foam structures largely contain closed cells and are two-dimensional (2D) in nature. However, foams in reality usually possess 3D random pore shapes, sizes, and varying connectivities, and such nanofoams with open cells have been synthesized in laboratory via de-alloying.…”

Shock responses of nanoporous aluminum by molecular dynamics simulations

“…11(b2-b3) , the total amount of the dislocation lines is not obviously changed during the release stage, which is consistent with dislocation density history curve in V2, while B2 locates between voids V5 and V6, as illustrated in Fig.1(b). The amplitude of the elastic precursor, the maximum press and the maximum shear stress 26 of B1 are 7.2 GPa, 14.1 GPa and 2.8 GPa. These values have attenuated to be 4.1 GPa, 11.9 GPa and 1.4 GPa in the material slice B2.…”