Shock response of a model structured nanofoam of Cu

Abstract

Elastic superlattices with simultaneously negative effective mass density and shear modulus J. Appl. Phys. 113, 093508 (2013) Identifying local characteristic lengths governing sound wave properties in solid foams J. Appl. Phys. 113, 084905 (2013) A semi-phenomenological model to predict the acoustic behavior of fully and partially reticulated polyurethane foams J. Appl. Phys. 113, 054901 (2013) Tracking all-vapor instant gas-hydrate formation and guest molecule populations: A possible probe for molecules trapped in water nanodroplets J. Chem. Phys. 137, 204501 (2012) Nanoxerography utilizing bipolar charge patterns Appl. Phys. Lett. 101, 203106 (2012) Additional information on J. Appl. Phys. Using large-scale molecular dynamics simulations, we investigate shock response of a model Cu nanofoam with cylindrical voids and a high initial porosity (50% theoretical density), including elastic and plastic deformation, Hugoniot states, shock-induced melting, partial or complete void collapse, nanojetting, and hotspot formation. The elastic-plastic and overtaking shocks are observed at different shock strengths. The simulated Hugoniot states can be described with a modified, power-law P À a (pressure-porosity) model, and agree with shock experiments on Cu powders, as well as the compacted Hugoniot predicted with the Gr€ uneisen equation of state. Shock-induced melting shows no clear signs of bulk premelting or superheating. Voids collapse via plastic flow nucleated from voids, and the exact processes are shock strength dependent. With increasing shock strengths, void collapse transits from the "geometrical" mode (collapse of a void is dominated by crystallography and void geometry and can be different from that of one another) to "hydrodynamic" mode (collapse of a void is similar to one another); the collapse may be achieved predominantly by flow along the {111} slip planes, by way of alternating compression and tension zones, by means of transverse flows, via forward and transverse flows, or through forward nanojetting. The internal jetting induces pronounced shock front roughening, leading to internal hotspot formation and sizable high speed jets on atomically flat free surfaces.

On shock response of nano-void closed/open cell copper material: Non-equilibrium molecular dynamic simulations

“…It can be observed from Figure 7 that stress increases whereas ultimate specific volume decreases for decreasing porosity for both closed and open-cell pore structure. For the case of closed-cell pore structure, the simulation results are found to match experimental observation 17 as well as previous MD simulation results 8 carried out at similar porosity. No such validations could be made for open-cell pore structure due to unavailability of any previous data.…”

“…Good correlation could be observed between experimental and simulation results 17 carried out for closed-cell pore structure with approximate porosities of 16% and 34%. Similarly, good correlation of simulation results could also be observed with previous MD simulations of close-cell Cu foams 8 difference in slope could be observed in between the linear fit of U s -u p lines for closed and open-cell pore structure with different porosities. Table IV shows the statistic for the intercept with the shock velocity axis, slope of the linear fit and also R 2 goodness of fit to the linear regression line for U s -u p curve.…”

Scaling laws and deformation mechanisms of nanoporous copper under adiabatic uniaxial strain compression

“…4(f)), resulting in strong hardening. In the previous research, 27 the local temperature at the shock front was observed to be very high, and the internal jetting occurred at the void area. However, the loading method is adiabatic uniaxial strain compression in our case, which is a "homogeneous-like" deformation method.…”

“…34 With increasing strengths, void collapse was observed to transit from the "geometrical" mode to "hydrodynamic" mode in Cu nanofoam with high initial porosity of 50%. 27 Interacting of multiple voids was also found to decrease the stress required for the onset of plasticity under adiabatic uniaxial compression, compared to that for isolated void. [34][35][36][37]39 However, the scaling laws and the underlying atomistic mechanisms of nanoporous metals under adiabatic uniaxial strain compression are still open to further investigations.…”

“…These deformation mechanisms at an atomic level can be investigated using molecular dynamics (MD) simulation, which is a proven tool in modeling shock response and providing valuable physical insights for experimental results conducted at extreme conditions. [25][26][27][28] Previous MD simulations have been conducted to investigate the collapse of a single nanovoid or a collection of nanovoids in both fcc and bcc metals at high strain rates. 27,[29][30][31][32][33][34][35][36][37][38][39] These studies have focused on dislocation activities and the resulting porosity evolution in nanoporous metals.…”