Maximo Victoria

Bio: Maximo Victoria is an academic researcher from Paul Scherrer Institute. The author has contributed to research in topics: Nanocrystalline material & Deformation (engineering). The author has an hindex of 1, co-authored 1 publications receiving 258 citations. Previous affiliations of Maximo Victoria include Lawrence Livermore National Laboratory.

Ultrahigh Strength in Nanocrystalline Materials Under Shock Loading

Abstract: Molecular dynamics simulations of nanocrystalline copper under shock loading show an unexpected ultrahigh strength behind the shock front, with values up to twice those at low pressure. Partial and perfect dislocations, twinning, and debris from dislocation interactions are found behind the shock front. Results are interpreted in terms of the pressure dependence of both deformation mechanisms active at these grain sizes, namely dislocation-based plasticity and grain boundary sliding. These simulations, together with new shock experiments on nanocrystalline nickel, raise the possibility of achieving ultrahard materials during and after shock loading.

Shock deformation of face-centred-cubic metals on subnanosecond timescales

Abstract: Despite its fundamental importance for a broad range of applications, little is understood about the behaviour of metals during the initial phase of shock compression. Here, we present molecular dynamics (MD) simulations of shock-wave propagation through a metal allowing a detailed analysis of the dynamics of high strain-rate plasticity. Previous MD simulations have not seen the evolution of the strain from one- to three-dimensional compression that is observed in diffraction experiments. Our large-scale MD simulations of up to 352 million atoms resolve this important discrepancy through a detailed understanding of dislocation flow at high strain rates. The stress relaxes to an approximately hydrostatic state and the dislocation velocity drops to nearly zero. The dislocation velocity drop leads to a steady state with no further relaxation of the lattice, as revealed by simulated X-ray diffraction.

Influence of single crystal orientation on homogeneous dislocation nucleation under uniaxial loading

Abstract: Atomistic simulations are used to investigate how the stress required for homogeneous nucleation of partial dislocations in single crystal copper under uniaxial loading changes as a function of crystallographic orientation. Molecular dynamics is employed based on an embedded-atom method potential for Cu at 10 and 300 K. Results indicate that non-Schmid parameters are important for describing the calculated dislocation nucleation behavior for single crystal orientations under tension and compression. A continuum relationship is presented that incorporates Schmid and non-Schmid terms to correlate the nucleation stress over all tensile axis orientations within the stereographic triangle. Simulations investigating the temperature dependence of homogeneous dislocation nucleation yield activation volumes of ≈ 0.5 – 2 b 3 and activation energies of ≈ 0.30 eV . For uniaxial compression, full dislocation loop nucleation is observed, in contrast to uniaxial tension. One of the main differences between uniaxial tension and compression is how the applied stress is resolved normal to the slip plane on which dislocations nucleate—in tension, this normal stress is tensile, and in compression, it is compressive. Last, the tension–compression asymmetry is examined as a function of loading axis orientation. Orientations with a high resolved stress normal to the slip plane on which dislocations nucleate have a larger tension–compression asymmetry with respect to dislocation nucleation than those orientations with a low resolved normal stress. The significance of this research is that the resolved stress normal to the slip plane on which dislocations nucleate plays an important role in partial (and full) dislocation loop nucleation in FCC Cu single crystals.

Femtosecond visualization of lattice dynamics in shock-compressed matter.

Abstract: The ultrafast evolution of microstructure is key to understanding high-pressure and strain-rate phenomena. However, the visualization of lattice dynamics at scales commensurate with those of atomistic simulations has been challenging. Here, we report femtosecond x-ray diffraction measurements unveiling the response of copper to laser shock-compression at peak normal elastic stresses of ~73 gigapascals (GPa) and strain rates of 10 9 per second. We capture the evolution of the lattice from a one-dimensional (1D) elastic to a 3D plastically relaxed state within a few tens of picoseconds, after reaching shear stresses of 18 GPa. Our in situ high-precision measurement of material strength at spatial (