Dynamic structures in shock-loaded copper

Abstract

Shock loading of polycrystalline copper under uniaxial strain conditions at 6.2÷ 7.3 GPa results in nucleating the dissipative structures of 5 ÷ 25 m in diameter. Interior of each structure is a network of microshear bands of 100÷ 300 nm spacing. Nucleation of structures occurs at the impact velocity where particle velocity dispersion begins to grow faster than mean particle velocity or when the local strain rate at the mesoscale becomes higher than the macroscopic strain rate. Simultaneously, defect of particle velocity at the plateau of compressive pulse, macrohardness, and spall strength grow in the same manner. Physically, nucleation of dissipative structures is estimated to be initiated under resonance condition between space periods of polarized dislocation structure and driving plastic front.

Quantum Effects on the Mesoscale

“…Experimental results, obtained in the study of non-equilibrium processes in different branches of mechanics (hydrodynamics of turbulent flows, multi-phase flows, shock-induced processes in solids, biomechanical processes), show many similar features of the non-classical system response to external perturbations. Far from equilibrium processes are often accompanied by self-organization of new dynamic structures [8][9][10][11][12][13][14][15][16] such as boundary layers, mass velocity pulsations, vortex structures, various localized inhomogeneities, etc. The observable self-organization effects are characterized not only by the medium properties (composition, phase state) but also by the loading and boundary conditions and the system geometry.…”

“…In Section 2, the problems arising in the description of shock-induced processes in condensed matter are presented. Experimental studies of shock-wave processes in condensed media characterized by such scales [1][2][3][4][5][6]10,11,[15][16][17][18][19][20][21][22][23] show that so-called mesoparticles become carriers of momentum and energy which are much larger than the quantum, but much smaller than the macro-size of the system. At present, even a separate discipline "mesomechanics" has emerged which deals with the study of mesostructures that arise in various materials under the influence of external loading [24,25].…”

On the Shock-Induced Structures in Copper

“…Physically, breakdown of the free surface velocity means that kinetic energy of medium obtained from external loading goes on swinging the large-scale fluctuations (particle velocity pulsations). The criterion for transition from evolutional to catastrophic regime of momentum and energy exchange between mesoscale and macroscale has the following form [1]:…”

“…Experimental and theoretical studies of dynamic straining show that one of basic mechanisms of momentum and energy transportation from scale level to another under conditions of multiscale dynamic deformation is the pulsations of particle velocity [1]. The quantitative characteristic of the velocity pulsations is the particle velocity variance at the mesoscale (in West literature the mesoscale pulsations call a "granular temperature").…”

“…Specifically, it concerns to formation of localized 3D-structures at the mesoscale [1]. Some years ago we found that during the shock loading of M3 copper within narrow strain rate range of 5•10 6 -5.7•10 6 s -1 the 3D-formations of 5-30 µm in diameter are nucleated.…”