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.

Results of the observation in situ, using synchrotron radiation, of periodic variations of structural parameters of actively deformed aluminium and copper are reported. In order to explain the experimental data, a theoretical model is proposed of oscillatory variations in the dislocation ensemble of the type 'randomly distributed dislocations-partial disclination dipoles'.

No abstract

No abstract

No abstract