Shock-wave studies of anomalous compressibility of glassy carbon
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Shock-Wave Studies of Anomalous Compressibility of Glassy Carbon A. M. Molodetsa*, A. A. Golysheva, A. S. Savinykha,b, and V. V. Kima a Institute of Problems of Chemical Physics, Russian Academy of Sciences, pr. Akademika Semenova 1, Chernogolovka, Moscow oblast, 142432 Russia b Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia *e-mail: [email protected]
Received August 7, 2015
Abstract—The physico-mechanical properties of amorphous glassy carbon are investigated under shock compression up to 10 GPa. Experiments are carried out on the continuous recording of the mass velocity of compression pulses propagating in glassy carbon samples with initial densities of 1.502(5) g/cm3 and 1.55(2) g/cm3. It is shown that, in both cases, a compression wave in glassy carbon contains a leading precursor with amplitude of 0.135(5) GPa. It is established that, in the range of pressures up to 2 GPa, a shock discontinuity in glassy carbon is transformed into a broadened compression wave, and shock waves are formed in the release wave, which generally means the anomalous compressibility of the material in both the compression and release waves. It is shown that, at pressure higher than 3 GPa, anomalous behavior turns into normal behavior, accompanied by the formation of a shock compression wave. In the investigated area of pressure, possible structural changes in glassy carbon under shock compression have a reversible character. A physico-mechanical model of glassy carbon is proposed that involves the equation of state and a constitutive relation for Poisson’s ratio and allows the numerical simulation of physico-mechanical and thermophysical properties of glassy carbon of different densities in the region of its anomalous compressibility. DOI: 10.1134/S1063776116020102
1. INTRODUCTION Glassy carbon is one of amorphous allotropic modifications of carbon. On a macroscopic level, glassy carbon possesses typical properties of glass: it is a brittle isotropic material with high hardness impenetrable to gases, liquids, etc. [1]. On a microscopic level, glassy carbon represents a nanostructured material whose submicrostructure depends on the temperature at which samples are obtained. Glassy carbon obtained at temperature lower than 2500 K mainly consists of irregularly distributed bent graphene layers [2, 3]. Such glassy carbon is denoted as type-I glassy carbon. Glassy carbon fabricated at temperature of about 3000 K consists of nanometer-sized multilayer fullerene-like spheroids encased in a three-dimensional disordered multilayer graphene matrix. This glassy carbon is denoted as type-II glassy carbon. In [3], it is shown that type-II glassy carbon under isothermal conditions of static compression displays a number of unusual physicomechanical properties. For example, type-II glassy carbon preserves its irreversible elasticity at high strains, and its elasticity moduli anomalously decrease as pressure increases. The moduli of elasticity attain their minima at pressure of 1–2 GPa at which Poisson’s ratio decreases
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