Crystalline lattice under extreme conditions

Mikhail Mogilevsky
Institute of Hydrodynamics, Siberian Division of Rus. Acad. Sciences

Explosive methods are widely used since the 1960s, not only in technical applications, but also in scientific research. Characteristic parameters of processes under shock loading extend far beyond the ranges in which materials were studied previously [1]. The level of shear stresses in experiments with plane shock wave loading with pressure 100 GPa (1 mln. atm.) exceed by several times the generally accepted value of theoretical strength: the deformation velocity at the shock front reaches values of 107-108 sec-1, whereas in test machines it is limited by quantities of 102-103 sec-1. Phase transitions take place in Fe, C and other substances. I will present physical models of some processes that occur in conditions of extreme stresses, temperatures, and time intervals.

In the generation and development of plastic deformation:
1. Refinement of the concept of "theoretical strength" [2,3,4]
2. Defects generation at the shock front, ideal lattice and on point defects [5]
3. Deformation mechanism under plane shock wave loading [5,6]
4. Generation of intensive localized deformation: a) adiabatic shear [5,6], and b) spark erosion and cavitation erosion
5. Effective device for energy absorption under car crash impact [7].

In thermal processes
6. Nature of thermal fluctuations in solids. Role of collective thermal displacements of atoms in generation of point defects and melting [4,5]
7. Discovery of a nano-technological process for producing super strong cast steel parts with the fine grain cementite structure [8,9]
8. Specific features of microstructure development in iron meteorites (successive stages of life; effects of millions of years of low-temperature diffusion)

The overall goal of the talk is to suggest a set of approaches which favor success in investigations of processes under extreme conditions:
• From the beginning focus on the final aim – constructing the physical model of the phenomenon under study
• Accurate analysis of available data, especially when the observed effects do not match the predictions of existing models
• Consideration of the phenomenon as a whole with special attention to parameters that are changed essentially in new conditions
• Operational definition of concepts in accordance with P.W. Bridgman [10].

References
[1] M. A. Mogilevsky, "Mechanisms of Deformation under Shock Loading", Physics Reports v.97, # 6 (1983)
[2] J. Frenkel, T. Kontorova, "On the theory of plastic deformation and twinning", Phys. Z. Sow., 13(1), 1 (1938)
[3] G. E. Cowan, "Shock deformation and the limiting shear strength of metals", Trans. Metallurg. Soc. AIME, 233 (6), 1120 (1965)
[4] M. A. Mogilevsky, "Theoretical strength of a crystal under shock loading condi-tions", Combustion, Explosion and Shock Waves (CESW), 21(1), 738 (1985)
[5] M. A. Mogilevsky, "Defect Nucleation under Shock Loading", in Shock-Wave and High-Strain-Rate Phenomena in Metals,Intern.Conf., San-Diego, p.875 (1990)
[6] M. A. Mogilevsky and L.S. Bushnev, "Deformation structure development in Al and Cu crystals on shock wave loading up to 50 and 100 GPa", CESW, 26(2), 215 (1990)
[7] M. Mogilevsky and C. Albertini, " Energy Absorption Apparatus", U.S.Patent No.6,279,973 B1, Aug.28, 2001
[8] M. A. Mogilevsky, Method for Forming Cast Alloys having High Strength and Plasticity", U.S.Patent No. 6,764,561 B1, Jul. 20, 2004
[9] M. A. Mogilevsky, "Cast Ultrahigh Carbon Steels with Damascus Type Microstructure", Materials Technology, 20(1), 12 (2005)
[10] P. W. Bridgman, "The Logic of Modern Physics", N.Y. (1927)