Yoji Shibutani, Jun-ichi Toryu and Yoshihiro Tomita
Graduate School of Science and Technology, Kobe University, Kobe 657
A stress-induced phase transformation phenomenon is one of the hierarchical mechanical behaviors in which atomistic rearrangements are simultaneously and dually reflected to macroscopic strength of material. It has so far been recognized as one of the bifurcation problems in the fields of thermodynamics and continuum mechanics. Softening of phonon dispersion curves has also been acknowledged as precedence of transformation as well. Movements of atoms in an α-iron under uniaxial tension are first traced by the molecular dynamics (MD) simulations on the assumption of a constant applied stress ensemble proposed by Parrinello & Rahman. Stress dependency of phonon dispresion curves obtained from the deformed lattice structures are then examined. Bifurcation conditions derived from positive definiteness of strain energy in the whole deformed matters are, at the same time, investigated using analytical elastic constants defined from only an atomic configuration and the force constants which are the second derivative of an employed interatomic potential. It is found that softening of phonon dispersion curves, especially the long-wavelength acoustic branch, could correspond to the macroscopic bifurcation conditions over the scale.
(Received March 31, 1997)
stress-induced phase transformation, molecular dynamics, softening of phonon dispersion curves, continuum mechanics, bifurcation, α-iron
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