The variation of strain ratio in single crystals subdued to tensile test

Abstract

The relation of the strain ratio versus strain of f.c.c. single crystals has been used in the elaboration of methods of the calculation of the r(ε) function in mono- and polycrystalline materials. The criteria were the following: (i) the function properly describes the experimental data of the tensile test of high accuracy single crystals characterized by axial symmetry of slip systems and relatively small values of α and ρ parameters (ρ is the angle between the sample axis and the nominal [u v w] crystallographic direction, p is the half-width of the rocking curve). In perfect f.c.c.. single crystals with the [100] or [110] or [111] orientations the r _0theor is equal to 1.000 or 0.500 or 1.000, respectively. The r _0theor values have been calculated with the use of Krupkowski’s method [7.1] considering the model of a perfect f.c.c. lattice and taking into account the criterion of minimum work of deformation. We have shown previously [7.2, 7.3] that these conditions are fulfilled when a ≤ a _crit and p ≤ p _crit ; then the deformation of a single crystal at the tensile test is stable, i.e. r(ε) = const. in the whole zone of uniform elongation. (ii) The parameters of the function r(ε) have a well defined physical meaning.