Development Of Lattice Preferred Orientation Research Articles

High temperature deformation of octachloropropane: dynamic grain growth and lattice reorientation

Abstract Dynamic grain growth and lattice preferred orientation development in octachloropropane polycrystals simple-sheared at 0.8 Tm using synkinematic microscopy are discussed. Both soft and hard grains are observed to grow. It is suggested that globular grains are not necessarily an indicator of coaxial deformation. Strain heterogeneity is induced by partitioning of deformation into relatively increased components of rigid-body rotation in hard grains and strain in soft grains. With dominant grain rotation, similar lattice preferred orientation to that of a single-slip model is introduced although the unlocking process is different.

A Continuum Theory For Lattice Preferred Orientation

Summary A 2-D model for the development of lattice preferred orientation (LPO) in aggregates of crystals (such as high T/Tm olivine) which deform with a single dominant slip system is presented. In two dimensions, an arbitrary LPO can be described by an orientation distribution function (ODF) g(o, t), such that g(o, t)do represents the fraction of crystals for which the orientation of the slip plane lies between o and o+ do at time t. A differential equation which describes the evolution of the ODF during an arbitrary deformation history is described. This evolution is controlled by the vorticity number λ(t) = Ω/e of the deformation, where 2Ω(t) is the vorticity and e(t) is the strain rate. For λ = O (Uniaxial compression or pure shear), the ODF of an initially isotropic aggregate consists of two growing peaks oriented symmetrically about the extensional axis. For |λ|= 1 (simple shear), the ODF consists of two unequal peaks which migrate relative to the extensional axis, and which eventually merge into a single peak centred on the shear plane orientation. If |λ| exceeds a critical value ˜1.15, the ODF periodically returns to its initial isotropic state. the theory gives an excellent fit to data from olivine aggregates deformed in uniaxial compression, and an acceptable fit to data from ice aggregates deformed in simple shear.

Temporal development of fabric in uniaxially stressed polycrystalline media?A theory

We present a kinetic theory for the development of lattice-preferred orientation in a uniaxiallystressed aggregate consisting of elastically uniaxial crystals. The fabric is brought about by grain-boundary migration alone; other fabric-producing mechanisms, such as plastic deformation, syntectonic recrystallization, and dissolution/reprecipitation, are specifically excluded from the theory. The formulation statistically averages the mass transfer between a typical crystal and its adjacent neighbors over all the possible crystallographic orientations of these neighbors and over all the possible orientations of the interfaces between the neighbors and the crystal of interest. The rate of mass exchange between two adjacent crystals is proportional (1) to the difference between chemical potentials and (2) to the surface area common to them. With these assumptions we find an equation for the massfraction density of crystals that have a given orientation (with respect to the stress) at any given time. The theory predicts that beyond a certain time a gap develops in the distribution of crystal orientations allowed: the only crystals that continue to exist are those for which the c-axis is within a certain, timedependent range about the stress.