SHAPE FABRICS OF PARTICLES IN LOW CONCENTRATION SUSPENSIONS - 2D ANALOG EXPERIMENTS AND APPLICATION TO TILING IN MAGMA

Jeffery's equations ascribe a theoretical cyclic nature to the shape f abric of non-interacting rigid particles immersed in a viscous fluid u ndergoing simple shear flow. This theoretical behaviour is confirmed a t 'low' shear strains (gamma < 6) by two-dimensional experiments in a torsion apparatus, inducing shape fabric development of particles even ly distributed on the surface of a silicon fluid and at low particle c oncentrations (13-14% in area). For larger shear strains however (6 < gamma < 20), the shape fabric orientation tends to remain close to the shear plane, its magnitude remains at low values and the cyclicity of the fabric disappears. This is due to interactions between particles, forming tiling features with variable shape ratios. Interactions rapi dly increase in number for gamma > 5 (first experiment: 134 identical particles) or gamma > 1 (second experiment: 178 particles with two siz e classes), then become stable at 17% (first experiment) and at more t han 50% (second experiment) of the population of particles. Due to the contribution of the tiled particles, the shape fabric becomes asymmet rical in its orientation distribution, with a maximum lying above the shear plane. The latter result provides a new shear sense indicator, i n addition to the statistical determination of the tiled features. The study also suggests that crystalline fabrics in magmas could be acqui red at high melt fractions, i.e. early in the crystallization history of the magma. Copyright (C) 1996 Elsevier Science Ltd.