Volume fraction

About: Volume fraction is a research topic. Over the lifetime, 16312 publications have been published within this topic receiving 374181 citations.

Strain softening, yielding, and shear thinning in glassy colloidal suspensions.

Abstract: A microscopic theory for the dependence on external strain, stress, and shear rate of the transient localization length, elastic modulus, alpha relaxation time, shear viscosity, and other dynamic properties of glassy colloidal suspensions is formulated and numerically applied. The approach is built on entropic barrier hopping as the elementary physical process. The concept of an ideal glass transition plays no role, and dynamical slowing down is a continuous, albeit precipitous, process with increasing colloid volume fraction. The relative roles of mechanically driven motion versus thermally activated barrier hopping and transport have been studied. Various scaling behaviors are found for the relaxation time and shear viscosity in both the controlled stress and shear rate mode of rheological experiments. Apparent power law and/or exponential dependences of the elastic modulus and perturbative and absolute yield stresses on colloid volume fraction are predicted. A nonmonotonic dependence of the absolute yield strain on volume fraction is also found. Qualitative and quantitative comparisons of calculations with experiments on high volume fraction glassy colloidal suspensions show encouraging agreement, and multiple testable predictions are made. The theory is generalizable to treat nonlinear rheological phenomena in other soft glassy complex fluids including depletion gels.

Solidification processing and tribological behavior of particulate TiC-Ferrous Matrix composites

Abstract: Particulate TiC-reinforced ferrous matrix composites were processed by solidification of (1) an FeTiC melt of appropriate composition from which particulate titanium carbide precipitates and (2) an FeC melt in which particulate titanium carbide is dispersed through electromagnetic stirring. The microstructure of composites processed by precipitating titanium carbide was controlled by controlling melt composition and homogeneity, as well as cooling rate. That of composites processed by dispersing titanium carbide powder in a steel or cast iron melt was controlled by controlling the original melt composition, volume fraction and particle size of titanium carbide added, mixing temperature and time, and cooling rate. The specific wear rate and the friction coefficient between a diamond stylus and the polished surface of composite specimens decreased with increasing volume fraction of titanium carbide and decreasing carbide particle size and spacing. They also decreased with increasing steel matrix microhardness, achieved through heat treatment and martensitic transformation.

Dielectric constant of a composite inhomogeneous medium

Abstract: We derive an expression for the effective dielectric constant of a composite medium considering the contributions from both the electric and the magnetic dipole terms. We show that the form of the size distribution of small metallic particles determines the value of the volume fraction at which a sharp increase in ac absorption of a composite material occurs. Depending on the width and mode radius of the size distribution, the effective dielectric constant of a composite medium can be increased by several orders of magnitude.