Volume fraction

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

Steady state creep behaviour of silicon carbide particulate reinforced aluminium composites

Abstract: The roles of volume fraction and size of reinfrecement on the steady state creep behaviour of pure aluminium matrix-silicon carbide particulate composites have been studied in the temperature range 623–723 K. The observed apparent stress exponents are higher than 15 and apparent activation energy is 249 kJ mol−1. By considering the existence of a threshold stress, the data for 1.7 μm particulate reinforced composites with different volume fraction can be rationalized according to the substructure invariant model. The effective stress-strain rate behaviour of composites with 10 vol.% of coarser particulates (14.5 and 45.9 μm), however, agree with the stress dependent substructure model. The present analysis is validated by constructing a new type of “dislocation creep mechanism map”. The observed threshold stress varies with the volume fraction of reinforcement and is independent of particulate sizes and test temperatures. It is suggested that a model based on applied stress independent load transfer is required to explain the origin of such a threshold stress.

Crystallization kinetics of suspensions of hard colloidal spheres

Abstract: The crystallization of suspensions of sterically stabilized polymer particles, with hard-sphere-like interactions, is studied by laser light scattering. Over the range of volume fractions examined, from just below melting to the glass transition, crystallization occurs by homogeneous nucleation. After the suspensions are shear melted, the intensity, position, and width of the main interlayer Bragg reflection are measured as functions of time. From these the amount of crystal, the average linear crystal dimension, the number of crystals, and the volume fraction of the crystal phase are obtained. No assumptions are made concerning the functional time dependence of nucleation or growth processes. Below the melting concentration the observed crystallization process is compatible with the classical picture of sequential nucleation and growth of isolated crystals. However, when the melting concentration is exceeded, nucleation events are correlated, nucleation is accelerated, and high nucleation rate densities suppress crystal growth. Above the melting concentration we infer, with the aid of the equations of state for the hard-sphere fluid and solid, that the first identifiable crystals are in mechanical equilibrium with the embedding fluid and, consequently, strongly compressed by it. Ensuing nucleation lags expansion of the crystal lattice.