THE IMPACT OF AN INTERPHASE ON THE EFFECTIVE PROPERTIES OF PARTICULATE COMPOSITE MATERIALS

Abstract

The interphase of a composite material is a region that lies between the material’s particulate filler and the matrix of surrounding material. In the research of composite materials, the effects of the interphase on the effective properties of composites still need to be fully understood. They are an active research area for inclusions or shell-like inclusions in the nano or micro scales. In this dissertation, we examine the role of the interphase on the effective mechanical properties of a composite which has spherical particles to reinforce its matrix. We begin by discussing the background of research on composite materials. We then look at simple examples of the thermal conductivity of composite materials before continuing with the primary area of research which are the bulk modulus and shear modulus results of composite materials. We use analytical mathematical methods as opposed to numerical techniques, which can take a lot of effort and time to run and from which results can be gained. Analytical approximations can be very useful as a first estimate. We use classical mechanics of composite material methods, composite spherical assemblage and the generalised self-consistent method to derive equations for the thermal conductivity, shear and bulk modulus of composite materials. These methods approximate the interaction between the particles. Hollow spherical particles are our primary filler of interest, mixed with a polyurethane matrix the particles are in the micro-scale and have nano-scaled shell thickness. The thickness of the inclusion’s shell is significant as we anticipate that it can be of the same order of magnitude as the interphase thickness. The particular filler we use in our simulations is expancel, a micro-sized hollow plastic shell. We find in general that the presence of an interphase leads to a softening of the composite. For fixed interphase thickness, its presence also leads to effective mechanical properties that are dependent on the size of the microsphere. This is not standard in the usual separation of scales regime but this effect has been noted before for nano-sized particles. For realistic expancel microspheres, it transpires that a much stronger effect arises from the fact that the shell thickness is certainly of the same order of magnitude as the interphase. This certainly leads to a softening effect, and this effect is stronger at higher volume fractions. Generally, we find the bulk modulus less sensitive to lower thicknesses of interphase than the shear modulus. Our intention is to provide a helpful approximation tool of the properties of composite materials filled with hollow particles.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	William Parnell (Supervisor) & Paola Carbone (Supervisor)