Seven samples of ceramic materials; glasses and marbles with different mineralogy and effective conductivities were selected. These samples were labelled from P1 to P7. These materials are classified into two types of samples, rock marbles and ceramic glasses. The rocks were two grey-red gneissic granite samples labelled P1 & P2 and the other five were either provided through a private communication with Dr. Vlastimil Bohac from the Institute of Physics, Slovak Academy of Sciences (SAS) or selected from the A-Z materials database within the www. amazon. com website...


Results and discussion

Two types of multiphase composite materials have been selected, namely; wood and ceramics. As it was mentioned in section 2, in particular we investigate the effect on thermal conduction due to structural morphology in woods and structural mineralogy in ceramics.

4.1 Woods

It is known that wood is a fiber-based ligno-cellulosic material (Avramidis & Lau, 1992). In this type of materials, the crystalline structure of cellulose chains may be altered, due to temperature variations, leading to a permanent loss in strength and considerable changes in physical behaviour including its ability to conduct heat. The purpose of this study is to investigate the relation between the thermal conductivity of wood and the various factors affecting this property...


Non-steady state(transient) techniques

In the 2nd group, a periodic or transient heat flow is established in the sample. In comparison with the first group, the transient or non-steady state techniques for thermal conductivity are appealing in that the test time is comparatively short, small specimens can be measured, and formed products can be tested (e. g. films, sheets and mouldings). Two Examples of this group are the transient plane source (TPS)( Gustafsson, 1991) to determine the thermal conductivity, thermal diffusivity and their anisotropy (Suleiman et al. 1999) & (Fan et al.,2006), and the transient line-source probe method (Dawson et al., 2006).

The transient line-source probe technique, also known as the needle probe method, is a development of the hot wire method but is suited for testing molten composites in both t...


Experimental techniques

The reliability of a specific technique to measure thermal properties is determined by several factors, such as the speed of operation, the required accuracy and performance under various environmental conditions, the physical nature of material, and the geometry of the available sample. However, in most techniques the main concern is to obtain a controlled heat flow in a prescribed direction, such that the actual boundary and initial conditions in the experiment agree with those assumed in the theory. There are several methods (techniques) used to measure the effective thermal conductivity of composites...


Historical background of theoretical models

Estimation of the effective thermal conductivity of composite material has been subject of many theoretical and experimental investigations. The earliest model was proposed by Maxwell (Maxwell, 1892). He derived an expression for the simplest kind of two-phase dispersion consisting of spherical particles suspended or imbedded into a continuous medium of another material neglecting the interactions between the particles. The derived expression was valid only for very low concentrations of the dispersed phase i. e. for dilute volume fraction.

For non-dilute volume fractions, The interaction between the spherical particles has a significant effect and cannot be neglected, the work of Maxwell was later followed by the work of Rayleigh in 1892 to account for these interactions...


The Effective Thermal Transport in Composite Materials

Bashir M. Suleiman

Department of Applied Physics, College of Sciences, University of Sharjah, P. O. Box 27272, Sharjah, United Arab Emirates

1. Introduction

Composite materials are promising materials, which should exhibit an improve on several aspects of the physical properties such as mechanical, thermal, electrical etc.. A composite material is a system of materials composed of two or more components randomly mixed and bonded on a macroscopic scale. For example, metal-alloys Silicon carbides such as Aluminum Silicon Carbide (AlSiC) is made up of Aluminum, Silicon and Carbone on a microscopic scale. It is a metal matrix composite (MMC) packages that have a unique set of material properties...


Application of uniform temperature change, AT

Подпись: Hexagonal Array, 10-6 0° Ply 90° Ply 1,396 -52 -52 1,396 -670 -825

Next, consider the cross-ply and angle-ply laminates subjected to a uniform temperature change of AT = -100 °C. The macroscopic strain state in each lamina is determined using the classical laminate theory analysis outlined in Section 5.3 with a lamina thickness, t, of 0.2 millimetres. The homogenized mechanical strains in the cross-ply and angle-ply laminates are given in Tables 10 and 11 respectively. The strain within both representative volume element is found from the homogenized states of strain by applying the influence matrices and thermal superposition vectors according to Equation 8. Mechanical strains are present at the lamina level and at the micro-level for the thermal loading case...


Application of uniaxial force resultant, Nx

First, a purely mechanical loading is considered. The lamina level homogenized material properties calculated in Section 5.3 are used to determine the macroscopic state of strain in a

both laminates subjected an axial force resultant, Nx, in the absence of other two force resultants, Ny and Nxy. The laminate resultants are defined in Figure 4.

Consider the cross-ply and angle-ply laminates under a loading case in which the resulting edge forces are [Nx, Ny, Nxy] = [100 kN/m, 0, 0] without a temperature change. The macroscopic strain state in each lamina is determined using the process described in Section 5.3 with a lamina thickness, t, of 0.2 mm. The homogenized mechanical strains in the cross-ply and angle-ply laminates are given in Tables 6 and 7 respectively...


Review of classical laminated plate theory

To illustrate the full process of using the self-consistent micromechanics method described herein, two laminate stacking sequences are investigated, the [0/90/90/0] cross-ply laminate and the [45/-45/-45/45] angle-ply laminate. For this example, the laminate level analysis is preformed using classical laminate plate theory but, finite element methods can also be used for more complex geometries and loading conditions.

Consider only the in-plane resultant forces, [Nx, Ny, Nxy] as defined in Figure б, and thermal loading. Under these conditions, Equation 14 gives relationship between the lamina stresses and strains referenced to the principal material axis (i,2).

a, = QjSj (i, j = 1,2,6) (14)

Here, Qij is the reduced stiffness matrix in the material principal coordinate system...


Determination of influence matrix and thermal superposition vector

The influence matrix and thermal superposition vector can be extracted from the same set finite element analyses used to determine the effective lamina properties. It should be noted that both the influence matrix and the thermal superposition vector are field variables. That is, each specific geometric point within a representative volume element yields a unique influence matrix. Presented as field variables, the terms of the influence matrices and thermal superposition vectors are illustrated graphically in Figures 4 and 5, respectively.

The micro-strain field can be extracted at every node or integration point within the representative volume element. The enhanced strain field at every point within a volume element can be used in a point failure criteria...