ABSTRACT of the Doctoral Thesis
The thermal conduction and thermomechanical properties of materials used for making thermal management devices often constitute bottlenecks in the development of new technologies in many important fields, such as the development of faster microprocessors, of fusion nuclear reactors, or more efficient heat engines, amongst others. There is an urgent need for new materials than can withstand increasingly extreme working conditions.
The present thesis is devoted to the development of computer tools for supporting the design and manufacturing of new materials. Analytical, semi-analytical and numerical continuum-level descriptions for studying the macroscopic and local thermophysical and thermomechanical behaviours of discontinuously reinforced composites that contain reinforcements of non-ellipsoidal shapes and general size distributions are reviewed, extended and/or developed. An issue of special interest are the effects of thermally imperfect interfaces between the constituents on the macroscopic thermal conduction behaviour. The methods are applied to diamond reinforced metal matrix composites (DRMMCs).
The use of semi-analytical "replacement tensor" Mori-Tanaka methods for estimating the effective conductivity of DRMMCs at moderate and elevated particle volume fractions is validated. Windowing methods using essential, natural and mixed uniform boundary conditions as well as Periodic Microfield Approaches (PMAs) are applied to computer-generated volume elements for studying the thermal conduction of DRMMCs. Good agreement between the results obtained with the different approaches is found, which supports the validity of the different modeling approaches.
Semianalytical methods and PMAs are used for extracting the macroscopic elasticity and coefficient of thermal expansion tensors of DRMMCs, with good agreement between the prections of the two approaches. Unit cell analyses of the thermoelastoplastic behaviour of DRMMCs indicate a tendency towards yielding of the matrix for rather moderate temperature excursions. In addition, incremental Mori-Tanaka methods for studying the behaviour of components made of inhomogeneous materials exposed to thermal cycling are implemented.
The modelling methods reviewed, extended or developed in this work contribute a set of tools for the assessment of the macroscopic conductivity of inhomogeneous materials. These tools cover considerable ranges of detail that can be resolved and of numerical requirements. Moreover, they help in achieving an improved understanding of the local thermomechanical and thermophysical behavior of these composites at the microscale.