Multi-scale modeling of composite materials

Abstract

The objective of this thesis is the determination of effective thermomechanical properties of carbon-carbon (C/C) plain weave fabric composites, particularly the effective thermal coefficients and the effective stiffness matrices. The selection of mechanical and heat conduction problems is promoted not only by available experimental measurements but also by their formal similarity. The C/C plain weave composites belong to an important class of high-temperature material systems. An exceptional thermal stability together with high resistance to thermal shocks or fracture following rapid and strong changes in temperature have made these materials almost indispensable in a variety of engineering spheres. While their appealing properties such as high strength, low coefficients of thermal expansion and high thermal conductivities are known, their prediction from the properties supplied by the manufacturer for individual constituents is far from being trivial since these systems are generally highly complicated. Apart from the characteristic three-dimensional structure of textile composites the geometrical complexity is further enhanced by the presence of various imperfections in the woven path developed during the manufacturing process. A number of models properly accounting for the three-dimensional effects have been developed in the past. However, a major shortcoming of many of these models is the omission of the porous phase, which in real systems may exceed 30% of the overall volume.

The objective of this thesis is the determination of effective thermomechanical properties of carbon-carbon (C/C) plain weave fabric composites, particularly the effective thermal coefficients and the effective stiffness matrices. The selection of mechanical and heat conduction problems is promoted not only by available experimental measurements but also by their formal similarity. The C/C plain weave composites belong to an important class of high-temperature material systems. An exceptional thermal stability together with high resistance to thermal shocks or fracture following rapid and strong changes in temperature have made these materials almost indispensable in a variety of engineering spheres. While their appealing properties such as high strength, low coefficients of thermal expansion and high thermal conductivities are known, their prediction from the properties supplied by the manufacturer for individual constituents is far from being trivial since these systems are generally highly complicated. Apart from the characteristic three-dimensional structure of textile composites the geometrical complexity is further enhanced by the presence of various imperfections in the woven path developed during the manufacturing process. A number of models properly accounting for the three-dimensional effects have been developed in the past. However, a major shortcoming of many of these models is the omission of the porous phase, which in real systems may exceed 30% of the overall volume.