Evolution of complex morphologies, and morphology-property relationships in engineering systems

Date of Completion

January 2002


Engineering, Mechanical




Engineering systems frequently involve complex morphological patterns, arising from either instability or growth phenomena. These morphologies manifest themselves either at an interface (typically owing to an interfacial instability process) or within the microstructure of materials (such as crystalline morphologies, grain structures, etc.). The morphologies are geometrically complex, and depending upon the application, the morphological patterns range in length scales from the macroscopic (on the order of mm to m) down to the nanoscale. In almost all applications, the morphological patterns strongly influence the performance or properties. Examples include the dependence of the overall properties of engineered materials (plastics, alloys, composites) on their microstructural morphologies, and the transport behavior (e.g., mixing and chemical reactions) at a fluid-fluid interface being governed by the interfacial morphology. ^ Prediction of the evolution of such morphologies, and relating the morphological characteristics to the engineering properties, are therefore imperative for an effective analysis and design of engineering systems, and this forms the overall focus of the thesis. Specifically, morphological evolution is considered in the context of two applications: (1) the interfacial fluid instability phenomenon of viscous fingering that occurs in a rectilinear Hele-Shaw cell, and (2) spherulitic crystal growth process (on the order of μm) during the solidification step of thermoplastic-matrix composites processing. Parametric effects of processing parameters on the respective morphological evolution in both applications are elucidated. The morphology-property relationship is studied by considering the problem of determining the mechanical properties of semicrystalline thermoplastics in terms of their lamellar level (on the order of nm) morphologies. ^