James H. Saunders

A model of structure optimization for a functionally graded material

Abstract A simple model is developed for the spatial variation of composition of a metal/ceramic functionally graded material. The composition profile is optimized, subject to certain constraints, such that the flow of heat through the material is either maximized or minimized. Normal thermal-stress profiles are calculated and are found to exhibit unusual behavior in some cases.

Control strategies for the improvement of corrosion resistance

The corrosion resistance of a metal surface in contact with an aqueous medium can, in principle, be improved by imposing conditions that cause the otherwise chemically active surface to be passivated. In this work, several different control strategies directed toward achieving this end are investigated using the two-dimensional Sato model as a prototype for metal passivation. First, the classic linear feedback theory is applied and is shown quite generally to be unusable in the sense of achieving complete passivation of a chemically active surface. Then, extension of the model by addition of a third state variable is shown to be capable of yielding complete passivation. Finally, a third strategy, based on feedback control of the two-dimensional model, is shown to result in significantly increased levels of passivation, and therefore in correspondingly improved corrosion resistance.

A discrete model for particle deposition

Simulation of deposit growth on a two-dimensional substrate was studied based on a new model that tracks individual cubic particles as they form a deposit structure. The present model is an extension of the classical ballistic deposition model. Effects of three different parameters were studied. These include an attraction parameter that is a measure of the particle to particle attractions, an interaction length within which the particles are assumed to influence and be influenced by surrounding particles, and allowed sticking positions (face-face, edge-edge and corner-corner) that favor particular growth directions. Structures with widely varying properties were obtained using this model. The three parameters were found to have considerable effect on the structure including indications of morphological phase transformations. A new property of the system (saturated roughness/deposit growth rate) was identified that can classify the different types of growth into a single type.