<p> Ferroic materials, as notable members of smart materials, have been widely used in applications that perform sensing, actuation and control. The macroscopic property change of ferroic materials may become remarkably large during ferroic phase transition, leading to the fact that the macroscopic properties can be tuned by carefully applying a suitable external field (electric, magnetic, stress). To obtain an enhancement in physical and/or mechanical properties, different kinds of ferroic composites have been fabricated. The properties of a ferroic composite are determined not only by the properties and relative amounts of the constituent phases, but also by the microstructure of individual phase such as the phase connectivity, phase size, shape and spatial arrangement. </p><p> This dissertation mainly focuses on the computational study of microstructure &ndash; property &ndash; mechanism relations in two representative ferroic composites, <i>i.e.,</i> two-phase particulate magnetoelectric (ME) composite and polymer matrix ferroelectric composite. The former is a great example of ferroic composite exhibiting a new property and functionality that neither of the constituent phases possesses individually. The latter well represents the kind of ferroic composites having property combinations that are better than the existing materials.</p><p> Phase field modeling was employed as the computing tool, and the required models for ferroic composites were developed based on existing models for monolithic materials. Extensive computational simulations were performed to investigate the microstructure-property relations and the underlying mechanism in ferroic composites. In particulate, it is found that for ME composite 0-3 connectivity (isolated magnetostrictive phase) is necessary to exhibit ME effect, and small but finite electrical conductivity of isolated magnetic phase can beneficially enhance ME effect. It is revealed that longitudinal and transverse ME coefficients of isotropic 0-3 particulate composites can be effectively tailored by controlling magnetic domain structures without resort to anisotropic two-phase microstructures. Simulations also show that the macroscopic properties of the ferroelectric- polymer composites critically depend on the ferroelectric phase connectivity while are not sensitive to the sizes and internal grain structures of the ceramic particles. Texturing is found critical to exploit the paraelectric&harr;ferroelectric phase transition and nonlinear polarization behavior in paraelectric polycrystal and its polymer matrix composite. Additionally, a Diffuse Interface Field model was developed to simulate packing and motion in liquid phase which is promising for studying the fabrication of particulate-polymer composites.</p>

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvi, 147 p.; also includes graphics Includes bibliographical references (p. 143-147). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2006. / Sathya V. Hanagud, Committee Chair ; George Kardomateas, Committee Member ; Xia Lu, Committee Member ; George Simitses, Committee Member ; Massimo Ruzzene, Committee Member ; Ravindra Annigeri, Committee Member.

Thesis (M.S.)--George Mason University, 2009. / Vita: p. 64. Thesis director: Rainald Löhner. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Computational Sciences. Title from PDF t.p. (viewed June 10, 2009). Includes bibliographical references (p. 60-63). Also issued in print.

Thesis (Ph.D.)--Michigan State University. Dept. of Mechanical Engineering, 2008. / Title from PDF t.p. (viewed on July 22, 2009) Includes bibliographical references. Also issued in print.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 159-166).

The objective of this dissertation is to provide, for a fiber reinforced MMC, an understanding of the evolution of strains as a result of thermo-mechanical loadings and the relationship of the deformation evolution to microstructural factors. Both analytical and finite element approaches were used to predict global and local properties. The analytical approach involved rigorous modifications to the shear-lag model to account for fiber end effects. It was demonstrated that the modification not only results in a correct prediction of the modulus increases in the small aspect ratio regime, but is also able to correctly predict the values of local stress variations in the matrix and whisker. The elasto-plastic behavior of the composite including fiber/fiber interactions was investigated in detail. Cyclic stress-strain hysteresis and Bauschinger effect due to the presence of fibers was also analyzed. It was found that plastic constraint generates a triaxiality in the matrix and so gives a substantial increase of fiber axial stress and an elevation of composite flow stress. Detailed deformation evolution was evaluated both under monotonic and fatigue conditions. Role of thermal residual stresses due to thermal mismatch in MMCs were investigated using the thermo-elasto-plastic FEA with temperature dependent matrix properties. It was found that the spatial distribution of the residual stresses during cooling is sensitive to constraint effects. The evolution of the "caging" plasticity surrounding fibers during cooling including the shape and size of the plastic zones were determined. While FEA solutions give good results, the application of FEA to composites requires careful attention to the geometry of the optimum mesh used in the analysis. The optimization strategy was based on an error energy norm calculation for global convergence and traction differential approach for local convergence at the fiber/matrix interface. It was shown that this optimization approach provides the optimum mesh with a much more rapid convergence than conventional automatic codes. The mesh patterns generated are also shown to be significantly different from using this approach. A converged local property values can be obtained using a significantly lower degree of freedom than by conventional methods.

This dissertation explores the effect of processing and environmental conditions on the mechanical performance of photoresist coatings. Characterization of the mechanical performance included a comparison of the state of stress with the strength of the coating. Various techniques were compiled and developed to explore the effect of processing and environmental parameters on the state of stress and mechanical properties. Techniques used to determine the stress as a function of temperature changes, swelling, or curing (UV or thermal) were: vibrational holographic interferometry, thermal mechanical analysis (constant strain) as a function of temperature and ultraviolet dosage, and a newly developed technique, membrane deflection. The mechanical properties were examined using standard tensile tests. It was found that a thermal or ultraviolet cure resulted in a significant residual stress (3 to 10 MPa). This stress was compared to the strength of the coating (20-40 MPa). The stress was found to be a result of cooling the sample following cure. A reduction in the temperature experienced during cure resulted in a decrease in the final stress. This reduction in cure temperature, if carried out above the glass transition, did not result in a decrease in the mechanical properties. It was also established that the stress increased linearly as a function of decreasing the temperature. The stress increase as a function of temperature was determined to be $-$0.32 MPa/$\sp\circ$C, with the stress reaching over 45 MPa at $-$65$\sp\circ$C. It was established that the coatings followed a maximum normal stress failure criterion; that is, failure occurred when the 2-dimensional coating stress equaled the ultimate strength. It was also illustrated that the stress due to thermal shock was 10-30% higher than stresses measured during a slow equilibrium cool. A model using linear elasticity was used to describe this phenomenon. It was also shown that swelling the photoresist coatings with water and isopropanol resulted in a complete reduction in the stress. Upon drying, this stress was recovered.

This thesis consists of two closely related parts: Microstructure characterization and homogenization. Homogenization is a procedure to determine the effective properties of a material on macroscopic scale based on its heterogeneity on microscopic scale. The effective properties of a material are dependent on the spacial distribution of heterogeneity such as the distributions of material phases, the shapes of the continents, the distribution of microcracks, etc. The determination of the distribution of this geometrical heterogeneity is the task of microstructure characterization. The originality of the following work is claimed by the author: (1) Microstructure characterization: (a) Revealed a simple and useful relationship between volume fraction and mean chord-length. Volume fraction is the most important statistical property in homogenization and many other fields. Mean chord-length of a phase is mean size of the continents of that phase, which is easy to measure from the profile of material cross-sections. (b) Developed a method to obtain the two-point probability function for general anisotropic random material based on chord-length distribution and chord-center distribution. The two-point probability is the probability of finding the g-th phase at point P and finding the h-th phase at point Q simultaneously. Two-point probability has been identified as the basic function for characterizing the microstructures of random materials for the purpose of homogenization. (c) Introduced the concept of subphase which enables us to characterize the microstructure as detailed as one wishes without lazy higher order probabilities but more and more subphases. Materials are conventionally considered as multi-phase in terms of the difference of the mechanical properties of the continents such as elastic moduli and permeabilities. These multi-phase materials can be subdivided into more phases in terms of the geometrical differences (size, orientation of continents neighbor continents). Generally, to characterize the microstructure with n-point probabilities, higher-point probabilities are necessary in order to determine the microstructures in detailed. However, this will cause difficulties in two aspects. Firstly, for n $>$ 3, the n-point probabilities are usually very complex and difficult to obtain. Secondly, the complexity of the n-point probabilities will further cause difficulties in homogenization. These difficulties are overcome at a large degree by making subphases and combining the linear model of two-point probability. (2) Homogenization: (a) Developed a homogenization method for general anisotropic random materials with a probability approach. With this method, the effective moduli of n-phase anisotropic random elastic materials can be found. (b) Developed a homogenization method for conductivity problems for general anisotropic random materials with approach. The method can be used to calculate the effective permeabilities of n-phase anisotropic random materials. (c) Developed a homogenization method for randomly microcracking materials. With this method, the effective moduli of randomly cracking materials can found. The cracks under consideration can be any shape, any orientation distribution and dry or fluid-filled. It should be emphasized that the interaction between phases or cracks is fully considered in all these three methods. The effects of microstructures on effective properties are brought to the lights. In particular, the following effects are demonstrated: effects of microstructures on effective Young's moduli, effects of microcrack distributions on effective Young moduli, and effects of microstructures on effective permeabilities.