As a part of a larger effort towards the fundamental understanding of structureproperty relationship in nanoplatelet-reinforced polymer nanocomposites, a set of model epoxy systems containing α-Zirconium Phosphate (α-ZrP) have been prepared and studied in this dissertation. A new surface modification approach, i.e., the porous pathway approach, for improving intercalation efficiency and exfoliation of layered nanoplatelets has been proposed and the effectiveness has been demonstrated. In order to clearly understand the roles of nanofillers and the effects of their geometric factors on the physical and mechanical properties of nanocomposites, variables such as nanoplatelet loading level, degree of exfoliation, and aspect ratio have been carefully controlled in the epoxy matrices. Morphological information of the prepared nanocomposites was unambiguously confirmed by carrying out X-ray diffraction and transmission electron microscopy (TEM). Tensile and thermo-mechanical properties of the model epoxy/α-ZrP nanocomposites have been investigated. Furthermore, fracture behavior of the model nanocomposites is examined in this study. This work has enhanced the understanding of the effects of nanoplatelet, i.e., loading level, degree of exfoliation, aspect ratio, and the type of surface modifiers, on the mechanical properties and fracture behavior of polymer nanocomposites.

The proposed research investigates the unique structure of the rostrum of the paddlefish (Polyodon spathula) for use in bio-inspiration. The rostrum comprises three different materials: midline cartilage, a network cartilage structure, and matrix tissue. The structure-property relationships of these materials were studied with various mechanical testing and imaging techniques. The mechanical properties and stress-strain behavior were applied to a material model that characterizes each material. A three-dimensional model was constructed from computed tomography images, and a mesh was exported for use in finite element simulations. Different boundary conditions were applied to show how the rostrum responds under deformation giving a stress distribution arising from different loadings. Finally, a new robust design paradigm is introduced with bio-inspiration introducing constraints and is explained through using the paddlefish rostrum as an example of a cell tower or antenna.

A need exists for a more robust method of evaluating musculoskeletal injuries resulting from impact conditions, particularly blasts. Computational modeling is a promising method of achieving this goal. The accuracy of a model depends on high quality mechanical properties for each component. This study examined the mechanical properties of porcine muscle along with structure property relationships. Fresh muscle was tested in compression and tension at strain rates of 0.1 s-1, 0.01 s-1, and 0.001 s-1. Viscoelastic properties were observed including strain rate dependency, stress state dependency, anisotropy, relaxation, and hysteresis. Image analysis was conducted in compression on controls, 30% strain, and 50% strain, relating stress-strain data with structural changes. The effect of rigor was also seen in the tensile response of muscle. Thawed tissue was examined to investigate the effects of freezing. It was found that freezing did not significantly change the mechanical properties, but substantial microstructural changes did occur.

No description available.

The overall theme of the research discussed in this dissertation has been to explore processing-structure-property relationships for submicron polymeric fibers produced by electrospinning (Part I) and to ascertain whether or not the length of the short chain branch has any effect on the physical properties of films of linear low-density polyethylenes (LLDPEs) (Part II). Electrospinning is a unique process to produce submicron fibers (as thin as 100 nm) that have a diameter at least two orders of magnitude smaller than the conventional fiber spinning processes based on melt and solution spinning. As a result, the electrospun fibers have a very high specific surface. The research efforts discussed in Part I of this dissertation relate to some fundamental as well as more applied investigations involving electrospinning. These include investigating the effects of solution rheology on fiber formation and developing novel methodologies to fabricate polymeric mats comprising of high specific surface submicron fibers of more than one polymer, high chemical resistant substrates produced by in situ photo crosslinking during electrospinning, superparamagnetic flexible substrates by electrospinning a solution of an elastomeric polymer containing ferrite nanoparticles of Mn-Zn-Ni and substrates for filtration applications. More specifically, it was found that the solution rheological parameters like concentration and viscosity, in addition to molecular weight play an important role in governing the fiber formation during electrospinning of polymer solutions. Furthermore, it was found that fiber formation depends strongly on the solution concentration regime, i.e., at low and dilute concentrations, droplets and beaded fibers were formed whereas uniform fibers were observed to form at a solution concentration greater than at least six times than that of the critical chain overlap concentration, c*, for linear homopolymers of poly(methyl methacrylate) that had molecular weight distributions ranging from 1.03-1.35 (Mw/Mn). In contrast, uniform fibers were observed at ten times the value of c* for the relatively broader molecular weight polymers (Mw/Mn~1.6-2.1). Novel methodologies were developed to in situ photocrosslink the electrospun jet to produce a crosslinked network in the form of a submicron fiber that could potentially be utilized for applications where a high resistance to chemical environments is required. In addition, flexible superparamagnetic substrates were developed by electrospinning a solution of an elastomeric polymer containing magnetic nanoparticles based on "mixed" ferrites of Mn-Zn-Ni where the specific saturation magnetization and the magnetic permeability of these substrates were found to increase linearly with the wt% loading of the nanoparticles. The methodology to simultaneously electrospin two polymer solutions in a side-by-side fashion was developed to produce bicomponent fibers with the rationale that the resulting electrospun mat will have properties from a combination from each of the polymer components. Bicomponent electrospinning of poly(vinyl chloride)- polyurethane and poly(vinylidiene fluoride)-polyurethane was successfully performed. In addition, filtration properties of single and bicomponent electrospun mats of polyacrylonitrile and polystyrene were investigated. Results indicated lower aerosol penetration or higher filtration efficiencies of the filters based on submicron electrospun fibers in comparison to the conventional filter materials. In addition, Part II of this dissertation explores whether or not the length of the short chain branch affects the physical properties of blown and compression molded films of LLDPEs that were synthesized by a single site metallocene catalyst. Here, three resins based on copolymers of ethylene/1-butene, ethylene/1-hexene, and ethylene/1-octene were utilized that were very similar in terms of their molecular weight and distribution, melt rheology, density, crystallinity and short chain branching content and its distribution. Interestingly, at higher deformation rates (ca. 1m/s), the breaking, tear and impact strengths of films based on ethylene/1-hexene and ethylene/1-octene were found to be superior than those based on ethylene/1-butene. While the origin of these differences in mechanical properties with increasing short chain branch length was not fully understood, the present investigation did confirm this effect to be pronounced only at high deformation rates for both the blown and compression molded LLDPE films. / Ph. D.

Integration of material composition, microstructure, and mechanical properties with geometry information enables many product development activities, including design, analysis, and manufacturing. To address such needs, models of material composition have been integrated into CAD systems, creating systems called heterogeneous CAD modeling. In order to support the heterogeneous CAD system, extensive process-structure-property relationships have to be captured and integrated into current CAD system. A new method for reverse engineering of materials will be presented such that microstructure models can be constructed and used in the heterogeneous CAD system. Reverse engineering of material consists of three parts: image analysis, structure-property-process relationship, and repository. In this research, an image processing method, which comprises the Radon transform and the wavelet transform, will be used in order to recognize geometric features from a microstructure image. Recognizing geometric features can be obtained by combinations of three techniques, masking, clustering, and high frequency component on wavelet transform, that are integrated with the Radon transform. Then, recognized geometric features can be used to construct an explicit geometric model of microstructure. The proposed work will provide an explicit mathematical method to recognize and to quantify microstructure features from an image. In addition, explicit geometric models of microstructure can be automatically constructed and utilized to get effective mechanical properties, establishing structure-property relationship of the material. In order to demonstrate this, polymer nano-composite sample and metal alloy sample will be used.

The Materials Genome Initiative was announced by the White House in June of 2011, and is a multi-agency initiative which calls the materials community to find ways to discover, develop, manufacture, and deploy advanced materials systems faster and more cost-efficiently. Currently, the amount of time it takes to discover and develop a new material system, optimize its properties, integrate it in to a system, certify that system, and develop the manufacturing capability so that it can be deployed in a commercial component takes at least 20 years. Since this trend holds regardless of the material system in question, the implication is that it is the process by which we as a community move through these seven steps, which causes the lengthy timeline. Historically, the discovery, development, and property optimization of a material system relies heavily on deep scientific knowledge, intuition and trial-and-error physical experimentation. Therefore much of the design and testing of materials in these early stages is currently performed through time-consuming and repetitive experimental and characterization feedback loops. Some of these feedback loops could be eliminated in the property optimization step with improved powerful and accurate computational modeling tools. However, while the ability of computational models to be used in this way is not new, models that have been developed in this space have consistently underperformed. Oftentimes, these models fail because they fail to accurately account for the various physical and chemical mechanisms that are driving the system, or because they fail to account for all of the variables which must be included. Here we propose a standard method of communication for these relationships in the form a process-structure-property-performance map, which leverages the known knowledge database of the material system to clearly and visually communicate the relevant variables and their various relationships in a defined materials design space. Such a map is developed here for high-strength Al-Zn-Mg-Cu alloys, which offer a good example of a material system which could benefit from such a standard. This class of alloys, which are typically utilized in aircraft components, have been incorporated in commercial components for nearly 75 years, and due to its long history is a well characterized and well developed system that is highly suited to this kind of examination. In Part I of this work, we develop this standard by first examining the known knowledge database in this system to deduce what the important process, microstructure, and mechanical property variables are that are of interest. Once these variables and the relationships between them are identified, they are organized into a PSPP map according to a proposed set of steps, and can act as a visual standard that can clearly communicate critical information about the mechanisms of the system. For example, if a model developed within this system does not include a variable or a mechanism depicted within the map, it can be used to communicate the ways in which the model will be constrained. Similarly, when experimental data is collected within this space the map can be used to clearly communicate which variables in the space were held constant, which variables were tracked and accurately measured, and if any variables were unaccounted for. This information can help to communicate what situations the data can be used in, and how the space that the experimental data can be used in is constrained. In Part II of this work, we vary multiple parameters within the high-strength Al-Zn-Mg-Cu system defined in Part I, and attempted to track and measure as many of the variables within the space as possible using commonly available testing and characterization methods. In tackling such a large project in the complicated materials system of high-strength wrought Al-Zn-Mg-Cu alloys, we are able to understand which current testing and characterization methods are well suited to tracking these variables when the number of test specimens becomes quite large and when variability among those specimens is involved. We are also able to identify opportunities for future work in this area, which could be focused on improving our ability to implement projects of the scope that is required here. In addition to evaluating the feasibility of the various measurement and characterization methods, the raw data and the analyzed results for this work are cataloged in an associated data repository and have been made available for use in future work in this and other areas.

The reformulation of pressurized metered dose inhalers (MDIs) with hydrofluoroalkanes (HFAs) from chlorofluorocarbons (CFCs) has given rise to many solubility challenges. Compounds and excipients previously used in CFCs were observed to have significantly different solubility values in HFA-134a. In this investigation, the solubility values of solid organic solutes were determined in pure HFA-134a and HFA-134a with cosolvent (0 - 20% w/w ethanol). The solubilities of solid solutes in HFA-134a were also compared with those in 2H,3H-decafluoropentane (DFP) in order to assess the suitability of DFP as a liquid model propellant. The experimental set of solutes display diverse physico-chemical properties and yielded solubility values that ranged over four orders of magnitude. The experimental solubilities were compared to calculated values obtained from ideal solubility and regular solution theory models. While the theoretical models did not offer absolute solubility estimations, a clear correlation with the ideal solubility (melting point) was noted. Further consideration utilizing multiple linear regression models afforded correlations based on molecular properties. Regression models, containing melting point and logP (or molar volume) resulted in promising correlations in both pure HFA-134a and HFA-134a/cosolvent systems where the average absolute errors ranged from 0.49 to 0.82 log units, (average factor errors of 3.09 and 6.61, respectively). In general, a linear relationship was observed between log mole fraction solubility in HFA-134a and fraction ethanol. The effect on solubilization ranged from 1.3 to 99.4 times when 20% w/w ethanol was introduced, relative to pure HFA-134a. DFP appears to be a promising liquid model for pure HFA-134a for pre-formulation calculations. A two parameter equation were found to be significant in pure HFA-134a where the average absolute error (AAE) value was 0.61 log units (average factor errors of 4.07).

Photopolymerization is a growing field within the realms of polymer and material science. With diverse applications, ranging from coatings and adhesives to newer technologies such as 3D printing photopolymerization continues to increase its prevalence and influence. This research examines fundamental structure property relationships between large prepolymer structures within a formulation and the resulting impact on thermo-mechanical properties in photocurable resins. Most prepolymer molecules utilize a “one pot” synthesis with little to no control over the placement of photoreactive moieties such as epoxies and (meth) acrylates. We have utilized novel prepolymer molecules synthesized using controlled radical polymerization to allow direct control over the placement of reactive groups. The ability to control the location of reactive groups in prepolymer molecules can also lead to the formation of multiple domains within the resulting photocured thermoset. This separation is achieved by concentrating the reactive groups at specific locations in the prepolymer backbone, e.g. at the end or near the center of the prepolymer molecule. The nonreactive groups may form one domain within the thermoset network while the reactive portion of the prepolymer forms a second phase with reactive diluent molecules. Additionally, various architectures allow greater control over polymer network formation and crosslink density. Through these manipulations of macromolecular architecture, we have been able to manipulate various thermo-mechanical properties. Using various architectured prepolymer, we have been able to generate materials with multiple glass transitions while also increasing the rate of reaction and total conversion as compared to randomly functionalized control formulations.

A new but relatively simple processing study was conducted to investigate the microstructure-property relationships of alumina/aluminium titanate (AAT) composites. The objectives of this study were: (a) to develop a process for fabricating AAT and β-spodumene modified AAT composites using a solid-state reaction method and functionally-graded AAT using an infiltration technique, and (b) to evaluate the effects of dispersed aluminium titanate (AT) on the phase relations, microstructure and mechanical properties of alumina-based composites. The study has revealed that the processing procedures played an important rule in the microstructural development of AAT composites. The microstructure and properties of AAT composites have been found to be strongly influenced by the presence of dispersed AT. The phase relations in the AAT system have been characterised by x-ray diffraction (XRD) and neutron diffraction (ND). Rietveld analysis showed that the AT content increased in proportion with the amount of rutile added. The dynamic ND study showed that AT commenced to form at ~1310°C The presence of AT caused a reduction of hardness but an improvement in fracture toughness. In addition, the presence of AT hindered the processes or kinetics of sintering and densification. The use of β-spodumene has been investigated as a liquid-phase-sintering aid for the densification of AAT composites. XRD, ND, differential thermal analysis (DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Vickers indentation were used to characterise the effect of β-spodumene on the phase relations, densification, microstructure and mechanical properties of AAT composites. The presence of β-spodumene was found to have a profound influence on the phase relations, densification, microstructure and properties of AAT composites. / The addition of β-spodumene caused a small reduction of AT content and a commensurate increase of alumina phase. Functionally-graded AAT composites have been successfully synthesised through infiltration of porous alumina preform with a solution containing TiCl4. The infiltration kinetics of liquid into porous alumina preform has also been investigated and modelled. It was found that the infiltration rate equation proposed by Washburn was proven to be suitable for describing the kinetics of infiltration in terms of preform sintering temperature, viscosity, and multiple infiltrations. The influence of applied pressure was consistent with the model proposed by Travitzky and Shlayen, where the applied pressure enhanced the rate of infiltration. Pre-sintering of alumina preform at 900, 1000 and 1100°C for 2 h resulted in different rates of infiltration which may be attributed to a varying degree in tortuosity of the pore channels. The graded composition character of functionally-graded AAT composites has been determined by XRD and grazing incidence synchrotron diffraction (GISRD). Graded compositions from Rietveld refinement analysis showed that the concentration of AT decreased with depth. In contrast, the α-A12O3 content increased with depth. Microstructural examination by SEM showed that the content of AT grains was the most abundant near the surface and decreased gradually with an increase in depth. The hardness results showed that FGM had a soft graded-region (AT rich) but hard non-graded alumina region. / The lower hardness in the graded region can be attributed to the presence of intrinsically soft AT phase. The presence of graded AT caused a considerable improvement in damage tolerance. The isothermal decomposition of AT at 1100°C both in air and vacuum has been studied. Both ex-situ and in-situ studies have been conducted to examine the effect of environment on the decomposition behaviour of AT. The addition of MgO was effective in enhancing the thermal stability of AT against decomposition both in air and in vacuum.