In this thesis, the focus has been on micro-mechanical mechanisms in polymer-based materials and structures. The first part of the thesis treats length-scale effects on polymer materials. Experiments have showed that the smaller the specimen, the stronger is the material. The length-scale effect was examined experimentally in two different polymers materials, polystyrene and epoxy. First micro-indentations to various depths were made on polystyrene. The experiments showed that length-scale effects in inelastic deformations exist in polystyrene. It was also possible to show a connection between the experimental findings and the molecular length. The second experimental study was performed on glass-sphere filled epoxy, where the damage development for tensile loading was investigated. It could be showed that the debond stresses increased with decreasing sphere diameter. The debonding grew along the interface and eventually these cracks kinked out into the matrix. It was found that the length to diameter ratio of the matrix cracks increased with increasing diameter. The experimental findings may be explained by a length-scale effect in the yield process which depends on the strain gradients. The second part of the thesis treats mechano-sorptive creep in paper, i.e. the acceleration of creep by moisture content changes. Paper can be seen as a polymer based composite that consists of a network of wood fibres, which in its turn are natural polymer composites. A simplified network model for mechano-sorptive creep has been developed. It is assumed that the anisotropic hygroexpansion of the fibres leads to large stresses at the fibre-fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear in stress. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive creep effects in compression than in tension. Furthermore, moisture dependent material parameters and anisotropy are taken into account. Theoretical predictions based on the developed model are compared to experimental results for anisotropic paper both under tensile and compressive loading at varying moisture content. The important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined. / QC 20100910

Solar technology has been a major topic in sustainable design for many years. In the last five years, however, the solar technology industry has seen a rapid growth in installations and technological advances in cell design. Combined with a rapidly declining overall system cost, the idea of introducing solar technology into a wider range of applications is becoming a focus for engineers and scientists around the world. So many variables which alter solar energy production, such as the sun and surrounding environment, determine whether a solar design is beneficial. This thesis presents a bridge deck surface integrated with solar cells tested under all AASHTO LRFD pedestrian bridge loadings. A detailed solar analysis of the University of Massachusetts’s campus is presented to determine if solar integration is even plausible for the Northeastern United States with the energy limitations created by the deck integration, as well as an economic evaluation of the deck design. The purpose of this thesis was to determine if a walking surface could be integrated with solar technology and be a plausible alternative to conventional walking surfaces, while providing a source of sustainable power.

Mode I interlaminar fracture of 3k 8-Harness-Satin Carbon cloth, with identical fill and weft yarns, pre-impregnated with Newport 307 resin was investigated through the DCB test (ASTM D5528). Crack propagations along both the fill and weft yarns were considered for both post-bonded (co-bonded) and co-cured laminates. A patent-pending delamination insertion method was compared to the standard Teflon film option to assess its applicability to mode I fracture testing. The Modified Beam Theory, Compliance Calibration method, and Modified Compliance Calibration method were used for comparative purposes for these investigations and to evaluate the validity of the proposed Equivalent Stiffness (EQS) method. Crack propagation, in all specimens, proceeded in a run-arrest manner for both delamination directions. Energy dissipation in the form of transverse yarn debonding, matrix deformation, and out of plane crack growth was witnessed for specimens with delaminations along weft yarns. A complete comparison between post-bonded and co-cured laminates was not achieved. The patent pending delamination insertion method was found to cause fewer instances of non-linear crack initiation behavior than the Teflon insert and, when non-linear behavior did occur, it was less prevalent. The EQS method was found to achieve fracture toughness values within 5% of the other three data reduction methods for 63% of the propagation values and achieved conservative values for over 33% of the propagations. Suggestions for future studies aimed at completing the comparisons above are provided in Chapter 5.

While composite structures exhibit exceptional strength and weight saving possibilities for engineering applications, sometimes their overall cost and/or material performance can limit their usage when compared to conventional structural materials. Meanwhile ‘biocomposites’, composite structures consisting of natural fibers (i.e. bamboo fibers), display higher cost efficiency and unique structural benefits such as ‘sustainability’. This analysis will determine if the integration of these two different types of composites are beneficial to the overall structure. Specifically, the structure will consist of a one internal bamboo veneer biocomposite ply; and two external carbon fiber weave composite plies surrounding the bamboo biocomposite. To acquire results of this study, the hypothesized composite structure will consist of varied trapezoidal corrugated specimens and tested in uniaxial compression loading. Thereafter, this test data will be used to ultimately design, manufacture, and test a structural biocomposite/composite box, intended to carry extremely high compressive loads; relative to its own weight. A finite element analysis of this test will be used to validate experimental data. After running the experiment, the carbon fiber with bamboo test sample results were compared to that of only carbon fiber test sample. The carbon fiber samples resulted in a maximum compressive load difference of only 23% higher loads when compared to the carbon fiber with bamboo, on average. These findings are discussed throughout.

Traditional Lithium-Ion Batteries (LIBs) are a reliable and cost-efficient choice for energy storage. LIBs offer high energy density and low self-discharge. Recent developments in electric-based technologies push for replacing historically used Lead-Acid batteries with LIBs. However, LIBs do not yet meet the demands of modern technology. Silicon and graphene oxide (GO) have been identified as promising replacements to improve anode materials. Graphene oxide has a unique sheet-like structure that provides a mechanically stable, light weight material for LIB anodes. Due to its structure, reduced graphene oxide (rGO) is efficiently conductive and resistive to environmental changes. On the other hand, silicon-based anode materials offer the highest theoretical energy density and a high Li-ion loading capacity of various elements [20]. Silicon-based anodes that have previously been studied demonstrated extreme volumetric expansion over long cycles due to lithiation. Polysiloxane may be an interesting alternative as it is a Si-based material that can retain the high Li-ion loading capacity of Si while lacking the unattractive volumetric expansions of Si. Polymer derived ceramic-decorated graphene oxide anodes have been suggested to increase loading capacity, thermal resistance, power density, and mechanical stability of LIBs. Coupled with mechanically stable graphene oxide, polymer derived ceramic nanoparticle decorated graphene oxide anodes are studied to establish their efficiencies under operating conditions.

Carbon emissions are known to cause decay of the Ozone layer in addition to creating pollutant, poisonous air. This has become a growing concern among scientists and engineers across the globe; if this issue is not addressed, it is likely that the Earth will suffer catastrophic consequences. One of the main culprits of these harmful carbon emissions is fuel combustion. Between vehicles, power plants, airplanes, and ships, the world consumes an extraordinary amount of oil and fuel which all contributes to the emissions problem. Therefore, it is crucial to develop alternative energy sources that minimize the impact on the environment. One such technology that is currently being researched, is the Solid Oxide Fuel Cell (SOFC). This is a relatively simple device that converts chemical energy into electrical energy with no harmful emissions. For these devices to work properly, they require an electrolyte material that has high ionic conductivity with good phase stability at a variety of temperatures. The research presented in this study will concentrate intensively on just one of the many candidates for SOFC electrolytes. 1 mol% CeO2 – 10 mol% Sc2O3 – 89 mol% ZrO2 manufactured by Treibacher Industries was analyzed to better understand its sintering properties, phase stability, and molecular structure. Sintering was performed at temperatures ranging from 900oC to 1600oC and the shrinkage, density and porosity were examined for each temperature. Raman Spectroscopy and X-Ray Powder Diffraction were also conducted for comparison with other known compositions to see if the powder undergoes any phase transitions or instability.

Tailored fluoropolymers remain the leading choice for a wide variety of advanced high-performance applications, including electronic/optical and energy conversion, owing to their unique blend of complementary high-performance properties. Amorphous semi-fluorinated polymers exhibit improved solubility and melt processability when compared to traditional perfluoropolymers. A leading class of semi-fluorinated aryl ether polymers includes perfluorocyclobutyl (PFCB), perfluorocycloalkenyl (PFCA), and fluoroarylene vinylene ether (FAVE) polymers. Monomers containing aromatic trifluorovinyl ethers (TFVE) are used to synthesize PFCB polymers via radical-mediated [2+2] cyclodimerization. On the other hand, FAVE and PFCA polymers are polymerized via base-mediated nucleophilic addition/elimination of bisphenols with TFVE monomers and decafluorocyclohexene respectively. The use of different monomer cores (aromatic, aliphatic, contorted, and renewable) should help to develop general structure/property relationships for this versatile and expanding approach to semi-fluorinated aryl ether polymers. The enchainment of polycyclic aromatic hydrocarbon (PAH) cores with functional fluorocarbon groups (or segments) recently afforded a new class of semi- fluorinated polymers in the continuing quest for novel organic materials for potential applications in optoelectronic, gas-separation, and advanced composites. Chapter 2 details the incorporation of commercially available acenaphthenequinone was achieved to afford PFCB aryl ether polymers with excellent solubility, high thermal stability, and film-forming capability. Chapter 3 represents base-promoted nucleophilic addition/elimination of commercial bisphenols with TFVE-triphenylene monomers affording FAVE aryl ether polymers possessing excellent solution processability, high thermal stability and photostability. In addition, triphenylene-enchained FAVE polymers exhibit extreme thermal-oxidative photostability and emit blue light after heating in air at 250 °C for 24 h. Further, time-dependent density functional theory (TD-DFT) computations were performed to understand electronic polymer structures. In one case, post-polymerization Scholl coupling converted the central triphenylene core to afford a hexabenzocoronene containing semi-fluorinated polymer with new optoelectronic properties. Chapter 4 demonstrates synthesis and characterization of renewable semi-fluorinated polymers obtained using aliphatic diol isosorbide. This renewable diol readily polymerizes with bis-TFVE derivatives of bisphenol A and 6F to provide high molecular weight thermoplastics exhibiting excellent solubility and tough, transparent film-forming capability. Finally, Chapter 5 presents synthesis of TFVE enchained corannulene which gave blue-light emission and outstanding processability. Synthesis and characterization, including the new materials' optical, thermal, and electronic properties, is presented.

Dynamic testing provides valuable insight into the behavior of materials undergoing fast deformation. During Split-Hopkinson Pressure Bar testing, stress waves are measured using strain gauges as voltage variations that are usually very small. Therefore, an amplifier is required to amplify the data and analyze it. One of the few available amplifiers designed for this purpose is provided by Vishay Micro-Measurements which limits the user’s options when it comes to research or industry. Among the challenges of implementing the Hopkinson technology in the industry are the size and cost of the amplifier. In this work, we propose a novel design of a signal conditioning amplifier that provides the following functionalities: voltage excitation for strain gauges, wide gain range (1-1000), signal balancing, shunting, and filtering. The main objective is to make a smaller and cheaper amplifier that provides equivalent or better performance allowing larger application of the Hopkinson technology in the industry.

Fossils belonging to the genus Homo, dating as far back as two million years ago, exhibit uniquely efficient features suggesting that early humans had evolved to become exceptional endurance runners. Although they did not have the cushion or stability-control features provided in our modern day running shoes, our early human ancestors experienced far less of the running-related injuries we experience today. The injury rate has been estimated as high as 90% annually for Americans training for a marathon and as high as 79% annually for all American endurance runners. There is an injury epidemic in conventionally shod populations that does not exist in the habitually unshod or minimally shod populations around the world. This has led many to conclude that the recent advent of highly technological shoes might be the problem. Although current literature has been inconclusive, there are two main limitations in virtually all of the studies: 1) transition phases of less than three months and 2) transition phases without rehabilitation exercises. These two aspects are key to the treatment of the structural consequences on the muscles and tendons of the foot and calf that habitually shod individuals have faced. This study includes a discussion of the cumulative consequences that lifelong shoe usage has on the development of the feet and lower legs. I propose a 78-week study that addresses the limitations of past studies by implementing a gradual, 32-week, multi-shoe transition complemented by an evidence-based rehabilitation program. I believe that this approach will restore strength and elasticity to muscles and tendons that have been inhibited by lifelong usage of overconstructed shoes and adequately prepare runners for the increased demand brought on by a­­­­­ changing running mechanic. This comprehensive, multifaceted transition plan to a fully minimalist shoe will provide novel insight into the ongoing barefoot debate. Can this approach finally demonstrate the proposed benefits of losing the shoes?

AlNiCo magnets are known for high-temperature stability and superior corrosion resistance and have been widely used for various applications. Reported magnetic energy density ((BH) max) for these magnets is around 10 MGOe. Theoretical calculations show that ((BH) max) of 20 MGOe is achievable which will be helpful in covering the gap between AlNiCo and Rare-Earth Elements (REE) based magnets. An extended family of AlNiCo alloys was studied in this dissertation that consists of eight elements, and hence it is important to determine composition-property relationship between each of the alloying elements and their influence on the bulk properties. In the present research, we proposed a novel approach to efficiently use a set of computational tools based on several concepts of artificial intelligence to address a complex problem of design and optimization of high temperature REE-free magnetic alloys. A multi-dimensional random number generation algorithm was used to generate the initial set of chemical concentrations. These alloys were then examined for phase equilibria and associated magnetic properties as a screening tool to form the initial set of alloy. These alloys were manufactured and tested for desired properties. These properties were fitted with a set of multi-dimensional response surfaces and the most accurate meta-models were chosen for prediction. These properties were simultaneously extremized by utilizing a set of multi-objective optimization algorithm. This provided a set of concentrations of each of the alloying elements for optimized properties. A few of the best predicted Pareto-optimal alloy compositions were then manufactured and tested to evaluate the predicted properties. These alloys were then added to the existing data set and used to improve the accuracy of meta-models. The multi-objective optimizer then used the new meta-models to find a new set of improved Pareto-optimized chemical concentrations. This design cycle was repeated twelve times in this work. Several of these Pareto-optimized alloys outperformed most of the candidate alloys on most of the objectives. Unsupervised learning methods such as Principal Component Analysis (PCA) and Heirarchical Cluster Analysis (HCA) were used to discover various patterns within the dataset. This proves the efficacy of the combined meta-modeling and experimental approach in design optimization of magnetic alloys.