Thesis (Ph.D.)--Lehigh University, 2007. / Adviser: A. R. Marder.

Thesis (Ph. D.)--University of Toronto, 2008. / Includes bibliographical references.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6677. Adviser: Joseph E. Greene. Includes bibliographical references (leaves 92-93) Available on microfilm from Pro Quest Information and Learning.

<p> Adhesive bonding is a common, robust, and inexpensive method of joining materials. Of particular interest is the behavior under shear loading, where adhesive bonding excels compared to alternative joining methods. However, while the quasi-static response of these joints is well understood, the dynamic behavior is largely unknown. </p><p> To this end, a series of experiments were devised and performed where two bars are adhesively bonded using a simple lap joint and subjected to a high-speed impact from a steel slug. These tests were configured to, as much as possible, isolate the type of wave that generates adhesive shear and minimize the effect of reflected and induced waves. While keeping the overall geometry constant, the adhesive material, substrate material, and projectile velocity were varied. </p><p> The wave behavior was recorded using surface-mounted strain gages. Also, digital image correlation techniques were developed to analyze high-speed video of the impact event. From these experiments, a number of useful measures can be extracted, including the critical input (projectile) kinetic energy and the specific energy absorbed by the adhesive. </p><p> The techniques developed in this thesis allow for the suitability of different substrate/adhesive combinations under ballistic shear impact to be quantitatively evaluated. </p><p> Additionally, dynamic plate theory is used to derive an analytical model of the substrate/adhesive system. Several solutions to this model which were solved using a Finite Difference approach are included. These solutions were then compared to the strain histories recorded in the physical experiments. </p><p>

<p> Cadmium Telluride (CdTe) thin film photovoltaic technology has shown favorable progress due to inexpensive and efficient processing techniques. However, efficiencies have yet to reach the overall projected CdTe device efficiency, with the back contact being a main source of CdTe performance limitations. Tellurium (Te) applied as a back contact has led to significant increases in fill factor and an overall progress in device efficiency. Devices deposited with Te show significant improvement in uniformity, even without intentional Cu doping, when compared to devices without Te. In current - density measurements, Te shows stability even at low temperatures, which is indicative of a low barrier developed at the CdTe/Te interface. X-ray and ultra-violet photoelectron spectroscopy were carried out to examine the valence band offset at the CdTe/Te back contact interface. The valence band offset was shown to be highly dependent on the Te thickness and was largely affected by oxidation and contamination at the surface. Capacitance measurements were carried out to study the effect Te has on the absorber depletion width. Data indicate a decreased depletion width with Te applied at the back of thin film CdTe devices, which agrees with increased device performance. Te thickness was varied in all studies to understand the effect of application thickness on device performance and material characteristics. With a thicker Te layer leading to overall improvement in device performance and favorable device characteristics. </p><p>

The presence of a distinct compound in the Pt-Fe Cu system at Pt FeCu composition was hypothesised by Nemilov in 1944, but tre compound (Tulameenite) was first identified by Cabri et al in natural alloys from the platinum placer deposits of the Tulameen river in British Columbia. The present research was initiated to determine the Pt-Fe-Cu phase diagram in the Pt FeCu region and thus to determine the composition range of Tulameenite and its compositional and structural changes during different thermal treatments using synthetic material. Primary investigations have revealed that the compound is a single phase disordered f.c.c. solid-solution above 1178°c. On quenching, it transforms, probably by a martensitic transformation, to an ordered tetragonal structure. Multiple twinning on {101} habit planes avoids any macroscopic shape change due to the ordering. The twinned structure is unstable, and thermal treatments produce stress-relief recrystallization accompanied by deformation twins and grain-boundary fractures as further stress-relief mechanisms. Tulameenite forms an extensive single phase region of solid- solution continuous with the binary region based on the compound FePt. At lower temperatures the stoichiometric compound Pt2 FeCu enters a two-phase field comprising a non­- stoichiometric compound together with an ordered cubic phase. The transformation to this two-phase structure occurs by different precipitation mechanisms which are accompanied by recrystallization of the matrlx in some cases.

<p> Quasi static and intermediate strain rate (5 s^&ndash;1 and 500 s^&ndash;1) tests are conducted on various aluminum and steel ASTM E8 subsize tensile specimens to validate a newly developed testing method which combines a previously developed serpentine bar for load monitoring and a newly described high-speed actuator. This new actuator is controlled by a semi-passive piezoelectrically actuated brake system mounted to a standard actuator, which allows for the actuator to produce high loads and quick response times (&ap; 100 &micro;s). Limitations of this experimental method are that tests must be monotonic (tension or compression but not cyclic loading) and strain rate rise times limit this method to the intermediate strain rate regime (below 500 s^&ndash;1).</p><p>

<p> Thermoplastic elastomers are a class of rubbery polymeric materials that exhibit solidlike properties due to physically associating moieties. Block copolymers are often used as the network forming component of thermoplastic elastomers. Additionally, block copolymers can be modified with block selective solvents that contribute a specific functionality to the system; these solvent modified systems will be referred to throughout as thermoplastic elastomer gels. Thermoplastic elastomers and their gels have a long history of applications as specialty materials for passive systems where traditional rubbers cannot meet the required design criteria&mdash;often properties of softness, toughness and low hysteresis are of interest. Herein, we discuss the use of thermoplastic elastomer gels as active materials that respond to external stimuli to change their mechanical and thermal properties.</p><p> First, the text will introduce concepts of phase behavior and resultant physical behavior of block copolymers in the presence of a selective solvent. Included are specific details pertinent to materials used in experimental discussions presented in this work. Following this broad discussion, the introduction of a specific class of smart and responsive materials, known as dielectric elastomer actuators, is detailed in a survey of recent technological developments in the field.</p><p> The main body of the text describes multiple applications of thermoplastic elastomer gels. It begins with an entirely novel use of a semi-crystalline olefin block polymer gel as a dielectric elastomer actuator exhibiting programmable anisotropy and promising actuation behavior. The subsequent study uses specific control over the architecture of a polydimethylsiloxane elastomer to make ultra-soft films for exceptional dielectric elastomers. These so-called bottlebrush elastomers are formed from heavily grafted polymer backbones that reduce entanglements resulting in incredibly soft elastomers. As dielectric elastomers, these materials operate with no mechanical prestrain and achieve strains greater than 300% by area. This is followed by the use of a traditional ABA triblock copolymer (poly[styrene-bethylene- co-butylene-b-styrene]) with a crystallizing selective solvent to impart shape memory behavior. This is the first demonstration of a dielectric elastomer utilizing crystallization for electroactive strain fixation. Finally, we conclude with the discussion of thermoplastic copolyester based gels as form-stable phase change materials. These phase change gels have applications in passive thermal energy management systems and compete with existing commercial technologies.</p><p>

<p> Recently, increased awareness of the significance of developing sustainable materials for construction has renewed the interest in exploring Alkali activated concrete (AAC), a concrete that contains no cement, but only industrial by-products such as fly ash and slag, as a low energy alternative to the conventional concrete. Although the feasibility of making alkali&ndash;activated concrete with acceptable strength and mechanical properties is well documented, the information regarding the long-term durability, including resistance to acid attack and alkali silica reaction (ASR), is far from comprehensive and there is a need to increase the understanding of these durability issues. In this dissertation, these durability issues are addressed, and improvements in this novel technology will increase acceptance in industry. This dissertation presents a comprehensive evaluation into the acid leaching resistance of Alkali-Activated Concrete (AAC) and Ordinary Portland Cement (OPC). The deterioration in AAC and OPC when exposed to different types of acid laden (organic and inorganic) environments are quantified by characterizing the strength degradation, mass change and visual appearances. The changes in microstructure development and chemical composition are examined and analyzed in order to determine the mechanism of deterioration. Additionally, the effect of the addition of nanoparticles on the mechanical properties and resistance to sulfuric leaching of Alkali Activated Slag concrete (AAS) are also explored in this study. </p><p> Furthermore, this dissertation summarizes the findings of an experimental evaluation of alkali silica reaction (ASR) in cement free alkali activated concrete (AAC). The susceptibility of AAC to deleterious ASR was evaluated in this study in accordance with relevant ASTM standards. This study also compares the resistance of AAC with ordinary portland cement concrete (OPC) while exposed to ASR under ASTM C 1293 and ASTM C1567 tests. In particular, the focus of this investigation is to assess the effectiveness of existing ASTM test methods in identifying the occurrence of ASR in alkali activated slag cement (AAS) concrete. In addition to that, influences of activator parameters including the effect of binder type, activator concentration, activator type and water content to the resistance of ASR in AAC were also evaluated. Finally, a scanning electron microscopic study coupled with EDX analyses was used to explain the mechanism of ASR occurrence in AAC and OPC.</p><p>

<p> HNBR is a widely used oil resistant polymer with good tear strength. Due to these properties, HNBR is used in oil wells. However, harsh working environments require high equipment maintenance fees and HNBR will be degraded when contacted with H₂S. This study aims to improve the mechanical properties and H₂S resistance of HNBR through molecular dynamics simulations. Some of the simulation results are compared with experimental results and literature values. In this study, the solubility parameters and densities of pure HNBR with varying acrylonitrile content, FKM and three surfactants (KBM503, a trimethoxysilane methacrylate, A10, a perfluoroalkoxy bis(alkylamide), and Capstone-62MA, a semifluorinated methacrylate) are calculated by molecular dynamics simulation. The cohesive energy densities of 50/50 HNBR/FKM blends with different kinds and content of surfactants are calculated. The diffusion of H₂S and CO₂ are predicted by molecular dynamics simulation. The solubility coefficients of H₂S and CO₂ are predicted by Grand Canonical Monte Carlo (GCMC) simulations. A series of NPT simulations (constant of number of atoms, pressure and temperature) are used to estimate the glass-transition temperature of Capstone-62MA grafted HNBR. Dissipative Particles Dynamics (DPD) simulations are used to obtain the micro phase separation of Capstone-62MA grafted HNBR. The results shows that the solubility parameter values and densities we obtained from molecular dynamics simulations are fitted very well with literature values. According to our calculation of energy of mixing for HNBR/FKM blends with three surfactant (KBM503, A10 and Capstone-62MA), KBM503 has the largest effect. Based on the experiment results for HNBR/FKM blends with different mass fractions of KBM503, the tensile stress at break and elongation at break increases with the increases of KBM503 content until the mass fraction KBM503 is equal to 5%. When the mass fraction of KBM503 is 5%, adding more KBM503 decreases both mechanical properties. However, the tear strength keeps increasing when the mass fraction of KBM503 increases. The conclusion obtained from these experiments and simulations indicates that mixing HNBR with FKM can improve some mechanical properties but this method has disadvantages due the large discrepancy between the solubility parameters of HNBR and FKM. Gas diffusion and solubility calculations indicate that the diffusion and solubility of H₂S decrease with the content of Capstone-62MA increases. The gas diffusion of H₂S also decreases with increasing content of acrylonitrile in HNBR. However, the solubility of H₂S also increases with the content of acrylonitrile in HNBR. For comparison with H₂S, the diffusivity and solubility of CO₂ are calculated. The diffusion of CO₂ increases with the increase of Capstone-62MA content. The solubility of CO₂ decreases with increases of Capstone-62MA in HNBR with 17 wt% acrylonitrile content. For HNBR with 36 wt% acrylonitrile content, increasing the content of Capstone-62MA first increases the solubility of CO₂ and then reduces it when the content of Capstone-62MA is larger than 2%. The calculation also indicates that diffusion and solubility coefficient are reduced when the content of acrylonitrile increases in HNBR. Calculations for the glass-transition temperature of HNBR with different numbers of Capstone-62MA chains suggest that the glass-transition temperature is not changed by grafting Capstone-62MA onto the backbone of HNBR. These results are compared with experimental results. Although the glass-transition temperatures obtained from simulations are higher than those obtained from experiment, they have the same trend as the content of Capstone-62MA is changed. DPD simulations suggest that micro phase separation exists in the Capstone-62MA grafted HNBR and this phenomenon improves the mechanical performance of polymers. In summary, we have used computer modeling to design new polymer materials and perform molecular dynamics simulations, Monte Carlo simulations and DPD simulations to predict some properties of these new materials. Some simulation results are compared with experimental results indicating that we indeed obtain a newly a polymer material with improved properties with the help of computer simulations.</p><p>