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Yes / Nickel coated multi-walled carbon nanotubes (NiMCNTs) are favorable reinforcing nanofillers for modifying cementitious composites due to their preeminent mechanical properties, electrical conductivity, thermal properties and dispersibility. This paper investigates the mechanical properties and compatibility of NiMCNTs filled cementitious composites, having two different types of cement, two water to cement ratios, and two dosages of five types of NiMCNTs. The results show that 0.06 vol.% NiMCNTs with small aspect ratios can significantly enhance the mechanical properties of cementitious composites, while NiMCNTs with large aspect ratios play a better strengthening effect at 0.03 vol.%. The flexural strength/toughness of cementitious composites containing 0.06 vol.% NiMCNTs with an aspect ratio of 200 can be increased by 19.65%/116.78%. Adding 0.03 vol.% NiMCNTs with an aspect ratio of 1000 enhances the compressive strength/toughness of composites by 18.61%/47.44%. Besides, NiMCNTs have preferable compatibility to cementitious composites prepared by P·O 42.5R cement with a water to cement ratio of 0.3. The enhancement mechanism is related to the denser microstructure and effective suppression of microcracks in the cementitious matrix by NiMCNTs with filling, bridging and pull-out effects, as well as the high interface bond strength between NiMCNTs and matrix. A strength prediction model for NiMCNTs reinforced cementitious composites is also established to estimate the mechanical strength of cementitious composites containing NiMCNTs with different aspect ratios/contents, showing a small relative error within ±6%/±13% for predicted flexural/compressive strength values in comparison with the experimental results. / Funding supported from the National Science Foundation of China (51908103 and 51978127), and the Fundamental Research Funds for the Central Universities (DUT21RC(3)039).

Traditional methods for calculating lateral pressures in silos, such as Janssen's Method and Coulomb's Method, have limitations due to the underlying assumptions of each methodology. This research investigates an approach which adapts Coulomb's Method to account for the cylindrical geometry of silos. The Silo Wedge Method (SWM) distinguishes between two cases based on the aspect ratio (height/diameter) of the silo. Comparative analysis reveals that the SWM accurately matches Coulomb's Method for linear retaining walls when the silo aspect ratio approaches zero. As the aspect ratio increases above 0.25, the SWM exhibits behavior similar to Janssen's Method. This suggests a potential connection between these two classical methods across different silo geometries. The SWM consistently predicts lower lateral pressures when compared to established methods, primarily due to volumetric differences between the silo failure wedge and linear failure wedge assumptions. Key factors influencing these lower predictions, including potential earth pressure states, lateral pressure coefficients, and silo wall deformations, are suggested for further investigation. If validated through physical testing and advanced numerical modeling, the SWM could enable more accurate lateral pressure predictions, leading to material savings, cost reductions, and a lower carbon footprint in silo design and construction, while maintaining structural safety. This research contributes to a comprehensive understanding of lateral pressure calculations across different silo geometries and retaining structures.

Long fiber reinforced thermoplastic composites are used for creating lightweight, but mechanically sound, automotive components. Injection molding is a manufacturing technique commonly used for traditional thermoplastics due to its efficiency and ability to create complex geometries. Injection molding feedstock is often in the form of pellets. Therefore, fiber composites must be chopped for use in this manufacturing method. The fibers are cut to a length of 13 mm and then fiber attrition occurs during processing. The combination of chopping the fibers into pellets and fiber breakage creates a distribution of mostly short fiber lengths, with some longer fibers remaining. Discontinuous fiber reinforcements are classified as long for aspect ratios greater than 100. For glass fibers, that distinction occurs at a length of 1 mm, and for carbon fibers 0.5 mm. Traditional composite materials and manufacturing processes utilize continuous fibers with a controlled orientation and length. The use of chopped discontinuous fibers requires a method to predict the orientation of the fibers in the final molded piece because mechanical properties are dependent on fiber length and orientation. The properties and behavior of the flow of a fiber reinforced polymer composite during molding are directly related to the mechanical properties of the completed part. Flow affects the orientation of the fibers within the polymer matrix and at locations within the mold cavity. The ability to predict, and ultimately control, flow properties allows for the efficient design of safe parts for industrial uses, such as vehicle parts in the automotive industry. The goal of this work is to test material characterization techniques developed for measuring and predicting the orientation of fiber reinforced injection molded thermoplastics using commercial grade long carbon fiber (LCF) reinforced nylon 6,6 (PA 6,6). Forty weight percent LCF/PA 6,6 with a weight averaged fiber length of 1.242 mm was injection molded into center gated disks and the orientation was measured experimentally. A Linux based Numlab flow simulation process that utilizes the finite element method to model the flow and orientation of fiber reinforced materials was tested and modified to accurately predict the orientation for this composite and geometry. Fiber orientation models used for prediction require the use of empirical parameters. A method of using non-lubricated squeeze flow as an efficient way to determine the strain reduction factor, , and Brownian motion like factor, CI, parameters for short glass fiber polypropylene orientation predictions using the strain reduction factor (SRF) model was extended to use with the LCF/PA 6,6 composite. The 40 weight percent LCF/PA 6,6 material was compression molded and underwent non-lubricated squeeze flow testing. The flow was simulated using finite element analysis to predict the fiber orientation using the SRF model. The empirical parameters were fit by comparing the simulated orientation to experimentally measured orientation. This is a successful method for predicting orientation parameters that is significantly more efficient than optimizing the parameters based on fitting orientation generated in injection molded pieces. The determined orientation parameters were then used to reasonably predict the fiber orientation for the injection molded parts. The authors proved that the experimental and simulation techniques developed for the glass fiber reinforced polypropylene material are valid for use with a different, more complex material. / Doctor of Philosophy / Fibers reinforce thermoplastic polymers to create lightweight, but mechanically sound, automotive parts. Thermoplastics flow when heated and harden when cooled. This work compares two of the commonly used thermoplastics, polypropylene (plastic grocery bags, food storage containers) with a glass fiber reinforcement and a form of nylon called PA 6,6 with a carbon fiber reinforcement. Injection molding is a manufacturing technique commonly used for un-reinforced thermoplastics due to its efficiency and ability to create complicated shapes. Injection molding feedstock is often in the form of pellets. Therefore, fiber composites must be chopped for use in this manufacturing method. The fibers are cut to a length of 13 mm and then fiber breakage occurs in the injection molder. The combination of chopping the fibers into pellets and fiber breakage creates a range of lengths. This distribution consists of mostly short fiber lengths, with some longer fibers remaining. Discontinuous fiber reinforcements are classified as long for aspect ratios (the ratio of length over diameter) greater than 100. For glass fibers, that distinction occurs at a length of 1 mm, and for carbon fibers 0.5 mm. Traditional composite materials and manufacturing processes utilize continuous fibers with a controlled orientation and length, such as the weave pattern one might see in a carbon fiber hood. The use of chopped fibers requires a method to predict the orientation of the fibers in the final molded piece because mechanical properties are dependent on fiber length and orientation. The way that the plastic flows during molding is directly related to the mechanical properties of the completed part because flow affects the way that the fibers arrange. The ability to predict, and ultimately control, flow properties allows for the efficient design of safe parts for industrial uses, such as vehicle parts in the automotive industry. The goal of this work is to test the techniques developed for measuring and predicting the orientation of fiber reinforced injection molded thermoplastics using commercial grade long carbon fiber (LCF) reinforced nylon 6,6 (PA 6,6). LCF/PA 6,6 with an average fiber length of 1.242 mm was injection molded into a disk and the orientation was measured experimentally. A computer flow simulation process that utilizes the finite element method to model the flow and orientation of fiber reinforced materials was tested and modified to accurately predict the orientation for this composite and geometry. Fiber orientation models used for prediction require the use of parameters. There is no universal method for determining these parameters. A method of using non-lubricated squeeze flow as an efficient way to determine the parameters for short glass fiber polypropylene orientation predictions was extended to use with the LCF/PA 6,6 composite. The LCF/PA 6,6 material was compression molded and underwent non-lubricated squeeze flow testing. The flow was modeled to predict the fiber orientation. The empirical parameters were fit by comparing the simulated orientation to experimentally measured orientation. This is a successful method for predicting orientation parameters. The determined orientation parameters were then used to reasonably predict the fiber orientation for the injection molded parts. The authors proved that the experimental and simulation techniques developed for the glass fiber reinforced polypropylene material are valid for use with a different, more complex material.

Plasmonic polymer nanocomposites contain plasmonic nanoparticles that are dispersed within a polymer. The polymer matrix strongly influences the optical properties of plasmonic nanoparticles. It is imperative to understand the interaction between plasmonic nanoparticles and polymers so that one can develop functional devices using nanocomposites. The utilization of plasmonic nanoparticles as fillers has great potential to transform critical nanotechnologies where light management is crucial, such as refractive index based nanosensors, optical coatings, and light actuated devices. Despite the great potential, effective integration of plasmonic nanoparticles with polymers remains challenging. This dissertation presents i) the effects of dielectric media on the optical properties of plasmonic nanoparticles, ii) the sensing of polymer brush formation on nanoparticles, iii) the fabrication of plasmonic nanocomposite thin-films with controlled optical properties, and iv) the development of electrically conductive membranes for electrostatic speakers. The optical response of plasmonic nanoparticles (referred to as wavelength of localized surface plasmon resonance, λLSPR) is sensitive to changes in refractive index of the medium. The sensitivity (S) plays a critical role in determining the performance of nanoparticles in sensing applications. In this dissertation, I have conducted a systematic study on the sensitivity of plasmonic nanoparticles as a function of various parameters: shape, size, composition, initial plasmonic resonance wavelength, cross-sectional area, and aspect ratio. Among the parameters investigated, aspect ratio (R) is determined to be the key parameter that controls S, following an empirical equation, S = 46.87 R + 109.37. This relationship provides a guideline for selecting fillers in plasmonic polymer nanocomposites, and it predicts the final effect of plasmonic nanoparticles on the optical properties of polymer nanocomposites. Plasmonic nanoparticles are employed to probe polymer grafting on the surfaces of metal nanoparticles. Using ultraviolet-visible (UV-vis) spectroscopy, I have demonstrated the quantification of polymer grafting density on the surface of plasmonic nanoparticles. The λLSPR of plasmonic nanoparticles red-shifts as the polymer concentration near the nanoparticle surface increases. I have investigated the formation of polymer brush by grafting the nanoparticles with thiolated polyethylene glycol (PEG-SH) and revealed the three–regime kinetics in situ. Importantly, this study suggests that a latent regime arises due to fast polymer adsorption and prolonged chain rearrangement on nanoparticle surfaces. When the polymer chains rearrange and chemically tether to the surface, they contract and allow more polymer chains to graft onto the particle surface until saturation. This analytical method provides a new surface probing technique for polymer brush analysis, complementary to conventional methods such as quartz crystal microbalance, atomic force microscope, and microcantilivers. Commercial tinted glass employs expensive metalized films to reduce light transmittance but has limited spectral selectivity. To reduce the cost of metalized films and to improve the spectral selectivity, I have employed plasmonic nanoparticles in polymers to fabricate spectral-selective tinted films. First, I have synthesized two-dimensional (2D) plasmonic silver nanoparticles (AgNPs) using multi-step growth. The nanoparticles have a tunable plasmon resonance and provide spectral selectivity. The multi-step growth forgoes polymeric ligands such as poly(vinylpyrrolidone) (PVP) and solely relies on a small molecule sodium citrate. Briefly, small citrate-capped Ag seeds are first grown into small 2D AgNPs. The small 2D AgNPs are then used to grow large 2D AgNPs via multiple growth steps. The PVP-free method allows for fast synthesis of 2D AgNPs with large sizes and tunable plasmon resonance across the visible and NIR region. The 2D AgNPs are integrated with polymers to produce thin-film plasmonic nanocomposites. By controlling the planar orientation of the 2D AgNPs through layer-by-layer assembly, the polymer nancomposites have achieved reduced light transmittance and enhanced reflectance across the visible and NIR range. In contrast to conventional polymer nanocomposites where the AgNPs are randomly oriented, the thin-film polymer nanocomposites exhibit excellent control over nanoparticle density and hence the optical properties, that is, tunable light transmittance and reflectance across the visible and NIR. Lastly, graphene is used to prepare conductive free-standing polymer thin-films. Graphene, an ultralight weight 2D material with excellent electrical and mechanical properties, has potential for use in thin-film composites essential for photovoltaics, electrostatic speakers, sensors, and touch displays. Current graphene-based composite films contain graphene flakes randomly mixed in a polymer matrix and usually possess poor mechanical and electrical properties. In this dissertation, I have developed thin-film nanocomposites comprised of chemical vapor deposited (CVD) graphene and high-performance polyetherimide (PI). The CVD-grown graphene is polycrystalline, and it cannot be used as a free-standing film. By enforcing the polycrystalline graphene with a thin layer of PI, I have prepared free-standing thin-film composites with a high aspect ratio of 105. Mechanical and electrical property characterization reveals a Young's modulus of 3.33 GPa and a resistance of 200 - 500 Ω across the membrane. A typical spring constant of the membrane is ~387 N/m. Dynamic electromechanical actuation shows that the membrane vibrates at various input frequencies. The polymer/graphene film has excellent acoustic properties, and when used as a speaker membrane, it reduces the electrical power consumption by a factor of 10-100 over the frequency range of 600–10,000 Hz. / Doctor of Philosophy / Nanomaterials such as plasmonic nanoparticles and graphene have optical, electrical, and mechanical properties that are important for light filters, sensors, printing, photovoltaics, touch screens, speakers, and biomedical devices. To fully employ the nanomaterials, a support such as polymer is often required. However, when the nanomaterials and polymers are combined, their optical, electrical, and mechanical properties drastically change. Therefore, it is imperative to understand the interactions between nanomaterials and polymers, as well as the resulting properties. Towards this goal, I have studied the sensitivity of plasmonic nanoparticles in a dielectric media and then utilized the sensitivity to investigate polymer brush formation on nanoparticle surfaces. In addition, I have investigated the integration of plasmonic nanoparticles and graphene with polymers to develop thin-film nanocomposites for window coatings and audio speakers, respectively. Plasmonic nanoparticles can detect trace amounts of chemicals, biomolecules, toxics, warfare agents, and environmental pollutants. Sensitivity is the key criterion that determines the performance of nanoparticles for such applications. Firstly, I have conducted a detailed and comprehensive study of the plasmonic sensitivity as a function of various nanoparticle parameters including shape, size, composition, cross-sectional area, initial plasmonic resonance wavelength, and aspect ratio. I have found that the sensitivity scaled linearly with aspect ratio. The strong dependence of sensitivity on aspect ratio provides insight into designing effective plasmonic sensors. Based on the sensitivity study, I have used plasmonic nanoparticles as sensors to probe and understand the mechanism of polymer brush formation in situ. When the concentration of polymer increases on the nanoparticle surfaces, the optical response of the nanoparticle changes. Through functionalizing the plasmonic nanoparticles with polymers, I have confirmed the three different regimes of polymer brush formation. Plasmonic nanoparticles resonating in the visible and near infrared have a great potential in designing polymer nanocomposites for window coatings. Among different exotic shapes, two-dimensional nanoplates are the most important as their optical properties can be easily tuned across a wide range of wavelengths. However, most of the current methods require polymers, long hours of reaction time, and multiple purification steps. I have developed a new multi-step strategy to synthesize Ag nanoplates which absorb in the range of 500–1660 nm. Utilizing the plasmonic nanoparticles, the spectral-selective plasmonic nanocomposites comprised of polymers and planarly oriented Ag nanoparticles of judiciously selected sizes and compositions were prepared. The plasmonic polymer nanocomposites spectral-selectively reflect, scatter, and filter light of any desired wavelength. The nanocomposites will impact on the tinted glass in modern energy-efficient buildings. The outstanding electrical and mechanical properties of graphene have stirred a large volume of research in the last 15 years. Most graphene-based technologies focus on graphene at the nano or micro scale. To further the practicality of graphene in large devices like audio speakers, large areas and thin films are needed to reduce energy consumption. Graphene on its own cannot be used over large areas due to the inherent defects arising during the growth. Here I present results on combining suspended sheets of single layer graphene with a mechanically strong polymer thin film. The acoustic properties of speakers made of polymer/graphene thin films are similar to those of conventional electrodynamic speakers in modern cellphones. The energy consumption, however, reduces sharply by a factor of 10-100 for the polymer/graphene based speakers. This sharp decrease in energy is attributed to the lightweight, flexibility, and excellent electrical conductivity. Apart from speakers, the membrane designed here also has huge potential in other devices like touch panels, capacitive sensors, and photovoltaics.

Timber shear walls comprise the vertical element of the lateral force resisting system in many low-rise buildings in North America. A typical shear wall consists of a solid panel product connected to a light timber frame with either a dowel-type fastener, such as nails, or elastomeric adhesives. Shear walls vary in size, depending on their use in a structure, and sometimes contain openings for windows and doors. These changes in wall configuration have an effect on the response of shear walls. A parametric study was performed to determine the effect that aspect ratio (ratio of wall length to height) and openings have on the response of timber shear walls subjected to monotonic and seismic loading. Twenty-five shear wall models of various aspect ratios and opening configurations were created and then analyzed using WALSEIZ, a program developed by the author which utilizes finite element analysis to analyze shear wall models. The maximum resistance, initial stiffness, distribution of forces in the wall and at the reactions, and maximum relative drift (ratio of displacement at the top of the wall to wall height), seismic base shear, and velocity and acceleration at the top of the wall were recorded and examined for each model. The results from the parametric study were used to develop a modified design procedure for timber shear walls. / Ph. D.

Microcalorimetric measurements and contact angle measurements were conducted to assess the surface chemistry of the mineral talc. The contact angles were performed on both flat and powdered samples and the results were used to determine the surface free energy components and parameters (SFEC) using the acid-base theory for solids, according to the van Oss-Chaudhury-Good approach. It was found that the surface hydrophobicity of talc increases with decreasing particle size up to a limit after which hydrophilicity (polarity) increases. The increase in hydrophobicity was attributed to the increase of the delamination of the lamellar talc particles. Delamination is a comminution mechanism that preferentially exposes talc's hydrophobic basal planes, while fracture is another mechanism that breaks the lamellae, rupturing covalent bonds thus exposing more hydrophilic edge surfaces. The decrease in hydrophobicity, beyond a given particle size, could be related to the prevail of fracture over delamination during grinding which generated more hydrophilic edge surfaces. The flow microcalorymetry combined with thin layer wicking allowed the separate estimation of the SFEC at the basal plane and edge surfaces of talc. The results suggested that the basal surface of talc is monopolar basic, while the edge surface is monopolar acidic, which are in agreement with the crystal structure of the mineral. The combination of two particle size distribution techniques, which are based on different physical principles, permitted the quantitative determination of the aspect ratio of highly anisometric particles, such as talc. The same trend obtained using flow microcalorimetry was observed for the evolution of the aspect ratio as a function of particle fineness, i.e. the fracture prevails over delamination after achieving a maximum aspect ratio value of about 35. The agreement between two distinct methods was considered rather encouraging. / Master of Science

Since past more than hundred years, fluvial geomorphologists all across the globe have been trying to understand the basic phenomena and processes that control the behavioral patterns of streams. A large number of stream classification systems has been proposed till date, but none of them have been accepted universally. Lately, a large amount of efforts have been made to develop bankfull relations for estimating channel geometry that can be employed for stream restoration practices. Focusing on these two objectives, in this study a new stream classification system based on elevation above mean sea level has been developed and later using elevation as one of the independent and nondimensionalising parameters, universal and regional regime equations in dimensionless forms have been developed for predicting channel geometry at bankfull conditions. To accomplish the first objective, 873 field measurement values describing the hydraulic geometry and morphology of streams mainly from Canada, UK and USA were compiled and statistically analyzed. Based on similar mode values of three dimensionless channel variables (aspect ratio, sinuosity and channel slope), several fine elevations ranges were merged to produce the final five elevation ranges. These final five zones formed the basis of the new elevation based classification system and were identified with their unique modal values of dimensionless variables. Performing joint probability distributions on each of these zones, trends in the behavior of channel variables while moving from lowland to upland were observed. For the completion of second objective, 405 data points out of initial 873 points were selected and employed for the development of bankfull relations by using bankfull discharge and watershed variables as the input variables. Regression equations developed for width and depth established bankfull discharge as the only required input variable whereas all other watershed variables were proved out to be relatively insignificant. Channel slope equation did not show any dependence on bankfull discharge and was observed to be influenced only by drainage area and valley slope factors. Later when bankfull discharge was replaced by annual average rainfall as the new input variable, watershed parameters (drainage area, forest cover, urban cover etc.) became significant in bankfull width and depth regression equations. This suggested that bankfull discharge in itself encompasses the effects of all the watershed variables and associated processes and thus is sufficient for estimating channel dimensions. Indeed, bankfull discharge based regression equation demonstrated its strong dependence on watershed and rainfall variables. / Master of Science

In order to reduce the use of landfilling within waste management great emphasis is being placed on waste reduction and recycling. Each year in the UK approximately 2.5 Mt of waste glass is produced and approximately half of this waste is not recyclable. Therefore alternative ways need to be found for using waste glass and one possibility is to use it within concrete as a replacement for cement and/ or aggregate. In the research programme concrete mixes were tested which had 0%, 25%, 50% and 100% of the fine aggregate replaced by crushed waste glass. All glass was originally in bottle form and was crushed to produce ‘sand’ which had a grading curve more-orless identical to fine aggregate obtained from a commercial supplier. Three colours of glass were studied, i.e. flint (clear), amber and green. Concretes were also made which contained a mixture of colours (in proportion according to the weight of each type of waste glass produced annually within the UK) and also a mixture of unwashed waste glasses. The overall concrete mix adopted for investigation, i.e. 1:2:4, was selected because of its wide use within industry, and all concrete was made with a water:cement content of 0.6 without the addition of plasticiser or ASR-retarding agents. The suite of laboratory tests included; slump, flow, initial and final setting time, ultrasonic pulse velocity, water absorption by immersion and capillarity rise, ASR measurement (volumetric and linear), compression strength at ages from 7 days to 365 days. Techniques of developed digital imaging and processing have been applied to the glass aggregate to quantify various particle shape factors, i.e. aspect ratio, percentage concavity, Riley inscribed sphericity and surface texture index. Statistical analysis has been used to compare the distribution of particle forms present within the fine aggregate materials used in the experimental work. Dimensional changes (in three orthogonal directions) were measured as concrete cubes hardened over a period up to 365 days. The length changes of concrete prisms were also measured over the same period of time. The resultant data indicated that a fine aggregate which comprised 25% glass and 75% sand would be categorised as “non-expansive”, i.e. the same as the sand on its own. As the proportion of glass in the fine aggregate became greater than the aggregate became more expansive but it did not exceed recommended limits.