<div> <p>Due to harsh environmental conditions, the deterioration of prestressed concrete bridge girders is a commonly observed phenomenon in Indiana and much of the Midwest. Concordantly, one widely observed damage scenario is deteriorated end regions of prestressed concrete girders. Damaged or failed expansion joints expose prestressed concrete girder end regions to chloride-laden water, resulting in a corrosive environment in which reinforcement section loss and concrete spalling can occur. For bridges experiencing this type of deterioration, action is needed to ensure the structure remains safe and serviceable. As such, an experimental program was developed to investigate the effectiveness of three repair techniques in restoring the structural behavior of prestressed concrete bridge girders with end region deterioration. The three examined repair techniques are (i) an externally bonded fiber reinforced polymer (FRP) system, (ii) a near-surface-mounted (NSM) FRP system, and (iii) a concrete supplemental diaphragm. Additionally, installation procedures for the three end region repair techniques were developed. Results, conclusions, and recommendations from the experimental program are presented to help advise best practices for implementing end region repair techniques in the field. </p> </div> <br>

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis provides an approach to incorporate natural composites like Flax Fiber using a resin with 30% bio-content to enhance the packaging boxes made of corrugated cardboard. The objective of introducing natural composite skins is to reduce/eliminate the compressive loading subjected to the boxes while stacking in warehouses.

No description available.

[pt] Materiais compósitos pultrudados poliméricos reforçados com fibra de vidro (PRFV) são aplicados em diversos setores da indústria por apresentarem boas resistências mecânicas, baixo peso específico e alta resistência à corrosão. A exposição a ambientes agressivos tais como imersão em água, condicionamento sob alta umidade relativa, temperatura baixa e elevada, ciclos térmicos e úmidos, bem como a combinação desses efeitos, tornou-se cada vez mais objeto de estudo para esses tipos de materiais. A compreensão dos efeitos das condições ambientais no comportamento do material é essencial para avaliar seu desempenho e, desta forma, garantir a segurança necessária ao projeto estrutural. Com o objetivo de compreender melhor a influência de diferentes condições ambientais nas propriedades do material compósito PRFV, foram estudados os efeitos da temperatura e umidade, além da ação combinada dessas duas condições, nas suas propriedades físicas, químicas, térmicas e mecânicas. Neste estudo, foram levados em conta aspectos importantes que influenciam o comportamento do material, como a resina utilizada, o grau de cura, e características químicas e físicas do material. Os ensaios experimentais foram conduzidos em quatro condições ambientais: (i) exposição a temperaturas moderadas/elevadas (70 graus C à 330 graus C), (ii) imersão em água deionizada (25 graus C, 55 graus C e 70 graus C), (iii) exposição à névoa salina em câmaras de envelhecimento higrotérmico (35 graus C, 55 graus C e 70 graus C), e (iv) exposição a ambiente externo real. Além disso, foram aplicados modelos teóricos para avaliação dos resultados. Foi observado que a temperatura, o tempo de condicionamento e a umidade são fatores preponderantes no comportamento do material. Adicionalmente, uma questão importante para o estudo de pultrudados reside na compreensão das propriedades interlaminares do material. Nesse contexto, a fratura interlaminar, associada às fissuras no plano longitudinal entre as camadas do material, é uma das principais causas de falha em compósitos pultrudados. Consequentemente, a análise da fratura em modo II, que avalia o mecanismo da propagação da fissura no plano interlaminar, vem ganhando espaço no estudo de materiais compósitos. A análise de fratura em modo II não é trivial ou normatizada para compósitos pultrudados PRFV, de forma que poucos dados e conclusões efetivas foram obtidos até o momento a esse respeito. Com o objetivo de suprir essa lacuna, realizou-se uma extensa investigação experimental, culminando na proposição de uma nova metodologia para avaliação da fratura em modo II em materiais compósitos poliméricos pultrudados reforçados com fibra de vidro (PRFV). / [en] Pultruded glass-fiber reinforced polymer (GFRP) composites are applied in various industrial sectors due to their good mechanical strength, low specific weight, and high resistance to corrosion. Exposure to aggressive environments has become an increasingly studied topic for these materials, such as immersion in water, conditioning under high relative humidity, low and high temperatures, thermal and humid cycles, as well as the combination of these effects. Understanding the effects of environment condition on material behavior is essential to evaluate its performance and ensure the necessary safety for structural design. In order to better understand the influence of environmental conditions on the properties of GFRPs, the effects of temperature and humidity, as well as the combined action of these two effects, on their physical, chemical, thermal, and mechanical properties were studied. Important aspects that influence the material s behavior were considered, such as the resin used, the degree of curing, and the chemical and physical characteristics of the material. Experimental tests were conducted under four environmental conditions: (i) exposure to moderate/high temperatures (70 degrees C to 330 degrees C), (ii) immersion in deionized water (25 degrees C, 55 degrees C, and 70 degrees C), (iii) exposure to salt spray in hygrothermal aging chambers (35 degrees C, 55 degrees C, and 70 degrees C), and (iv) exposure to real outdoor environment. In addition, theoretical models were applied to evaluate the results. It was observed that temperature, conditioning time, and moisture are predominant factors in material behavior. Additionally, a important issue for the study of pultruded composites lies in understanding the interlaminar properties of the material. In this context, interlaminar fracture, associated with longitudinal cracks between the layers of the material, is one of the main causes of failure in pultruded composites. Consequently, mode II fracture analysis, which evaluates the mechanism of crack propagation in the interlaminar plane, has been gaining ground in the study of composite materials. Mode II fracture analysis is not trivial or standardized for pultruded GFRP composites, so few data and effective conclusions have been obtained in this regard so far. In order to fill this gap, an extensive experimental investigation was carried out, culminating in the proposal of a new methodology for evaluating mode II fracture in pultruded GFRPs.

<p>This investigation delineates the optimal synthesis and characterization of innovative epoxy-carbon nanotube (CNT) nanocomposite filaments via electrospinning. Electrospinning thermosetting materials such as epoxy resins presents significant challenges due to the polycationic behavior arising from intermolecular noncovalent interactions between epoxide and hydroxyl groups, resulting in a substantial increase in solution surface tension. In this study, electrospinning submicron epoxy filaments was achieved through partial curing of epoxy via a thermal treatment process in an organic polar solvent, circumventing the necessity for plasticizers or thermoplastic binders. The filament diameter can be modulated to as low as 100 nm by adjusting electrospinning parameters.</p> <p><br></p> <p>Integrating a minimal amount of CNT into the epoxy matrix yielded enhanced structural, electrical, and thermal stability. The CNTs were aligned within the epoxy filaments due to the electrostatic field present during electrospinning. The modulus of the epoxy and epoxy-CNT filaments were determined to be 3.24 and 4.84 GPa, respectively, resulting in a 49% improvement. Epoxy-CNT nanofibers were directly deposited onto carbon fiber reinforced polymer (CFRP) prepreg layers, yielding augmented adhesion, interfacial bonding, and significant mechanical property enhancements. The interlaminar shear strength (ILSS) and fatigue resistance demonstrated a 29% and 27% increase, respectively, under intense stress conditions. Up to 45% of the Barely Visible Impact Damage (BVID) energy absorption was increased. In addition, the strategic incorporation of CNT (multi-walled) networks between the layers of CFRP resulted in a significant increase in thermal and electrical conductivities.</p> <p>This study also introduces a scalable fabrication procedure to address large volume processing, reproducibility, accuracy, and electrospinning safety. Electric fields of the experimental multi-nozzle setups were simulated to elucidate the induced surface charges responsible for the Taylor cone formation of the epoxy-CNT solution droplet on the nozzle tips. Electrospinning parameters were subsequently optimized for the multi-nozzle system and analyzed alongside simulated data to improve stability and synthesize fibers with smaller diameters.</p> <p><br></p> <p>Smaller diameter epoxy-CNT nanofibers proved critical as CNTs maintained alignment within the nanofibers when compared to larger diameter nanofibers. This research examines the impact of effective parameters on the diameter of electrospun epoxy-CNT nanofibers using artificial neural networks (ANNs). Consequently, employing a genetic algorithm (GA) and Bayesian optimization (BO) methods enable accurate prediction of epoxy-CNT nanofiber diameters prior to electrospinning. The presented models could aid researchers in fabricating electrospun thermosetting and thermoplastic scaffolds with specified fiber diameters, thereby tailoring these scaffolds for specific applications.</p>

No description available.

Magnetic nanoparticles that display high saturation magnetization and high magnetic susceptibility are of great interest for medical applications. Nanomagnetite is particularly desirable because it displays strong ferrimagnetic behavior, and is less sensitive to oxidation than magnetic transition metals such as cobalt, iron, and nickel. Magnetite nanoparticles can be prepared by co-precipitating iron (II) and iron (III) chloride salts in the presence of ammonium hydroxide at pH 9-10. One goal of this work has been to develop a generalized methodology for stabilizing nanomagnetite dispersions using well-defined, non-toxic, block copolymers, so that the resultant magnetite-polymer complexes can be used in a range of biomedical materials. Hydrophilic triblock copolymers with controlled concentrations of pendent carboxylic acids were prepared. The triblock copolymers contain carboxylic acids in the central urethane segments and controlled molecular weight poly(ethylene oxide) tail blocks. They were utilized to prepare hydrophilic-coated iron oxide nanoparticles with biocompatible materials for utility in magnetic field guidable drug delivery vehicles. The triblock copolymers synthesized contain 3, 5, or 10 carboxylic acids in the central segments with Mn values of 2000, 5000 or 15000 g/mol poly(ethylene oxide) tail blocks. A method was developed for preparing ~10 nm diameter magnetite surfaces stabilized with the triblock polymers. The carboxylic acid is proposed to covalently bind to the surface of the magnetite and form stable dispersions at neutral pH. The polymer-nanomagnetite conjugates described in this thesis have a maximum of 35 wt. % magnetite and the nano-magnetite particles have an excellent saturation magnetization of ~66 - 78 emu/g Fe3O4. Powder X-ray diffraction (XRD) confirms the magnetite crystal structure, which appears to be approximately single crystalline structures via electron diffraction spectroscopy analysis (EDS). These materials form stable magnetic dispersions in both water and organic solvents. / Ph. D.

The Tom's Creek Bridge is a small-scale demonstration project involving the use of fiber-reinforced polymer (FRP) composite girders as the main load carrying members. The project is intended to serve two purposes. First, by calculating bridge design parameters such as the dynamic load allowance, transverse wheel load distribution and deflections under service loading, the Tom's Creek Bridge will aid in modifying current AASHTO bridge design standards for use with FRP composite materials. Second, by evaluating the FRP girders after being exposed to service conditions, the project will begin to answer questions about the long-term performance of these advanced composite material beams when used in bridge design. This thesis details the In-Service analysis of the Tom's Creek Bridge. Five load tests, at six month intervals, were conducted on the bridge. Using mid-span strain and deflection data gathered from the FRP composite girders during these tests the above mentioned bridge design parameters have been determined. The Tom's Creek Bridge was determined to have a dynamic load allowance, IM, of 0.90, a transverse wheel load distribution factor, g, of 0.101 and a maximum deflection of L/488. Two bridge girders were removed from the Tom's Creek Bridge after fifteen months of service loading. These FRP composite girders were tested at the Structures and Materials Research Laboratory at Virginia Tech for stiffness and ultimate strength and compared to pre-service values for the same beams. This analysis indicates that after fifteen months of service, the FRP composite girders have not lost a significant amount of either stiffness or ultimate strength. / Master of Science

Roller conveyors are critical components in various industries for material handling, enabling the efficient transportation of items in assembly lines, warehouses, and distribution centers. Traditionally constructed from materials such as steel, aluminum, or plastic, roller conveyors are now being innovatively designed using composite materials. This study investigates the design, analysis, and optimization of roller conveyors utilizing composite materials to achieve weight reduction while maintaining or enhancing structural integrity and operational efficiency. Composite materials offer enhanced properties compared to their individual components. Typical composites include fibers like carbon, glass, or aramid within a matrix of epoxy resin, providing superior strength, corrosion resistance, and customization capabilities. The research employs finite element analysis (FEA) and other advanced modeling techniques to evaluate the performance of composite roller conveyors under various loading conditions. The findings suggest that using composite materials can significantly reduce the weight of roller conveyors, leading to decreased energy consumption, lower operational costs, and improved handling efficiency. The optimized design enhances productivity and contributes to sustainability by minimizing environmental impact. This thesis advances the understanding of composite-based roller conveyors, demonstrating their potential to replace conventional materials and achieve higher efficiency in industrial applications.

Yes / To investigate the shear performance of poplar laminated veneer lumber (LVL) beams with holes in bending-shear spans, six specimens were designed and tested by four-point bending tests. Among these, five specimens were provided with a single hole of varying diameter-to-height ratio in the bending-shear span and two of these beams were also reinforced with circumferential carbon fiber reinforced polymer (CFRP) wrap layers. Furthermore, a 3D finite element models for poplar LVL beams with a hole were established, based on the extended finite element method (XFEM) using ABAQUS software. The validated model was utilized to conduct parametric studies on the diameter-to-height ratio, the hole shape, and the vertical eccentricity ratio. A simplified theoretical analysis for predicting the cracking and ultimate loads for LVL beam with a hole was also proposed. The results indicated that beams without a hole failed due to bending, characterized by mid-span tension cracks, whereas beams with a hole exhibited shear failure along the beam's grain direction due to stress concentration around the holes. The maximum normal tensile strain perpendicular to grain around the hole had an angle of 45° or 225° relative to the beam's longitudinal axis, consistent with the crack initiation angle. As the diameter-to-height ratio increased, the cracking and ultimate loads of beams with a hole decreased, indicating more brittle failure characteristics. The circular hole beam showed significant improvements in cracking and ultimate loads compared with the square hole beam with side length equal to the diameter of the circular hole. When the hole center's vertical eccentricity was in the compression zone, an increase in vertical eccentricity led to enhancements in both the cracking load and ultimate loads. Wrapping the beam with CFRP sheet around the hole effectively mitigated crack propagation, enhancing the load-bearing capacity of beams. The simplified formulas provided accurate prediction for the ultimate load, but highly overestimated the cracking and ultimate loads for poplar LVL beams with a hole. The research findings can be provided as a technical support for the design and application of LVL beams with holes. / The full text will be available at the end of the publisher's embargo: 13th Nov 2025