<p dir="ltr">Reaction zone thickness directly affects detonation properties such as detonation velocity and critical diameter. It is hypothesized that the effective reaction zone thickness is influenced by the particle size distribution and solids loading (wt.%) (solids loading) of an explosive material. In this study, we test several paste extrudable explosive (PEX) samples, to study the effects that varying particle size distribution and solids loading have on detonation properties. The PEX samples are based on four different explosives (RDX, PETN, HMX and DAAF), created by suspending explosive particles of different size distributions within an inert binder. A novel half- cone geometry is used to test the samples allowing for the capture of detonation speed (using a high-speed camera) and failure thickness data, by using the polycarbonate half-cone as a witness plate. Using this data, we create a diameter effect curve for each of the samples, allowing us to indirectly compare relative reaction zone thicknesses by measuring the slope of the linear region of the plots. Data found in open literature was compared to the PEX samples used in this study, but data was scarce. This study hopes to narrow the gap found in open literature.</p>

<div>The practice of delivering an electrical current waveform to an excitable tissue such as a structure in the brain, nerve fiber, or muscle to relieve the symptoms of disease constitutes an electrical stimulation therapy. Electrical stimulation therapies supported by implantable devices provide effective treatment options for people suffering from treatment-resistant chronic diseases that often fail to respond to medication and other traditional therapies [1, 2]. However, implantable electrical stimulators traditionally approved by the Food and Drug Administration (FDA) use implanted batteries that require surgical replacement over years of operation and limit therapies to applications with minimal constraints on implant mass, volume, and rigidity [3, 4]. Previous works have proposed to eliminate batteries in implantable stimulators by using magnetically-coupled coils to deliver energy through radio-frequency (RF) fields, exciting alternating currents on implantable devices to be converted into stimulus pulses by rectifiers [5, 6]. Implantable stimulators without batteries may be excited by an alternative theory of operation without the use of RF fields that eliminates the need for a rectifier and permits stimulators with minimal complexity.</div><div><br></div><div>This work proposes an original use of magnetically-coupled circuits theory for the wireless excitation of electrical stimulation current waveforms on passive stimulators that eliminates the need for an implanted battery. The principle of the technique is to drive stimulation current waveforms on passive stimulators with electromotive forces excited by applied time-varying magnetic fields via the phenomena described by Faraday’s law of induction [7-9]. The proposed systems require a wearable driving component and a passive driven component that may either be worn or implanted. The wearable driving component must include a battery, pulse-generating circuitry, and a primary coil, whereas the driven component is a passive device requiring only a secondary coil with electrodes to contact tissue. The pulse-generating circuitry of the driving component may be implemented readily such that the design of the coils defines the challenge in the implementation of the proposed systems. The design of the coils for the proposed systems presents the potential for a nontrivial optimization problem with conflicting objectives; possible objectives for the design of the coils include maximizing the attainable peak amplitudes of the stimulation currents, obtaining various characteristics of a desired stimulation current waveform, and minimizing the variation of the stimulation currents with varying displacements between the coils. The problem posed by the design of the coils for the proposed systems is addressed by direction obtained from theoretical analyses and experiments performed in this work that supplement direction from the literature [5, 10-12]. The potential utility of the proposed theory of operation is demonstrated by enabling the first chronic electrical stimulation therapy for glaucoma, the leading cause of irreversible blindness worldwide. The system designed for the glaucoma stimulation therapy and the methods used to quantify its electrical performance are presented along with data from experimental therapeutic trials with human participants.</div><div><br></div>

<p dir="ltr">McAlester Army Ammunition Plant (MCAAP) was established in 1943 as the U.S Naval Ammunition Depot. In World War II, MCAAP played a crucial part in supplying ammunition for the war efforts. Today, MCAAP is home to nearly 45,000 acres of land, producing almost all the bombs for the Army, Air Force, and Navy.</p><p dir="ltr">In November of 2023, the Army launched their 15-year modernization plan for their Organic Industrial Base (OIB). The plan aims to modernize facilities, processes, and the workforce to bring the OIB into the 21^st century. The Army’s OIB consists of 17 arsenals, depots, and ammunition plants, including MCAAP.</p><p dir="ltr">This thesis optimizes the operational variables of the U.S. Air Force’s Mark-84 production process at MCAAP. Using software (AnyLogic) to construct a Digital Twin of the existing process provides insights into the current operational dynamics, enabling a deep understanding of the system’s inefficiencies. Then, utilizing this understanding and the capabilities of the Digital Twin, we offer targeted recommendations for process improvement. This study aims not only to enhance the Mark-84 production process, but also to demonstrate the transformative potential of Digital Twins in optimizing manufacturing operations.</p>

<p>In this doctoral thesis work, the impacts of alternative constituent material’s impact on low-cost prepreg manufacturing for high volume applications will be considered. Unidirectional prepregs offer the potential for significant increase of specific-properties and thereby weight savings. Hence the automotive industry is seeking to utilize composite components in their design, in order to meet new fuel economy ratings and global emissions targets imposed by governments. New resin formulations to achieve 3-minute cycle times or low-cost carbon fiber manufacturing have been created to address the needs of the automotive and other cost-sensitive industries, however these innovations have led to challenges in the composites manufacturing process. Quality control issues may include variations in resin saturation of the fiber bed, consolidation, porosity, and fiber volume fraction. These quality issues arise in the part forming step or from the initial resin infiltration during prepregging.</p> <p> </p> <p>Some low-cost carbon fiber has a kidney-bean shaped cross-section which has implications on the compaction and permeability of the fiber bed. The kidney-bean shaped fibers were shown in this work to follow a different compaction trend compared to circular fibers. Furthermore, these fibers required an order of magnitude larger force to compact than circular fibers to achieve similar fiber volume fraction, which had implications on the infiltration and consolidation step. A shape correction factor based on the fiber cross-sectional aspect ratio was proposed to extend the existing compaction model to fibers with irregular cross-sectional shapes. Additionally, permeability simulations were performed on the kidney-bean shaped carbon fiber in various fiber packing unit cells. Since the kidney-bean shaped fiber had some degree of asymmetry, there are two valid hexagonal packing arrangements. At a minimum, the hexagonal packed unit cell orientation caused a 17% reduction in permeability for the same unit cell and fiber volume fraction between the <u>+</u>90° and 0° orientations. In the most extreme case, a 47% reduction in the permeability was observed between the <u>+</u>90° and 0° orientations. Depending on the fiber orientation, comparable permeabilities to circular fibers were attained or up to a 74% reduction in permeability. This means a selection of low-cost carbon fiber could cause the infiltration time to be up to 3.86 longer than for a traditional carbon fiber.</p> <p> </p> <p>The low-cost carbon fiber was paired with a rapid cure epoxy resin which contained internal mold-release to further improve part cycle times to 3-minutes and reduce part costs. The effect of polar and non-polar internal mold-release was studied for its potential influence on cure kinetics. The polar internal mold-release caused a 20 second delay in the 3-minute part cycle, which increased the cycle time by 10% and would therefore influence part production schedules. This prepreg system was reported to have prepreg quality issues related to solids filtering during infiltration. A hot-melt prepregging process was modeled for S-wrap and nip-roller configurations. The S-wrap process was found to better suited for prepregging multi-phase resins since lower pressures were used. Additionally, a general rule was established when working with multi-phase resins was established, particle diameters should not exceed fiber radii.</p> <p> </p> <p>The general design principles from the thermoset hot-melt prepregging were used to develop a thermoplastic prepreg tape line. Thermoplastic composites lend themselves to efficient manufacturing processes such as hybrid overmolding which is suitable for the automotive industry. polyamide-66/Kevlar^® prepreg tapes were manufactured at various line tensions. Neat, rubber toughened, and glass bead filled polyamide-66 based resins were considered. The neat polyamide-66 resin provided a baseline and was able to consistently saturate the fiber bed up to 400µm regardless of manufacturing conditions. The addition of rubber particles did reduce the infiltration distances from the base resin by 20% with significant a significant 50% reduction when the fiber volume fraction reached 0.70. While the addition of glass particles significantly reduced the infiltration distances by up to 70% across all manufacturing conditions. The reduction in flow distance resulted in poor infiltration in thicker fiber beds.</p>

Low-dimensional semiconductors have been intensely explored as alternative active materials for future generation ultra-scaled smart electronics. However, significant roadblocks (e.g., poor carrier mobilities, instability, and vague potential in scaling-up) exist that prevent the realization of the current state-of-the-art low-dimensional materials’ potential for energy-efficient electronics. We first time developed hydrothermal method to solution-grown two-dimensional Te, which exhibits attractive attributes, e.g., high room-temperature mobility, large on-state current density, air-stability, and tunable material properties through a low-cost, scalable process, to tackle these challenges.

Heat can be used as a reliable biomarker of cell metabolism. Assessing changes in metabolic activity is useful to study normal bioactivity or factors which may stimulate or inhibit cell proliferation. Methods which measure the heat of cell metabolism over time must be sensitive to the small changes. Thermoelectric sensors, which work by the Seebeck effect, are one method which has shown adequate sensitivity. This type of sensor directly converts heat energy into electrical energy without the use of a power source. Current research into sensors for cell metabolism may list lengthy, complex, and expensive procedures or include materials with rare or toxic elements. This work establishes a design approach of a silicon-based thermoelectric sensor for cell metabolism measurement which incorporates abundant and non-toxic materials and a simple procedure based on standard MEMS fabrication methods. The foundation for the sensor design is discussed. Fabrication was done using optical lithography, reactive ion etching, and electron beam evaporation which are standard and well known in industry. Sensor quality was characterized successfully based on the defined design parameters. Preliminary data has been recorded on the Coli cell metabolism. Finally, recommendations to improve heat insulation, include sensor calibration, and optimize manufacturing parameters are given for future work on this design to advance sensitivity and commercial potential.

<p>This dissertation, while sometimes broad in scope, attempts to tie together the author’s work with the goal of better understanding the phenomenon of explosives initiation at the mesoscale. Discussion of the need for such an investigation will be covered, including how mesoscale phenomena and the dominant theory of explosives initiation–hot spot theory–are intimately related. Furthermore, some difficulties in designing mesoscale experiments will be mentioned. Sample preparation–one of the more difficult tasks in this regime–will be covered, including single crystal growth, mechanical machining with a quasi-CNC machine, laser machining, and hacks to a tungsten wire saw for novel sample production. The author will go on to show work done in a quasi-static regime, at low strain rates, and at medium- high strain rates. These novel experiments start to show how pore collapse functions in single-crystal HMX. Additional work with thermophosphors, which may be relevant to future experiments, is also presented. New experimental diagnostics designed and constructed by the author are laid out for future reference, along with improvements to a gas gun apparatus.</p>

<p>Purdue University is facing an increasing undergraduate student enrollment every year. Laboratory courses in fluid mechanics at the School of Aeronautics and Astronautics and the School of Mechanical Engineering are facing challenges due to increased enrollments. On the other hand, the internet and computer technology have made education more conveniently delivered in recent years. The onset of these technologies has made way for innovative forms of teaching. One such application is virtual laboratories. This document will describe the challenges in the current method of teaching and learning fluid mechanics laboratory courses, explain how a virtual lab is a potential solution to supplement the current learning methods, and discuss its development. This document will discuss the virtual fluid mechanics laboratory development from the fluid mechanics perspective- generating flow data and designing realistic measurement probes. The use of CFD to generate flow data sets, along with their post-processing for virtual labs, will be discussed. Furthermore, simulation results for flow around cylinders and through pipes will be presented. And finally, design ideas conceptualized for developing a virtual pitot-static probe and a virtual hot-wire anemometer will also be presented. Finally, this document summarizes the work done till now and presents conclusions on what has been achieved along with recommendations that could be completed in the future.</p>

<p dir="ltr">Piezoelectric polymers and ceramics have applications throughout many fields, including their use as pressure sensors and transducers. Of the polymers, poly(vinylidene fluoride – trifluoroethylene) (P(VDF-TrFE)), has been the go-to for its high piezoelectric performance. With the addition of aluminum nanopowders (nAl), P(VDF-TrFE) acts as a binder and oxidizer, creating an energetic composite, a so-called piezoenergetic. However, this typically results in lower d₃₃ coefficients and can have lower reactivity since ideal mixtures may short when poled. Here, we develop and demonstrate single-layer and multilayer polymer composite films with high piezoelectric and energetic content. We prepared single-layer thin film piezoelectric energetic composites of nAl and P(VDF-TrFE) and a combination of thermal annealing and poling at elevated temperatures enabled full poling of 9 wt.% nAl/P(VDF-TrFE) films with d₃₃ of 22.7 pC/N that is comparable to P(VDF-TrFE) films. We also investigated the addition of barium titanate (BaTiO₃) particles as a piezoelectric ceramic to enhance the d₃₃ coefficient. In the neat polymer, BaTiO₃ had differing effects depending on the particle size, with 200 nm particles improving the d₃₃ coefficient more than the 1 μm particles. However, neither size of BaTiO₃ particle had a substantial effect on the piezoelectricity in the 9 wt.% nAl/P(VDF-TrFE) films. We also prepared hot-pressed, three-layer “sandwich” P(VDF-TrFE) – 30 wt.% nAl/P(VDF-TrFE) – P(VDF-TrFE) composites, which had marginally lower d₃₃ coefficients than the single-layer 9 wt.% nAl/P(VDF-TrFE) films. However, the 30 wt.% nAl/P(VDF-TrFE) sandwich films were far more energetic than the 9 wt.% nAl/P(VDF-TrFE) films, as confirmed by simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC/TGA) and deflagration studies. The single films will often fail to fully sustain a deflagration, while the sandwich films burn completely. In addition, we can ignite the sandwich samples with an electrical discharge making these films also useful in ignition applications. To demonstrate the use of piezoenergetic films, 9 wt.% nAl/P(VDF-TrFE) single layer and 30 wt.% nAl/P(VDF-TrFE) sandwich films were calibrated as pressure gauges using a mini drop weight setup, and then demonstrated as a pressure gage. The improvements in the piezoelectric coefficient of the 9 wt.% nAl/P(VDF-TrFE) single layer films, as well as the energetic performance in the form of the 30 wt.% nAl/P(VDF-TrFE) sandwich films strongly amplify the existing potential of these multifunctional composites in energetic and pressure sensing applications.</p>

<p>Vertically aligned nanocomposite (VAN) configuration has been recognized as the state-of-the-art architecture in the complex oxide epitaxial thin films, which are constructed by two immiscible phases simultaneously and vertically growing on a given substrate and forming various columnar microstructures, such as nanopillars embedded in matrix, nanomaze, and nanocheckboard. Due to its architectural features, VAN structure enables a powerful control on the multifunctionalities via vertical strain engineering, microstructural variations, and interfacial coupling. It provides flexibility in complex oxide designs with various functionalities (e.g., electrical, magnetic, optical, etc.), as well as a platform to explore the correlations between strain, microstructure, and multifunctionalities of the nanocomposite thin films.</p> <p>In this dissertation, integrated VAN systems with multilayer configuration have been constructed as a new three-dimensional (3D) framework, e.g., inserting 1-3 layers of CeO₂ (or LSMO) interlayers into the La_0.7Sr_0.3MnO₃ (LSMO)-CeO₂ VAN system and forming 3D interconnected CeO₂ (or LSMO) skeleton embedded in LSMO matrix. This new VAN 3D framework enables both lateral and vertical strain engineering simultaneously within the films and obtains highly enhanced magnetotransport properties, such as the record high magnetoresistance (MR) value of ~51-66%, compared with its VAN single layer counterpart. In order to demonstrate the flexibility of this design, other systems such as 3D ZnO framework embedded in LSMO matrix have been constructed to explore the thickness effects of the ZnO interlayers on the magnetotransport properties of the LSMO-ZnO system. The maximum MR value is obtained at the ZnO interlayer thickness of ~2 nm, which enables the optimal magnetoresistance tunneling effect. Meanwhile, the significance of the interlayer selection in the microstructure and magnetoresistance properties of the LSMO-ZnO system has been investigated by varying the interlayer materials yttria-stabilized zirconia (YSZ), CeO₂, SrTiO₃, BaTiO₃, and MgO. The formed 3D heterogeneous framework provides a new dimension to tailor the microstructure, strain and functionalities within the films.</p> <p>Moreover, a new strain engineering approach with engineered tilted interfaces has been demonstrated by multilayering different VAN layers with various two phase ratio and creating a hybrid nanodumbbell structure within the LSMO-CeO₂ VAN thin films. The nanodumbbell structure accomplishes a more efficient strain engineering and exhibits highly enhanced magnetic and magnetoresistance properties, compared with its VAN single layer and interlayer counterparts. </p> <p>These examples presented in the thesis demonstrate the flexibility and potential of 3D strain engineering in complex VAN systems and a higher level of property control, coupled with unique microstructures and interfaces. Beyond perovskites, these 3D designs can be extended to other material systems for a broader range of applications, such as energy conversion and storage related applications.</p>