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Over the last three decades, the aerospace industry has gradually shifted from metals to composites in many different applications due to the lightweight properties of composite materials. Some benefits of composites include higher strength-to-weight ratio and corrosion resistance. At this point in time, the composite industry researchers are focusing on renewable and sustainable materials (bio-composites). By understanding the structural capabilities of bio-composites that have been used for centuries, new developments of sustainable materials will spark more interest throughout the industry. Bio-composites include fibers such as hemp, bamboo, flax, etc. The high demand for bio-composites in composite structures can also reduce raw material costs. This study investigated, through experimental and numerical analysis, the mechanical behavior of sandwich panels under edgewise compressive loading. The first task of the study was to use four different facesheet materials and the same Nomex honeycomb core. The number of facesheet layers consecutively increased from one layer to four layers on each side of the core for each material. The facesheet materials used were Hexply AGP280-5H Carbon Fiber Pre-Preg, B601 Plain Weave Hemp, D118DKBR Split Herringbone Weave Hemp, and NB308T 7725 Texalium Fiberglass Pre-Preg. The sandwich panels were cured using a composite heat press and followed the recommended cure cycle for the material’s resin matrix. The variation of the facesheet materials while keeping the core consistent showed how the edgewise strength and displacement of the composite sandwiches were affected under compressive loading. The second task of the study was to try and create a multifunctional hybrid composite sandwich with two different facesheet materials; using one hemp material and one pre-preg material. The goal of this task was to try and minimize the damage occured upon failure. Being that the pre-preg materials are more brittle than the hemp material, the hybrid composite sandwiches can potentially create a superior composite structure. The sequence of stacking of the facesheet materials was manipulated to study how changing the outer and inner layers affected the results. All the specimen were loaded at a rate of 0.05 in/min in a steel jig specifically made per ASTM C364 standard using an Instron 8801 to determine the mechanical behavior. These experimental results combined with results from theoretical and finite element analysis using Matlab and Abaqus, respectively, were used to compare composite sandwich designs under compressive loadings. Failure mode comparison between the individual material composites and the hybrid composites were also discussed.

The goal of this effort was to build an analysis tool for aircraft wings and incorporate it into a program that optimizes the wing structure for the lowest weight for the conceptual design phase. The analysis tool calculates the internal stresses in primary load carrying members using established analysis methods for semimonocoque beams. Via a Graphical User Interface (GUI) built in MATLAB, the user can define the structural layout and material properties of the load carrying members. The program requires a degenerate geometry model built with Vehicle Sketch Pad (OpenVSP) to define the outer mold line (OML) of the wing, and a section of the program in MATLAB calculates the geometric parameters of the wing structure based on the model and user inputs in the GUI. Another section generates a lift curve using a Schrenk distribution, the vehicle weight, and load factors as defined by the user. The GUI also allows the user to define other external loads in addition to the aerodynamic loads. With the loads and structural model defined, the program uses the analysis tool to find a minimum structural weight while maintaining positive structural margins for all structural members. The analysis tool was compared against examples in structural analysis books from Bruhn and Peery to validate the method. The average relative difference between the normal and shear stresses calculated by the tool and the sources was 1.6%. To test the program, a Cessna 210G wing was modeled in the program and using Finite Element software. The comparison showed the tip deflection of the MATLAB model was 1.4 times that of the Finite Element Model. When the areas of the structural members were multiplied by 1.4, the normal stress in the stiffeners had an average difference of 5.8 ksi and the shear stresses in the webs had an average difference of 0.33 ksi. The program estimated the weight to be 198 lbs, underestimating the weight when compared to other existing methods.

In this dissertation, we present work on the first-principles informed phenomenological modeling of the optical properties of materials. We use density functional theory and time-dependent density functional theory calculations to inform parameterized models of the response to light in materials. We include the effect of ultrafast nonequilibrium effects, as well as the importance of quantum mechanical lattice vibrations. Using these models, we validate the approaches, and predict the effect of both ultrafast phenomena as well as quantum mechanical vibrations on the optical properties of bulk and 2D materials. Such modeling opens up avenues for efficient phenomenological approaches to describing optical phenomena in materials while keeping the accuracy of first-principles simulations.

In this dissertation, I present methods to improve the sensitivity and specificity of Silicon nanowires field-effect transistors (SiNWs FETs)-based biosensors. Our detection mechanism is based on ion-sensitive field-effect transistors (ISFET) and biosensor field-effect transistors (bioFET), allowing chemical ion and protein biomarker concentrations to be monitored in physiologically relevant solutions, such as 1x PBS buffer solutions. Our results have important implications and applications in fundamental sciences, environmental monitoring, disease diagnosis, drug discovery, pharmacology, and medicine. SiNWs FETs aroused great attention in the past few years due to their unique characteristics, such as high surface-to-volume ratio, sensitivity, mechanical strength, and stability in solutions. However, their major limitation is to detect the biomarkers in the high-salt buffer environments, such as 1x PBS, human serum, or whole blood. The sensing scheme is that the binding of charged entities such as protein or DNA biomolecules onto the nanowire surface (applying a top gate voltage) will induce a field-effect, therefore a change in the conductance of the semiconducting SiNWs underneath in which SiNWs act as the conductance channel between the source and drain of FET device. The difference in conductance provides valuable information on the selective binding of the biological target analyte species to their covalently linked counterparts on the nanowire surface. The experimental part of this dissertation presents the experimental details, a newly designed top-down wafer fabrication process with scalable manufacturing enabled, the optimized parameters for sequential processes were chosen to produce a complete silicon nanowire (down to 50 nm wire width) measurement circuit on silicon on insulator (SOI) wafers. I also refined the surface functionalization chemistry recipes for improved performance. The results show that after surface functionalization including salination, SiNWs FETs biosensors can be used as efficient and sensitive pH sensors. After the application of an external electric field on the side-gate field pads, there is a growing dipolar separation due to the increasing DC electric field which causes a better signal-to-noise ratio and higher conductance. A new biomarker sensing technique using RF electric field has been developed for the detection of protein biomarkers in the frequency domain. The RF signals have a clear biomarker concentration dependence and RF signals from the biomarkers are easily distinguishable from the control groups. Lastly, the results after the application of DC superimposed AC electric field show a slight shift in the concentration sensitive region and DC offset enhances the signals in the concentration range of interest. Our results provide further insights into overcoming the Debye length limitations of SiNWs FETs biosensors, bringing the real-time, label-free, high-selectivity, and high-specificity silicon nanowire-based biosensor platforms one step closer to being realized for Point-of-Care (POC) medical healthcare applications. / 2029-05-31T00:00:00Z