Theses/Dissertations - Mechanical Engineering

Permanent URI for this collectionhttps://hdl.handle.net/2104/4817

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Comprehensive experimental investigation of liquid piston gas compression for energy storage applications.
(2023-12) Ahn, Barah, 1992-; Ro, Paul I.
A liquid piston gas compressor can alleviate the efficiency issue of a conventional compressed air energy storage system by realizing a near-isothermal compression process due to its capability to incorporate heat transfer enhancement techniques. In this work, a range of heat transfer enhancement techniques is experimentally examined under various conditions. To explore the possibility of further efficiency improvement of the spray injection technique, two different approaches are taken: integrating a metal wire mesh insert and using an air atomization nozzle. With a mesh insert, the possible best condition of each technique does not always lead to the highest isothermal performance because droplet heat transfer is compromised by the existence of the insert. Even though air atomization spray can generate fine droplets, the addition of air accelerates the pressure increase during the compression, which results in a rapid decline of the spray effectiveness. To evaluate the actual applicability, the liquid piston and heat transfer enhancement techniques are evaluated at various pressure levels. The baseline compression is performed at three different initial pressures of 1, 2, and 3 bars with a pressure ratio of 2. A higher-initial pressure leads to a decreased isothermal efficiency. With the gas dissolution considered, the impact of the initial pressure level on an actual efficiency is expected to be greater than what can be observed with the computed efficiency values. Under the same pressure conditions, the use of the spray injection boosts the isothermal efficiencies to 98 – 98.5%. However, with the gas dissolution and spray work input considered, the overall efficiencies are substantially lower than the computed isothermal efficiencies, and this trend is more significant at a higher-pressure level. Aqueous foam and metal wire mesh inserts are evaluated under the same pressure conditions. For both techniques, the results show a consistent trend that a higher-initial pressure leads to a lower isothermal efficiency. In addition, a comprehensive comparative study of the spray injection, aqueous foam, and a metal wire mesh insert is performed based on the experimental results and their working mechanisms.
Air entrainment dynamics of droplet impact on thin films : from Newtonian to non-Newtonian fluids and its applications.
(2023-12) He, Ziwen, 1995-; Pack, Min Y.
Drop impacts on thin liquid films are commonplace in various natural and industrial contexts. Before a droplet can wet solid or liquid surfaces, it’s imperative that the layer of surrounding fluid (typically air) separating the two interfaces ruptures. Recent studies, revealed by advanced optics, have delineated the relationship between micrometer-thick intervening air layers and the dynamics of millimetric droplet impacts. In this investigation, we delve into the interrelationship between the air layer and the characteristics of the impacting droplets, encompassing both Newtonian and non-Newtonian fluids. We embark with an exploration of Newtonian fluid droplet impacts. Chapter Two focuses on the deformability of thin liquid film with varying thicknesses (hL ∼ O(10^0 µm) − O(10^2 µm)). This flexibility is deformability in ascertaining the outcomes of droplet impacts by mediating air drainage dynamics. In Chapter Three, we transition to the examination of the role played by vapor pressure in the impacts of volatile droplets on thin viscous oil films hL ≈ 2 µm. This leads to the discovery of a bifaceted wetting behavior for acetone-IPA mixture droplets. In Chapter Four, our focus shifts to polymeric droplets spanning from dilute to semi-dilute unentangled regimes when impacting thin viscous oil films. Here, a conspicuous correlation emerges between polymer concentration and air film morphologies. Chapter Five broadens the scope to assess the influence of non-Newtonian flow properties on droplet impact dynamics. This includes investigations into capillary wave generation and progression, and the central collapse mode induced by the capillary waves. To conclude, this study provides a comprehensive study on air layer dynamics during droplet impacts, bridging Newtonian to non-Newtonian fluids. Our research elucidates the onset of wetting but offers promising outcomes that might be leveraged as innovative tools for examining polymer rheology. This is a pivotal component for scenarios involving non-Newtonian droplet impacts.
Establishing the process-structure-property-performance relationship and viable repair pathways for expeditionary airfield surfacing systems.
(2023-08) Kinser, Ryan P., 1996-; Allison, Paul Galon, 1981-; Jordon, J. Brian (James Brian), 1979-
Expeditionary airfield (EAF) surfacing systems, or airfield matting, have enabled the operation of aircraft in austere environments for over eight decades. However, there is a need to evaluate newly proposed and legacy EAF systems to establish compatibility with current and next-generation aircraft. Furthermore, due to logistical issues, there is a need for improving sustainability of EAF systems once deployed in theater. As such, the overall objective of this research seeks to establish a process-structure-property-performance (PSPP) relationship of EAF surfacing systems to enable characterization and performance predictions for legacy and next-generation designs while evaluating repair pathways that can be performed onsite at the Point-of-Need. This first objective of this present work was to determine failure mechanisms within an EAF surfacing prototype system to establish fundamental links between manufacturing processes and mechanical performance under full-scale trafficking experiments. Local numerical simulations and analytical techniques were integrated into the root-cause analysis to illuminate causes of failure and potential pathways for improvement, compare and contrast with legacy failure modes, and generalize findings for other metallic EAF systems. The second objective of this research focused on developing a global EAF framework in which full-scale arrays of matting can be modeled and the response to static aircraft loads can be analyzed in a manner consistent with full-scale trafficking experiments. Flexural and shear anisotropy in the mat core and non-linearity in the interlocking joints is integrated into the framework to provide flexibility to accommodate other matting systems. Additional comparisons with experimental data ensure reasonable fidelity within the developed framework. The third objective of this research was to couple the global modeling framework to performance models based on global and local boundary conditions such as lay pattern, subgrade strength, gear load, and end connector geometry. Emphasis was placed on model efficiency and fidelity across a wide range of subgrade CBRs while retaining sufficient flexibility to accommodate other systems. Additional comparisons with experimental data support the robustness of the predictive framework. Finally, the fourth objective was to investigate a novel repair approach for EAF surfacing systems. This solid-state additive manufacturing (AM) and repair method can be implemented with minimal infrastructure once an EAF surfacing system has been damaged or rendered failed. Particular focus was placed on reducing time at elevated temperatures and increasing the cooling rate in the deposited material and underlying substrate to mitigate deleterious precipitation coarsening effects.
Designing and testing unloaded-tip propellers for improved efficiency and reduced noise.
(2023-08) Day, Ryan S., 1998-; Van Treuren, Kenneth W.
Propellers are currently experiencing a resurgence in interest as propulsion systems on novel aircraft. This thesis examines novel unloaded-tip propeller designs on the basis of efficiency and noise using a new static propeller test stand. 13” diameter propellers with unloaded tips were manufactured from different materials to assess the influence of blade stiffness on propulsive and acoustic performance. Larger, 21” propellers were also designed and manufactured to examine the acoustic and propulsive effects of the unloaded- tip design with new airfoil combinations. Both 13” and 21” blade series were compared to corresponding commercial baseline designs. The 13” blade tests demonstrated that the unloaded tip design is capable of superior efficiency with only a weak dependance on stiffness. 21” tests revealed that the unloaded-tip design reduces near-field noise while maintaining competitive efficiency. A parametric study of unloaded-tip designs with new or hybrid airfoil sections is recommended.
Development of a diamagnetically stabilized magnetically levitated gravimeter.
(2023-08) Rafiq, Kazi Rifat Bin, 1996-; Yokochi, Alexandre F.T.
The aim of this work is to create a new type of gravimeter that can function effectively in the challenging conditions of space, specifically on the surfaces of planets and moons. The proposed device, called a diamagnetically stabilized magnetically levitated gravimeter (DSMLG), uses magnetic forces to balance a test mass against the force of gravity, allowing for accurate measurements. A diamagnetically stabilized levitation structure comprises a floating magnet, diamagnetic material, and a lifting magnet. The floating magnet levitates between two diamagnetic plates without the need for external energy input due to the interaction between the magnetic forces of the floating magnet and the stabilizing force of the diamagnetic material. This structure allows for stable levitation of the floating magnet without requiring additional energy. The goal is to design a gravimeter that is lightweight, requires minimal power, can withstand extreme temperatures and shocks, and has a low data rate. The authors envision this gravimeter being used on various robotic spacecraft, such as landers and rovers, to study the interiors of rocky and icy celestial bodies.
Understanding the process-structure-property relationship of lightweight aerospace alloys processed using additive friction stir deposition.
(May 2023) Williams, Malcolm B., 1996-; Jordon, J. Brian (James Brian), 1979-; Allison, Paul Galon, 1981-
Recently additive manufacturing has become an alternative method to fabricate components with forged-like properties and reduced lead times when compared to traditional manufacturing methods. However, some fusion-based additive manufacturing methods create deleterious effects, such as hot cracking and alloy vaporization, on the mechanical performance of lightweight aerospace alloys. A novel solid-state additive manufacturing process, known as Additive Friction Stir Deposition (AFSD), offers the ability to combat these deleterious effects by fabricating fully dense components with forged-like properties in lightweight alloys. This research investigates the process-structure-property (PSP) relationship of magnesium alloy WE43 and aluminum alloy 7020, through in-depth characterization of the resulting microstructure and mechanical properties post AFSD processing. The first work on the PSP relations of AFSD processed magnesium alloy WE43 is focused on the microstructural evolution of the as-deposited WE43 in comparison to forged feedstock. Additionally, mechanical performance was evaluated between the forged feedstock and the as-deposited WE43 to elucidate the role of microstructure on the mechanical properties with particular interest in the quasi-static and fatigue performance of each method of manufacturing. The subsequent research on AFSD of AA7020 investigates the microstructural evolution and mechanical performance of the as-deposited AA7020 in comparison to wrought AA7020 feedstock. Additionally, the strain-rate effects and cyclic behavior were assessed between the feedstock material and the as-deposited AA7020 to determine the effects of the microstructural evolution during the AFSD process on the monotonic and fatigue properties. Particular interest was focused on quantifying the as-deposited layer dependence and failure mechanisms from the resulting monotonic and cyclic loading experiments compared to the wrought material. The final work establishes a fundamental relationship between acceptable process parameters and build direction mechanical properties on AFSD processed AA7020. Additionally, the effect of process parameters on the microstructural evolution of the AFSD AA7020 was investigated. An emphasis on failure mechanisms of select parameters to elucidate the role of processing conditions on the mechanical performance was assessed to achieve depositions with isotropic behavior.
Investigation of parallel deposition passes on the microstructure and mechanical properties of a high-strength aluminum alloy processed with AFSD.
(May 2023) Cahalan, Logan P., 1998-; Jordon, J. Brian (James Brian), 1979-; Allison, Paul Galon, 1981-
Additive manufacturing (AM) provides a unique solution to quickly develop prototype components and produce features with complex geometries. Additive Friction Stir Deposition (AFSD) is a solid-state method of metal AM that produces near-net shape depositions with high deposition rates. As AFSD is utilized for a broader range of applications, there is a need to understand strategies for larger and more complex depositions. Depositions with a larger surface area would require a certain amount of material mixing between deposition passes within a single layer. In this study, the AFSD process was used to create depositions utilizing a varying deposition path overlap width (OW) and the effects of overlapping parallel pass depositions on the mechanical and microstructural properties of aluminum alloy 7075 (AA7075) were examined. An ideal OW value is found that produced acceptable post-deposition material properties while considering the increased resource consumption necessary to produce a build using a higher OW.
Applications of the wavelet synchrosqueezed transform for ultrasonic inspections : quantifying layer height and visualizing missing extrudates in material extrusion printed samples and visualizing wrinkles in carbon fiber laminates.
(May 2023) Battershell, Luke William, 1998-; Jack, David Abram, 1977-
In the aerospace industry there is a push to find uses for additively manufactured components with the goal of taking advantage of the increased freedom of design that it allows. Material extrusion, specifically fused filament fabrication (FFF), is one of the most prevalent methods for additive manufacturing currently used in industry. Currently the main use of additive manufacturing in the aerospace industry is for use in rapid prototyping. To move from that to functional use, additively manufactured components need to be inspectable. This thesis aims to improve existing inspection methods for material extrusion printed components by introducing the use of the wavelet synchrosqueezed transform (WSST) in the analysis of ultrasonic testing (UT) inspection data. The proposed method uses the WSST to quantify layer height and visualize missing extrudate. The method for quantifying layer height was extended to the visualization of wrinkles in carbon fiber laminates which are commonly used in the aerospace industry.
Characterization of sub-surface wrinkles within a laminated composite using a novel phased array ultrasonic scanning technique incorporating a portable nozzle and robotic arm.
(May 2023) Khan, Irrtisum, 1993-; Jack, David Abram, 1977-
Due to their superior strength to weight ratio as compared to metals, the use of laminated composites is growing in the aerospace, automotive and energy sectors. This increased performance is severely compromised by the presence of out-of-plane wrinkles, a manufacturing defect that occurs in thick complex curvature composite stacks. This thesis presents an ultrasound scanning technique utilizing a novel phased array approach to detect out-of-plane wrinkles and, unlike previous literature results, quantify wrinkle dimensions. Multiple nozzle designs are provided for phased array probes to improve portability and scanning setup. A robotic system is presented that incorporates the novel scanning technique, which allows inspection of parts with non-planar geometries. The measured quantities are validated using 𝜇-CT scans, and results are provided that show average relative errors of 8.33%, 22.79% and 9.72% for, respectively, wrinkle height, width, and intensity corresponding to an average absolute error of, respectively, 0.057mm, 1.59mm and 4.7 × 10−3 .
Stability analysis and robust control of human intention-based physical human-robot interaction.
(May 2023) Chen, Jingdong, 1992-; Ro, Paul I.
Two main challenges that need to be addressed in physical human-robot interaction (pHRI) are efficient recognition of human intention and interaction safety. Human intention adaptation is usually realized by changing admittance parameters according to human interaction in physical human-robot interaction (pHRI). However, admittance parameters inferred from human intention may result in instability. This dissertation conducts a fundamental and systematic study on variable admittance control for assistive pHRI considering human intention adaptation, system passivity, and system stability. Human-intention-governed variable admittance control (VAC) is applied under a general human intention framework to shape the mechanical admittance to desired interaction. For the changing trends of these parameters (i.e., increasing or decreasing), those impacting system passivity are studied. A power envelope regulation (PER) concept is then proposed to impose constraints on variable admittance parameters inferred from human intention to maintain safe interaction and to preserve system passivity. It allows drastic changes in admittance controller dynamics, which usually result in instability, to be restrained. Our initial results suggest that the passivity condition is a necessary condition for system stability in pHRI. To yield stable and robust performance of VAC, a new sliding mode control (SMC) strategy is proposed. A universal sliding surface, regardless of the order of admittance equation, is defined first, and its validation in realizing desired variable admittance is theoretically proved. The reachability and robustness of the proposed controller are proved based on Lyapunov stability for VAC. Then, a trade-off between chattering removal and tracking performance is achieved by developing a new variable-boundary approach. Furthermore, acceleration feedback is applied to the proposed controller to improve robustness and tracking performance further. For human-leading case, the developed method in this dissertation yields an average 0.0035 m/s deviation on velocity tracking with 7% outliers (maximum deviation is 0.021 m/s) compared with 0.0664 m/s for conventional SMC method. The robustness of the proposed controller is verified by modifying the modeling error of the most distal link’s mass higher than 200%. The effectiveness of the proposed methods and the theoretical derivation are validated via numerical simulation and experiments on a manipulator in a 3-degree-of-freedom (DoF) planar configuration.
Performance of chillers under variable operating conditions and the effectiveness of energy recovery via enthalpy wheels for building applications.
(August 2022) Gerrard, Nicole M., 1996-; O'Neal, Dennis.
The in-situ performance of the chillers and energy recovery via enthalpy wheels in air handling units in the HVAC system in the Baylor Research and Innovation Collaborative (BRIC) were evaluated. The data used in the evaluation were collected by the Siemens Building Automation System (BAS). Data were measured on the two identical 500-ton York chillers in the building for over twelve months and coefficient of performance (COP) was calculated. Each chiller operated over a range of chilled water and condenser water temperatures. Performance was modeled with the universal Gordon-Ng chiller model. Data were measured on the enthalpy wheels in four air handling units and was used to estimate sensible and total energy removed from the incoming air for an eight month period. For three of those months, additional data were collected to estimate the sensible and latent effectiveness of each enthalpy wheel which was used to estimate energy cost savings.
The effect of defects and imperfections on the structural integrity of adhesively bonded laminated composites.
(2021-03-26) Pisharody, Akash P., 1987-; Smith, Douglas E., 1962-
The increased demand for long range, fuel efficient and high performance, high fuel economy automobiles has resulted in the growth of use of composites in aerospace and automotive sectors . Adhesive bonding is the preferred method to join composites as it does not require extra machining such as drilling of holes and avoids stress concentrations. As in other manufacturing processes, defects and imperfections may occur in bonded joints which can reduce the load carrying capacity of the joint. Nondestructive test methods such as ultrasonic scanning is used to determine the shape, size and position of defects and imperfections, and the reduction in strength due to defects has been predicted using both analytical and numerical methods. Previous studies on defects have primarily focused on defects within the adhesive bond such as voids and inclusions. Other bond imperfections such as improper adhesive distribution and thickness variations, occur in the bonded joints as well, which often result from improper fabrication techniques. The aim of the current study is to determine the effect of selected defects and imperfections on bonded joint integrity, which have not been previously addressed, and develop a suitable methodology for analyzing the strength of single lap bonded joints that have been compromised by the defects and imperfections. The primary focus here is to understand the effects of adhesive joint imperfections such as improper adhesive distribution and bond line thickness variations, and adherent defects in the form of inclusions, on the strength of adhesive bonded unidirectional carbon fiber reinforced polymer composite joints. Results show that a linear variation in bond line thickness decreases the failure strength of single lap bonded joints when compared with joints of uniform bond line thickness. The investigation with improper adhesive distribution across the overlap shows that the failure strength of bonded joints depends on the shape and size of the adhesive distribution. For the bonded joints with inter-ply inclusion defects, the location of the defect and the ply orientation of the adherend influences the failure strength of bonded joints. The study on the effect of increase in bond line thickness of single strap joints reveals a decrease in bond strength with an increase in bond line thickness. The failure strengths of bonded joints with uniform and varying bond line thickness along with that of single strap joints with uniform bond line thickness is predicted using the Critical Zone method. An insight into the change in stress states due to the presence of imperfections and defects studied, is established.
Photogrammetric measurements of frost roughness evolution on a cold-soaked wing tank model.
(2020-07-15) Ahmed, Salahuddin, 1992-; McClain, Stephen Taylor.
An aircraft subjected to cold-soaked fuel frost (CSFF) on its wing surface is not allowed to take off without FAA certification because of aerodynamic performance degradation caused by frost accretion. A physical model of transient frost roughness on an aircraft wing was developed using a 3D photogrammetry technique. Experiments were carried out in an atmosphere-controlled wind tunnel climatic chamber where the wing-tank thermal model replicates the internal heat transfer to the surface. An automated photogrammetry method was employed in the test section and validated with two fabricated rough surfaces. In this study, the frost roughness evolution and the corresponding effects of atmospheric conditions were presented. The air velocity was found to have the most dominant effect on CSFF roughness evolution. Furthermore, the interaction effect of air velocity and air temperature at a certain condition is responsible for producing the most critical frost case in cold-soaked conditions.
Variation of cold-soaked fuel frost roughness with location on a flat plate.
(2021-11-09) Forslund, Nicholas, 1998-; McClain, Stephen Taylor.
Cold-soaked fuel frost occurs when moist air flows over an aircraft surface that is colder than the dew point temperature following a flight. Previous studies show that cold-soaked fuel frost depends on surface temperature, air temperature, surface geometry, exposure time, and Reynolds number. However, variation in frost roughness due to location on a plate is not well established for surfaces which scale to sizes expected for commercial aviation. In this thesis, photogrammetry and infrared imaging are used to characterize cold-soaked fuel frost roughness. The roughness variation is explained by the viscous and thermal boundary layer development. The roughness measurements from this study suggests that frost forms rapidly towards the leading edge of the plate because the viscous boundary layer thickness is small, which amplifies the forced convection over the plate because there is a larger effective velocity over the plate at the leading edge.
Mechanical and thermal property prediction in single beads of large area additive manufactured short-fiber polymer composites.
(2021-12-06) Russell, Timothy D., 1993-; Jack, David Abram, 1977-
The prediction of mechanical and thermal properties of 3D printed short-fiber reinforced polymers (SFRPs) are investigated in this study. Methods are demonstrated for predicting the internal spatially varying fiber orientation state and resulting internal spatially varying stiffness, coefficient of thermal expansion, and strength properties in a single bead of 13% carbon fiber filled acrylonitrile butadiene styrene. The methods allow determination of both the spatially varying microstructural properties and the effective, bulk properties in any direction by finite element analysis. The focus of this work is specifically on Large Area Additive Manufacturing, an extrusion-based process for manufacturing thermoplastic parts that are several feet long, but the methods are applicable to other SFRP processing methods as well. For the experimental validation portion of this dissertation, a large-scale 3D printing system was constructed to fabricate test specimens. Tensile, compressive, and flexural specimens were fabricated with this system and tested. It is demonstrated that correct order of magnitude predictions can be made for the effective stiffness, CTE, and strength of LAAM-printed SFRP beads using the presented computational methodology. In addition, the computational methodology lays a framework that lends itself to improvement by using more accurate modeling inputs as they are measured, and more accurate underlying equations as they are developed.
Evaluation of carbon fiber laminates via the use of pulse-echo ultrasound to quantify ply-stack orientation and manufacturing defects.
(2021-11-10) Blackman, Nate J., 1994-; Jack, David Abram, 1977-
The use of carbon fiber composites have become more prevalent. Laminated composites provide advantages over traditional materials as the final properties of the part can be tuned. These materials also provide new challenges relating to testing and validation. Traditional testing methods are destructive in nature, creating additional costs. Non-destructive testing can be used to verify the safety of composite parts. This research addresses challenges in the quantification of the ply stack of laminated plain-weave carbon fiber composites and the detection and sizing of foreign objects within carbon fiber laminates via the use of pulse-echo ultrasound. The first scientific contribution of this work is a method to determine the number of lamina and orientation of each lamina for plain weave carbon fiber laminates. Current methods to verify the ply stack are destructive, increasing product waste and costs. The method developed uses pulse-echo ultrasound causing no damage to the inspected part. The method is demonstrated by analyzing 12 unique laminates ranging from 3 lamina to 18 lamina in thickness. The ply stacks represented are also varied. The technique accurately determines the number of lamina and correctly predicted the orientation of 115 out of 117 plies within ±3° of the true orientation. The second scientific contribution of this work is the development of a method to detect and quantify foreign objects in carbon fiber composites. Foreign objects create localized weakness within the composite leading to safety concerns. The method presented can detect various materials of concern common to a manufacturing environment and likely to be foreign objects. In addition, the technique provides an advancement in the quantification of foreign objects with an average error in determining the area of foreign objects of 2.5% in one study presented. The final contribution of this work is the presentation of a portable ultrasonic housing that allows for the acquisition of ultrasound scans with comparable resolution to those taken from an immersion system. Foreign object detection and quantification is demonstrated using this housing and compared with scans taken from an immersion system. The housing allows for additional real-world applications of the developed techniques presented in this dissertation.
High-fidelity simulation of air-assisted atomization with inlet gas turbulence.
(2021-11-03) Jiang, Delin, 1992-; Ling, Yue (Stanley)
Atomization is the process for bulk liquids to disintegrate into small droplets, which is commonly seen in nature and and industrial applications. Airblast atomization is an air-assisted atomization approach and is widely used in gas turbine engines. It utilizes a high speed parallel gas stream to enhance the atomization of the bulk liquid. The velocity difference between the two fluids at the interface triggers a shear instability. The instability induces interfacial waves, which grow, roll up, and eventually break into ligaments and droplets. In order to optimize the design of airblast atomizers, it is crucial to have a comprehensive understanding of the effects of inlet gas turbulence on interfacial instability development, the primary liquid breakup mechanisms and the droplet statistics. In simulation, the turbulent velocity fluctuations are introduced in the gas inlet using a digital filtered method. A parametric study on the effect of inlet gas turbulence is studied using high-fidelity simulation. The the mass-momentum consistent volume of fluid method has been used to resolve the sharp interface. To characterize the topology evolution of the atomizing liquid jet, a novel skeletonization method has been developed.
Internal fiber orientation measurements and void distribution for large area additive manufactured parts using optical and SEM imaging techniques.
(2021-08-10) Nargis, Rifat Ara, 1994-; Jack, David Abram, 1977-
The use of additively manufactured parts for industrial applications has grown is often limited by their structural performance and compromised thermal dimensional stability. The addition of carbon fiber reinforcements, to the polymer matrix, has the potential to mitigate both limitationsits. Quantification of the fiber orientation within the processed beads is required to correlate mechanical and thermal performance to processing variations. This study presents the sample preparation, image acquisition, and analysis methods to quantify the internal fiber orientation and void content. Imaging is performed through optical and scanning electron microscopy (SEM) of an additive manufactured bead with 13% by weight carbon fiber reinforced ABS, with SEM providing a higher resolution and contrast. Fiber orientation is measured using the Method of Ellipses (MoE). A new method using SEM to remove the ambiguity problem inherent to MoE is presented using electrical shadowing afforded by the semi-conductive behavior of the carbon fibers. The spatial change in fiber orientation across the deposited bead cross section is studied as a function of several process parameters, The thesis concludes with an investigation of the correlation between fiber orientation and void content, upwards of 10% by volume for the samples studied, on final part performance. This will hamper the final part performance by a nearly 40% knockdown factor, and void nucleation must be further studied.
Moment analysis methods of ultrasonic waveforms to characterize the internal temperature and melt transition boundary for materials with irregular porosity.
(2021-08-05) Watson, Tyler R., 1996-; Jack, David Abram, 1977-
The utilization of acoustic measurements occurs frequently in a multitude of industries. Monitoring the internal thermal and phase states of materials is of particular interest to the petro-chemical, food, and polymer processing industries, and ultrasound has found limited investigation within the literature for such applications. In this thesis, ultrasound is shown to be useful for monitoring spatial thermal variations through the thickness of a material system without the need to access the interior of the medium in question. The research presented within this thesis will show how the characterization of the internal thermal state of a structure containing random and irregularly shaped internal voids is possible using the internal moments of the captured acoustic waveform. Studies are presented to demonstrate the sensitivity of the resulting analysis to variations in the experimental configuration. The results of this research demonstrate how the proposed methodology is capable of quantifying the internal thermal and phase states of porous mediums with thermal gradients and approximating the two-dimensional variation of the temperature from ultrasonic waveforms.
Nondestructive evaluation of out-of-plane wrinkles within woven carbon fiber reinforced plastics (CFRP) using ultrasonic detection.
(2021-08-10) Minnie, William Hugh, 1989-; Jack, David Abram, 1977-
In the automotive and aerospace industries composite materials are heavily utilized as they provide a great strength to weight ratio relative to their metallic counterparts. A drawback is they require complex manufacturing processes, and the final part performance is sensitive to internal defects. Of focus in the present study are out-of-plane wrinkles, specifically those not identifiable by visual inspection. A methodology is presented to manufacture composite laminates with intentional wrinkle defects requiring a multistage fabrication process. The manufactured parts are inspected using ultrasonic immersion scanning with full waveform capture. An automated methodology is presented in this thesis to track the wrinkle within a single lamina across the scan area resulting in a 3D plot of the wrinkle. The ultrasound data was aligned with 3D microscopy data resulting in average relative errors over all sample regions studied for the height, width, and intensity of the wrinkle of, respectively, 4.9%, 4.5% and 6.0%, with average absolute errors were 0.037 mm, 0.47 mm and 0.002, respectively.

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