Skip to Main Content

Basic Search

Skip to Search Results
 
 
 

Left Column

Filters

Show More

Show More

Show More

Right Column

Search Results

Search Results

(Total results 79)

Mini-Tools

 
 

Search Report

  • 1. Farran, Abdulrhman Optimal Design of Magnetic (Eddy Current) Dampers for Tuned Damping Applications

    Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Mechanical Engineering

    Damping is an essential element of any structure prone to vibration. The energy dissipation provided by dampers reduces structural vibration, enhancing serviceability of the structure and in some cases prevents damage caused by fatigue. When most of the vibration energy in a structure resides in a single mode, the go-to method of abating such vibration is tuned mass damping. Numerous applications, including pipework and structures, necessitate that the tuned mass damper be tuned to a specific natural frequency in a particular vertical or horizontal direction. When structure vibration occurs at multiples modes with their corresponding natural frequencies, then viscous dampers are the more suitable choice due to their broadband damping capacity. The motivation for conducting this study is to explore the use of eddy current damping as an alternative to liquid-based viscous and solid-based viscoelastic damping mechanisms in tuned mass dampers as well as stand-alone/broadband viscous dampers. Eddy current damping (also known as magnetic damping) is generated by the eddy current induced in a conductive material subjected to a time-varying magnetic field (normally created by several rare earth permanent magnets) and tuned mass damper that is used eddy current damper as damper element are explored. The eddy current in the conductor generates its own magnetic field resulting in an electromagnetic force opposing the force of the original time-varying magnetic field. The main contribution of this effort is the development of a numerical tool for synthesizing eddy current dampers and optimizing them for particular applications. The utility and efficacy of this numerical tool are demonstrated and verified by synthesizing two different designs of eddy current dampers and laboratory testing one of them. The first design consists of a stack of eight axially magnetized NdFeB (N42) permanent magnets that are separated by seven iron pole sections moving within a tubular (open full item for complete abstract)
    ... More

    Committee: Reza Kashani (Advisor); Timothy Reissman (Committee Member); David Myszka (Committee Member); Youssef Raffoul (Committee Member) Subjects: Mechanical Engineering

  • 2. Gupta, Ankita Nondestructive Evaluation of Non-oxide Ceramic Matrix Composites using Electrical Resistance.

    Doctor of Philosophy, University of Akron, 2024, Mechanical Engineering

    For CMCs with an electrically conductive matrix, direct current potential drop techniques have the potential to detect composite state such as conductive constituent content (e.g., Si in melt infiltrated composites) or local defects such as delamination or porosity. Melt-infiltrated SiC based composites are an ideal candidate material for such to verify this since the Si content of the matrix is the primary current carrier in the system. In our study, we aimed to evaluate the effectiveness of Electrical Re-sistance (ER) as a NDE method for different 2D woven SiC-based Melt-infiltrated composites, each exhibiting varying degrees and types of processing defects. We con-ducted four types of ER measurements: a. Bulk Resistivity b. Through-thickness c. Axial d. Surface, along the length of the dogbone specimens in the gauge section and on a large plate. Microstructural analysis was performed to correlate observations with microstructure. The bulk resistivity of the specimens in our study exhibited a linear correlation with the infiltrated Si content of the matrix even with different percentage and type of porosities present, allowing us to comment on Si-content of the speci-mens. The Through-thickness set-up incorporates current leads to supply current in a through-thickness manner and determine the nature of current spreading (voltage drop) some distance   away from the current source. The absolute values of the measured through thickness potential represent Si-content, but it is unresponsive for processing defects. The axial set-up is more conventional and can generate local axial current flow. In some cases, such flow of current is affected by and able to locate the local and distinct type porosi-ty. Resistance was sensitive for regions of poor Si-infiltration i.e., “dry-slurry” type defects as well as for isolated larger rounded porosity. It was very sensitive to local surface porosity but not as sensitive for cases where porosity was homogenously pre-sent throug (open full item for complete abstract)
    ... More

    Committee: Dr. Gregory N Morscher (Advisor); Dr. Wiesław K Binienda (Committee Member); Dr. Siamak Farhad (Committee Member); Dr. Jun Ye (Committee Member); Dr. Manigandan Kannan (Committee Member) Subjects: Mechanical Engineering

  • 3. Jang, Eun Tempering Kinetics and Carbide Precipitation in Low Alloy Steel Heat Affected Zones in Temper Bead Welding

    Doctor of Philosophy, The Ohio State University, 2024, Welding Engineering

    Welding low alloy steels can result in formation of undesirable properties in the heat affected zone with high hardness and low toughness caused by martensite formation. Such issues often require tempering procedures to improve properties and reduce cracking susceptibility. The temper bead welding technique has been applied by the power generation industry to produce tempered heat affected zones without post-weld heat treatment. The development of good temper bead procedures can be cumbersome which served as motivation for a portion of the work in this study. This research contained four elements focused on performance of low alloy steel heat affected zones after temper bead welding. These included development of an experimental and computational approach to evaluate tempering response and tempering efficiency, application of the developed methodologies using a finite element model-based design of experiment approach, characterization of the effect of short-term tempering reheats on impact properties, and evaluation of the precipitation kinetics during short-term tempering reheats. The tempering response quantification method was developed to quantify the tempering effect of the multiple non-isothermal cycles during multi-pass welding processes. A novel computational framework was developed to evaluate and quantify the tempering response and tempering efficiency in the heat affected zone in temper bead welding. This involved integrating finite element models with the tempering response methodology to allow distribution analysis of hardness, microstructure, corresponding surface areas, and other tempering response indicators. These methodologies were demonstrated and validated in temper bead weld overlays on Grade 22 steel. Efforts to facilitate temper bead procedure optimization motivated development of a computational finite element model-based design of experiment framework to evaluate a range of weld process parameters and tailor procedures to optimize perfor (open full item for complete abstract)
    ... More

    Committee: Boian Alexandrov PhD (Advisor); Avraham Benatar PhD (Committee Member); Carolin Fink PhD (Committee Member) Subjects: Materials Science

  • 4. Zhao, Xudong BOND BEHAVIOR OF GLASS FIBER REINFORCED POLYMER (GFRP) BARS EMBEDDED IN CONCRETE

    Doctor of Philosophy, Case Western Reserve University, 2024, Civil Engineering

    This dissertation presents a comprehensive study on the bond behavior of sand coated glass fiber-reinforced polymer (GFRP) bars embedded in concrete, utilizing a series of pull-out tests to evaluate the effects of various bonded lengths and bar diameters on bond performance. The study includes five bonded lengths (5db, 10db, 20db, 30db, and 40db) and three nominal bar diameters (6 mm, 12 mm, and 20 mm). The experimental setup involves measuring loaded-end displacement using three linear variable displacement transformers (LVDTs), and for some specimens, free-end displacement with two additional LVDTs. The results are presented as load responses, including applied load versus machine stroke, loaded-end slip, and free-end slip for different bonded lengths. The average shear stress is plotted against the bonded length, and the maximum axial stress from pull-out tests is compared with predictions from ACI 440.1R-15. This comparison provides a basis for evaluating design guidelines against experimental data. In addition to static pull-out tests, the fatigue behavior of the bond between sand-coated GFRP bars and normal strength concrete is examined. Pull-out fatigue tests are conducted on 6 mm and 12 mm bars, with varying load ranges and loading frequencies. The study compares the fatigue load responses and post-fatigue pull-out test results for different bar diameters at similar load range percentages of their tensile strengths. Bond stiffness and loaded-end slip are analyzed in relation to the number of fatigue cycles. Finally, this study presents a finite element analysis (FEA) of GFRP bars embedded in concrete. The interaction between the concrete and GFRP bars is modelled using a surface-based cohesive behavior model, which is based on a calibrated local shear stress-slip model. The analysis compares isotropic and orthotropic properties of the bar, highlighting differences in stress distribution. Mesh convergence has been carried out. Results align well with exper (open full item for complete abstract)
    ... More

    Committee: Christian Carloni (Advisor); Xiong Yu (Committee Member); Tommaso D’Antino (Committee Member); Elias Ali (Committee Member); Anna Samia (Committee Member); Yue Li (Committee Member) Subjects: Civil Engineering

  • 5. Zuo, Kaiwen Vision-based Force Estimation Using Deformable Grippers

    Master of Sciences, Case Western Reserve University, 2024, EMC - Mechanical Engineering

    Sensing tool-tissue interaction forces and providing haptic feedback can enhance surgeon performance in Robotic Minimally Invasive Surgery (RMIS). Two major sensing techniques in RMIS are direct sensing and indirect sensing. Direct sensing relies on sensor measurement approaches. By deploying sensors directly on the surgical instruments, direct sensing has the advantage of high accuracy and reliability while restricting the sensor's size and biocompatibility. Current indirect sensing methods rely on tracking visual deformation of the environment or the tool or measuring motor torques. They can be more biocompatible and cost-efficient but trade off sensing accuracy and reliability. One promising approach to indirect force sensing has been to use data-driven approaches such as neural networks. One promising approach to indirect force sensing has been to use data-driven approaches such as Neural Network (NN). However, these data-driven models require significant amounts of labeled training data, which can be costly or infeasible to acquire, especially in vivo. Furthermore, they can fail to generalize when tracking visual deformation in complex environments. To address data-driven models' data-reliance problems of low capability in complex environments, we proposed a new Vision-based Force Estimation System (VFES) using a model-based deformable inverse Finite Element Analysis (FEA) approach to conduct force estimation in real-time. Our method requires no training data but rather takes deformation data captured by a structure light camera as input for the inverse FEA simulation in Simulation Open Framework Architecture (SOFA). We demonstrate that our system can achieve high accuracy under static scenarios with a RMSE less than 0.18 N and an NRMSD of 4.25 %. Through dynamic evaluations, our system was validated to have less than 0.66 N and a NRMSD under 15 % when moving frequency of the observed object is less than 2 Hz. We also test the bandwidth of our system to show i (open full item for complete abstract)
    ... More

    Committee: Brian Taylor (Committee Chair); Zonghe Chua (Advisor); Kathryn Daltorio (Advisor) Subjects: Engineering; Mechanical Engineering

  • 6. Queiroz Avedissian, Nicholas Experimental Study and Finite Element Modeling of Distortion and Densification During Sintering of Al6061 Parts Printed by Binder Jetting Additive Manufacturing

    Master of Science, The Ohio State University, 2024, Welding Engineering

    Metal Binder Jetting (MBJ) is a room-temperature additive manufacturing process that utilizes a liquid binder to selectively bind regions of sequential layers of powder feedstock until a three-dimensional shape is achieved. A sintering step is required to burn out the binder and densify the part after the build process. For aluminum powders, sintering is usually done at temperatures above their solidus temperature. This results in a liquid phase sintering (called super solidus liquid phase sintering) that can result in significant shrinkage and distortion. It requires careful temperature control to achieve near-full dense parts while minimizing distortion. Therefore, it is interesting to have a predictive model that calculates the final distortion and relative density for a given combination of geometry, material, and sinter cycle since all these factors will impact the outcome of the sintering process. For some stainless steels, material properties that allow for the development of such models are available in the literature. Still, such data is unavailable for aluminum alloys or only available with significant uncertainties. This research studied the sintering behavior of Al6061 MBJ parts experimentally and numerically. Round-bar samples were sintered in a dilatometer where the change in sample length was measured as a function of time and temperature. For furnace sintering, bridge and cantilever geometries were used to evaluate distortion, and prismatic samples were used to evaluate densification. Different methods were tested for relative density measurements including dimensions-based, Archimedes' principle-based, and optical image based. It is found that low densification occurred for the lower temperature cycle, while distortion was more significant in the higher temperature cycle. While these sintering behaviors are expected, an important finding is that densification and distortion are very sensitive to temperature for liquid phase sintering. For example, (open full item for complete abstract)
    ... More

    Committee: Avraham Benatar (Committee Chair); Wei Zhang (Advisor) Subjects: Materials Science

  • 7. Bolar, Abhishek Lokesh Automation of a Multi-Stage T-Joint Assembly of Stamped Components and Prediction of Performance Parameters Using Machine Learning

    Master of Science, The Ohio State University, 2023, Mechanical Engineering

    Flexible sheet metal assemblies such as automobile bodies undergo different sources of manufacturing variations during production due to material anisotropy, springback, and distortion after clamping and joining processes. The assembly sequence also introduces variations in assemblies' geometry and tolerance zones. Minimizing these variations requires individuals with expert knowledge of complex multi-stage non-linear finite element analysis. The primary objective of the research is to investigate the use of machine learning for predicting output performance parameters in T-Joint assemblies and their corresponding components. To achieve this, an automated simulation workflow for the TJoint assembly is created to generate large datasets of components and assemblies. These datasets are then utilized for training different machine learning algorithms. The workflow is constructed by setting up two component-level forming simulations, one for the vertical component and one for the horizontal component, using explicit FEA. The results from the forming simulation are then transferred to the assembly simulations for clamping and joining using a stress file for flexible parts (*.k). An assembly clamping and joining simulation is set up as a two-stage process where the vertical and horizontal components are clamped together with flat sheets and brackets to form the T-Joint. The clamping process happens in a three-stage, where two sub-assemblies are created initially and later clamped together to form the final assembly in a single simulation. After the clamping process, the results are transferred to the joining simulation where the different iv flanges of the components are joined using simplified spot welds. Following this simulation, the required results were extracted from the simulation. Furthermore, this entire process is automated by parametrizing the model and using Python scripts and macros to generate a large dataset of components and assembli (open full item for complete abstract)
    ... More

    Committee: Yannis P Korkolis (Committee Member); Jami J Shah (Advisor) Subjects: Mechanical Engineering

  • 8. Alhusban, Mohannad Textile Reinforced Mortar (TRM) Jacketing of Concrete Structures at Component and Global Levels

    Doctor of Philosophy, University of Toledo, 2022, Engineering

    Textile reinforced mortar (TRM) is a new class of composite materials that can be used to strengthen and upgrade existing infrastructures. The present research investigates the applicability of TRM in improving the local and global responses of reinforced concrete (RC) structures. With this intention, this study highlights the aspects of the reinforcing textile mesh performance bonded by cementitious matrix, and the significance of key parameters that need to be considered in the design guidelines and field applications. As importantly, this work proposes new mathematical solutions for the design of TRM strengthened RC columns subjected to simulated seismic loading which helps widening their implementation in field applications. In pursuit of the research aim, three-dimensional comprehensive nonlinear finite element analysis (FEA) models of as-built and TRM strengthened RC structural members including beams, columns, wall-like columns, walls with cut-out openings, and moment resistant frames were developed using ANSYS software program. The FEA results demonstrated that the performance of RC structural members at local and global levels were improved significantly when strengthened with TRM jackets. On a local level, the use of TRM in shear strengthening of deficient RC beams limited the crack propagation in the critical span and, hence, increased the shear capacity and deformability of the beams. Confinement of compression members resulted in considerably higher ductility and strength under axial and simulated seismic scenarios. On a global level, seismic strengthening of RC frames using TRM led to substantial improvements in the ductility and energy dissipation and, to a lesser degree, to stiffness and strength enhancements. When compared with corresponding frames retrofitted with traditional global techniques through placement of masonry infilled walls, local strengthening of individual members would be sufficient if the fr (open full item for complete abstract)
    ... More

    Committee: Azadeh Parvin (Committee Chair); Liangbo Hu (Committee Member); Meysam Haghshenas (Committee Member); Luis Mata (Committee Member); Mohamed Hefzy (Committee Member) Subjects: Civil Engineering

  • 9. Jamunkar, Trilochan Digital Twin modeling of surface roughness generated by the electrical discharge machining process

    MS, University of Cincinnati, 2022, Engineering and Applied Science: Mechanical Engineering

    The manufacturing industry is going through a complex transformation phase due to the current supply chain interruptions by the pandemic, intricate customer custom designs, and just-in-time methodology adopted by various industries. Manufacturers shift towards Industry 4.0 capable machines with expanded data analysis capabilities to tackle process disruptions. From a machine operator's perspective, the lack of advanced real-time monitoring in machining processes using sparks such as Electrical discharge machining (EDM) and Electro-chemical discharge machining (ECDM) can lead to delayed response time in case of any mishaps. There is a need for an advanced process monitoring tool to acquire feedback in real-time and control the machining process. Digital twins can be a key in such situations. It can provide the required data across the platforms to ensure proper and timely communication between the machine, operator, and stakeholders. The work presented in this study proposes a novel model for making a digital twin of an Electrical discharge machining process. Accurate prediction of surface roughness generating capabilities of the manufacturing process is a prerequisite to enhancing their uses in areas such as surface texturing. Textured surfaces have numerous applications in various industries such as Automotive, Aerospace, Energy, and Defence. The electrical discharge machining process can be used for surface texturing of conductive materials, particularly hard surfaces. A three-step approach is used in this work to develop a digital twin model to simulate a live surface texture of surfaces created by the EDM process. The prediction is based on the three input process parameters for EDM, namely the spark-on-time, current, and voltage. Finite element method is used in the first step to generate a single crater formed by an individual spark. In the next phase, the single spark FEM data is processed (open full item for complete abstract)
    ... More

    Committee: Murali Sundaram Ph.D. (Committee Member); Jing Shi Ph.D. (Committee Member); Milind Jog Ph.D. (Committee Member) Subjects: Mechanical Engineering

  • 10. Conover, Simon Design of Bidirectional Wicket Gate Blades for a Hydro Pump-Turbine System

    Master of Science, The Ohio State University, 2022, Mechanical Engineering

    In the past decade, renewable energy production has grown considerably. While this is necessary to face the challenges global warming presents in today's world, much renewable power is inconsistent and difficult to store in an efficient manner. Pump-turbine systems are the traditional approach for energy storage; however, they contain different complexities, including a high cost of installation and long lead times for the generation of power. The toroidal pump turbine system attempts to solve these issues by enabling the installation of the system in a single hole, created using a drilling rig. The turbine turns the flow 180 degrees between the outer and inner piping of an annulus. The novelty of this system necessitates the development of new turbomachinery components in the creation of such a device. This work seeks to develop wicket gate blades to control the flow rate and power output for such a new design. The wicket gate blade structure was created using the inverse design method in MATLAB and tested using numerical fluid simulations of the system in ANSYS CFX. Furthermore, the mechanical effects of the blades developed were tested using ANSYS Mechanical APDL to understand the stresses seen throughout the blade shape. The final blade structure effectively controls the flow rate and power output of the system, while ensuring the system still runs at a high efficiency. As well, finite element analyses shows the blade effectively holds the hydrostatic weight of water when in the closed position.
    ... More

    Committee: Clarissa Belloni (Advisor); Randall Mathison (Committee Member); Zhenyu Wang (Advisor) Subjects: Energy; Fluid Dynamics; Mechanical Engineering

  • 11. Glaspell, Aspen Thermal Stress Characteristics of Friction Welding

    Doctor of Philosophy in Materials Science and Engineering, Youngstown State University, 2022, Materials Science

    Linear friction welding (LFW) is a solid-state joining process that is increasingly gaining interest in its use for bonding dissimilar metals. The parameters necessary for successful bonding are not well understood for various dissimilar metal combinations. Laser welding (LW) is also a solid-state joining process that has gained interest for joining shape memory alloys to other metals. Similarly, the parameters needed for bonding these dissimilar metals are not well documented. Understanding what parameters are necessary for joining is essential for advancing knowledge in this field. This thesis focuses on the development and validation of computational models to address this issue. A 2D numerical and computational model was developed for the LFW, while a 2D thermal and a 3D structural computational model was developed for the LW. The numerical model was developed using MATLAB, while the computational models were developed using the finite element analysis software ANSYS Workbench. The models were validated with experimental data taken during the experimental welding. The results showed for LFW increasing frictional heat flux and pressure increased deformation, while for LW increasing laser power increased deformation and increasing thickness decreased deformation. In conclusion, the aims of this thesis were successfully addressed, thus increasing understanding of both the LFW and LW processes. The work showed the implicit decoupled 2D models can capture results necessary for parametric and geometric studies. The work also has a deeper insight into the necessary process parameters needed for successful bonding on dissimilar metals under both linear friction and laser welding.
    ... More

    Committee: Kysoung Choo PhD (Advisor); Pedro Cortes PhD (Committee Member); Timothy Wagner PhD (Committee Member); Jaejoong Ryu PhD (Committee Member); Holly Martin PhD (Committee Member) Subjects: Materials Science

  • 12. Luther, Samuel Quantification of the Susceptibility to Ductility-Dip Cracking in FCC Alloys

    Doctor of Philosophy, The Ohio State University, 2022, Welding Engineering

    Ductility-dip cracking (DDC) in face-centered cubic (FCC) alloys, such as nickel-based alloys and 300-series stainless steels, is a challenge faced by nuclear power generation. Aging reactors need to be repaired via multipass weld overlays to extend their lifetime. DDC often occurs in the first few layers of these overlays, and the nuclear industry has low flaw tolerance, making DDC subject to costly repair and rework. The prevailing theory describing DDC is based on observations of grain boundary (GB) sliding, microvoid formation, and the effect of GB tortuosity. This work aims to quantify the effect welding process parameters and welding generated stresses have on the formation of DDC and to provide clear avenues for productive future research. The main project objectives include the development of methodology, based on combining physical experiments and computational modeling, for prediction of DDC in multipass welds of austenitic alloys that is applicable for materials selection and process optimization. An additional study on the DDC fracture surface was conducted due to findings from the experimental component. Research began with the development of a Gleeble-based experimental procedure that evaluates a material's susceptibility to elevated temperature embrittlement. The procedure is called simulated strain ratcheting (SSR), and preliminary testing led to the use of the imposed mechanical energy (IME), defined as the integral of experienced stress vs. strain, as a parameter for quantification of thermo-mechanical loading in Gleeble tests and FEA models of multipass welds. This experimental procedure was used to successfully generate DDC in various nickel-based alloys and 310 stainless steel. Fracture surfaces generated from this testing were found to exhibit thermal faceting (TF), which warranted further study. Samples which contained high amounts of DDC, or those which experienced fracture, also generally experience higher IME than those which showed no s (open full item for complete abstract)
    ... More

    Committee: Boian Alexandrov (Advisor); Avraham Benatar (Committee Member); Carolin Fink (Committee Member); John Lippold (Committee Member); Michael Mills (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

  • 13. Sadeqi, Sara Effect of Whole-Body Kinematics on ACL Strain and Knee Joint Loads and Stresses during Single-Leg Cross Drop and Single-Leg Landing from a Jump

    Doctor of Philosophy, University of Toledo, 2022, Engineering

    Anterior cruciate ligament (ACL) injury is quite common among young athletes, with the number of injury cases exceeding 120,000 annually in the United States alone. Over 70% of which account for non-contact injuries. Forces and moments acting on the knee joint play essential roles in these injuries. Motions of the other body segments are effective in increasing or decreasing these loads. In this study, the effect of whole-body (WB) kinematics on the knee joint biomechanics was investigated using in vivo and in silico methods. Motion analysis experiments were done on 14 able-bodied young participants wearing a full-body marker set and performing two variations of single-leg landings, using their left and right limbs (4 tasks). Marker trajectories and force plate data were recorded from the in vivo experiments of these participants. The in silico investigations consisted of two separate parts. First, musculoskeletal simulations were done to obtain whole-body kinematics, kinetics, and muscle forces, using inverse kinematics, inverse dynamics, and static optimization techniques. The next part was non-linear dynamic finite element (FE) analyses. A FE dynamic/explicit knee model was developed from medical images of a healthy young female and validated against in vitro experiments for the knee joints kinematics and ligaments strains. Ligaments' material properties for the knee cruciate and collateral ligaments were obtained through optimization to the experimental tensile test data in the literature. Then, the participants' data from musculoskeletal simulations were used as the input to the FE analyses. The FE outputs included ACL strain, knee joint contact forces, contact pressures, and soft tissue stresses. In order to find the relationship between WB kinematics and knee joint biomechanics, correlation analysis was used. Using Spearman correlation coefficients and P-values, the correlation between WB modifiable parameters and knee biomechanics along with their stat (open full item for complete abstract)
    ... More

    Committee: Vijay Goel Dr. (Advisor) Subjects: Biomechanics; Biomedical Engineering

  • 14. Friedrich, Brian Thermal-Stress Characteristics of Large Area Additive Manufacturing

    Doctor of Philosophy in Materials Science and Engineering, Youngstown State University, 2022, Materials Science

    Common failure modes to Big Area Additive Manufacturing (BAAM) are the phenomenon of slumping and excessive distortion. Slumping or sagging usually occurs when the printed structure retains excessive heat. This phenomenon is commonly seen when the build has insufficient cooling between layers and, therefore, inadequate mechanical strength due to the high-temperature material properties to support the layers above. Distortion is the planar deviation from the desired geometry. Significant residual stresses typically distort BAAM builds. Stresses often occur due to the thermal cycling and large temperature gradients found in additively manufactured parts. This study developed a transient thermal and structural simulation model to predict the slumping phenomenon and distortion, specifically applicable to overhanging features. A pyramidal model was crafted in Ansys Workbench software to simulate a large layer overhang to investigate the necessary slumping conditions. The pyramid was designed to have 53 layers and utilized symmetry to reduce the pyramid to one-quarter of the overall size and was modeled using standard ABS material. The simulation model matches the dimensions in the experimental pyramid, which had bead dimensions of 12.5 mm wide with a thickness of 5 mm. The overall structure size was 1.06 m by 0.77 m by 0.43 m. Each layer in the model independently allows for element birth/death commands and individual layer mesh parameters. The built-in element birth/death commands enable the layers to activate and progress the same way as the experimental build. As each new layer is activated, a temperature input of 200°C is applied then turned off just as the next layer is activated. The feedstock material selected for this study is Acrylonitrile Butadiene Styrene (ABS), which was selected based on the physical properties and the availability of the temperature-dependent material properties. The availability of these temperature-dependent material properties is ess (open full item for complete abstract)
    ... More

    Committee: Kyosung Choo Ph.D. (Advisor); Jae Joong Ryu Ph.D. (Committee Member); Donald Priour Ph.D. (Committee Member); Brian Cockeram Ph.D. (Committee Member); Matthew Caputo Ph.D. (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

  • 15. Humagain, Santosh FRP Strengthening of Steel I-Beams with Web Openings

    Master of Science in Civil Engineering, University of Toledo, 2021, Civil Engineering

    The present study involves fiber reinforced polymers (FRP) flexural strengthening of steel I-beams with web openings under static loading. ANSYS nonlinear finite element analysis (FEA) software was used to model control and carbon-FRP (CFRP) strengthened solid steel I-beams which were first validated using the data and results from an existing experimental study in the literature. Subsequently, steel beams with ten different opening shapes (with equal cross-sectional area) combination of circle, rectangle, square, and oval, with and without CFRP plate strengthening were analyzed to find the best opening shape combination. The effective length and thickness of CFRP plates applied to steel beams with two and four circular web openings were studied. In addition, the steel beams with two circular openings were strengthened with various number of plates and FRP types [CFRP, aramid-FRP (AFRP), and basalt-FRP (BFRP)] to investigate their effect in improving the load-carrying capacity. The effective length of CFRP plates was determined as 40% and 67% of the total length of the beams with two and four circular openings, respectively, resulting in an approximately 25% increase in the ultimate load capacity. As compared to the control solid beam, the load capacity of the steel beams with two and four circular openings was recovered by 98.9% and 74.2%, respectively, when strengthened with a 6 mm thick CFRP plate. A 28% increase in the ultimate load capacity was observed when the steel beams with two circular openings were strengthened at the tension flange face with three plates of CFRP (thickness of each plate was equal to 1.4 mm). The use of CFRP, AFRP, and BFRP plates showed a similar improvement in the load capacity of the beams with two circular openings. The highest enhancement was in the beams with the CFRP plates followed by AFRP and BFRP strengthened beams, respectively. Finally, for various shape openings with equal cross-sectional areas, the oval-oval-sh (open full item for complete abstract)
    ... More

    Committee: Dr. Azadeh Parvin (Committee Chair); Dr. Luis Mata (Committee Member); Dr. Liangbo Hu (Committee Member) Subjects: Civil Engineering

  • 16. Palmer, Asa Characterization of Additive Manufacturing Constraints for Bio-Inspired, Graph-Based Topology Optimization

    Master of Science (M.S.), University of Dayton, 2021, Aerospace Engineering

    With more efficient computational capabilities, the use of topology optimization (TO) is becoming more common for many different types of structural design problems. Rapid prototyping and testing is often used to further validate optimized designs, but depending on a design's complexity, the structural behavior of physical models can vary significantly compared to that of their computational counterparts. For graph-based topologies such differences are caused, in part, by a need to realize finite-thickness structures from the infinitely thin geometries described by graph theory. Other differences are caused by limitations on manufacturing processes such as the need to fabricate large models from smaller components. While additive manufacturing (AM) can be more conducive for fabrication of complex topologies, its limitations are generally less understood than those for traditional subtractive manufacturing processes. Understanding and incorporating limitations on AM into a TO process in the form of added constraints would allow the algorithm to produce not only optimal designs, but also those that are feasible for AM. In this work, two specific AM constraints are characterized for Lindenmayer system (L-system) graph-based topologies of a multi-material, diamond-shaped, morphing airfoil in supersonic flow. One constraint is related to the feasible generation of thick structural members from the infinitely thin beams of graph-based topologies. To characterize the effects of geometric overlap, structural behavior of finite element models made of lower-fidelity beam elements is compared to that of finite element models made of higher-fidelity volume elements. Results indicate that at intersections where 10% or more of a member's length is overlapped, there will be significant variations in stress and effective torsional stiffness when thin members are converted to thick members. The second AM constraint characterized in this work is related to partitioning of large mo (open full item for complete abstract)
    ... More

    Committee: Markus Rumpfkeil (Committee Chair); Richard Beblo (Committee Member); Alexander Pankonien (Committee Member); Raymond Kolonay (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

  • 17. Soudah, Majd MODELING AND CHARACTERIZATION OF A GENERAL MULTIMECHANISM MATERIAL MODEL FOR ADVANCED ENGINEERING APPLICATIONS OF PRESSURE SENSITIVE MATERIALS

    Doctor of Philosophy, University of Akron, 2021, Civil Engineering

    Numerous constitutive models have been developed over the past 5 decades for modeling voided materials under different types of loadings and tests. Since the effective use of these materials rests on the comprehensive understanding of the factors which influence their performance under various practical conditions, different experimental and computational efforts have been made towards such exercise. In this research many aspects of pressure sensitive materials, such as material behavior and its performance in a practical application are studied using a newly developed three-dimensional general model with an eye towards civil engineering voided materials such as different types of soils and concrete. Firstly, the integral part of this study lies in the suitable mathematical formulation of the voided materials model for easy implementation, exact computation and effective utilization in commercial finite element codes. In particular, to embrace all the different levels of complexities regarding the voided materials, i.e., from material point characterization to large-scale analyses of devices, the constitutive model is established for both implicit and explicit-time integration algorithms. This allows smooth adaptation of the model for wide range of initial/boundary value problems, i.e., from simple to complex cases without any severe computational cost and unnecessary loss of accuracy. Secondly, the formulated model is calibrated to characterize a number of the essential responses seen among the different types of voided materials under different loading conditions. These aspects are heavily depended on the availability of experimental data for the various types of voided materials, such as different types of soils and concrete. Finally, the more challenging behavior of these materials is that the shear strength of these materials is dependent on several factors, such as the confining pressure, over consolidation ratio, loading rate, permeability of a particul (open full item for complete abstract)
    ... More

    Committee: Atef Saleeb (Advisor); Ala Abbas (Committee Member); Wieslaw Binienda (Committee Member); Nariman Mahabadi (Committee Member); Jun Ye (Committee Member) Subjects: Civil Engineering

  • 18. Li, Jiayuan Fast Modeling of the Patient-Specific Aortic Root

    Master of Sciences (Engineering), Case Western Reserve University, 2021, EMC - Mechanical Engineering

    The aortic root is a significant cardiac organ, which transports the blood from ventricle to the rest of our body. Nowadays a great number of finite element models of the patient-specific aortic root have been constructed to analyze the pathology of individual patient. However, the methodology to generate a valid patient‐specific aortic root model in a fast speed is not available. The current methods resort either to reconstruction of aortic root from sliced pictures of MDCT or to manual construction from commercial CAD applications, which is accurate but not efficient. In this thesis, we offer a robust and efficient algorithm called Fast Patient‐specific Aortic Root Generation Algorithm (FPAG) to generate the finite element model of the patient‐specific aortic root in a very fast speed. A couple of critical parameters that define the geometry of the patient‐specific root and valve will be extracted from the pictures created MDCT & 3D echocardiogram. Then we use B‐rep to build the skeleton curves and use Delaunay triangulation algorithm to mesh the patient‐specific aortic root model. The process of generation of the B‐rep curve and the Delaunay mesh for the patient‐specific aortic root is very speedy. The result of the FPAG algorithm will be a patient‐specific meshed aortic root model that is discretized by tetrahedral mesh. Currently, the FPAG algorithm is coded in Matlab. There is a good agreement in terms of geometry between the patient‐specific aortic root models constructed by FPAG and the one reconstructed by MDCT. The dynamics of a tricuspid patient‐specific aortic valve constructed by FPAG is validated by the finite element analysis (FEA). The valve is applied by the physiologically realistic pressure condition in a cardiac cycle. The dynamic test of the valve shows a good compatibility with that of pre-validated aortic valve. By minor modifications of the FPAG algorithm, patient‐specific bicuspid aortic valve can also be generated. Although some detailed (open full item for complete abstract)
    ... More

    Committee: Bo Li (Committee Chair) Subjects: Biomechanics; Mathematics; Mechanical Engineering

  • 19. Tong, Xiaolong A Constitutive Model for Crushable Polymer Foams Used in Sandwich Panels: Theory and FEA Application

    Doctor of Philosophy, University of Akron, 2020, Mechanical Engineering

    The objective of this research was to develop a constitutive model for Divinycell PVC H100 foam in order to accurately predict its mechanical behaviors under triaxial crushing. Nowadays, sandwich panels with polymer foam core are widely used because of its low weight-stiffness ratio and high energy absorption capability. Many of these applications require the sandwich panels to have curvature to some extent which causes triaxial stress state in the foam. In this research, a 3D anisotropic elastic-plastic-viscoelastic-damage model was developed to predict the multiaxial crushing behavior of polymer foams used in the core of sandwich structures. This model was based on previous pressure vessel experiments on Divinycell H100, whereby the post-yield response of the foam was characterized by anisotropic hardening during plastic flow, as well as damage and viscoelastic hysteresis. By assuming Tsai-Wu plasticity, post-yield properties from only uniaxial compression/tension and simple shear material responses were used to develop a three-dimensional material constitutive relationship for the foam. This solution methodology was shown to be very effective in predicting the hysteresis response of the foam under triaxial compression, triaxial compression-tension and triaxial compression-shear. Good agreement was found between the theoretical predictions and experimental results. An ABAQUS user-defined subroutine (VUMAT) for the proposed elastic-plastic-viscoelastic-damage model was implemented. By using the VUMAT to simulate the single element and meshed specimen, the proposed material model was verified to be valid and accurate. The VUMAT was then used to simulate the response of a curved sandwich panel with Divinycell H100 foam core under blast load. The results were used to compare with ABAQUS built-in isotropic crushable foam model. Results showed that the commonly-used isotropic crushable foam model overestimated the stiffness, strength and energy dissipation of th (open full item for complete abstract)
    ... More

    Committee: Michelle Hoo Fatt (Advisor); Xiaosheng Gao (Committee Member); Alper Buldum (Committee Member); Wieslaw Binienda (Committee Member); Lingxing Yao (Committee Member) Subjects: Materials Science; Mechanical Engineering; Mechanics

  • 20. Ding, Menglong Development of Advanced Numerical Tools for Aircraft Crash Analysis

    Doctor of Philosophy, University of Akron, 2020, Civil Engineering

    The study aims to explore advanced tools for air crash analysis with universal meaning in air-crash analysis and uses the crash of Tu-154M large transport airplane in Smolensk, Russia on April 10, 2010, as an example. The crash was initiated by the impact of the left wing into a large birch tree according to the Russian investigation report. Nevertheless, some facts caused the attention and suspicion to this explanation. The research is devoted to investigate how far the wing has to be damaged for the airplane to lose balance, how a pilot can compensate the degraded aerodynamic performance of the aircraft, how to reconstruct the trajectory of a fall of major debris separated from the airplane in the air are critical in the air-crash analysis, what the most possible mechanism of airplane door is to end up one meter deep and perpendicular berried in the ground, and what the most possible outcome of the airplane wing impact into the birch tree. First of all, the aircraft in landing configuration with various wingtip damage on the left wing was under consideration while the no-damaged case was also studied as the baseline. Wind tunnel test results with a 1:100 scale model were correlated using CFD simulations. The variations of lift force, drag force, and asymmetric rolling moment with respect to the angle of attack and sideslip were investigated for different damage situations. The methods to compensate for the lift force and the asymmetric rolling moment were also investigated for the possibility of a safe landing. Secondly, estimating the trajectory of separated objects after disintegration caused by the impact will be useful in crashes analysis of airplane, especially in the circumstance when the impact condition cannot be determined. Since the motion of an airplane's fragments in the air is highly affected by the aerodynamic loads, computational fluid dynamics with an automated unstructured tetrahedral mesh approach using spring-based smoothing and remeshing a (open full item for complete abstract)
    ... More

    Committee: Wieslaw Binienda (Advisor); Qingdan Huang (Committee Member); Atef Saleeb (Committee Member); Xiaosheng Gao (Committee Member); Lingxing Yao (Committee Member) Subjects: Aerospace Engineering; Civil Engineering