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Seven, IbrahimTools for Improved Refractive Surgery: Computational and Experimental Study
Doctor of Engineering, Cleveland State University, 2014, Washkewicz College of Engineering
The cornea is the outermost layer of the human eye where the tissue meets with the external environment. It provides the majority of the eye’s refractive power and is the most important ocular determinant of visual image formation. The refractive power of the cornea derives from its shape, and this shape is a function of the ocular biomechanical properties and loading forces such as the intraocular pressure (IOP). With having the majority of refractive power in the eye, the cornea is the primary tissue of interest for refractive intervention. Globally, the predominant mode of surgical treatment of refractive disorders is photoablation. However, optical power regression over time and under/over correction due to neglected corneal biomechanical properties were still observed following refractive procedures including LASIK, PRK, Astigmatic Keratotomy etc especially at high degree corrections. Also, some evolving procedures such as corneal collagen crosslinking (CXL), a collagen stiffening procedure most commonly performed through UVA photoactivation of riboflavin in the corneal stroma, currently lack surgical guidance for optimizing visual outcomes. Thus, there is a need for methods that explore the patient specific treatment planning strategies for refractive procedures. This work will have a potential impact in translating mechanical principles into corneal surgical planning in order to provide a better guidance and predictive environment to the corneal surgeons. The goals of this thesis are three fold: 1) To develop patient specific models from clinical LASIK cases and to compare the outcomes of these models with clinical outcomes in a patient population. 2) To simulate investigational procedures that utilize CXL. 3) To advance a potential approach to characterize corneal mechanical properties in vivo.

Committee:

William J. Dupps, Jr., MD, PhD (Committee Chair); Nolan Holland, PhD (Committee Co-Chair); Ahmet Erdemir, PhD (Committee Member); Antonie Van den Bogert, PhD (Committee Member); Andrew Resnick, PhD (Committee Member); Abhijit Sinha Roy, PhD (Committee Member)

Subjects:

Engineering

Keywords:

Ocular Biomechanics, Cornea, Finite Element Analysis, Inverse Finite Element Analysis, Crosslinking

Luckshetty, Harish KumarSpace-Time Finite Element Analysis on Graphics Processing Unit Computing Platform
MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering
Space-time finite element method provides a robust and accurate alternative to the traditional FEM based on semi-discrete schemes due to its extended capability in establishing approximations in both space and time. The extended capability, however, requires the simultaneous discretization of spatial and temporal domains. This subsequently results in a system of equations that is considerably larger in size than those obtained in the standard finite element formulation. In general, solving equations generated based on the space-time formulation requires substantially more computing time. In some cases, it becomes a bottle neck for practical implementation due to the large number of degrees of freedom. There is thus a need to explore ways to accelerate the procedure for finding a solution to the system of equations in the space-time method. With the recent developments in the use of Graphics Processing Units (GPUs) for general purpose parallel computations (GPGPU), an effort is made in this thesis to explore the possibility of developing a GPU based solver for the space-time finite element method to accelerate the computation. A two-step approach is taken: In the first step, the GPU version of the direct solver based on LAPACK and a preconditioned conjugate gradient method are tested for systems of linear equations involving both dense and sparse matrices. Both methods are shown to significantly accelerate the process of finding the solution. Subsequently, the developed GPU-based algorithms are implemented on the system of linear equations obtained from space-time FEM and enriched space-time FEM. It is reported that GPU-based implementation yields significant speed up. Based on these implementations, it is concluded that the GPU-based system could serve as an effective platform for the space-time method.

Committee:

Dong Qian, PhD (Committee Chair); Donald French, PhD (Committee Member); Yijun Liu, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

CUDA GPU;Space-time Finite element analysis;Conjugate Gradient method;enriched space-time finite element analysis;;;

Gopalan, BabuINVESTIGATION OF HYDROGEN STORAGE IN IDEAL HPR INNER MATRIX MICROSTRUCTURE USING FINITE ELEMENT ANALYSIS
Master of Science (MS), Ohio University, 2006, Mechanical Engineering (Engineering)

Studies have proven hydrogen gas as a highly efficient, renewable and alternative energy source and it is expected to serve as a common fuel for all mobile and stationary applications. However, currently the on-board storage difficulties prevent the practical usage of hydrogen in automotive applications. A more efficient and innovative method of hydrogen storage for automotive fuel cell application is to compress hydrogen in minute hollow spherical bubbles incorporating the Hydrostatic Pressure Retainment (HPR) technology. In a HPR vessel, the material properties and the inner matrix structure are two critical design parameters that determine the hydrogen mass efficiency. The focus of this study is devoted to investigating the performance characteristics of one configuration; spherically shaped bubbles homogenously arranged in a simple cubic inner matrix packing structure for a HPR vessel, using Finite Element Analysis.

Committee:

Hajrudin Pasic (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Hydrogen storage; Pressure vessel; Fuel tank; Hydrostatic Pressure Retainment; Finite Element Analysis; Metal Foam

Kulkarni, Kanchan AvinashExperimental Characterization and Finite Element Simulation of Laser Shock Peening Induced Surface Residual Stresses using Nanoindentation
MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering
As a non-destructive technique, nanoindentation has been extensively used in the determination of material properties such as hardness and Young’s modulus at both the macro and micro scale. This thesis explores the use of nanoindentation for measuring the surface residual stress induced by laser shock peening. While the technique has been studied by a number of groups, accurate measurement using nanoindentation is hindered by a good method of estimating the contact area, which is the basis of all the calculations in the literature. Due to the sink-in and pile-up effects, the contact area can be underestimated leading to erroneous values of the residual stresses. The overall objective of the thesis is to improve the existing methodology by incorporating the pile-up effects for the contact area calculation. The accuracy of the residual stresses is further validated with the experimental measurements conducted using X-ray diffraction technique. Along with this experimental development, the thesis also aims at developing a finite element model for simulating the nanoindentation process. A simulation model for nanoindentation in region with and without residual stresses is developed and the results reported are in agreement with the experimental results. A parametric study is performed to understand the effect of stress and strain hardening on the indentation curves for the Nickel based alloy IN718.

Committee:

Dong Qian, PhD (Committee Chair); Janet Dong, PhD (Committee Member); Vijay Vasudevan, PhD (Committee Member)

Subjects:

Engineering

Keywords:

Nanoindentation; Residual Stress measurement; Finite Element Analysis; X-ray diffraction; Different methods

Chen, LinlingTear Energy of Natural Rubber Under Dynamic Loading
Master of Science, University of Akron, 2008, Mechanical Engineering
This study focuses on the fracture behavior of natural rubber under dynamic loading. Experiments were performed to determine the tear energy of rubber using trouser and pure shear specimens. The sample strain rates of the pure shear specimen were allowed to range from 0.01 to 311 s-1 by performing the tests with an MTS servo-hydraulic machine for sample strain rates 0.01 to 10 s-1 and a Charpy tensile impact apparatus for sample strain rates exceeding 10 s-1. Finite element analysis was used to define the pure shear region of the pure shear specimen. It was found that the tear energy varied with sample strain rates and specimen geometry and therefore, it may not be a proper parameter to predict the fracture of natural rubber. Finite element analysis of the fractured specimen indicated that comparing the strain energy density and the maximum principal stress at the crack tip to the toughness and tensile strength, respectively, may be more valuable in predicting crack initiation.

Committee:

Michelle Hoo Fatt (Advisor)

Subjects:

Mechanical Engineering

Keywords:

Natural Rubber; fracture mechanics; Finite Element Analysis

Hunn, Zachary DA Finite Element Study of Non-Orthogonal Bolted Flange Plate Connections
MS, University of Cincinnati, 2017, Engineering and Applied Science: Civil Engineering
In high seismic areas of the world, dissipation of energy created by earthquakes is vital to keep structures intact and more importantly the conservation of life. Steel structures use braced and moment frames to dissipate this energy through various mechanisms. This paper’s focus is on moment frames, and more specifically on Bolted Flange Plate connections with non-orthogonal geometry. With the complexity of designs increasing due to advancements in research and the want for large open spaces in many structures, moment frames are a popular option because no diagonal bracing members are required. Yet, in AISC 358-10 (AISC, 2010b), only orthogonal moment frame connections are discussed without any mention of how to design for a non-orthogonal connection. Using the finite element software ABAQUS, the effects of non-orthogonal geometry on Bolted Flange Plate connections, both skewed and sloped, were analyzed. Unlike welded moment connections, this connection requires bolts, and therefore two different bolt configurations were also studied, one having the bolt rows staying parallel to the column face and the other having the bolt rows perpendicular to the beam axis. The performance of these finite element models were compared to previous experimental results, based on the orthogonal connection, conducted at the University of California – San Diego. Using the moment-rotation capacity of the connection, distribution of stresses, and location of the plastic hinge, recommendations for the design of non-orthogonal Bolted Flange Plate connections were determined.

Committee:

Gian Andrea Rassati, Ph.D. (Committee Chair); Thomas Burns, Ph.D. (Committee Member); James Swanson, Ph.D. (Committee Member)

Subjects:

Civil Engineering

Keywords:

Non-Orthogonal;Bolted Flange Plate;Seismic;Sloped Connections;Skewed Connections;Finite Element Analysis

Kulkarni, Abhishek NA Model for Prediction of Fracture Initiation in Finite Element Analyses of Eccentrically Loaded Fillet Welds
MS, University of Cincinnati, 2017, Engineering and Applied Science: Civil Engineering
Data scaling methodology developed for prediction of fracture initiation in welded steel connection simulations using instability, ductility and shear (IDS) failure criteria presents significant potential for validating complex welded connections. The IDS failure criteria is defined by three different parameters, namely fracture strain, stress triaxiality and strain rate. This research investigated the use of the data scaling methodology for welded connections subjected to eccentric loads. Experimental work done by previous researchers was used as the basis for validation in this research. Finite element models were created to test and validate this methodology. Shear lag specimens with balanced and unbalanced weld configurations as well as one full scale model representing a case of out-of-plane eccentricity were modeled in finite element software ABAQUS. The study concluded that the data scaling methodology predicts fracture initiation in the case of welded joints subjected to eccentric loads within acceptable limits and yields realistic results.

Committee:

James Swanson, Ph.D. (Committee Chair); Thomas M. Burns, Ph.D. (Committee Member); Gian Rassati, Ph.D. (Committee Member)

Subjects:

Civil Engineering

Keywords:

Finite Element Analysis;Damage Mechanics;Fillet Welds;Eccentricity;Data Scaling;IDS Failure Criteria

Whip, Bo RyanEffect of Process Parameters on the Surface Roughness and Mechanical Performance of Additively Manufactured Alloy 718
Master of Science in Mechanical Engineering (MSME), Wright State University, 2018, Mechanical Engineering
Metal additive manufacturing (AM) is a method to create complex components in a layer-by-layer process. Currently, there is a lack of understanding in the processing-structure-properties-performance relationship, particularly related to defects inherent to the AM process. This work investigates the relationship of process parameters, as-built surface roughness, and mechanical performance for nickel-based superalloy 718 built using laser powder bed fusion. The surface roughness of components built using varied processing parameters was characterized using both nondestructive and destructive measurement techniques. Finite element analysis was used to study the stress concentration on surface profiles. Statistical correlations are presented between contour processing parameters and surface roughness metrics. Results show that destructive measurements are required to expose obstructed features and highly concentrated stress is present on crack-like surface features. The discovered understanding of the surface roughness behavior can be used for further process optimization and to inform the certification and qualification strategy for AM components.

Committee:

Joy Gockel, Ph.D. (Advisor); Onome Scott-Emuakpor, Ph.D. (Committee Member); Craig Baudendistel, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Additive Manufacturing; AM; Laser powder bed fusion; process parameters; surface roughness; alloy 718; mechanical performance; profile and areal surface roughness measurement techniques; finite element analysis; stress concentration

Sudershan, Sushil PrasenBiomechanical Evaluation of Lumbar Interbody Fusion Surgeries with Varying Interbody Device Shapes, Material Properties, and Supplemental Fixation
Master of Science, University of Toledo, 2017, Bioengineering
Low back pain (LBP) is one of the most commonly reported problems in the United States. The most common causes of LBP are injury or overuse, pressure on neural tissue from different pathologies (disc herniation, stenosis, degenerative disc disease, etc.). Interbody fusion is a well-established treatment option for patients with LBP. For each patient, the pathology and the surgeon’s preference determine the surgical approach. The implants are usually manufactured from either PEEK or Titanium in a variety of shapes and sizes. Usually, the spacers are supplemented with supplemental fixation for motion restriction. However, the initial surgery studies showed success for standalone scenarios without any major complications. Ideally, a standalone surgery that provided stability while fusion occurred, could help decrease operation time and cost. To this date, a large scale study that compared various surgical approaches, implant footprints and materials, and addition of supplemental fixation has not been conducted. To conduct this parametric study, the experiment was separated into an in-vitro and in-silico study. The in-vitro study will allow us to record ROM data that can be used in conjunction with the in-silico model to determine parameters such as stress, strain, and load on the endplate. The in-vitro study showed that a standalone PLIF surgical approach may be a viable option but the TLIF standalone case does not successfully restrict the motion to less than intact or stabilize the motion segment with peek cages. However, for both surgical approaches the pedicle screw fixation successfully restricted motion or stabilized the motion segment. The in-silico study showed that the ALIF and LLIF surgical approaches may be viable options for standalone scenarios but require further investigation. Similar, to the in-vitro study, pedicle screw greatly restricted the motion segment for all surgical approaches regardless of implant size or material property. The study showed that an increase in implant footprint resulted in higher overall motion restriction for all surgical approaches. The various simulated supplemental fixation stabilized the motion for all loading conditions. For the anterior and lateral approaches, lumbar plates provide an additional means of stabilization instead of pedicle screw fixation. The study also observed that a larger implant footprint also shifted the endplate stresses to the periphery, which is composed of stronger bone. Overall, PEEK cages produced lower endplate stresses than titanium cages which may help reduce subsidence incidence. Supplemental fixation always reduced the endplate stresses compared to standalone scenarios except for some cases in the TLIF surgery. The TLIF surgery also showed higher endplate shear load when compared with other surgeries.

Committee:

Vijay Goel, Ph.D (Committee Chair); Anand Agarwal, M.D. (Advisor); Ronald Fournier, Ph.D (Advisor)

Subjects:

Biomechanics; Biomedical Engineering

Keywords:

Lumbar Interbody fusion, Finite element Analysis, Biomechanics, Interbody cage

Abdollahi Nohouji, NedaEvaluation of the Role of Cross-links on Microtubule Mechanics Using a Co-rotational Finite Element Simulation
Master of Science in Mechanical Engineering, Cleveland State University, 2018, Washkewicz College of Engineering
Traumatic injuries and neurodengerative disease are two primary and debilitating causes of cell damage and death in the nervous system. Understanding the mechanobiological behavior of the neuron, and in particular the influence of the mechanical environment on microtubules, is integral to the prevention and treatment of many of these conditions. Within the axon, microtubules are the primary filament that provide structural support and cargo transport. The central nervous system has been a primary focus, where axonal microtubules have been studied for both traumatic brain injury [1] and many neurodegenerative diseases. Beyond the many invaluable experimental tools, modeling is a complementary tool to study the mechanics of a “bundle” of microtubules. Previous work adopted a discrete element formulation [1], though it is unclear how these assumed dynamic simulations affect modeling capabilities. A finite element (FE) based approach offers the possibility to model potentially important bending behavior (i.e. beam elements), may result in more efficient simulations, and when implemented with a co-rotational formulation [2] can account for large deformations. Hence, the goal of this work was to 1. verify implementation of a co-rotational formulation for traditional beam and truss finite elements and 2. apply the framework to predict the mechanical response of a typical microtubule bundle.

Committee:

Jason Halloran (Advisor); Richter Hanz (Committee Member); Kothapalli Chandra (Committee Member)

Subjects:

Biomechanics; Biomedical Engineering; Biomedical Research; Mechanical Engineering

Keywords:

Microtubule Bundle; Tau Protein; Finite Element Analysis; Co-rotational Formulation; Tension

Ramanathan, Arun Kumar KumarDynamic response of a shipping container rack and suspended automotive parts under random excitation: Experimental, Computational and Analytical Studies
Master of Science, The Ohio State University, 2017, Mechanical Engineering
Shipping containers are exposed to complex dynamic loading conditions during transport via truck, rail, and air. The loading conditions are further complicated by contact gap nonlinearities between the cart and ground, cart holders and suspended parts, and between neighboring suspended parts. This study focuses on developing a modeling strategy to simulate a container cart with parts undergoing random vibration tests based on standard road profiles. Initially, the linear system response to a random excitation profile of the cart structure is examined in frequency domain and correlated with experimental measurements. The linear system predictions lacked the required modeling fidelity to capture the nonlinear dynamic behavior observed during the testing as the container is loaded. Thus, the nonlinear response is then simulated in time domain using the explicit integration method with contact-driven boundary conditions using a commercially available finite element software. The total run time is determined to be prohibitively long for the time domain formulation, say over 5 seconds with a time step size of 0.3 microsec. Finally, a dynamic substructuring strategy is employed and implemented using super elements in the commercial finite element code. This particular method captured the dynamic amplification of the cart, maintained the contact nonlinearities, and reduced the computational burden. Further, a minimal order lumped model of the dynamic system is developed to understand the physics of the problem. Both lumped and finite element models consistently captured the nonlinear random vibration phenomenon and predicted the overall acceleration levels within 20% of measurements.

Committee:

Rajendra Singh (Advisor); Jason Dreyer (Committee Member); Scott Noll (Committee Member)

Subjects:

Engineering; Mechanical Engineering; Packaging

Keywords:

packaging, transport vibrations, dynamic substructuring, finite element analysis FEA, nonlinear lumped models, numerical modeling, random vibration tests

Yang, PeiyuExperimental Techniques and Mechanical Behavior of T800/F3900 at Various Strain Rates
Master of Science, The Ohio State University, 2016, Mechanical Engineering
Mechanical behavior of the composite material T800/F3900, a strengthened epoxy carbon-fiber reinforced polymer, is investigated in multiple types of loading conditions at various strain rates. The objective of the project is to generate experimental data for calibration of the material model, MAT_213, in LS-DYNA for better predictive accuracy of the composite material in numerical simulations. Anisotropic material properties, strain rate effects and geometry effects are studied. In-plane and out-of-plane tension and compression tests are conducted at strain rates ranging from 0.001 1/s to 1000 1/s. In-plane shear experiments are performed to learn shear characteristics of the material in 1-2 and 2-1 directions. In-plane tension, compression and shear test samples are cut from a 0.125” 16-ply panel, and out-of-plane tension and compression test samples are cut from a 0.7” 96-ply panel. Strain rate effects are noticeable in compression in the 90-degree and through thickness orientations, and more test data is required to see if strain rate effects exist in tension in the transverse direction. Anisotropic mechanical behavior is also significant in each orientation. Four geometries of tension test samples are attempted in tension test series since pre-mature failure is seen taking place in tension test samples. Tension test data from each geometry are studied and compared in order to learn how geometry influences the mechanical responses. Double notch shear specimen is used for investigating in-plane shear properties of the material. The physical loading conditions applied on the test samples and failure modes in 1-2 shear and 2-1 shear experiments are studied in the shear test series. Two-dimensional and three-dimensional Digital Image Correlation are used to measure full field strains. Numerical simulations are done using LS-DYNA for investigating the hydrostatic stress states at the endpoint of the parallel gage section of the tension dobgone test samples. Strain states from simulation results are also compared to DIC measurement data.

Committee:

Amos Gilat, Dr. (Advisor); Brian Harper, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Composites, split Hopkinson bar, Digital Image Correlation, Dynamic test, LS-DYNA, Finite Element Analysis

Jain, Akshay AshokDesign and LENS® Fabrication of Bi-metallic Cu-H13 Tooling for Die Casting
Master of Science, The Ohio State University, 2013, Industrial and Systems Engineering
Thermal fatigue is one of the most common causes leading to die failure in die casting. This thesis investigates and presents the results of thermal fatigue life in a bi-metallic H13-Copper die which can be manufactured using laser additive manufacturing technologies now commercially available. Using finite element method, computational models are developed to simulate the thermal fatigue tests of Wallace (Benedyk, Moracz, and Wallace 1970). Numerical solutions to the thermal-mechanical problem are obtained. The solutions include temperature, strain and stress distributions within the test sample. Solutions were obtained for varying amounts of copper in the test sample geometry. Results from the pure H13 sample computational model compared very well with experimental values obtained by Wallace (Benedyk, Moracz, and Wallace 1970). The maximum temperature reached by the test sample is shown to decrease with increasing amounts of copper. The fatigue life is calculated using the `method of universal slopes’ which relates the calculated cyclic strain ranges to the number of cycles necessary for fatigue crack initiation. The specimen geometry consisting of a half thickness of Cu and the other half thickness of H13 at the thinnest point in the full cross-section of the wall thickness was shown to provide the best balance between thermal and fatigue life performance.

Committee:

Jerald Brevick (Advisor)

Subjects:

Engineering; Industrial Engineering; Mechanical Engineering; Metallurgy

Keywords:

Die Casting; Bi-metallic tooling; Copper; H13; Die Casting Tooling; Ansys; Finite Element Analysis; FEA; Thermal Fatigue Die Casting; Laser Engineered Net Shaping; Laser Additive Manufacturing; Copper-H13; H13-Copper; Cu-H13; H13-Cu; Dunk Test;

Koya, BharathA Finite Element Study on Medial Patellofemoral Ligament Reconstruction
Master of Science in Engineering, University of Akron, 2013, Biomedical Engineering
Patellar instability is a major problem among young individuals. Chronic patellar instability termed as patellar dislocation occurs mainly due to the reduction in the medial restraining forces for the patella, excessive Q-angle, patella alta and trochlear dysplasia. It causes a tear of the medial patellofemoral ligament (MPFL) in the majority of instances. The MPFL is the main passive stabilizer preventing patellar instability and accounts for 50-60 % of the total restraining forces. Reconstruction of the torn MPFL is a surgical option performed in chronic cases to improve patellofemoral biomechanics and to provide better stability at the knee. Finite element analysis (FEA) makes it possible to simulate the surgical technique of reconstruction of the MPFL, observe the effects on the articular cartilage structures and determine the patellofemoral kinematics, which is not possible with in vivo imaging analysis. In the present study, subject specific computational (finite element) models were built in ABAQUS based on the 3D anatomical geometry of the patellofemoral joint from pre–op MRI scans. The femur and patella were modeled as rigid structures with quadrilateral elements. Patellofemoral articular cartilage was modeled as isotropic elastic structures with hexahedral elements. The quadriceps muscle group, patellar tendon and the MPFL graft were represented using linear tension-only springs. The quadriceps muscle force was calculated from the foot load that the patient was able to withstand at a particular flexion angle during the MRI scan. The MPFL reconstruction surgery was simulated by modeling the ligament with uniaxial connector elements and material properties representing the graft material. FE simulations with appropriate boundary and loading conditions showed that the lateral translation was restricted with a MPFL graft. Validation of these FE models was done by comparing the results with the kinematics obtained from an analysis based on MRI scans taken before and after the MPFL reconstruction surgery. FEA results matched the trends observed in the results of the experimental study, but they failed to replicate them quantitatively. In addition, the ratio of tension in the patellar tendon and quadriceps muscles and the tension in the MPFL graft elements was obtained from the simulations. The technique used in the present study can be improved by dealing with the limitations of the modeling like meshing of the structures and material properties. The FE models can be used to study the inter-subject differences, graft attachment points and graft tensioning to help with the ligament reconstruction procedures.

Committee:

John Elias, Dr (Advisor); Marnie Saunders, Dr (Advisor); Mary Verstraete, Dr (Committee Member)

Subjects:

Biomechanics; Biomedical Engineering; Biomedical Research; Engineering

Keywords:

MPFL, MPFL RECONSTRUCTION, SEMITENDINOSUS TENDON, PATELLA DISLOCATION, FINITE ELEMENT ANALYSIS OF PATELLOFEMORAL JOINT, PATELLAR KINEMATICS, PATELLAR SHIFT, PATELLAR TILT, Knee Biomechanics

Zhang, ChaoMulti-Scale Characterization and Failure Modeling of Carbon/Epoxy Triaxially Braided Composite
Doctor of Philosophy, University of Akron, 2013, Civil Engineering
Carbon/Epoxy two-dimensional triaxially braided composites are known to have excellent damage tolerance, energy absorption and impact resistance. Recently, many aircraft manufactures have used such braided composite for engine fan cases. The mechanical interlocking and large unit cell of the fabric architecture enable the material to behave like a structure. On the other hand, this complicated architecture increases the difficulty of experimental characterization and numerical simulation, due to the existence of free edge effect induced premature local damage in standard coupon specimens. The goal of this research is an attempt to identify the damage mechanism of this braided composite, develop analytical and numerical tools to simulate the elastic and failure behavior, and obtain accurate material properties for design of structures and components. Multi-scale modeling is a well established approach in simulating textile composites. In this work, a meso-scale finite element modeling framework is developed to simulate the local and global damage behavior and investigate the failure mechanisms. To achieve the accuracy of the meso-scale model, the micro-scale geometry features are examined in detail to provide support for building a realistic representative model; micromechanical finite element models are developed to predict the material constants of meso-scale fiber tows. On the macro-scale, both analytical models and numerical models are used to predict the global effective stiffness. A comprehensive analysis of the experimentally measured and numerical predicted elastic and strength properties are presented to verify the accuracy of numerical models and evaluate the ability of different types of specimens. The material constants of an infinite large plate are predicted using the numerical models. This can help to make design of structures more efficient and build accurate numerical models representing behavior of braided composites. Particular attention is paid on the analysis of free edge effect which was known to lead to premature local damage and failure. It is found in the numerical studies and confirmed by experiments that the free edge effect can also cause a reduction of effective stiffness. The edge effect that acts in the form of out-of-plane warping is found to be an inherent behavior of the triaxially braided architecture. It is also identified in experiments that some material properties may depend on the coupon width, especially in transversely loaded specimens. Through a numerical dimensional analysis, the relationship of specimen width and effective stiffness and strength is quantified. The long-term performance of the material is also studied by conducting thermal cycling test. Acoustic Emission and X-ray CT scanning are used to detect the aging induced microcracking damage behavior and predict the saturation number of thermal cycles. Multi-scale finite element models are utilized to predict the degradation of mechanical properties and impact resistance of microcracked braided composite panels.

Committee:

Wieslaw Binienda, Dr. (Advisor); Ernian Pan, Dr. (Committee Member); Anil Patnaik, Dr. (Committee Member); Xiaosheng Gao, Dr. (Committee Member); Erol Sancaktar, Dr. (Committee Member); Robert Goldberg, Dr. (Committee Member)

Subjects:

Aerospace Materials; Civil Engineering; Engineering; Experiments; Mechanical Engineering; Mechanics; Sustainability; Textile Research

Keywords:

Triaxially braided composites; Failure mechanics; Multi-scale simulation; Free edge effect; Out-of-plane warping; Thermal cycling aging; Microcracking; Fiber bundle undulation; Finite element analysis; Elastic behavior

Ma, XiaoyueFINITE ELEMENT MODELING OF COLLAGEN FIBERS IN THE MECHANICAL INTERACTION BETWEEN CELLS AND THE EXTRACELLULAR MATRIX
Doctor of Philosophy, The Ohio State University, 2012, Biomedical Engineering
Cells can sense, signal and organize via mechanical forces. The ability of cells to mechanically sense and respond to the presence of other cells over relatively long distances across extracellular matrix (ECM) has been attributed to the strain-hardening behavior of the ECM. In this study, we explore an alternative hypothesis that the fibrous nature of the ECM makes long-range stress transmission possible, which could provide a mechanism for long-range cell-cell mechanical signaling. To test this hypothesis, we built 2-D and 3-D finite element models of stress transmission within cell-seeded collagen gels. To examine the role of collagen fibers in lateral stress transmission, confocal reflectance microscopy was used to develop 2-D image-based finite-element models. Models that account for the gel’s fibrous nature were compared with homogenous linear-elastic and strain-hardening models to investigate the mechanisms of stress propagation. To examine the role of collagen fibers in cell thickness sensing, 3-D finite element models with idealized fiber networks were built, and the stress transmissions in fibrous and homogeneous ECM were compared. Finite-element analysis revealed that stresses generated by cell contraction are concentrated in the relatively stiff ECM fibers and are propagated farther in a fibrous matrix as compared to linear elastic or strain-hardening homogenous materials. These results support the hypothesis that ECM fibers, especially aligned ones, play an important role in long-range stress transmission. Further, fluid-structure interaction models were built to investigate the interplay between collagen fibers and interstitial fluid. The results suggest that in cell culture, cell movement is the key factor in defining fluid-flow development at the microscopic ‘cellular’ level, and the cross-links are the key factor that determines the micro-mechanical environment.

Committee:

Richard T. Hart (Committee Chair); Keith J. Gooch (Committee Member); Samir N. Ghadiali (Committee Member); Jun Liu (Committee Member)

Subjects:

Biomechanics; Biomedical Engineering

Keywords:

Extracellular matrix; stress propagation; fibrous matrix; strain-hardening; finite element analysis; collagen gel mechanics

Varghese, Bino AbelQuantitative Computed-Tomography Based Bone-Strength Indicators for the Identification of Low Bone-Strength Individuals in a Clinical Environment
Doctor of Philosophy (PhD), Wright State University, 2011, Biomedical Sciences PhD

The aim of the current study was to develop quantitative computed-tomography (QCT)-based bone-strength indicators that highly correlate with finite-element (FE)-based strength. We perform a combined numerical-experimental study, comparing FE-predicted surface strains with strain gauge measurements, to validate the FE models of 36 long bones (humerus, radius, femur and tibia) under three-point bending and torsion. The FE models were constructed from trans-axial volumetric CT scans, and the segmented bone images were corrected for partial-volume effects. The material properties (Young's modulus for cortex, density-modulus relationship for trabecular bone and Poisson's ratio) were calibrated by minimizing the error between experiments and simulations among all bones. The resultant R2 values of the measured strains versus load under three-point bending and torsion were 0.96-0.99 and 0.61-0.99, respectively, for all bones in our data set. The errors of the calculated FE strains in comparison to those measured using strain gauges in the mechanical tests ranged from -6% to 7% under bending and from -37% to 19% under torsion. The observation of comparatively low errors and high correlations between the FE-predicted strains and the experimental strains, across the various types of bones and loading conditions (bending and torsion), validates our approach to bone segmentation and our choice of material properties.

Based on the analysis of the various FE models of the long bones, the location of the CT slice on the bone that showed the highest propensity to fracture was identified for four loading conditions (compression, three-point bending, cantilever bending and torsion). The identified CT slice was then used to derive novel and improved bone-strength indicators. We evaluated the performance of area-weighted (AW), density-weighted (DW) and modulus-weighted (MW) rigidity measures as well as popular strength indicators like section modulus and stress-strain index. We have also developed a novel strength metric, the centroid deviation, which takes into consideration the spatial distribution of the centroids. Here, we observed that the MW polar moment of inertia and the MW moment of inertia were the two top-performers (average r < 0.87) for all bones and loading conditions. The MW centroid deviations correlated highly with the load to fracture for all bones under compression (r <0.83), except for the humerus (r = 0.67).

To test the power of the bone-strength indicators, a receiver operating characteristic (ROC) analysis of the MW rigidity measures that showed the two highest correlations in the femur under compression and three-point bending was performed. QCT scans of a subset of 10 white and 10 black males, who were subjects of a larger study, which reported ethnic differences in bone strength, were used. Results from this small pilot study indicated that the MW section modulus and the MW stress-strain index are the two top performing indicators (area under the ROC curve < 0.79).

Consistently DW or MW rigidity measures produced a statistically significant improvement in capturing bone strength compared to AW rigidity measures. The improvement in MW over DW rigidity measures was small yet statistically significant.

Committee:

Thomas Hangartner, PhD (Advisor); Robert Fyffe, PhD (Committee Member); Marvin Miller, MD (Committee Member); Ravi Penmetsa, PhD (Committee Member); Julie Skipper, PhD (Committee Member)

Subjects:

Biomechanics; Biomedical Engineering; Biomedical Research; Medical Imaging

Keywords:

Computed Tomography; Finite Element Analysis; Mechanical Testing; Long Bones; Bone-Strength Indicator

Hauber, Robert J.Finite element analysis of an integrally molded fiber reinforced polymer bridge
MS, University of Cincinnati, 2011, Engineering and Applied Science: Civil Engineering
A finite element model of a fiber reinforced polymer (FRP) bridge in Hamilton County, Ohio was conducted using the computer program SAP2000. The purpose of the model was to determine the vertical deflection under a specified truck loading and to compare the analytical results from the model with load test results of the actual bridge, which spanned approximately 20 feet. The bridge superstructure was composed of eight separate panels that were assembled on site. The panels were constructed of a sandwich panel deck with integral beams spaced approximately two feet on center with the panels themselves being approximately seven and a half feet wide. The finite element model utilized shell elements to represent the different FRP components of the bridge such as the top and bottom faces of the deck along with the beam webs and flanges. The material properties input into the model for the shell elements were provided by the manufacturer. A mesh sensitivity analysis was conducted to identify an adequate discretization of the bridge without creating an excessive amount of elements in the model. Once this was accomplished, the entire bridge was then modeled with the applied loading to mimic the truck loading tests to which the actual bridge was subjected in order to assess the validity of the finite element model. The results of the model showed good agreement with the experimental results, validating the model.

Committee:

Richard Miller, PhD (Committee Chair); Gian Rassati, PhD (Committee Member); Bahram Shahrooz, PhD (Committee Member)

Subjects:

Civil Engineering

Keywords:

fiber reinforced polymer;finite element analysis;bridge;shell elements;mesh sensitivity

Belisle, Kathryn J.Experimental and Finite Element Analysis of a Simplified Aircraft Wheel Bolted Joint Model
Master of Science, The Ohio State University, 2009, Mechanical Engineering

The goal of this thesis is to establish a correlation between experimental and finite element strains in key areas of an aircraft wheel bolted joint. The critical location in fatigue is the rounded interface between the bolt-hole and mating face of the joint, called the mating face radius. A previous study considered this area of a bolted joint but only under the influence of bolt preload. The study presented here considered both preload and an external bending moment.

This study used a more complete single bolted joint model incorporating the wheel rim flange and the two main loads seen at the bolted joints; bolt preload and the external load created by tire pressure on the wheel rim. A 2x3 full factorial DOE was used to establish the joint’s response to various potential load combinations assuming two levels of preload and three levels of external load. The model was analyzed both experimentally and in finite element form. The strain results around the mating face radius were compared between the two analyses. Several parameters were identified that could affect the correlation between the results. The finite element model was modified to incorporate each of these factors and the new results were compared against the original finite element results and the experimental data. The best correlation was found when the finite element model preload was adjusted such that the mating face radius strains under only preload matched those of the experimental results.

Committee:

Anthony Luscher, PhD (Advisor); Mark Walter, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

bolted joint; assembled joint; finite element analysis; aircraft wheel

Xu, QuanA Method to Evaluate the Interfacial Friction Between Carbon Nanotubes and Matrix
Master of Science in Engineering, University of Akron, 2011, Mechanical Engineering
A new method has been developed to determine the interfacial friction between carbon nanotubes (CNTs) and polymer matrix. A stripe made of Poly(methyl methacrylate) PMMA was imprinted as a specific contact pattern on a CNTs substrate with an ordered nanotube array. By simultaneously measuring the vertical displacement and monitoring load in the decohesion process, the interfacial friction was calculated based on analytical formula from micromechanics. To extract quantitative results, a 3D finite element model for the decohesion test was developed and a cohesive zone model was used to predict the complex equilibrium of crack front. The model predicts that the interfacial energy is a function of maximum separation force, sample size and CNTs height, and the model agrees well with full numerical results over a wide range of stripe and substrate property values. The overall method is applied here to determine the interfacial friction of CNTs/PMMA Matrix.

Committee:

Zhenhai Xia, Dr. (Advisor); Xiaosheng Gao, Dr. (Committee Member); Gregory Morscher, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Carbon Nanotubes; Polymer matrix; Finite Element Analysis; interface friction test

Zafaruddin, MohammedFinite Element Analysis of EMI in a Multi-Conductor Connector
Master of Science in Engineering, University of Akron, 2013, Electrical Engineering

This thesis discusses the numerical analysis of electrical multi-conductor connectors intended for operation at high frequencies. The analysis is based on a Finite Element Tool and looks at the effect of conductors on each other with a view to design for electromagnetic compatibility of connectors. When there is an electrically excited conductor in a medium, it acts as an antenna at high frequencies and radiates electromagnetic power. If there are any conductors in its vicinity they too act as antennas and receive a part of the EM power. Electromagnetic Interference (EMI) from nearby excited conductors causes induced currents according to Faraday's law which is considered as noise for other conductors. This noise is affected by factors such as distance between the conductors, strength and frequency of currents, permittivity, permeability and conductivity of the medium between the conductors.

To reduce the effects of EMI in a shielded multi-conductor connector, values of induced currents at various distances between the conductors have been calculated and analyzed. The currents have been calculated at high excitation frequencies varying from 0.2GHZ to 1GHZ and distances between the conductors varying from 0.2 mm to 0.8 mm.

Committee:

Nathan Ida, Dr (Advisor); George C Giakos, Dr (Committee Member); Hamid Bahrami, Dr. (Committee Member)

Subjects:

Electrical Engineering; Electromagnetics; Electromagnetism

Keywords:

Connector; EMI; EMC; Induced Currents; Finite Element Analysis, Dielectric

Seyed Vosoughi, ArdalanMitigating the Biomechanical Complications Following Pedicle Subtraction Osteotomy: A Finite Element Analysis
Master of Science, University of Toledo, 2017, Bioengineering
Following advances in spinal instrumentation and techniques, management of the sagittal malalignment has gone through a significant evolution. In this regard, spinal osteotomy surgeries have evolved to achieve balance, inhibit the deformity progression, and mitigate pain in the patients. Among the realignment techniques, pedicle subtraction osteotomy (PSO) has become a common method to correct adult spinal deformity. Despite multiple benefits of the PSO in addressing the sagittal spinal imbalance, it is a technically demanding procedure. A major complication associated with PSO is rod breakage, and the rate of postoperative complication has been reported to be as high as 31.6%. Despite various efforts to study PSO in recent years, the biomechanical reasons for the high rate of rod failure remain unclear. In this study, the finite element modeling of PSO is used to assess the biomechanical effects of the lumbar disc degeneration and various instrumentation techniques including the use of multi rods, interbody spacers, and cross connectors on the instrumentation. Multi-rod constructs included medially, laterally, and posteriorly affixed satellite rod configurations and the short-rod technique. Biomechanical studies were conducted to evaluate various parameters such as range of motion, maximum von Mises stress on the rods, and the force acting on the osteotomy site. The results of the current study showed that larger discs adjacent to the PSO lead to a greater motion and instability and superior maximum von Mises stress on the rods which occurred at the PSO region. In multi-rod constructs, adding satellite rods in various loading directions decreases the maximum von Mises stress at the PSO region which results in lower risk of rod fracture at this site. Furthermore, it was observed that in multi-rod constructs connected with side-by-side connectors the greatest stress concentration occurs adjacent to the connectors. At the PSO region by adding satellite rods medially and laterally the maximum von Mises stress occurs on the medial rods. These observations indicate that at the PSO region in the medially affixed constructs there is a greater risk of rod failure in satellite rods while in the laterally affixed constructs it is on the primary rods. These findings exhibit a significant benefit in supplementing the PSO setting with the medially affixed satellite rods over the laterally affixed satellite rods that in the case of rod failure the surgeon can easily replace the satellite rods instead of the primary rods. The findings demonstrated that placing the satellite rods posteriorly allows for more stress reduction on the instrumentations. The current FE study also signified that except short-rod technique all other multi-rod constructs decrease the magnitude of the load acting on the osteotomy region which may cause in delayed union or non-union of the PSO site. Interbody spacer placement in the PSO setting decreases the maximum von Mises stress on the rods while it increases the stability and the force acting on the osteotomy region. Finally, adding cross-connectors to a PSO acute setting has a slight stabilizing potential in axial rotation motion, and the greater number of cross-links may increase the rate of rod fracture.

Committee:

Vijay Goel (Advisor); Anand Agarwal (Committee Member); Ronald Fournier (Committee Member); Amanda Bryant-Friedrich (Committee Member)

Subjects:

Biomechanics; Biomedical Engineering

Keywords:

Pedicle Subtraction Osteotomy; Rod Fracture; Spine; Instrumentation; Finite Element Analysis; Biomechanics

Syed Shah, Taqiuddin QAn Alternative Strengthening Technique using a Combination of FRP Sheets and Rods to Improve Flexural Performance of Continuous RC Slabs
Master of Science, University of Toledo, 2016, Civil Engineering
The present research in this study is directed towards improving the flexural performance, namely the load and displacement ductility capacities, and exploring the various failure modes, of continuous reinforced concrete (RC) slab strips. This improvement is accomplished by applying fiber reinforced polymers (FRP) of two types: FRP sheets and FRP rods, in both positive and negative regions of moment of the continuous RC slab strip. Currently, experimental research has shown that applying FRP rods using the near surface mounted (NSM) method to strengthen continuous RC structures can greatly improve flexural capacity and moment redistribution. Despite the benefits of FRP rods through the NSM method, applying FRP sheets using the externally bonded reinforcement (EBR) method is more common due to its ease of application and cost. Thus, this study takes into account the benefits of both NSM & EBR strengthening techniques, and presents an alternative strengthening combination using EBR-FRP sheets to strengthen the positive moment or sagging region, and NSM-FRP rods to strengthen the negative moment or hogging region of continuous RC slabs strips. Currently, the challenges faced when using FRP strengthening depends on the type of FRP material used. The EBR-FRP sheets suffer from debonding (loss of stress transfer between concrete-FRP) failures when facing high moments. To prevent these, anchorages can be provided. These anchorages are however, expensive and their applicability is limited. NSM-FRP rods suffer from sudden FRP rupture but are generally safer to use than FRP sheets. However, they require cutting of grooves on the concrete surface limiting their applicability in certain regions as well. The presented alternative strengthening combination aims at overcoming these drawbacks by applying EBR-FRP sheets in most locations while reducing the need for anchorages, and using NSM-FRP strengthening only in locations that benefit from concrete cover. Through, complex finite element analysis (FEA), the effectiveness of this combined strengthening method is investigated. Parametric studies to study the influences of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP), various FRP reinforcement ratios (¿_frp^ ), and width of EBR sheet, on the flexural load and displacement ductility capacities, concrete-FRP bond strength, and failure modes, are also discussed. The general conclusion from this study indicates that the combination of using both EBR and NSM techniques simultaneously is more effective than using either EBR or NSM independently. CFRP material provided better load capacity and displacement ductility than GFRP; however GFRP led to more predictable failure modes. Overall, the sagging region FRP showed higher influence in increasing the load capacity and ductility. The hogging region FRP showed higher influence on the type and location of failure mode. Additionally, the hogging region FRP had a detrimental effect on the ductility when increased. The width of FRP sheets had a low impact on the bond strength or failure modes when lower ¿_frp^ values were used. However, using higher ¿_frp^ values required wider FRP sheets to prevent FRP debonding failures. Using wider FRP sheets also resulted in slightly higher displacement ductility.

Committee:

Azadeh Parvin (Committee Chair); Mark Pickett (Committee Member); Eddie Chou (Committee Member)

Subjects:

Civil Engineering; Engineering; Polymers

Keywords:

Near surface mounted, NSM, fiber reinforced polymers, FRP, externally bonded reinforcement, EBR, reinforced concrete, RC, continuously supported, applied loading, finite element analysis, FEA, debonding, failure mode, ANSYS

Warrell, Gregory RalphComputational and Experimental Evaluations of a Novel Thermo-Brachytherapy Seed for Treatment of Solid Tumors
Doctor of Philosophy, University of Toledo, 2016, Physics

Hyperthermia has long been known as a radiation therapy sensitizer of high potential; however successful delivery of this modality and integrating it with radiation have often proved technically difficult. We present the dual-modality thermo-brachytherapy (TB) seed, based on the ubiquitous low dose-rate (LDR) brachytherapy permanent implant, as a simple and effective combination of hyperthermia and radiation therapy. Heat is generated from a ferromagnetic or ferrimagnetic core within the seed, which produces Joule heating by eddy currents. A strategically-selected Curie temperature provides thermal self-regulation. In order to obtain a uniform and sufficiently high temperature distribution, additional hyperthermia-only (HT-only) seeds are proposed to be used in vacant spots within the needles used to implant the TB seeds; this permits a high seed density without the use of additional needles.

Experimental and computational studies were done both to optimize the design of the TB and HT-only seeds and to quantitatively assess their ability to heat and irradiate defined, patient-specific targets. Experiments were performed with seed-sized ferromagnetic samples in tissue-mimicking phantoms heated by an industrial induction heater. The magnetic and thermal properties of the seeds were studied computationally in the finite element analysis (FEA) solver COMSOL Multiphysics, modelling realistic patient-specific seed distributions. This distributions were derived from LDR permanent prostate implants previously conducted at our institution; various modifications of the seeds' design were studied. The calculated temperature distributions were analyzed by generating temperature-volume histograms, which were used to quantify coverage and temperature homogeneity for a range of blood perfusion rates, as well as for a range of seed Curie temperatures and thermal power production rates. The impact of the interseed attenuation and scatter (ISA) effect on radiation dose distributions of this seed was also quantified by Monte Carlo studies in the software package MCNP5.

Experimental and computational analyses agree that the proposed seeds may heat a defined target with safe and attainable seed spacing and magnetic field parameters. These studies also point to the use of a ferrite-based ferrimagnetic core within the seeds, a design that would deliver hyperthermia of acceptable quality even for the high rate of blood perfusion in prostate tissue. The loss of radiation coverage due to the ISA effect of distributions of TB and HT-only seeds may be rectified by slightly increasing the prescribed dose in standard dose superposition-based treatment planning software.

A systematic approach of combining LDR prostate brachytherapy with hyperthermia is thus described, and its ability to provide sufficient and uniform temperature distributions in realistic patient-specific implants evaluated. Potential improvements to the previously reported TB seed design are discussed based on quantitative evaluation of its operation and performance.

Committee:

Diana Shvydka, Ph.D. (Advisor); E. Ishmael Parsai, Ph.D. (Committee Member); Victor Karpov, Ph.D. (Committee Member); Yanfa Yan, Ph.D. (Committee Member); Sorin Cioc, Ph.D. (Committee Member)

Subjects:

Biophysics; Medicine; Physics

Keywords:

thermo-brachytherapy, brachytherapy, hyperthermia, dual-modality, self-regulating, blood perfusion, Curie temperature, prostate carcinoma, prostate cancer, interseed effect, Monte Carlo, finite element analysis

Baver, Brett CProperty Identification of Viscoelastic Coatings Through Non-contact Experimental Modal Analysis
MS, University of Cincinnati, 2016, Engineering and Applied Science: Mechanical Engineering
Viscoelastic coatings are currently being used in a variety of industries to provide shock absorption, energy absorption, noise reduction, and vibration isolation. They are commonly used through aerospace, automotive, and electronic industries. These materials have a complex behavior that causes their mechanical properties to vary with both temperature and frequency. Testing historically has been done on a composite material due to the inability of the coatings to support themselves at high temperatures. One common method is the vibrating beam technique, which examines two cantilever beam specimen, an uncoated beam and a coated beam. The change in modal properties is used to determine the properties of the viscoelastic material by itself. However, when the environment is harsh or space is restricted, measurements and excitations cannot be made in a traditional contacting manor. This paper examines methods of non-contact excitation and measurements and explores the effects from these methods. Specifically, magnetic excitation was examined as a source of non-contact excitation on a non-ferrous material. This requires that a magnetic material be attached to the beams in order for the magnetic excitation to be successful. The mass loading effects were examined for the two beam specimen to most accurately define the modal parameters of the beams. This excitation source was also used to test the specimen at a range of temperatures to determine the effect temperature had on the modal parameters of the specimen as well. Finite element models were subsequently created to see if the results from the experimental modal analysis could be confirmed with the FEA results.

Committee:

Randall Allemang, Ph.D. (Committee Chair); Jay Kim, Ph.D. (Committee Member); Allyn Phillips, Ph.D. (Committee Member)

Subjects:

Mechanics

Keywords:

Experimental Modal Analysis;Finite Element Analysis;Vibrating Beam Technique

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