Department: EMC - Mechanical Engineering ![[clear]](close-x.png "Remove this limiter")
60 matches in the database.
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1.
Bachmann, Richard Joseph.
A Hybrid Vehicle for Aerial and Terrestrial Locomotion.
Degree: PhD, EMC - Mechanical Engineering, 2009, Case Western Reserve University
► A durable hybrid vehicle has been developed capable of both aerial and…
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▼ A durable hybrid vehicle has been developed capable of both aerial and terrestrial locomotion. The motivation for the work was a wide range of sensor deployment scenarios that would benefit from a vehicle capable of 1) flying long distances to a target area and 2) walking around the target to perform near-field inspection. A technology survey was performed to identify the candidate terrestrial and aerial locomotion technologies for integration. The Mini-Whegs robot, developed at Case Western Reserve University, was selected as the terrestrial running gear, and the flexible-wing micro air vehicle (MAV), developed at University of Florida, was selected as the aerial platform. A rigorous trade-off analysis led to a remote control prototype that had a fully functional airframe augmented with two R/C servos, modified for continuous rotation, driving independent music wire wheel-legs at the front of the vehicle. This vehicle achieved most of the original performance requirements. It could fly, land, crawl, and regain flight by crawling off the edge of a rooftop. A critical performance evaluation illuminated improvements to the design and fabrication necessary to create a viable hybrid vehicle for field deployment. The vehicle design and fabrication processes were overhauled to improve the durability and reproducibility of the final design. A custom-built terrestrial locomotion subsystem, with compliance in the drive train, was crucial to improved durability. CNC fabrication of the fuselage mold and a one-piece tail design were central to repeatability. A commercially available autopilot was implemented for autonomous operation. Vehicle mass increased from 118 to 365 grams. The wingspan was subsequently increased to 16", but wing loading increased from 37 to 64 N/m2. A corresponding decrease in controllability was observed. Winglets were found to increase lift, but decrease stability by mitigating wing flexibility. The final vehicle was able to fly, land, and crawl repeatedly. Over 8 flights (and landings) have been performed by the vehicle, and the vehicle has yet to show any signs of damage. The vehicle cruises at 14 m/s and crawls at 0.33 m/s (0.8 body lengths per second). For comparison, a typical Mini-Whegs runs at 5 body lengths per second.
Advisors/Committee Members: Quinn, Roger.
Subjects: Mechanical engineering
Keywords: hybrid; locomotion; MAV; Whegs; terrestrial; aerial; integration
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2.
Baldwin, Zachary D.
Characterization of Anode Conditions and Limitations in Direct Carbon Fuel Cells.
Degree: MS, EMC - Mechanical Engineering, 2009, Case Western Reserve University
► Direct carbon fuel sells hold the promise of providing a clean and…
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▼ Direct carbon fuel sells hold the promise of providing a clean and efficient way to utilize the abundant supplies of coal world‐wide. Lower than expected fuel utilization efficiencies and the evidence of carbon monoxide in the cell anode are an indicationthat problems exist within the cell. A reliable experimental setup and cell design were designed in order to facilitate this investigation. Mass transport and kinetic resistances were suspected as the limiting factors. Through DCFC half cells, and a low temperature phosphoric acid analog, the extent of the mass transport issues were illustrated. Gas bubbles were being trapped in the anode itself, and hurting cell performance. The use of a theoretical model also illustrated that along with poor mass transport of reaction products out of the system, ion transport through the anode may also present a significant problem.
Advisors/Committee Members: Prahl, Joseph.
Subjects: Chemistry; Engineering; Mechanical engineering
Keywords: CARBON; Bed; Bubble; Foam; Phosphoric; Electrolyte; CELLS
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3.
Bartkus, Tadas Patrick.
An Analytical Model Based on Experimental Data for the Self-Hydrolysis Kinetics of Aqueous Sodium Borohydride.
Degree: PhD, EMC - Mechanical Engineering, 2011, Case Western Reserve University
► The objective of this work is to determine the self-hydrolysis kinetics of…
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▼ The objective of this work is to determine the self-hydrolysis kinetics of sodium borohydride (NaBH4) in a solution with liquid water (H2O) for hydrogen (H2) generation and storage purposes. In order to be able to derive two semi-global rate expressions, an extensive series of batch process experiments was performed in a glass flask where the following parameters were systematically varied: solution temperature varied from 298 K (25°C) to 348 K (75°C), NaBH4 concentration ranged from 0.5 wt% to 25.0 wt%, and the concentration of the hydrolysis stabilizer sodium hydroxide (NaOH) varied from 0.0 wt% to 4.0 wt%, which corresponds to initial solution pH values ranging from 9.5 to 12.95. Transient hydrogen generation rates and transient solution pH were measured during hydrolysis. Based on the data collected, the decomposition rate for NaBH4 when the effect of the transition period diminishes is found to be: -d[NaBH4]/dt=A1e(-49860 J/mol/R/T)[NaBH4][H+]0.788 Where A1=1.72x109(1/s)(L/mol)0.788 [NaBH4] represents the NaBH4 concentration in units of moles per kilogram of solution, [H+] represents the concentration of the hydrogen ion, H+, in units of moles per liter of water, R in the Arrhenius term is the universal gas constant and T is temperature in Kelvin. The expression for the rate of change of [H+] (or equivalently pH level) is: -d[H+]/dt=A2f([NaBH4]O)e(-7930 J/mol/R/T)e(-4.529(1-[NaBH4]/ [NaBH4]O))[H+]B2f([NaBH4]O) Where A2f([NaBH4]O)=(-2.236[NaBH4]O+36.608)(1/s)(L/mol)B2 B2f([NaBH4]O)=0.0973[NaBH4]O -2.763 The quantity [NaBH4]O represents the initial concentration of sodium borohydride and f is symbolic for a function. In principle, given initial conditions (temperature, NaBH4 concentration and H+ concentration), the two quasi-global coupled equations can be integrated to obtain the transient time history of H2 (or NaBH4) and solution pH (or H+). The model transient hydrogen generation rate and transient pH trends were compared with experimental data. Good agreement between analytical and experimental data was reached for many conditions, especially for elevated solution pH values, levels at which NaBH4 solutions are used practically.
Advisors/Committee Members: T'ien, James S.
Subjects: Chemical engineering
Keywords: sodium borohydride; self-hydrolysis; kinetics; analytical expressions; storage
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4.
Bartsch, Adam Jesse.
Biomechanical Engineering Analyses of Head and Spine Impact Injury Risk via Experimentation and Computational Simulation.
Degree: PhD, EMC - Mechanical Engineering, 2011, Case Western Reserve University
► Head and spine injuries, such as traumatic brain injury, skull fracture, concussion…
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▼ Head and spine injuries, such as traumatic brain injury, skull fracture, concussion and osteoligamentous cervical spine injury continue to be prevalent in motor vehicle crashes, athletics and the military. Automotive safety systems, athletic safety equipment and military personal protective paraphernalia designs have generally focused on protection discretely designed on a component basis – head or spine – but not a systems basis, considering the head-spine linkage simultaneously. But since the cervical spine acts as the attachment point for the head, the boundary conditions applied to the cervical spine influence the behavior of the head. Hence, in analyzing injury risk for the head and the spine, each structure composes one portion of an intrinsically linked osteoligamentous system; thus injury risk for the head and the cervical spine might be more appropriately considered concurrently as opposed to individually. Historically, component-based injury protection designs have utilized head and cervical spine injury risk criteria developed from human, animal and anthropomorphic surrogate studies. While a plethora of these prior studies separately analyzed head injury risk via linear acceleration, Head Injury Criterion (HIC) or Gadd Severity Index (GSI), or cervical spine injury risk via axial/shear forces, bending moments or the Neck Injury Criterion (Nij), relatively few of these studies employed a systems-based approach to understand coupled head-cervical spine injury risk behavior. Thus, designing for optimal head and cervical spine injury protection may not be as trivial as separate consideration of head or spine component injury thresholds. Therefore, through a series of six biomechanical engineering studies that comprised the chapters of this dissertation, the work presented here broadly investigated head and cervical spine injury protection on a systems-based approach considering head and cervical spine injury risk simultaneously. In Chapter 1, injury risk in inertial loading during real-world low energy minor rear car crashes was analyzed. In Chapter 2, these minor crashes from Chapter 1 were further investigated via use of numerical simulation in MADYMO. While Chapters 1 and 2 explored low energy car crash loading, Chapter 3 explored multivariate head and cervical spine injury implications from direct head loading during frontal airbag inflation in high energy experimental car crashes. Chapter 4 expanded the direct frontal head impact loading analyzed in Chapter 3 to include oblique and lateral impact loading during impact experiments with a Hybrid III anthropomorphic test device. The low- and high-energy injury analysis methods developed in Chapters 1 through 4 helped drive the study of multivariate injury risk in response to experimental omnidirectional athletic head impacts in Chapter 5. Chapter 6 further built on the high-energy athletic impacts from Chapter 5 via Matlab and Simulink simulation of helmeted impacts using a systems dynamics approach. Finally, Chapter 7 analyzed development of an impact pendulum, pilot cadaveric injury response to direct head impact and analysis of similar impacts in a helmeted human surrogate. The results of all of these related studies indicated that head and cervical spine injury risk were interrelated during direct or inertial car crash and athletic impacts.
Advisors/Committee Members: PRAKASH, VIKAS.
Subjects: Anatomy and Physiology; Biomechanics; Biomedical Engineering; Biomedical Research; Mechanical Engineering; Physics
Keywords: Head Injury; Neck Injury; Spine Injury; Injury Biomechanics; HIC; NIJ; Concussion; TBI; ATD; Dummy; Whiplash; Football; Athletics; Brain Injury; Car Crash; Low Speed; Cadaver; Hybrid III; Biorid
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5.
Belagod, Trivikram Srinivasan.
ALTERNATING LONGITUDINAL WEDGED COULOMB FORCES MINIMIZE TRANSVERSE TUBE VIBRATIONS THROUGH NON-LINEAR COUPLING.
Degree: MS, EMC - Mechanical Engineering, 2009, Case Western Reserve University
► The damping force and the self-excited force, which are a part of…
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▼ The damping force and the self-excited force, which are a part of Heat Exchanger tube vibrations, act in the same (transverse) direction. The wedging process introduces alternating longitudinal coulomb forces that act at double the frequency of transverse vibrations and is defined by the wave equation. The transverse vibrations and the alternating longitudinal coulomb forces are coupled and act orthogonal to each other. Physical observations show that the transverse vibrations cannot exist without longitudinal vibrations. The governing constitutive equations for coupling can be shown theoretically through material non-linearities by considering higher order terms for the elastic energy, and geometric non-linearities by considering non-linear strain displacement relations. This non-linear constitutive equation when used in the equation of motion for transverse vibrations, the Gol’dberg tensorial result emerges. Energy reorganization due to this coupling results in reduced transverse vibration amplitudes. A simple experimental setup simulating this wedging process validates that transverse vibrations cannot occur without longitudinal vibrations.
Advisors/Committee Members: Mansour, Joseph.
Subjects: Engineering
Keywords: heat exchanger; vibration; damping; self preloading; wedging; non linear coupling; heat exchanger tubes; transverse vibration; longitudinal vibration
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6.
Bennett, Daniel Alvin.
Angle Based Localization of an Autonomous Lawnmower via Radio Frequency Beacons and a Directional Antenna.
Degree: MS, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► Intelligent robots have the potential to become a major part of everyday…
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▼ Intelligent robots have the potential to become a major part of everyday life by performing menial household tasks, but are hindered by the high cost of sensors. Several companies have already started somewhat successful lines of autonomous robots, but as yet the functionality is too limited and the price is too high for widespread use. As a less expensive alternative to GPS for lawnmower navigation, this paper proposes the use of a rotating directional antenna to plot signal strengths verses angular displacement for several beacons of known locations to find their beacons relative to the mower. These angles are then used to triangulate the mower’s position. Preliminary testing of this method indicates possible antenna error of less than 4 degrees, which corresponds to a simulated position error of less than 1.5 meters. Such a system has the potential to be superior to inexpensive GPS units in both accuracy and cost.
Advisors/Committee Members: Quinn, Roger.
Subjects: Robots
Keywords: autonomous lawnmower; localization; directional antenna; wireless beacons; triangulation
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7.
Beno, Jonathan A.
CWRU Cutter: Design and Control of an Autonomous Lawn Mowing Robot.
Degree: M. Eng., EMC - Mechanical Engineering, 2010, Case Western Reserve University
► CWRU Cutter was designed to compete in the 2008 and 2009 ION…
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▼ CWRU Cutter was designed to compete in the 2008 and 2009 ION Autonomous Lawnmower Competitions. CWRU Cutter tests the feasibility of autonomously mowing grass with a high quality of cut using commercially available sensors and computers. The primary objective was to accurately and robustly mow predefined paths and perform reactive edging around stationary obstacles. The secondary objective of CWRU Cutter is to provide a platform to test less expensive, commercially viable sensors that will allow a safe and robust autonomous lawn mower to be brought to market. This thesis describes the mower hardware and mechanical design, the path driver, a 3D gimbaled LIDAR mount, and the potential for ultrasonic sensors on future mowers.
Advisors/Committee Members: Quinn, Roger.
Subjects: Mechanical engineering
Keywords: autonomous; robot; lawnmower; lawn mower; gps; LIDAR; ION; CWRU Cutter
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8.
Bifano, Michael F. P.
Theory and Measurements of Thermal Properties in Nanowires and Carbon Nanotubes.
Degree: PhD, EMC - Mechanical Engineering, 2012, Case Western Reserve University
► The extraordinary potential of nanoscale materials and nano-constituent composite materials coupled with…
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▼ The extraordinary potential of nanoscale materials and nano-constituent composite materials coupled with rapid progress in the capability to synthesize these materials has created a demand for their property characterization. To develop a better understanding of thermal transport in nanoscale wires and nanotubes, this thesis utilizes both theoretical and experimental techniques to determine how nanostructure geometry, surface properties, and heat treatment affect their ability to conduct thermal energy. As an example, the effect of heat treatment on the thermal conductivity of commercially available, chemical vapor deposition-grown, multiwalled carbon nanotubes (MWCNTs) is presented. The measurement device is implemented inside a scanning electron microscope equipped with nanomanipulators and a gas injected electron beam deposition system for repeatable in-situ sample characterization. MWCNT samples treated to 3000 C show a 5-fold increase in average thermal conductivity as compared to the as-synthesized samples. By including an estimation of thermal contact resistance due to phonon impedance mismatch, the average thermal conductivity of the heat-treated MWCNT specimens is estimated to be 228 W/m-K. The results suggest that heat treatment is a viable method to improve thermal conductivity and highlight the importance of MWCNTs quality in thermal management applications. Classical MD simulations are used to investigate the sensitivity of thermal conductivity to side-wall defects in SWCNTs. Vacancy repair is evident with heat treatment. 3000 C heat treatment of SWCNTs having varying degrees of defect concentrations is found to generally increase thermal conductivity by at least 10 %. The results suggest that phonon mean free path in (6,6) SWCNTs is nearly equally impeded by side-wall functionalization as compared to atomic vacancies. Classical MD simulations estimate that 2 atom % of hydrogenation and 1.5 - 2 % vacancy concentrations reduce thermal conductivity to the same degree. As compared to non-functionalized SWCNTs, the results suggest that the use of chemically functionalized SWCNTs as a second phase material in multifunctional CNT-polymer composites may reduce thermal transport. Nanoscale effects on thermal properties are further evaluated by an investigation into the dependency of specific heat and ballistic thermal conductance on cross-sectional geometry in free-standing isotropic non-metallic crystalline nanostructures. Analysis of phonon confinement is performed using dispersion relations found by numerically solving the Pochhammer-Chree frequency equation for a tube. These dispersion relations are used to evaluate the specific heat and ballistic thermal conductance in the nanostructures as a function of the nanostructure geometry, size, and surface stiffness. 1D, 2D, and 3D geometric phonon confinement regimes are recognized and found to depend on both the nanostructure’s wall thickness and outer radius. Compared to nanowires, the frequency reduction of acoustic phonon modes in thinner walled nanotubes is shown to elevate the ballistic thermal conductance of the thin-walled nanotube between 0.2 K and 150 K. At 20 K, the ballistic thermal conductance of the thin-walled nanotube is found to be 300% greater than that of a solid nanowire. Surface modification of nanotubes and nanowires is performed using a multilayer elastic model to increase the average Young’s modulus of the first three atomic surface layers. The acoustic stiffening of the interior and exterior lateral walls of nanotubes is found to have a contrasting effect on specific heat and thermal conductivity as compared to the outer surface modification of the nanowire. A 10% reduction in specific heat and a 2% reduction in lattice thermal conductivity at 50 K occur in a crystalline nanotube having a 10 nm outer and 5 nm inner diameter. In contrast, at the same temperature, an approximate 30% increase in thermal conductivity and specific heat occurs when the acoustically stiffened surface is applied to the outer diameter of a nanowire with a solid cross-sectional area. The simplified model has the potential to investigate the acoustic engineering of nanowires and nanotubes by inducing surface stiffening or softening via appropriate surface chemical functionalization protocols or coatings.
Advisors/Committee Members: Prakash, Vikas.
Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Mechanical Engineering; Physics
Keywords: Carbon Nanotube, Heat Treatment, Phonon Dispersion, Phonon Confinement
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9.
Boonyaprapasorn, Arsit.
FAULT DETECTION AND DIAGNOSIS PROCESS FOR CRACKED ROTOR VIBRATION SYSTEMS USING MODEL-BASED APPROACH.
Degree: PhD, EMC - Mechanical Engineering, 2009, Case Western Reserve University
► In this research, the fault detection and diagnosis using a model-based technique…
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▼ In this research, the fault detection and diagnosis using a model-based technique for the cracked rotor vibration system is developed and implemented. More specifically, the observer based or filter bank approach is employed in the fault detection and diagnosis process in order to detect the occurrence of a crack and diagnose the position and the depth of the crack in rotating machinery. The fault detection and diagnosis process is consisted of two parts. The first part is the filter bank or the residual generation which generates the residual vectors corresponding to each observer. The second part is a voting algorithm which searches the observer that corresponds to the behavior of the real system. The type of filter contained in the filter bank is the discrete time-variant Kalman filter. The filter is specifically designed to track the cracked rotor vibration system. Since the filter is time-variant, the state matrix at the current time step of the filter is updated by the state estimated value from the previous time step. Constructing the filter bank with the presented filter allows the fault detection and diagnosis process to perform very well under the environment of the process and measurement noises which is unavoidable in real systems. The voting algorithm evaluates every observer to find the observer behaving the closest to the real system based on the score achieved by each observer. The score is calculated by the information of the residual mean, the residual autocorrelation of each observer, the correlation coefficient between the real system measurements, and the observer outputs. In order to evaluate the fault detection and diagnosis process performance, the fault detection and diagnosis process is tested with the simulated real system containing various sets of system parameters. The results and discussions are presented.
Advisors/Committee Members: Loparo, Kenneth A.
Subjects: Mechanical engineering
Keywords: detection; diagnosis; cracked rotor; fault; vibration; rotating machinery; cracked shaft; cracked rotor vibration system; crack detection; crack localization; fracutre mechanic; model based
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10.
Boxerbaum, Alexander Steele.
A Whegs Robot Featuring a Passively Compliant, Actively Controlled Body Joint.
Degree: MS, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► In this work, I present the next generation of Whegs™ robots, DAGSI…
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▼ In this work, I present the next generation of Whegs™ robots, DAGSI Whegs™, which has been completed and extensively field-tested. Several innovations have made this robot more rugged and well suited to autonomous operation than previous designs. Specifically, an actively controlled, passively compliant body joint has been designed and tested. To date, it is the only Whegs body joint to have never failed. The chassis is a structural box design, which is both water and dirt resistant, and provides a flexible mounting system for electronics. New designs of the wheel-legs, torsion devices and steering mechanisms have also been developed and tested. Two large payload spaces have been created by moving the drive chains to the interior sides of the chassis, and the torsion devices to the outside. A two-dimensional dynamic simulation of the robot has also been constructed, and has been used to study the effects of weight distribution on obstacle climbing and to investigate future autonomous climbing strategies. Moving the center of mass forward allows the robot to climb taller obstacles. Using a weight distribution optimized using simulation, DAGSI Whegs™ can climb step shaped obstacles as tall as 2.19 times the length of a leg. Results from field testing show that the robot has good climbing capabilities in rugged unstructured terrain.
Advisors/Committee Members: Quinn, Roger.
Subjects: Mechanical engineering; Robots
Keywords: biorobotics; search and rescue robots; reduced actuation; whegs; body joint; worm gear; passive compliance; series elastic actuator
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11.
Boxerbaum, Alexander Steele.
Continuous Wave Peristaltic Motion in a Robot.
Degree: PhD, EMC - Mechanical Engineering, 2012, Case Western Reserve University
► This dissertation is a study of peristalsis, the method of locomotion earthworms…
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▼ This dissertation is a study of peristalsis, the method of locomotion earthworms use, and how to best achieve this in a robotic platform. A technique is presented that uses a braided mesh exterior to produce smooth waves of motion along the body of a worm-like robot. This braided mesh can be powered by a one degree-of-freedom cam mechanism, which is demonstrated, or by several independent motors. A new analytical model of peristalsis is presented and predicted robot velocity is compared to a 2-D simulation and a working prototype. It has been often assumed that this motion requires strong anisotropic ground friction. However, our analysis shows that with uniform, constant velocity waves, the forces that cause accelerations within the body sum to zero. Instead, transition timing between aerial and ground phases and the ability to generate strain play a critical role in the final robot speed. Lastly, we present a soft-body controller that uses simulated neuronal populations. This controller is designed for the next generation of soft, hyper-redundant systems and can intrinsically generate waves of a desired behavior while smoothly incorporating large amounts of simulated sensory input.
Advisors/Committee Members: Quinn, Roger.
Subjects: Biomechanics; Mechanical Engineering; Robotics
Keywords: soft robotics; biologically inspired robotics; peristalsis; biorobots; hyper-redundant; soft body control; neuronal modeling
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12.
Briggs, Maxwell H.
High Pressure Performance of Foil Journal Bearings in Various Gases.
Degree: M. Eng., EMC - Mechanical Engineering, 2008, Case Western Reserve University
► Foil bearings are being considered for use in high ambient pressure applications…
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▼ Foil bearings are being considered for use in high ambient pressure applications which use lubricants other than air. However, experimental performance data under these conditions is limited, which hinders the modeling efforts of system designers To collect a more comprehensive data set in these conditions, a new test facility is developed which measures bearing torque in helium, nitrogen, and carbon dioxide, at pressures up to 4.83 MPa and speeds up to 42,000 RPM. Bearing torque is found to increase with both pressure and test gas molecular weight, and this effect is amplified as speed increases. The effects of pressure and test gas molecular weight, and speed are analyzed in terms of the kinematic viscosity and modified Reynolds number. Finally, laminar inertial effects, transition to turbulence, and flow instability are evaluated as possible causes of the observed increase in torque using the modified Reynolds number, Reynolds number, and Taylor number, respectively.
Advisors/Committee Members: Prahl, Joseph.
Subjects: Aerospace Engineering; Mechanical Engineering
Keywords: High Pressure; Super Critical, Foil Bearing; Air Bearing; Tribology; Hydrodynamic Bearing; Bearing; Brayton Cycle; Closed Brayton Cycle; Air Bearing; Gas Bearing; Journal Bearing; Foil Journal Bearing
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13.
Brinkman, Jennifer G.
The Effect of Damage on the Long-Term Viability of Cortical Bone Allografts.
Degree: MS, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► Cortical bone allografts are frequently utilized in orthopaedic procedures to reconstruct defects…
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▼ Cortical bone allografts are frequently utilized in orthopaedic procedures to reconstruct defects in long bones. It is unknown whether these allografts are received in a mechanically compromised state due damage accumulated during the donor’s lifetime or during surgical handling and whether this damage will affect the life of the allograft after implantation. The aim of this project was to determine if either pre-existing mechanical damage had an effect on the fatigue life of cortical bone. Human cortical bone specimens were damaged in tensile creep as measured by a reduction in elastic modulus. The damaged specimens, along with unloaded controls were cyclically fatigued at physiologically relevant strains until failure or run-out was attained (10 million cycles). Microscopic tissue damage analysis was completed on tested specimens and on controls. It was determined that pre-existing mechanical damage did not reduce the fatigue life of bone nor did it increase the amount of microscopic tissue damage present in bone. These results suggest that damage, created by creep in tension, quantified by a 15% reduction in elastic modulus, may not have a substantial impact on the fatigue life of cortical bone allografts.
Advisors/Committee Members: Rimnac, Clare.
Subjects: Mechanical engineering
Keywords: Cortical Bone, Fatigue, Damage, Allograft
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14.
Chen, Guodong.
Thermal and Mechanical Behavior of Nano-structured Materials.
Degree: PhD, EMC - Mechanical Engineering, 2012, Case Western Reserve University
► This thesis consists of three parts. First, the numerical methods for Equation…
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▼ This thesis consists of three parts. First, the numerical methods for Equation of Phonon Radiative Transport (EPRT) in 3D domains are derived and implemented by COMSOL PDE module based on Equation of Phonon Radiative Transport and Boltzmann Transport Equation theory, which can be used to analyze the phonon dominant thermal conduction problems in multiple-domain nano-structures. Second, a new symmetric in-situ nano-scale tensile test MEMS device is presented, which can continuously observe the nano-specimen at large strain in SEM. The optimum platinum EBID clamping operation parameters are reported, and its strength is estimated per experiment results on polyaniline non-wire. Finally, the high strain rate dynamic properties of two nano-grained aluminum alloy groups are investigated by Split-Hopkinson-Pressure-Bar tests, which demonstrate the material dynamic flow strength enhancement by adding ceramic nano-particles.
Advisors/Committee Members: Prakash, Vikas.
Subjects: Materials Science; Nanoscience; Nanotechnology
Keywords: BTE; EPRT solution in 2D 3D multi-domains; EBID strength; Nano-tensile test MEMS-device; Nano-grained; SHPB
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15.
Conrad, Mason Christian.
An Experimental Investigation of Silicone-to-Metal Bond Strength in Composite Space Docking System Seals.
Degree: MS, EMC - Mechanical Engineering, 2009, Case Western Reserve University
► The National Aeronautics and Space Administration (NASA) is currently developing a new…
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▼ The National Aeronautics and Space Administration (NASA) is currently developing a new universal docking mechanism for future space exploration missions calledthe Low Impact Docking System (LIDS). In order to successfully mate two pressurized vehicles or structures in space, advanced seals are required at the interface to prevent the loss of breathable air to vacuum. The leading candidate LIDS main interface seal design is a composite assembly of silicone elastomer seal bulbs permanently molded into grooves in an electroless nickel-plated aluminum retainer. A composite seal of the style being developed has not been proven in a docking role in the history of manned spaceflight. High adhesive loads on the seal bulbs during undocking could potentially overcome the strength of the molded bond between the elastomer and the metal retainer. Bond failure would jeopardize the operation of the seal and docking port, and orbital debris could be liberated. The strength of the silicone-to-metal bond is a critical consideration for the new system, especially due to the presence of small areas of disbond created by the molding process. In the work presented herein, silicone- to-metal bonds of subscale seal specimens with different sizes of intentional disbond are destructively tensile tested. Tension is applied either uniformly on the entire seal circumference or locally in a single circumferential location. Bond failure due to uniform tension produces a wide scatter of observable failure modes and measured load-displacement behaviors. Although the ideal failure mode for the silicone-to- metal bond is 100% cohesive failure of the material, the highest observed cohesion amount is 20% of bond area for the uniform loading condition. Localized tension produces failure either as immediate tearing of the elastomer material outside the bond region or as complete peel-out of the seal bulb in one piece. In intentionally flawed specimens, neither load case considered shows a correlation between disbond size and bond strength.
Advisors/Committee Members: Prahl, Joseph.
Subjects: Aerospace materials; Engineering; Mechanical engineering; Polymers
Keywords: silicone; bond strength; seal; Orion
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16.
Das, Apurba K.
Combustion Characteristics of Moist H2 and H2/CO Mixtures and In-situ Temperature and Species Measurements Using Mid-IR Absorption Spectroscopy in a New RCM.
Degree: PhD, EMC - Mechanical Engineering, 2012, Case Western Reserve University
► The title study investigates the combustion characteristics of moist H2/oxidizer and moist…
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▼ The title study investigates the combustion characteristics of moist H2/oxidizer and moist H2/CO/oxidizer mixtures. It involves experimental determination of laminar flame speeds with emphasis on the effect of moisture addition (0–35% in fuel mixture) using a counterflow burner apparatus. Autoignition delays of H2/oxidizer mixtures at high pressure (10, 30 and 70 bar) and intermediate temperature (907–1048K) are also experimentally determined using a new Rapid Compression Machine (RCM). The H2/oxidizer mixture is further studied with 0–40% molar concentration of moisture in the mixtures to determine the effect of water addition on ignition delay at various post compression pressures. This new RCM is designed to attain higher post compression pressures (up to 140 bar) and wider compression ratios (5–25) compared to its predecessor. Experimental results provide extensive high fidelity data for H2/oxidizer and H2/CO/oxidizer mixtures with a wide range of water addition. It can be used for the refinement of the H2/CO/O2 combustion chemistry which not only is important for simulating syngas or high hydrogen content (HHC) fuel combustion but also forms the basic building block of the hydrocarbon chemistry. Additionally, a laser absorption setup meant for in-situ, real-time, non-intrusive measurement of temperature and important species in RCM is designed using a Quantum Cascade Laser (QCL) in the mid-IR region. The transition lines of water near 7.6 μm are used for the temperature and species measurements. A calibration test cell similar in dimension to the RCM reaction chamber is used to determine the line strengths and line broadening parameters in different bath gases required for the RCM study. The method of temperature and species concentration measurements in RCM is developed and demonstrated for non-reactive as well as reactive mixtures. Detailed discussions on uncertainty analysis for the temperature and species concentration measurements are also presented.
Advisors/Committee Members: Sung, Chih-Jen.
Subjects: Mechanical Engineering
Keywords: syngas; HHC; hydrogen; water; RCM; flame speed; autoignition; spectroscopy
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17.
Dickman, Joseph Robert.
An Investigation of Gas Foil Thrust Bearing Performance and its Influencing Factors.
Degree: M. Eng., EMC - Mechanical Engineering, 2010, Case Western Reserve University
► Three identical open source foil gas thrust bearings are manufactured and tested…
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▼ Three identical open source foil gas thrust bearings are manufactured and tested from 0-40 kRPM against two PS400 coated runners, and the results are reported. The bearings have a stiffness that varies from 20,000 to 140,000 lb/in. A 30% variability in load capacity is found between bearings against the same runner and a 25% variability is found with one bearing run against different runners. Bearing torque is proportional to speed and increases linearly with load once the bearing is fully lifted off. Load capacity increases linearly with speed until thermal effects cause top foil distortions and thermal runaway. Reducing the number of pads decreases the load capacity proportional to the change in area, but helps thermally stabilize the bearing. Finally, a simple ramp bearing model, in combination with a couette flow model and beam deflection in the top foil is compared to the bearing performance.
Advisors/Committee Members: Prahl, Joseph M.
Subjects: Engineering; Mechanical engineering
Keywords: foil bearing; bearing; foil thrust bearing; performance data
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18.
Dike, Shweta Srikant.
Dynamic Deformation of Materials at Elevated Temperatures.
Degree: MS, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► High Strength Low Alloy steel, grade 65 (HSLA-65) plates used by the…
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▼ High Strength Low Alloy steel, grade 65 (HSLA-65) plates used by the US Navy for ship building are to be joined by Friction Stir Welding (FSW) which subjects the work-piece material to high strain rates at high temperatures. The strength of materials varies with the strain-rate and temperature to which they are subjected. Development of constitutive models to get the optimum FSW weld parameters requires experimental determination of the dynamic behaviour of a material at different strain-rates and temperatures. In the current study, experiments using the Split Hopkinson Pressure Bar (SHPB) were conducted on HSLA-65 at high temperatures to generate the true stress-strain curves in compression. In addition, two other materials, which are used in practical applications where high strain rate loading occurs at high temperatures, namely Inconel-718 superalloy (precipitation hardened and annealed) and Aluminum alloy 7075-T6 were also tested using the SHPB.
Advisors/Committee Members: Prakash, Vikas.
Subjects: Engineering; Experiments; Mechanical engineering; Mechanics; Metallurgy
Keywords: Dynamic compressive response of HSLA-65 steel at high temperature; Dynamic compressive response of Inconel-718 at high temperature; High temperature SHPB experiments
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19.
Diller, Eric David.
Design of a Biologically-Inspired Climbing Hexapod Robot for Complex Maneuvers.
Degree: MS, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► Some insects are able to climb on nearly any surface and in…
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▼ Some insects are able to climb on nearly any surface and in many orientations using a variety of attachment mechanisms. In addition, these insects are capable of performing complex maneuvers such as transitioning between orthogonal surfaces, behaviors which are desirable in a climbing robot. A hexapod robot which climbs using biologically-inspired strategies was built for this purpose. DIGbot, a 2.8 kg robot, uses distributed inward gripping (DIG) to actively engage its spines with the surface. This enables the robot to climb vertical and inverted surfaces of high roughness, such as wire mesh, carpet or tree bark. DIGbot is the first robot able to perform tight turns on vertical as well as inverted surfaces.This thesis presents the design, construction and operation of DIGbot. The performance of the hexapod is quantified by analyzing its motion during these maneuvers.
Advisors/Committee Members: Quinn, Roger.
Subjects: Mechanical engineering
Keywords: climbing robots biologically-inspired
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20.
Doorly, Nicole C.
A Neuromechanical Model for Cockroach Locomotion.
Degree: MS, EMC - Mechanical Engineering, 2011, Case Western Reserve University
► Robotic models can be used to better understand complex biological systems. For…
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▼ Robotic models can be used to better understand complex biological systems. For this project, a robotic model of the left mesothoracic (middle) cockroach (Blaberus discoidalis) leg was built to explore the dynamics of the neuromechanical system underlying insect locomotion. The robotic hardware was designed to represent—as accurately as possible—cockroach morphology. To improve on previous robotic models of the cockroach leg, the Trochanter-Femur joint was added. Control of the robotic leg was designed to represent hypothesized neural connections in the cockroach—this controller was adapted from observed neural connections in the stick insect leg. The model was capable of generating stable locomotive actions (i.e. forward stepping and inside turning) and analysis of joint movements showed significant similarities to actual cockroach behavior. Finally, experiments addressing step frequency and behavioral transitioning showed the power of the model as a hypothesis-testing tool for biologists.
Advisors/Committee Members: Quinn, Roger.
Subjects: Robots
Keywords: robotics; insect locomotion; modeling
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21.
Drabousky, David Peter.
Prony series representation and interconversion of viscoelastic material functions of equine cortical bone.
Degree: MS, EMC - Mechanical Engineering, 2009, Case Western Reserve University
► The goal of this study was to examine the interrelationships among the…
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▼ The goal of this study was to examine the interrelationships among the viscoelastic property characterizations of cortical bone using Prony series representations for relaxation, creep and dynamic behavior. Equine cortical bone was tested in both relaxation and creep primarily to provide data for Prony series curve-fits and interconversions among linear viscoelastic material functions. In addition, other characteristics of linear viscoelasticity were examined. Loading modulus was not affected by the loading rates and the loading amplitudes chosen for this study. The linearity assumption of viscoelasticity was supported for the relaxation data and no damage accumulation behaviors were observed. The results from visual inspection of the Prony series models varied from the results of the statistical tests but some models did appear to outperform others. The conversions were of limited success; however, through the implementation of the routines better insight into the requirements for successful interconverting has been gained.
Advisors/Committee Members: Davy, Dwight.
Subjects: Biomedical research; Engineering; Mechanical engineering
Keywords: equine cortical bone; viscoelasticity; Prony series; viscoelastic material functions
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22.
Dux, Stephanie J.
The Effect of Gamma Radiation Sterilization on Yield Properties and Microscopic Tissue Damage in Dense Cancellous Bone.
Degree: MS, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► Cancellous bone allografts are increasingly attractive because the high porosity allows for…
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▼ Cancellous bone allografts are increasingly attractive because the high porosity allows for rapid in-growth and the stiffness closely matches that of the host bone. Allografts are sterilized with gamma radiation which can affect the mechanical properties and damage processes of bone. The purpose of this study was to determine the effects of gamma radiation sterilization on yield properties of dense cancellous bone and identify differences in microdamage accumulation. Compression tests of cylindrical bovine proximal tibia specimens sterilized at a dose of 29.32 kGy and control specimens were conducted to 1.3% strain. Histological sections were obtained to examine microscopic tissue damage. Sterilization had no effect on the yield properties of cancellous bone, but irradiated specimens had higher residual strain and significantly more microscopic tissue damage in the form of microfractures. This suggests that sterilization changes the damage processes of cancellous bone and could affect the performance of an allograft following overloading.
Advisors/Committee Members: Hernandez, Christopher.
Subjects: Mechanical engineering
Keywords: cancellous bone allograft, microscopic tissue damage, gamma radiation sterilization, microdamage
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23.
Endo, Makoto.
Wind Turbine Airfoil Optimization by Particle Swarm Method.
Degree: MS, EMC - Mechanical Engineering, 2011, Case Western Reserve University
► Two-dimensional shape of a wind turbine blade was optimized by means of…
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▼ Two-dimensional shape of a wind turbine blade was optimized by means of Particle Swarm Optimization. By following blade element theory, lift coefficient Cl and drag coefficient Cd were used as objective functions. In order to compute the objective functions, flow field around airfoils were calculated by Re-Normalization Group (RNG) k-ε model. Shapes of airfoils were defined by modified PARSEC method with 10 parameters.Two optimization cases were conducted with maximum thickness limited to 10% and 20% of the chord length respectively. In both cases, Reynolds number was set at 2.0×106, which is the design condition of S809 airfoil. S809 airfoil is a well known airfoil used in wind turbines and many experimental data are available. The angle of attack for the optimization was set at 5.13 deg., the mount angle of S809. Non-dominated solutions obtained by this research were compared with the performance of S809 at several angles of attack. The results of optimization showed that 1) there is a strong influence of maximum thickness of airfoil to its performance, 2) non-dominated solutions constitute a gradual relationship which implies that there are many airfoil shapes that could be considered as an optimum. The resulting shape along this Pareto front showed higher performance than the existing blade section (i.e. NREL S809) in certain conditions.
Advisors/Committee Members: T'ien, James S.
Subjects: Aerospace materials; Ecology; Energy; Engineering; Fluid dynamics; Mechanical engineering
Keywords: wind; wind turbine; airfoil; optimization; particle swarm; particle swarm optimization; PSO; S809; PARSEC
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24.
Floyd, Beatrice K.
Vision-Based Techniques for Cognitive and Motor Skill Assessments.
Degree: MS, EMC - Mechanical Engineering, 2012, Case Western Reserve University
► This thesis presents computer vision algorithms and associated applications for automating cognitive…
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▼ This thesis presents computer vision algorithms and associated applications for automating cognitive and motor skill assessments. These assessments are used to diagnose cognitive and motor impairments and behavioral problems. Due to the high prevalence of such disorders and the limitation of traditional diagnosis methods, there is an urgent need for improved approaches. Automation through computer vision enables low cost comprehensive assessments that can be more extensively implemented, further precision in measurement, provide quantitative behavioral and performance data, record results electronically, and allow professionals to concentrate on other assessment factors. The presented algorithms include wrist tracking, object recognition and tracking, and gaze detection. These algorithms are applied to create an automated version of the Wechsler’s Block Design subtest, kinematical modeling of the upper extremities, methods of path accuracy evaluation, an automated system for the Soda Pop Coordination Test, a tracking/scoring system for Cup Stacking, and a demonstration of gaze tracking.
Advisors/Committee Members: Lee, Kiju.
Subjects: Computer Engineering; Computer Science; Mechanical Engineering; Psychological Tests; Psychology
Keywords: Computer Vision; Image Processing; Automation; Performance Assessment; Fine-motor Skill Assessment; Cognitive Assessment; Wrist Tracking; Pose Estimation; Gaze Detection; Pose Estimation from Shape
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25.
Furlan, John Michael.
Particle Concentration Measurements in a Centrifugal Slurry Pump Using an A-Scan Ultrasound Technique.
Degree: PhD, EMC - Mechanical Engineering, 2011, Case Western Reserve University
► In the design of slurry transport equipment used in a variety of…
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▼ In the design of slurry transport equipment used in a variety of industries, the effects of solid particle concentration on hydraulic performance and wear need to be considered. An ultrasound A-mode imaging method has been developed to obtain local particle concentration measurements in slurry flows. Acoustic properties of slurry flows including velocity, backscatter, and attenuation as a function of volume fraction of solid particles, are examined in this study using various transducers. The most suitable transducer is selected to obtain concentration measurements in slurry flows. The technique is used to obtain concentration profiles in a homogeneous (vertical flow) and a non-homogeneous (horizontal flow) slurry flow of soda lime glass beads (195 µm diameter) and water through a one inch diameter loop with solid particle concentrations ranging from 1-10 % by volume. For horizontal flow, profiles are obtained for average flow velocities of 1.2, 2.0, 3.0, and 3.5 m/s. The algorithm developed utilizes acoustic backscatter and attenuation measurements obtained from the homogeneous loop as calibration data in order to obtain concentration profiles in other (i.e. non-homogenous) flow regimes. A computational study using FLUENT is performed and a comparison is made with the experimental results. A reasonable agreement between the experimental and computational results is observed in the one inch pipe. Following transducer selection and refinement and validation of the technique, it is employed to obtain local particle concentration measurements at multiple locations within the casing of a centrifugal slurry pump. A comparison is made between the experimental results and computational results using a two phase Eulerian-Eulerian finite element model. Computational fluid dynamics (CFD) and Experimental results at locations F→I share the same trends and relative patterns for differing locations but have substantial differences in magnitude. The CFD consistently shows higher concentration magnitudes than the experimental data. These differences are most likely a result of an un-matched casing inlet concentration boundary condition.
Advisors/Committee Members: Kadambi, Jaikrishnan.
Subjects: Mechanical Engineering
Keywords: slurry flow; ultrasound; particle concentration measurement; Centrifugal Pump
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26.
Hartwig, Jason William.
Acetone-LIF at Elevated Pressure and Temperature for 282nm Excitation: Experiments and Modeling.
Degree: MS, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► Acetone tracer-LIF in the gas phase is a widely used laser diagnostic…
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▼ Acetone tracer-LIF in the gas phase is a widely used laser diagnostic technique in low to intermediate temperature and pressure combustion systems. In this work, we design, characterize, and validate a flexible static and flow system to study the independent and coupled effect of elevated pressure and temperature on the photophysics of acetone more relevant to practical engine like conditions (0.5 atm< P <40atm, 295K< T <700K) for an excitation wavelength of 282nm in nitrogen and air. It is shown that relative fluorescence increases for all pressures at elevated temperatures up to a maximum isotherm of ~425K; for subsequently higher temperatures, acetone fluorescence decreases. Acetone fluorescence is only moderately quenched in the presence of oxygen. The current work offers insight into the competing vibrational energy decay rates at elevated temperature and pressure and proposes a global re-optimization of model parameters from the original photophysical model developed by Thurber (1999).
Advisors/Committee Members: Sung, Chih-Jen.
Subjects: Aerospace materials; Engineering; Mechanical engineering
Keywords: acetone; laser induced fluorescence; LIF; tracer; high pressure; high temperature; optimization; pyrolysis; photolysis; oxygen quenching
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27.
Hornfeck, Kenneth B.
A Customizable Socially Interactive Robot with Wireless Health Monitoring Capability.
Degree: MS, EMC - Mechanical Engineering, 2011, Case Western Reserve University
► This paper presents Philos, a socially interactive robot designed for use in…
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▼ This paper presents Philos, a socially interactive robot designed for use in homes of those who need special care, such as children or the elderly. Philos is capable of actively responding to wirelessly transmitted data from a wearable health monitoring device (WHMD). Philos can use this data to encourage physical activity, as well as provide emotional stimulation through human-robot social interactions (HRSIs), which are enabled through touch- and vision-based inputs. PhiloManager, a software interface designed to be integrated with Philos and the WHMD allows the user or healthcare professional to monitor health data in real time. A novel embedded behavior algorithm incorporating a system of behavioral parameters which continually change based on predefined "personalities" with which Philos can be programmed and external user inputs has been implemented. Preliminary tests confirm that both internal and external factors have a noticable impact on the behavioral responses enacted by Philos.
Advisors/Committee Members: Lee, Kiju.
Subjects: Robotics; Robots
Keywords: robotics; sociable robots; human-robot interaction
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28.
Hunt, Alexander.
A Biologically Inspired Robot for Assistance in Urban Search and Rescue.
Degree: MS, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► This research developed a robot capable of operating in urban search and…
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▼ This research developed a robot capable of operating in urban search and rescue conditions. USAR WhegsTM implements several new features in to WhegsTM robot design, some more successful than others. It is the first quadruped WhegsTM robot of this scale. It uses differential steering for control, and is able to switch between tracks and a wheel-leg system quickly and efficiently. This is also the first implementation of carbon fiber wheel-legs on a WhegsTM vehicle. The quick change-system is very effective, though the differential steering does seem to provide some control problems for the wheel-legs. The carbon fiber wheel-legs significantly decrease the inertia of the robot. The robot is 18.75 inches long, can travel 6.25 feet per second, and can climb 6 inch obstacles.
Advisors/Committee Members: Quinn, Roger.
Subjects: Engineering; Mechanical engineering
Keywords: Robotics; Biologically Inspired; Whegs; Urban Search and Rescue; USAR
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29.
Iyengar, Ananth Shalvapulle.
Synthesis and characterization of micro/nano material for thermoelectric applications.
Degree: PhD, EMC - Mechanical Engineering, 2010, Case Western Reserve University
► Various micro- and nanomaterials are explored to assess their potential for enhancing…
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▼ Various micro- and nanomaterials are explored to assess their potential for enhancing figure of merit (ZT) of the material. Free standing bismuth nanowires are synthesized by vapor deposition technique. Bismuth nanowires and commercial bismuth microparticles were uni-axially compressed into respective pellets. The anisotropy due to the compression process is investigated by measuring the directional thermal and electrical conductivities of the pellets. Thermal conductivity is measured by mirage technique, and dynamic plane source method. Electrical conductivity is measured by 4point probe in inline and over-under configurations. Seebeck coefficient is measured by the steady-state DC technique. The anisotropy is attributed to effects including, the particle interface, porosity, and the oxide layer on the particles. Quantum confinement effect is exhibited by the 20nm nanowire pellet. The ZT of the compressed nanowire pellets are one order of magnitude lower and the compressed microparticle pellets showed about half of the bulk bismuth ZT. These low ZT values are due to the various factors including dielectric surface oxide layer, pellet porosity, and particle interfaces. Among these factors, surface oxide layer plays the major role in reducing the electrical conductivity of the pellets. Another ongoing project is an investigation into the thermoelectric properties of electrolyte solutions to assess their viability as liquid thermoelectric materials. A steady-state thermal conductivity measuring setup for liquids was developed to measure its properties. The setup consists of a pair of coaxial cylinders with test fluid placed in the annular space between these cylinders with water tight cover plates at the top and bottom of the cylinders. Heat flow from the coil at the concentric-center of the inner cylinder raises the temperature of the assembly. Thermal conductivity is calculated by comparing the steady-state radial heat flow between the cylinders and the test fluid (comparative method). Thermal conductivity of water, glycerol, and ethylene glycol was measured for varying temperatures and is in good agreement with the published thermal conductivity values in literature.
Advisors/Committee Members: Abramson, Alexis.
Subjects: Mechanical engineering
Keywords: Compression, Nanowire, Bismuth, Anisotropy, quantum confinement, and Figure of merit
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30.
Jayaraman, Karthik.
DAMAGE AND WEAR OF NATIVE AND TISSUE ENGINEERED CARTILAGE.
Degree: MS, EMC - Mechanical Engineering, 2009, Case Western Reserve University
► Osteoarthritis is the second leading cause of disabilities in the USA. Although…
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▼ Osteoarthritis is the second leading cause of disabilities in the USA. Although total joint replacement remains the common treatment for severe cases of osteoarthritis, total joint resurfacing using tissue-engineered cartilage is proposed as a better alternative. However, to be a viable alternative, tissue engineered cartilage must have the integrity to withstand the mechanical and biological environment in a joint. This investigation focuses on tribological properties that are a key aspect of a tissue’s mechanical integrity. A test setup, in which a cartilage sample is subjected to compression and slides over a glass counter face, was built to measure friction and stimulate wear. Wear and damage of the cartilage surface were of particular interest as they are thought to be more accurate indicators of the mechanical integrity of the cartilage than friction. The effect of phosphate buffered saline and two formulations of hyaluronic acid (HA1 and HA2) on the tribology of cartilage were also studied. The friction behavior of the cartilage before and after the wear tests were compared .The amount of Glycosaminoglycan dissolved in the lubricant was used as a measure of wear. Scanning Electron Microscopy and histology were employed to visualize microscopic damage to the cartilage. Tests under intermittent sliding demonstrate that tissue engineered cartilage is capable of biphasic lubrication. Under continuous sliding, visually evident peeling of the cartilage surface was observed with PBS (7 of 12 samples) and HA1 (5 of 6 samples) as lubricant, but not with HA2. Cracks parallel to the surface of cartilage samples subjected to shear, was the predominant mode of damage observed in histology. With HA2 as lubricant, cracks were observed in all 4 of the available histology images (6 were tested), although no macroscopic damage was seen. Scanning electron microscopy showed wear tracks on samples subjected to shear. For native cartilage, assays used to quantify wear and damage did not result in any discernable effects of shear. In conclusion, although ex vivo tests are not a direct indicator of in vivo performance, these results suggest that the tribological characteristics of tissue engineered cartilage are inferior to those of native cartilage.
Advisors/Committee Members: Mansour, Joseph M.
Subjects: Mechanical engineering
Keywords: biotribology, tissue engineering,biomechanics,friction,wear,hyaluronic acid,cartilage
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