Master of Science in Engineering Mechanics, Cleveland State University, 0, Washkewicz College of Engineering

The research presented in this thesis delves into the mechanical behavior of Polyether Ether Ketone (PEEK) auxetic structures subjected to various mechanical loading conditions using finite element analysis (FEA). Auxetic structures are known for their unique deformation properties due to their negative Poisson's ratio, which causes them to expand laterally when stretched. The present study investigates how geometric configurations, particularly the number of unit cells, affect the auxetic response of PEEK structures. To conduct the research, four samples with different unit cell configurations (4x4, 5x5, 6x6, and 8x8) were created using SolidWorks and Abaqus software for simulation. These samples were then subjected to tension, compression, and cyclic loading conditions to analyze their Poisson's ratio, stress-strain behavior, and buckling characteristics. The results consistently showed a negative Poisson's ratio across all samples, with larger structures exhibiting a reduced auxetic effect under tension while maintaining stability under compression. The deformation analysis showed an initial linear elastic behavior with Young's modulus of 2.84–2.89 GPa in tension and 7.92–8.96 GPa in compression, followed by yielding and plastic deformation. The material's ultimate tensile strength (UTS) reached 99.23 MPa in tension and 99.11 MPa in compression, indicating it can withstand these maximum stress levels before breaking. The material is stiffer in compression than in tension. The results of the cyclic loading tests indicated energy dissipation and permanent deformation, as evidenced by clear hysteresis loops. The buckling analysis demonstrated stable and predictable deformation patterns, with critical buckling loads aligning with existing literature. These findings suggest that PEEK auxetic structures are well-suited for applications requiring high energy absorption and resistance to deformation, such as in aerospace (open full item for complete abstract)

Committee: Josiah Owusu-Danquah (Advisor); Stephen Duffy (Committee Member); Srinivas Allena (Committee Member) Subjects: Civil Engineering

Master of Science, The Ohio State University, 2024, Dentistry

Statement of problem: The introduction of carbon fiber-reinforced PEEK polymer screw in two-piece zirconia implants, facilitated the development of “metal-free" implant solutions. However, the literature lacks studies on the performance of such a screw joint assembly, particularly regarding reverse torque values. Purpose: To evaluate the effect of artificial aging and cyclic loading on reverse torque values and survival rates of carbon fiber-reinforced PEEK polymer screws in two-piece zirconia. Materials and Methods: A total of 20 implants were divided into two main groups. The testing group utilized 10 zirconia implants (NobelPearl Tapered RP 4.2 x 10 mm, Nobel BioCare, Kloten, Switzerland) with carbon fiber-reinforced polymer screws (VICARBO®, NobelPearl, Nobel BioCare, Kloten, Switzerland) to retain the zirconia crown cemented on zirconia abutments (NobelPearl abutment straight IX RP 1). The control group used 10 titanium implants (NobelReplaceTM Conical Connection, RP 4.3 x 10 mm, Nobel BioCare, Kloten, Switzerland) with titanium alloy screws (Clinical Screw Conical Connection, Nobel BioCare, Kloten, Switzerland) to retain zirconia crowns cemented on titanium abutments (Snappy abutment 5.5 CC RP 1.5, Nobel BioCare, Kloten, Switzerland). Implants were cemented into twenty glass cloth reinforced epoxy resin cylinders (G10, National Electrical Manufacturers Association, Rosslyn, Virginia, USA) using a dual-cured resin (Rock Core, Zest dental solutions, California, USA). All zirconia crowns were digitally designed to an identical shape maxillary central incisors, milled from zirconia blanks (IPS e.max ZirCAD Prime 25 x 98.5mm, Ivoclar, Vivadent USA), sintered, and then cemented with resin cement (Panavia V5, Kuraray Noritake, Okayama, Japan). A total of 60 screws were used in 6 groups. In the first two groups (T24 and Z24) a torque limiting wrench (NobelPearl Manual Torque Wrench, Nobel BioCare, Kloten, Switzerland) was used to deliver the manufacture's recomm (open full item for complete abstract)

Committee: Shereen Azer (Advisor); Hanin Hammoudeh (Committee Member); Damian Lee (Committee Member) Subjects: Dentistry

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

Reciprocating compressors are critical components for the natural gas energy infrastructure throughout the world. Proper lubrication of PTFE and PEEK based packings and piston rings (seals) in the compressor cylinder is necessary to prevent leaks of methane to the environment and allow efficient, reliable, and extended operation of the compressor. Cylinder lubrication is poorly understood and commonly cited as the reason for premature seal failures while being a major annual expense for compressor station operators. An industry priority is to reduce the amount of lubricant injected into the compressor cylinder. The lubricant is carried away by the process gas and collects in pipelines or other downstream equipment. To better understand the tribological aspects and physical phenomena of compressor cylinder lubrication, the effect of high pressure methane on the surface tension of common lubricants and sealing materials was investigated. Methane gas pressure exhibited an inverse relationship with liquid lubricant surface tension through a pendant drop test. Methane pressure also increased the contact angles of sessile drops of lubricants on the solid surfaces. Nitrogen pressure exhibited the same trends but to a lesser extent than methane. Analysis using the Owens, Wendt, Rabel and Kaelble calculation method revealed that as methane pressure increased, the surface free energy of the seal materials decreased. These results further revealed that increased gas pressure decreased the wettability of lubricants on the materials. PTFE based materials decreased much more than PEEK based materials. Spontaneous adsorption of the pressurized gases on the surface of the lubricant drops and sealing materials was determined to be the underlying cause of the reductions of surface energy. This new understanding is significant because it better explains the observed lubrication phenomena and may be able to guide the industry toward optimized lubrication, more efficient se (open full item for complete abstract)

Committee: Kevin Cavicchi (Advisor); Weinan Xu (Committee Chair); Christopher DellaCorte (Committee Member); Fardin Tayebeh Khabaz (Committee Member); Sadhan Jana (Committee Member) Subjects: Energy; Engineering; Materials Science; Mechanical Engineering

Master of Science in Mechanical Engineering, Cleveland State University, 2023, Washkewicz College of Engineering

Polyether ether ketone (PEEK) is a high-performance polymer material for developing implants for orthopedic, spinal, cranial, maxillofacial, and dentistry applications. However, the major limitation of PEEK implants is their bio-inertness, i.e., their incapability to integrate with tissues. Therefore, prior efforts have always focused on developing Hydroxyapatite (HA) coatings on PEEK or PEEK-HA composites or sulfonation of PEEK surface or plasma treatment. As opposed, in this study, we engineered a highly novel bio-ceramic known as amorphous magnesium phosphate (AMP), which surpasses the bioactivity and biodegradation kinetics of HA. In this study, we employed High-energy planetary ball milling, a mechanical alloying technique, to incorporate Amorphous magnesium Phosphate (AMP) into a PEEK matrix resulting in a novel polymer bio-ceramic composite. We systematically varied ball milling parameters to observe their effects on composite powders and thoroughly analyzed the composite mixture using a Scanning Electron Microscope (SEM). Subsequently, we developed a uniform-diameter filament of PEEK-AMP bioactive composite via a single screw extrusion process, such that it can be used in a Fused Filament Fabrication (FFF)-3D Printing setup to develop design-specific multifunctional implants. Our results indicate that controlling extrusion parameters such as temperature gradient, screw speed, tension, and cooling rate are essential to extruding uniform-diameter filaments suitable for 3D Printing. Furthermore, rheological properties confirmed the suitability of the PEEK-AMP filaments for 3D Printing, and SEM revealed the uniform dispersion of the AMP particles in the PEEK matrix. Importantly, 3D printed PEEK-AMP composite samples exhibited a yield Strength of 89 MPa and Young's Modulus of 3.5 GPa, confirming that AMP incorporation in PEEK does not deteriorate the inherent properties of PEEK. Apparently, mechanical properties are controlled by varying the 3D printing paramet (open full item for complete abstract)

Committee: Prabaha Sikder (Committee Chair); Prabaha Sikder (Advisor); Linqun Ning (Committee Member); Maryam Younessi Sinaki (Committee Member) Subjects: Biomedical Research; Mechanical Engineering

Master of Science in Mechanical Engineering, Cleveland State University, 2022, Washkewicz College of Engineering

3D printing, specifically Fused Deposition Modelling (FDM) of Poly-ether-ether-ketone (PEEK), was used to develop design-specific PEEK structures. In this study, we investigate the effect of specific 3D printing parameters such as nozzle and chamber temperature, print speed, and layer height on the mechanical properties of 3D printed PEEK. Moreover, we explored the effect of filament quality on the mechanical properties of the PEEK structures. In that regard, we developed PEEK filaments using a customized extruder setup in-house and used those laboratory-developed filaments (LD) to 3D print PEEK structures suitable for mechanical testing and compared them to the mechanical properties of 3D printed parts that were developed using commercially available (CA) filaments. Notably, results confirmed no significant differences but highlighting that the LD filaments were of comparable quality to the CA ones. Polyether-ether-ketone (PEEK) is a high strength semi crystalline thermoplastic and is one of the most common materials used for orthopedic devices. It is a promising biomaterial that could potentially replace metal and ceramic-based medical devices owing to its good mechanical properties and biocompatibility. However, the poor osseointegration property of PEEK implants have limited its' clinical applications. To address this issue, in this study, we developed PEEK scaffolds with controlled pore sizes. We hypothesize that the porous PEEK will help in efficient osseointegration while not compromising the mechanical properties of the scaffolds. PEEK scaffolds with controlled and designed pore sizes of 0.3mm, 0.4mm, 0.6mm, 0.8mm and 1mm will be manufactured via FDM. Amorphous Magnesium Phosphates (AMP) is one of the less explored bio ceramics which has good potential in bone regeneration. However, its application is limited by its poor mechanical properties such as brittleness. To address this issue, Graphene Nanoplatelets will be incorporated in AMP using ball millin (open full item for complete abstract)

Committee: PRABAHA SIKDER (Committee Chair); SAEED FARAHANI (Committee Member); TUSHAR BORKAR (Committee Member) Subjects: Mechanical Engineering

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

Additive Manufacturing (AM) has changed the manufacturing world by opening doors to develop structures that were either not possible before or extremely complex with regular manufacturing. This work investigated Powder Bed Fusion AM which allows the creation of complex structures for metal parts using high performance materials. Industries such as aerospace have seen benefits in using AM, not only in designing but replacing parts for aging aircrafts. Polyaryle Ether Ketones (PAEK) materials, in a Fused Filament Fabrication (FFF) system, were used because its mechanical performance is close to that of aluminum and the applications for aerospace and biomedical industries. Printing of PEEK and PEKK can be difficult due to the high melting point required of the materials. The recent availability of soluble support has allowed the printing of lattices with overhanging features. Density can be optimized to have a balance between weight and strength for aerospace structures and implants. 3D printing has been applied in a variety of ways, from printing with material extrusion printers and stopping the print to embed electronics in the structure and then resuming the print, to printing components in vat photopolymerization (VPP) printers in a jigsaw-like way, with cavities to fit electronics and overmold together, which will leave the components inside the structure. A lot of research has been done on wearable electronics, for things like cortisol, H2S, haptic feedback, pressure sensors and others, due to the demand for smaller electronics. The flexibility provided by AM, allows for these two well studied technologies to be combined into one, 3D printed wearable electronics.

Committee: Snjezana Balaz Ph.D. (Advisor); Holly Martin Ph.D. (Committee Member); Donald Priour Ph.D. (Committee Member); Clovis Linkous Ph.D. (Committee Member); Christopher Hansen Ph.D. (Committee Member) Subjects: Aerospace Materials; Engineering; Materials Science; Polymers; Technology

Doctor of Philosophy, University of Toledo, 2022, Biomedical Engineering

Additive manufacturing has many advantages in fabricating customized orthopedic implants and scaffolds, where complex geometries can be fabricated directly. This study aimed to use additive manufacturing, particularly fused deposition modeling (FDM) to fabricate and evaluate polymeric implants scaffolds to achieve optimal functionality in orthopedic applications by investigating the effect of pore sizes on cell activities. Another aim was to evaluate the capabilities of the FDM technique to overcome challenges associated with polymeric 3D-printable biocomposites. In this study, polyetheretherketone (PEEK) and polylactic acid (PLA) were chosen to represent non-biodegradable and biodegradable polymers. Ceramic materials such as the conventional tricalcium phosphate (TCP) and novel amorphous magnesium phosphate (AMP) were used as second phases in polymer composites. The first chapter presents a brief introduction and overview of this dissertation. The second chapter is a review of additive manufacturing technologies of biomaterials and clinical applications of 3D-printed structures for orthopedic applications. In the third chapter, the effect of pore size on cell activities was investigated in which 3D-printed PEEK scaffolds were fabricated with pore sizes ranging from 800 µm to 1800 µm. PEEK scaffolds with 800 µm pores showed higher cell attachment and proliferation as compared to the other sizes. In the fourth chapter, a one-step method was developed to process a novel ceramic-polymer 3D-printable biocomposite using a single screw extruder. Specifically, the novel AMP was mixed into PLA with the help of the melt-blending technique. Magnesium phosphate (MgP) was chosen as the bioactive component as previous studies have confirmed its biocompatible and bioactive properties. The AMP-PLA biocomposite filaments were characterized for its microstructure, mechanical, thermal, and rheological properties. Scanning Electron Microscopy (SEM) results confirmed a homogenous dispe (open full item for complete abstract)

Committee: Sarit Bhaduri (Advisor); Mohamed Samir Hefzy (Committee Member); Hossein Elgafy (Committee Member); Anju Gupta (Committee Member); Vijay Goel (Committee Member) Subjects: Biomechanics; Biomedical Engineering; Biomedical Research; Chemical Engineering; Mechanical Engineering

Master of Science (MS), Wright State University, 2017, Chemistry

The synthesis of functionalized, linear poly (ether ether ketone), tailored to be semi-crystalline and soluble in a variety of organic-solvents was explored. Nucleophilic aromatic substitution was a chemical reaction method used to condense 3,5,4'-trifluorobenzophenone (TFK) with four different phenols at its para-positioned carbon-fluorine site: 4-methoxyphenol, 3-aminophenol, 4-bromophenol, and m-cresol. Further poly-condensation of functionalized TFK occurred at the meta-positioned carbon-fluorine sites with 4,4'-Bis[4-hydroxyphenoxy] benzophenone (Big A2) and 4,4'-difluorobenzophenone at molar equivalents of 1 to 0.5, respectively. The reaction afforded products that became insoluble in solvents needed for nuclear magnetic resonance spectroscopic (e.g. DMSO-d6) analysis. The lack of desirable compounds compelled the necessity of examining the displacement of the fluorine groups in TFK located meta to the electron withdrawing group, the carbonyl moiety. Gas Chromatography/Mass Spectrometry (GC/MS) and Nuclear Magnetic Resonance Spectroscopy (NMR), 1H and 13C, were used to analyze samples at varying reaction times and revealed that while it is possible to displace at least one of the meta-fluorine atoms in mono-substituted TFK with Big A2 and Bisphenol A, more time and a potentially higher temperature may be needed to complete the reaction. The synthesis of 75:25 PEEK-co-meta-PEEK, 5, from a previous project was successfully replicated and verified using Differential Scanning Calorimetry (DSC).

Committee: Eric Fossum Ph.D. (Advisor); William Feld Ph.D. (Committee Member); Daniel Ketcha Ph.D (Committee Member) Subjects: Chemistry

Master of Science (MS), Wright State University, 2016, Chemistry

Two routes to semi-crystalline, potentially functionalizable poly(ether ether ketone), PEEK, analogues were explored using varying percentages of 4,4'-difluorobenzophenone and either 3,5-difluorobenzophenone or 2,4-difluorobenzophenone as the electrophilic component in nucleophilic aromatic substitution polycondensation reactions with hydroquinone. PEEK analogues utilizing 3,5-difluorobenzophenone were carried out in a “one-pot” fashion and their properties were compared to the same materials prepared previously by a multi-step synthetic procedure. The use of 2,4-difluorobenzophenone led to completely new PEEK analogues. The polymers were characterized via NMR spectroscopy, Size Exclusion Chromatography, Thermogravimetic Analysis, and Differential Scanning Calorimetry. Molecular weight determinations showed the synthesized polymers to be of a variety of molecular weights, with weight averaged molecular weight (Mw) values between 7,500 and 83,000 Da and dispersity (Ð) values between 2.5 and 2.9. The polycondensation reactions were also accompanied by the formation of cyclic species that could be, and were, removed via precipitation/trituration with isopropanol or mostly avoided by a judicious choice of reaction conditions. Solubility tests showed that the 3,5-homopolymers, which were semi-crystalline, and 2,4-homopolymers, which were completely amorphous, were soluble in many common organic solvents, while the solubility of the copolymers decreased as the percentage of 4,4'-difluorobenzophenone increased. Thermal analysis of the 3,5-difluorobenzophenone polymers possessed 5 % weight loss temperature values (Td 5%) that were similar to those of the previously synthesized polymers1, with values between 330 and 500°C. For both polymer systems, the glass transition temperatures (Tg) were between 86 and 129°C, which is consistently lower than those of the materials previously synthesized via the multistep protocols. The 3,5 homopolymer and 75%/25% (PEEK/PAMPPO) copolymer (open full item for complete abstract)

Committee: Eric Fossum Ph.D. (Advisor); William Feld Ph.D. (Committee Member); Daniel Ketcha Ph.D. (Committee Member) Subjects: Chemistry; Plastics; Polymer Chemistry; Polymers

Master of Science (MS), Wright State University, 2016, Chemistry

The oxyalkylene containing, meta linked monomers 1,2-bis(3-(4-fluorobenzoyl)phenoxy)ethane, 1,3-bis(3-(4-fluorobenzoyl)phenoxy)propane, 1,4-bis(3-(4-fluorobenzoyl)phenoxy)butane, 1,5-bis(3-(4-fluorobenzoyl)phenoxy)pentane can be prepared by a three-step process starting with the dialdehydes (1,2-bis(3-formylphenoxy)ethane, 1,3-bis(3-formylphenoxy)propane, 1,4-bis(3-formylphenoxy)butane and 1,5-bis(3-formylphenoxy)pentane, respectively). Polymerization of the monomers with bisphenol-A gave soluble, thermally stable amorphous poly(ether ether ketone)s. The polymers exhibited molecular weights of (Mw/Mn) (21,841/ 8721) g/mol, (21,195/ 7569) g/mol, (9,107/ 2819) g/mol and (12,990/ 4723) g/mol, respectively. Thermal analyses of the polymers revealed Tgs of 112º, 106º, 92º and 91º, respectively and 5% weight losses under a nitrogen atmosphere of 389º, 410º, 411º and 414º, respectively.

Committee: William Feld Ph.D. (Advisor); Eric Fossum Ph.D. (Committee Chair); Kenneth Turnbull Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Akron, 2014, Polymer Engineering

Two ultrasonic twin screw extrusion systems were designed and manufactured for the ultrasonic dispersion of multi-walled carbon nanotubes in viscous polymer matrices at residence times of the order of seconds in the ultrasonic treatment zones. The first design consisted of an ultrasonic slit die attachment in which nanocomposites were treated. A second design incorporated an ultrasonic treatment section into the barrel of the extruder to utilize the shearing of the polymer during extrusion while simultaneously applying treatment. High performance, high temperature thermoset phenylethynyl terminate imide oligomer (PETI-330) and two different polyetherether ketones (PEEK) were evaluated at CNT loadings up to 10 wt%. The effects of CNT loading and ultrasonic amplitude on the processing characteristics and rheological, mechanical, electrical, thermal and morphological properties of nanocomposites were investigated. PETI and PEEK nanocomposites showed a decrease in resistivity, an increase in modulus and strength and a decrease in strain at break and toughness with increased CNT loading. Ultrasonically treated samples showed a decrease in die pressure and extruder torque with increasing ultrasonic treatment and an increase in complex viscosity and storage modulus at certain ultrasonic treatment levels. Optical microscopy showed enhanced dispersion of the CNT bundles in ultrasonically treated samples. However, no significant improvement of mechanical properties was observed with ultrasonic treatment due to lack of adhesion between the CNT and matrix in the solid state. A curing model for PETI-330 was proposed that includes the induction and curing stages to predict the degree of cure of PETI-330 under non-isothermal conditions. Induction time parameters, rate constant and reaction order of the model were obtained based on differential scanning calorimetry (DSC) data. The model correctly predicted experimentally measured degrees of cure of compression molded (open full item for complete abstract)

Committee: Avraam Isayev Dr. (Advisor); Sadhan Jana Dr. (Committee Member); Alamgir Karim Dr. (Committee Member); Shing-Chung Wong Dr. (Committee Member); Wieslaw Binienda Dr. (Committee Member) Subjects: Materials Science; Polymers

Doctor of Philosophy, University of Akron, 2013, Polymer Engineering

This dissertation consists of two research subjects: High Temperature Shape Memory Polymers and Ionomer Modified Asphalts. Current development of thermally sensitive shape memory polymers (SMPs) has focused primarily on relatively low transition temperatures (Tc < 100°C) and elastomeric polymers, such as thermoplastic polyurethanes (TPU), crosslinked polyethylene, poly (e-caprolactone), sulfonated EPDM and polynorbornene. Those materials are appropriate for applications such as biomedical and surgical materials, smart fabrics and heat shrinkable tubing. Materials used as aerospace or structural components often require higher modulus and switching temperatures for shape change and actuation. To the best of our knowledge, there have been no reports of thermoplastic SMPs with controllable switching temperatures above 100°C. There has been research on high temperature SMPs but based on thermoset polymer systems. High temperature thermoplastic shape memory polymers were developed from metal salts of sulfonated PEEK (M-SPEEK, M=Na+, Zn2+, Ba2+, Al3+, Zr4+) ionomer and composites of the M-SPEEK ionomers with a fatty acid salt. M-SPEEKs were prepared by neutralizing sulfonated PEEK acid to metal salts. The glass transition temperatures of M-SPEEK ionomers increased with increasing Coulomb energy of ion pairs and the ionomers were thermally stable to ~320°C. The M-SPEEK ionomers exhibited microphase separated morphologies and the average correlation length was determined by small angle X-ray scattering. Al-SPEEK and Zr-SPEEK showed crosslinked characteristics such as rubbery plateau above Tg and much reduced water uptake. The M-SPEEK ionomers exhibited reasonable shape memory behavior, in which the permanent network was provided by ionic nanodomains formed by the interaction of ionic groups and glass transition temperatures served as the switching temperatures. The relative poor shape efficiency of Na-SPEEK and Zn-SPEEK (80-90%) can be improved by blendi (open full item for complete abstract)

Committee: Robert Weiss Dr. (Advisor); Kevin Cavicchi Dr. (Committee Chair); Jana Sadhan Dr. (Committee Member); Matthew Becker Dr. (Committee Member); Yi Pang Dr. (Committee Member) Subjects: Plastics; Polymer Chemistry; Polymers

MA, University of Cincinnati, 2001, Arts and Sciences : Psychology

Recent figures from the National Institute on Drug Abuse (1997) report that 54.3% of high school seniors reported using an illicit drug at least once in their lives. A larger percentage of adolescent males (22.1%) than females (20.5%) engage in illicit drugs (National Household Survey on Drug Abuse, 1998). Previous research has suggested that one of the strongest predictors of adolescent drug abuse is peer influence (Hawkins, Catalano, & Miller, 1992). Recently, Mears et al. (1998) suggested that delinquent peers have a greater effect on the drug use of males than females. In addition, research has implicated the role of the family in the drug behaviors of adolescents (Baumrind, 1985). Concerning gender differences within the family, Cernkovich & Giordano (1987) suggest that girls who have a close and positive family relationship have a lower incidence of delinquent behavior than boys who have the same relationship. Although this finding was based on delinquent behavior rather than drug use, it suggests that the relationship between the quality of family relationships and drug use may be stronger among females than males. The primary aims of this study were to 1) examine the relationships of peer influence and family bonding to drug use and 2) examine gender as a moderator of those relationships. Participants were 131 male and female teenagers who participated in a demonstration program for high-risk youth in Bloomington, Indiana. This project was a secondary analysis of the baseline data collected from a sample about to participate in a national study of high-risk youth. Participants were recruited from juvenile courts in the Bloomington, Indiana area. Most students were recruited because they were facing probation due to delinquent behavior. Results reveal there were no evidence of a relationship of family bonding to adolescent drug use and no differences between male and female participants in the relationships of either peer influence or family bonding to adoles (open full item for complete abstract)

Committee: Dr. A. Kathlelen Burlew (Advisor) Subjects: Psychology, General

Master of Science, The Ohio State University, 2012, Mechanical Engineering

In this study, a family of experimental evaluations is performed to rank order various combinations of plastic materials and greases for their suitability for automotive auxiliary drive applications in terms of their friction and wear performances. The tests included three common plastic materials (PA46 with 30% glass fiber filler, PA66 with 30% glass fiber filler, and PEEK with 30% carbon fiber filler) and four different proprietary greases. A twin-disk set-up is employed to test plastic disk specimens against a steel roller for their traction characteristics as a function of the slide-to-roll ratio and their wear performance as a function of loading cycles. Friction and wear test results from all twelve plastic-grease combinations are compared to determine particular combinations that provide the best combined wear and traction performance. Results indicate that grease type has a great influence on the friction of the contact, with two of the greases resulting in drastically lower friction coefficients. The PEEK material is found to be the best in terms of its wear resistance. PA46 and PA66 materials with proper grease selection exhibit friction values that are better than PEEK while their wear depths are two to three times that of PEEK.

Committee: Ahmet Kahraman PhD (Advisor); Carlos Castro PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2009, EMC - Mechanical Engineering

For over four decades, ultra high molecular weight polyethylene (UHMWPE) has been used as one-half of the metal- or ceramic-on-plastic bearing couple in total joint replacement (TJR) components. In 2004, over 700,000 total hip and total knee replacements were performed. In the absence of severe wear, gross fracture of total joint replacement components tends to originate from stress concentrations such as fillets, undercuts, and grooves. Recently, PEEK has become the subject of interest with regard to its suitability as composite matrix material for bearing surfaces. Therefore, it is of interest to study the behavior of both UHMWPE and PEEK in the presence of a stress concentration. Several formulations of clinically relevant UHMWPE (conventional, moderately crosslinked, and highly crosslinked) were investigated. Their monotonic stress-strain behavior in the presence of a notch was examined using a custom developed video based system, under physiologically relevant conditions. It was found that both an elevation of yield stress and a truncation of orientation hardening took place. Additionally these changes were found to be material and elastic stress concentration factor dependent. Examination of the crystallinity and lamellar thickness distributions revealed that their evolution is stress-state dependent. The micromechanism of fracture was also shown to change drastically in UHMWPEs and PEEK upon notching. Since the fracture of total joint replacement components is likely a fatigue process, the fatigue behavior of UHMWPE and PEEK was also investigated. The fatigue of both materials was modeled using a total life approach (the Basquin relationship). It was found for PEEK that increasing notch severity decreased fatigue life. However, curiously, for the conventional formulations of UHMWPE increasing elastic stress concentration actually led to improved fatigue life. For PEEK a linear elastic fracture mechanics approach was also utilized to estimate the fatigue life (open full item for complete abstract)

Committee: Clare Rimnac PhD (Advisor); Joseph Mansour PhD (Committee Member); Matthew Kraay MD (Committee Member); Roger Marchant PhD (Committee Member); Christopher Hernandez PhD (Committee Member) Subjects: Mechanical Engineering