Doctor of Philosophy, University of Toledo, 2016, Mechanical Engineering

Thermoplastic composites are suitable alternatives to metals in some load-bearing applications such as in the automotive industry due to a large number of advantages they present. These include light weight, ease of processing for complex geometries at high production rate, outstanding cost to performance ratio, ability to reprocess, and corrosion resistance. Addition of fillers such as talc or reinforcements such as short glass fibers can improve the mechanical performance of unreinforced thermoplastics to a high degree. Components made of thermoplastic composites are typically subjected to complex loadings in applications including static, cyclic, thermal, and their combinations. These applications may also involve environmental conditions such as elevated temperature and moisture which can dramatically affect their mechanical properties. This study investigated tensile, creep, fatigue, creep-fatigue interaction, and thermo-mechanical fatigue (TMF) behaviors of five thermoplastic composites including short glass fiber reinforced and talc-filled polypropylene, short glass fiber reinforced polyamide-6.6, and short glass fiber reinforced polyphenylene ether and polystyrene under a variety of conditions. The main objectives were to evaluate aforementioned mechanical behaviors of these materials at elevated temperatures and to develop predictive models to reduce their development cost and time. Tensile behavior was investigated including effects of temperature, moisture, and hygrothermal aging. Kinetics of water absorption and desorption were investigated for polyamide-6.6 composite and Fickian behavior was observed. The reductions in tensile strength and elastic modulus due to water absorption were represented by mathematical relations as a function of moisture content. In addition to moisture content, aging time was also found to influence the tensile behavior. A parameter was introduced for correlations of normalized stiffness and strength with different aging t (open full item for complete abstract)

Committee: Ali Fatemi Dr. (Advisor); Mohamed Samir Hefzy Dr. (Committee Member); Saleh Jabarin Dr. (Committee Member); Joseph Lawrence Dr. (Committee Member); Efstratios Nikolaidis Dr. (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science (MS), Ohio University, 2023, Mechanical Engineering (Engineering and Technology)

Bituminous coal was utilized as a particulate filler in polymer-based composites to fabricate standard 1.75 mm coal-plastic composite filaments for use in commercially available fused deposition modeling 3D printers. The composites were formulated by incorporating Pittsburgh No. 8 coal into polylactic acid, polyethylene terephthalate glycol, high-density polyethylene, and polyamide-12 resins with loadings ranging from 20 wt.% to 70 wt.%. CPC filaments were extruded and printed using the same processing parameters as the respective neat plastics. All coal-plastic composite filaments exhibited uniform particle dispersion throughout the microstructure. The mechanical properties of the 3D printed composites were characterized and compared to composites fabricated using traditional compression molding. Tensile and flexural moduli as well as hardness had direct proportionality with increasing coal content while flexural strength, tensile strength, and impact resistance decreased for most composite formulations. Interestingly, polyamide-based composites demonstrated greater maximum tensile and flexural strengths than unfilled plastic. Microscopy of as-fractured samples revealed that particle pull-out and particle fracture were the predominant modes of composite failure. The introduction of coal reduced the coefficient of thermal expansion of the composites, ameliorating the warping problem of 3D printed high-density polyethylene and allowing for additive manufacturing of an inexpensive and widely available thermoplastic. The high-density polyethylene composites demonstrated increased heat deflection temperatures, but all composites maintained comparable glass and metal transition temperatures, allowing them to be processed with commercial 3D printer extruders. The composites exhibited decreased specific heat capacities suggesting lower energy requirements for processing the material. Coal reduced the composite thermal conductivities compared to the neat plastics but improv (open full item for complete abstract)

Committee: Jason Trembly (Advisor); Yahya Al-Majali (Committee Member); Brian Wisner (Committee Member); David Drabold (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Sustainability

Doctor of Philosophy (PhD), Ohio University, 2021, Civil Engineering (Engineering and Technology)

Three experimental HDPE thermoplastic pipes manufactured by Advanced Drainage Systems (ADS) were installed as part of the drainage of the Southern Ohio Low Volume Experimental Road (SOLVER), a low-volume test road located on US Route 50 in western Vinton County near the border with Ross County. One pipe was a 60 in (1.52 m) inner diameter double wall pipe made with recycled content HDPE and the other two of the pipes were 42 in (1.07 m) inner diameter triple wall composite pipe made with thermoplastic and fiberglass. Each pipe was installed in Ohio Department of Transportation (ODOT) Item 304 backfill following procedures recommended by the manufacturer under its supervision. The main object of this experimental study was to investigate the short-term and the long-term performance of triple-wall composite thermoplastic pipes and the double-wall recycled thermoplastic pipes under load in terms of vertical and horizontal deflection, circumferential shortening, and soil pressure in the backfill. Abaqus was used to perform a viscoelastic analysis to model the behavior of the thermoplastic triple and double-wall pipes. The backfill was considered isotropic and homogeneous. Mohr-Coulomb plasticity model was used to define the surrounding soil and the backfill material. The models were analyzed for short-term and long-term performance. The short-term was chosen to be two days after the cover was completed. The first thirty days after that were considered the period of time for long-term analysis. This assumption was made because no significant changes in the results were noticed after those thirty days. Then, the models were calibrated using the experimental results obtained from pipe 1 for both the short-term and the long-term and then validated using those obtained from pipes 2 and 3. The results obtained from the models included deflections, stress, strain, and soil pressure. After that, the models were used to predict the behavior of different t (open full item for complete abstract)

Committee: Prof. Shad Sargand (Advisor) Subjects: Civil Engineering

Doctor of Philosophy, Case Western Reserve University, 2021, Macromolecular Science and Engineering

The step polymerization reaction between diisocyanates and diols results in a tremendously functional material with wide-ranging applications including medical devices and sealants, known as thermoplastic polyurethane (TPU). The microphase separation of urethane-rich hard segments (HS) and hydrocarbon soft segments (SS) provide TPU with the unique morphology responsible for its elastomeric properties. The structure-property relationships of TPU have been understood in terms of either a rubber-like material where HS-rich regions act as crosslink points or a nanocomposite where hard regions are the reinforcing agent. In both views, attempts to model the mechanical behavior based on morphology are hampered by the difficulty in determining parameters that describe the morphology from the chemical composition. The distribution of HS block length and the attractive hydrogen bonding forces make predicting the morphology using block co-polymer theory imprecise, especially for low HS content (HSC) TPUs. Furthermore, TPU has typically been viewed as a binary system with a hard phase dictated by the HSC and a soft phase whose properties are only dependent on the diol type and molecular weight. The first part of this thesis challenges the binary view of TPU through an experimental and modeling investigation. An analytical micromechanical model, the Eshelby double inclusion model, was used to evaluate the observed mechanical behavior of a series of polyester TPUs with increasing HSC, a series of polyether TPUs softened by triols in the SS, and a series of polyester TPUs softened by triol chain extenders. The model was used to probe the mechanical reinforcement contribution from morphological parameters. The TPU morphology was modeled as a composite of HS-rich “hard particles” and a SS-rich “soft matrix”, with the necessity of a third, intermediary phase, the “interphase” evaluated based on experimental results. The second part of the thesis goes beyond neat TPU by prepa (open full item for complete abstract)

Committee: Ica Manas-Zloczower (Advisor); Donald Feke (Committee Member); Michael Hore (Committee Member); Gary Wnek (Committee Member) Subjects: Polymers

Doctor of Philosophy (PhD), Ohio University, 2000, Mechanical Engineering (Engineering)

Vapor grown carbon fiber (VGCF) is a new and inexpensive carbon fiber produced by vapor deposition of hydrocarbons on metal catalysts. Unlike continuous conventional PAN or pitch-derived carbon fibers, VGCF is discontinuous with diameters of about 200 nanometers and lengths ranging from 10 to 200 micrometers. The microscopic size and random entanglement of the fibers create several problems when processing VGCF composites. It is particularly difficult to disperse the entangled fibers in the matrix and orient them along a preferred axis to provide directional reinforcement. This work introduces a technique to produce an improved polymene composite by alignment of vapor grown carbon nano-fibers in a polypropylene matrix. A twin-screw extruder was used to shear mix and disperse the fibers in the polymer matrix. The composite mixtures were extruded through a converging-annular die that generates flow-induced fiber alignment along the extrusion direction. The effect that the various extrusion conditions have on the bulk properties of the extrudate was investigated. It was found that the extrusion process is strongly dependent on the fiber content of the composite. The extrusion pressure increased and the flow rate decreased with fiber volume fraction. The tensile strength and modulus for the composite samples varied with extrusion temperature and screw speed, and the void content increased with fiber volume fraction. It was shown that fiber alignment could be improved by increasing the residence time in the die channel and was verified using x-ray diffraction. The mechanical properties of the aligned samples increased with fiber content. Also, the tensile strength improved with greater fiber orientation; however, more fiber alignment had little affect on the modulus. To better predict the strength of these partially aligned fiber composites, an experimental and theoretical approach was introduced. The experimental data correspond reasonably well when compared with the th (open full item for complete abstract)

Committee: M. Alam (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy (PhD), Ohio University, 2005, Industrial and Manufacturing Systems Engineering (Engineering)

Vapor grown carbon fiber (VGCF) is a new class of highly graphitic carbon nanofiber and offers advantages of economy and simpler processing over continuous-fiber composites. VGCF used in this work (Pyrograf® III) is grown by means of gas phase catalyst synthesis. The diameter of this fiber ranges from 60 and 200 nanometers and the length varies from 50 to 100 micrometers. There are several issues that must be resolved before VGCF can be a suitable reinforcement. The VGCF must be dispersed in the polymer matrix, a good interface with matrix must be obtained, and the VGCF must be aligned in a specific direction. The object of this study is the extrusion of VGCF/nylon composites. To produce the composite, VGCF and nylon 6 were premixed, and then extruded by twin-screw extruder. An annular converging die was used to produce different volume fractions of VGCF/nylon 6 composite in the form of a continuous strand. SEM analysis and X-ray diffraction results showed that VGCF is well dispersed, wetted, and aligned in the nylon 6 matrix. The tensile strength and modulus for extruded VGCF/nylon 6 composites increased as VGCF volume fraction increased, whereas the ductility decreased. For composite strands subjected to additional extension by drawing, it was seen that both the tensile strength and modulus of composites were increased as draw ratio increased. The theoretical strength prediction performed in this study is a combination of a strength prediction model based on fiber alignment, a model for fiber rotation in the polymer melt, and POLYFLOW simulation, which are sequentially correlated. The theoretical prediction was comparable with experimental results when fiber orientation was evaluated by x-ray diffraction; but the theory overestimated composite strength when fiber rotation was incorporated with the model.

Committee: M. Alam (Advisor) Subjects: