Master of Science in Mechanical Engineering (MSME), Wright State University, 2018, Mechanical Engineering

This research focuses on the compression and tensile behavior of three-dimensional printed polymer lattice structures with different printing parameters such as build orientation, infill density, and layer thickness. The body-centered cubic (BCC) lattice unit cell, which has been extensively investigated for energy absorption applications, is considered here to create compression and tensile specimens. Special test fixture was designed and developed to perform the tensile tests. The specimens were printed using Acrylonitrile Butadiene Styrene (ABS) polymer material on a Stratasys uPrint 3D printer. The printing parameters considered in this case are: (a) Three different build orientations (0, 45 and 90 degrees); (b) Two different infill densities (Sparse High and Solid); and (c)Two different layer thicknesses (0.010 and 0.013 inch). Once fabricated, the specimens were imaged using an optical microscope (OM) to capture their surface characteristics. Strut dimensions of all specimens are measured to understand their build accuracy. In addition, fabrication time for each configuration were recorded for comparison. The specimens were then tested under quasi-static compression and tension to determine the stiffness, failure loads, and energy absorption behaviors. Specific properties were also calculated by dividing the test properties by the specimen mass. All the test data obtained from OM and mechanical tests were then compared and interpreted with respect to all the three build parameters.

Committee: Ahsan Mian Ph.D. (Advisor); Zifeng Yang Ph.D. (Committee Member); Joy Gockel Ph.D. (Committee Member) Subjects: Mechanical Engineering

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, The Ohio State University, 2024, Welding Engineering

Ultrasonic vibration has widely been studied for potential in the metal forming industry for its ability to temporarily soften the material. The lack of understanding of the underlying mechanisms of ultrasonic softening and difficulty in scaling to industrial applications has limited its use. To better understand the fundamentals to the softening mechanism, ultrasonic-assisted (UA) micro-tensile tests of low-carbon steel, aluminum alloy 2219 varying grain size, and titanium grades 2 & 5 are conducted in this study. The ultrasonic vibration is oriented along the tensile axis, and the ultrasonic amplitude is uniform in micro-dogbone specimen. Acoustic softening is observed, increasing with ultrasonic amplitude for all materials. Further investigation on the unique residual effect after ultrasonic treatment based on the microstructure is conducted. Low-carbon steel exhibited residual softening increasing with ultrasonic amplitude. EBSD analysis was conducted on the steel samples strained to 10% strain to explain the reduction of strain hardening during UA and residual softening after UA. Two ultrasonic amplitude levels were compared along with a control NoUA case. Higher LAGB fractions were observed with increasing ultrasonic amplitude, attributed to enhanced dislocation motion resulting in dipole annihilation and subgrain formation. Lower amplitudes assisted in lattice rotation with minor change in the microstructure while higher amplitudes resulted in significant intragranular deformation. Aluminum alloy 2219 was friction stir processed to achieve a refined microstructure and compared to a Al2219-T4 temper with a larger grain size. The resultant reduction of flow stress from ultrasound with varying grain size was similar, however, residual hardening was observed in the T4 temper, while no residual effect was observed in the refined microstructure. Also, the ultimate tensile stress and elongation improved after ultrasonic treatment in the T4-temper. With the (open full item for complete abstract)

Committee: Xun Liu (Advisor); Avraham Benatar (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2019, Materials Science and Engineering

This research explores intrinsic properties of the carbon-rich subsurface zone (“case”) that low-temperature carburization generates in AISI-316 austenitic stainless steel. Foils of this steel were carburized to obtain concentrated interstitially dissolved carbon distributed uniformly throughout their thickness. Compared to the as-received AISI-316 foils, such “full” carburization increases the ultimate tensile strength to 3 times, the yield strength to 4 times, and Young's modulus to 1.5 times, respectively. On the other hand, the strain to failure decreases to (9 ± 1) 10^(-3). For comparison, foils with larger thickness were carburized as well. Decreasing the ratio of “case” to foil thickness was found to decrease the ultimate tensile strength, yield strength, and Young's modulus, while increasing the strain to failure. This research also investigates the impact of concentrated interstitial carbon on electrical conductivity, thermal conductivity, and conduction electron density and mobility. Foils with uniform carbon levels exhibit room-temperature electrical and thermal conductivity corresponding to only 0.8 and 0.7 times those measured in the as-received state, respectively. Hall-effect measurements revealed that concentrated interstitial carbon does not significantly reduce conduction electron mobility, but decreases the electron density to 0.7 of what we measured for as-received material. These observations suggest that the interstitial carbon atoms form covalent bonds with the metal atoms. With their unique combination of properties, free-standing uniform concentrated solid solutions of interstitial carbon in austenite can be regarded as a new material. Besides, this research also explores the thermal stability of the “case” at elevated temperature. Between 1300-1400 K, carbide transformation from M_{23}C_6 to M_7C_3 was observed. Finally, this research introduces a potential biomedical application of “case” on the Co–Cr–Mo alloy for surface wear improvement. (open full item for complete abstract)

Committee: Frank Ernst (Committee Chair); John Lewandowski (Committee Member); William Baeslack (Committee Member); Sunniva Collins (Committee Member) Subjects: Materials Science; Mechanical Engineering; Metallurgy

Master of Science in Engineering, University of Akron, 2018, Mechanical Engineering

In this thesis document, the results and interpretations of an experimental study aimed at investigating and rationalizing the mechanical behavior of a conventionally processed high strength aluminum alloy is presented and discussed. The aluminum alloy chosen for this study was the high strength Al-Cu-Mg alloy, designated as 2024 by the Aluminum Association of America (Washington, D.C., USA). In this study, a few mechanical tests, to include: tension, compression, hardness, shear and cyclic stress-controlled fatigue, were conducted in synergism with microstructural characterization and macroscopic observation and record of the nature of fracture with the objective of establishing the role of alloy microstructure in governing the macroscopic mechanical response and fracture behavior of the chosen aluminum alloy. The mechanical tests were conducted in accordance with procedures detailed in the standards of ASTM. The test specimens for each test were precision machined from the as provided wrought alloy stock. For the cyclic fatigue tests, the presence of a notch, conforming to specifications detailed in ASTM Standard, on cyclic fatigue life is presented. The test results are presented and briefly discussed with specific reference to nature of loading and microstructural influences.

Committee: Tirumalai Srivatsan Dr. (Advisor); Anil Patnaik Dr. (Committee Member); Craig Menzemer Dr. (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Master of Science (MS), Ohio University, 2005, Mechanical Engineering (Engineering)

ElectroStatic Precipitators (ESP) are widely used in coal fired power plants for control of particulate matter and other toxic gases. Traditionally, ESP's used metal plates as collecting surfaces for capture of particles in flue gas. However, back corona and re-entrainment of particles into flue gases hinder with the performance of ESP in collection of fine particulate matter (PM2.5). Metal plate ESP's also suffer from problems due to corrosion. Researchers at Ohio University developed a patented wet membrane based ESP to overcomes these difficulties. Wet membrane based ESP replaces the metal collecting surfaces with woven fabrics. Omnisil 1000, a silica fabric (98.5% silica), is found to be suitable for this application. The replacement of metal collecting plates with fabric requires application of tensile loads on the fabric during operation of ESP. A study of tensile and creep behavior is presented. A test facility for uniaxial tension and creep testing of Omnisil fabric is developed. The uniaxial tensile behavior of the fabric is typical to plain woven fabrics and the failure strength bears a linear relation to fabric width. The creep elongation of the fabric is negligible in the experimental conditions.

Committee: David Bayless (Advisor) Subjects: Engineering, Mechanical