Doctor of Philosophy, The Ohio State University, 2023, Mechanical Engineering

As emission standards of passenger vehicles become more and more strict, automotive manufacturers are seeking lightweight solutions to increase vehicle's fuel economy. Fibrous reinforced polymers (FRPs) are known to have high strength to weight ratios, and thus, made them good candidates for the application in the automotive industry. FRP is a composite material made of a polymer matrix reinforced with fibers. The inhomogeneity, anisotropy, visco-elasticity/plasticity, mechanical degradation due to temperature/damage, brittleness characteristics of the unidirectional FRP composites bring challenges to determine mechanical responses both experimentally and numerically. In this dissertation, mechanical behavior of unidirectional carbon fiber reinforced polymer (CFRP) made of Toray T700S carbon fiber and G83-CM prepreg system is studied. Specimens are fabricated from 8-ply and 16-ply CFRP plates. An experimental series is performed including tension, compression, and shear coupon tests at various strain rates ranging from 0.001 to 1000 s-1. Anisotropy is studied by conducting tension, compression, and shear coupon tests in different fiber orientations. Thermal dependence of the material is investigated by performing coupon tests under temperatures ranging from 25 °C to 120 °C. CFRP has been found that loading in one direction can potentially lead to damage in other directions. Thus, coupled, and uncoupled damage testing is performed to characterize such behavior. Digital image correlation (DIC) is applied for deformation and strain measurement on the surface of the specimens. The coupon test data and damage test data are used to calibrate the deformation and damage sub-models of the constitutive material model, *MAT_COMPOSITE_TABULATED_PLASTICITY_DAMAGE, also called *MAT_213, in LS-DYNA. The deformation sub-model predicts elasto-plastic behavior, and it uses a strain-hardening-based orthotropic yield function with a non-associated flow rule extended from Tsai-Wu fail (open full item for complete abstract)

Committee: Amos Gilat (Advisor); Prasad Mokashi (Committee Member); Kelly Carney (Committee Member); Jeremy Seidt (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Mechanical Engineering

Materials experiencing impact loading deform under complex three dimensional states of stress and at high strain rates. Accurately simulating impact events using finite element modeling requires material models capable of depicting the material behavior under these same conditions. In order to create accurate material models, this material behavior must first be determined experimentally. It is of particular interest to determine the equivalent plastic fracture strain at stress states consisting of in-plane biaxial tension and out-of-plane compression, and the plastic stress-strain response at strain rates on the order of 104 s-1. Both of these conditions are found during impact loading, and are outside the scope of current testing techniques. A new test technique is used to investigate Aluminum 2024, Titanium 6Al-4V, and Inconel 718 under in-plane biaxial tension and out-of-plane compression. The test consists of a small spherical or elliptical punch that is advanced into a thin specimen plate to induce in-plane biaxial tension on the back surface of the specimen. A second plate of an appropriate material is placed against the back surface of the specimen plate during loading in order to create out-of-plane compression. The equivalent plastic fracture strain at these stress states is determined from the experimental data and simulations using the commercial finite element software LS-DYNA. The same materials mentioned above are also tested using a modified, direct impact split-Hopkinson bar testing technique to induce strain rates greater than 104 s-1. For these tests, a small cylindrical specimen is placed in contact with the end of a larger cylindrical bar. The specimen is then impacted with a free flying cylindrical projectile to compress the specimen at a high rate of deformation. The stress-strain response of the material at these high strain rates is then investigated from the experimental data and in conjunction with LS-DYNA finite element simulati (open full item for complete abstract)

Committee: Amos Gilat (Advisor); Prasad Mokashi (Committee Member); Jeremy Seidt (Committee Member) Subjects: Aerospace Materials; Engineering; Experiments; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2021, Mechanical Engineering

Digital manufacturing is the use of an integrated, computer-based system comprised of simulation, 3D visualization, analytics, and collaboration tools to simultaneously create product and manufacturing process definitions. Digital manufacturing has become more feasible with the rise in the quantity and quality of computer systems. The advantage of digital manufacturing is the ability to modify or create manufacturing procedures within a virtual and controlled environment before being physically implemented. This enables the designers to see the results of their procedure before investing in physical products. The focus of this work is digital manufacturing of automotive wire harnesses. Current digital manufacturing software lack the ability to accurately simulate flexible components such as cables, hoses, and harnesses. The specific purpose of this work is to develop experimental procedures to characterize wire harnesses and obtain homogenized material properties for incorporation into digital manufacturing software. Experimental procedures are presented to characterize harness components and harness bundles. The different sizes of the components and various possible combinations of harness bundles make it difficult to experimentally characterize each one of them. Hence, limited experiments were conducted, and analytical models are proposed to characterize the components and use the available test data to validate the models. This research can fundamentally change the way harnesses are manufactured, designed and assembled. The experimental characterization and analytical models will help in harness routing, designing correct harness lengths to reduce vibration and rattling, residual stresses, and mechanical failure

Committee: Marcelo Dapino Prof. (Advisor); Soheil Soghrati Prof. (Committee Member); Noriko Katsube Prof. (Committee Member) Subjects: Automotive Engineering; Engineering; Mechanical Engineering; Mechanics

Master of Science, University of Akron, 2017, Geology

The response of the Earth's continental crust to the release of stress following earthquakes in the seismic cycle is an essential process to understand. However, quartz and quartzite must still be studied to determine additional flow equation variables that describe the deformation of the crust. Previous studies have determined the temperature, strain rate, pressure, and grain size dependences on the strength of quartz. This study attempts to determine the water content dependence of the strength of quartzite. Water weakening of quartz has previously been attributed to water fugacity. However, when experiments are performed on relatively dry quartzite (COH ~100 – 1500 H/106 Si) the material is significantly stronger than predicted by dislocation creep or grain size sensitive flow laws (experiments with COH ~2500 – 4000 H/106 Si). This increased strength in dry synthetic quartzite is evidence for water concentration dependence. To determine the flow equation variables, including COH, experiments were performed at the conditions: T = 1200 – 1370°C, Pc = 1230 – 1500, and strain rate = 1.6*10-6 to 1.6*10-4/s. Low-temperature (T = 1200 – 1250°C) experiments display microstructures consistent with dislocation creep but occasionally samples will have microstructures related to grain size sensitive creep. High-temperature (1300 – 1370°C) experiments display grain size sensitive microstructures including recrystallization. The stress exponents observed from my data are 3.5 ± 0.40 for low-temperature experiments and 1.8 ± 0.25 for high-temperature experiments. Using the mechanical data from the pressure-stepping experiment we observed the water fugacity exponent for high-temperature experiments to be 1.4 ± 0.24. Temperature dependence data was used to determine the activation energy for both the low-temperature and high-temperature experiments (Q = 378 ± 60 kJ/mol and 267 ± 30 kJ/mol). The COH dependence and exponent was determined by normalizing data to constant T = 1200 an (open full item for complete abstract)

Committee: Caleb Holyoke III (Advisor); LaVerne Friberg (Committee Member); John Senko (Committee Member) Subjects: Experiments; Geology

Doctor of Philosophy, The Ohio State University, 2016, Mechanical Engineering

Analytical solutions to fluid-structure interaction (FSI) problems provide a powerful design tool that has many applications within the automotive industry. The interaction of body panels with various fluid flows is of interest. Automotive panels that are made too thin become susceptible to a phenomenon known as oil-canning. The deformation can be temporary, or if the loading is large enough the panel can snap through, possibly resulting in permanent deformation. One common occurrence of oil-canning is when going through the dryer section of an automatic car wash. For small deformations the panel can shift between various unstable elastic configurations resulting in loud popping noises within the passenger compartment. Large deformations can result in permanent deformation and pitting of the roof panel. Automotive underbody panels are susceptible to water shock loadings that can be generated when driving over a puddle at high speeds. Panels that are made too thin can be permanently deformed or even fail in some cases when the water shock loading is strong enough. Accurate simulations of these scenarios are of interest since thinning body panels provides an easy way to realize significant weight reduction and increase fuel economy. An experimental program is introduced where full size automotive roof panels are subjected to air blast loading. The panels are stamped from thin alloy sheet steel. Roof panels are loaded into a custom test rig and clamped along the weld flanges. The air blast is generated using a commercial air compressor and a 35.1 mm pipe. Force imparted on the panel by the air jet is measured by three load cells and full-field displacement data is captured using three-dimensional digital image correlation (DIC). The flow field is characterized using piezo-resistive pressure transducers placed in a sensor bar apparatus that can be swept across the flow field to generate pressure maps. The pressure transducers are also mounted (open full item for complete abstract)

Committee: Amos Gilat (Advisor); Briam Harper (Committee Member); Chia-Hsiang Menq (Committee Member); Mo-How Shen (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2014, Mechanical Engineering

A custom punch-die fixture allowing full field three-dimensional Digital Image Correlation (DIC) measurements on the rear surface of the specimen is introduced for dynamic and quasi-static punch experiments. The punch fixture design methodology is described. Results from punch experiments on 5.08 mm Ti-6Al-4V disk specimens using three different punch geometries in both dynamic and quasi-static conditions are presented and discussed. These experiments can be used to generate material failure data under complex stress states. Such data is essential in developing and calibrating complex material models, like those developed for precipitate hardened Inconel 718. The plastic behavior of precipitate hardened Inconel 718 under various strain rates, orientations, and temperatures is examined; and a punch experiment that uses 3D-DIC measurements of the punch specimen is presented. The research presented herein is part of an ongoing project to develop and calibrate a material model in a finite element code, LS-DYNA. Such models are valuable for the simulation of dynamic events, such as blade off failure in aircraft engines. The equipment, theory, and methodologies used to complete experiments in tension and compression at different strain rates and temperatures are presented. Quasi-static experiments are conducted using a biaxial servo-hydraulic load frame and dynamic experiments using two split Hopkinson bars. A specially designed furnace and adapters are used to complete experiments at elevated temperatures. DIC is an optical method for measuring full field deformations and strains on the specimen surface that is utilized extensively in this work. Experimental results for precipitate hardened Inconel 718 are presented and discussed. The material shows significant strain hardening and some strain rate sensitivity in tension. Data from experiments at elevated temperature show complex temperature dependence. The material shows decreasing flow stress with increasing temp (open full item for complete abstract)

Committee: Amos Gilat (Advisor); Mark Walter (Committee Member) Subjects: Aerospace Materials; Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2010, Mechanical Engineering

Plastic deformation of 0.25” thick Ti-6Al-4V plate is investigated. Compression, tension and shear tests are carried out from quasi-static strain rates (10-4 s-1, 10-2 s-1) to high strain rates (up to 5x103 s-1) to study the strain rate sensitivity of the material. Tension and compression tests are carried out on specimens machined in different directions of the plate (at 0°, ±45°, 90° to the rolling direction of the plate in tension and at 0°, ±45°, 90° to the rolling direction and through the thickness of the plate for compression tests) to study the anisotropy effects. High temperature compression tests are carried out at 200° C, 400° C and 600° C to study the temperature effects on the plate. The setups required to perform all these tests and the theories behind the high strain rate tests are explained. The results show the strain rate sensitivity, anisotropy and the temperature effects on the Ti-6Al-4V plate. Johnson – Cook material constants are found out from the experimental data and simulations are run to fit the Johnson Cook model to simulate various tests.

Committee: Amos Gilat (Advisor); Brian Harper (Committee Member) Subjects: Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2010, Mechanical Engineering

The plastic deformation and ductile fracture behavior of 12.7 mm thick 2024-T351 aluminum plate is investigated. Tension, compression and shear experiments are conducted at strain rates ranging from 10-4 s-1 to 5000 s-1 and temperatures ranging from -50 °C to 450 °C. Anisotropy in the plate is studied by conducting tension and compression tests on specimens oriented in multiple directions within the plate. An anisotropic plasticity model is used in numerical simulations of select experiments. Comparison of the simulation results to the actual test data shows that the material behavior can be adequately captured in tension, compression and shear. Anisotropic plastic deformation behavior in an impacted target panel is also investigated. Numerical simulations using both a von Mises and anisotropic yield functions are compared to previously published experimental data. The choice of yield function has a dramatic effect on the predicted projectile residual velocities. Experimental impact data shows evidence of anisotropic behavior, the trends of which can be captured in simulations using the anisotropic yield function. The dependence of equivalent plastic fracture strain on the state of stress is studied through mechanical experiments on specimens with various geometries, subjected to multiple load conditions. Tension tests of plane stress (thin) specimens, axisymmetric specimens and plane strain (thick) specimens are conducted for this purpose. Combined tension – torsion, pure shear and compression – torsion tests as well as dynamic punch experiments are also used. The three dimensional digital image correlation (DIC) technique is used to determine the specimen surface strains in many of the experiments. A coupled experimental – numerical approach is used to generate fracture locus data points for the tension and punch experiments. The equivalent fracture strain dependence on three stress state parameters: stress triaxiality, Lode parameter and product triaxiality is de (open full item for complete abstract)

Committee: Amos Gilat PhD (Advisor); Mark Walter PhD (Committee Member); Brian Harper PhD (Committee Member); Mo-How Herman Shen PhD (Committee Member) Subjects: Aerospace Materials; Engineering; Experiments; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2005, Mechanical Engineering

The role of compressibility on the convective velocity of large-scale structures in axisymmetric jets is studied using a home-built pulse burst laser system and newly developed high-repetition rate experimental diagnostics. A pulse burst laser system was designed and constructed with the ability to produce a burst of short duration (10 nsec), high energy (order of 10 -100 mJ/pulse) pulses over a ~150 microsecond period with inter-pulse timing as low as 1 microsecond (1 MHz). The application of the pulse burst laser for flow measurements was investigated through the development of MHz rate flow visualization and MHz rate planar Doppler velocimetry (PDV). MHz rate PDV is a spectroscopic technique that produces 28 time-correlated realizations of the velocity over a plane with a maximum repetition rate of up to 1 MHz and accuracies on the order of 5%. Space-time correlations were used to track structures within the flow field and determine their convective velocity. Data produced using flow visualization images agrees with previous research and indicates a strong departure of the convective velocity from theory. Data produced using velocity data, however, shows starkly different trends and does not produce the same measurements of convective velocity. This difference in measurement is attributed to a misinterpretation of the use of space-time correlation for tracking structures. The presence of a distinct boundary between the mixing layer and the jet core as well as the mixing layer and ambient air in the flow visualization data and some of the velocity data leads to a bias in the measurement. The space-time correlation is found to preferentially follow these boundaries, thus leading to faster and/or slower measurements of convective velocity. For the Mach 2.0 jet, velocity data was obtained with seed particles marking the jet core and the mixing layer, but not the ambient air. This lack of velocity measurements on the low-speed side of the jet's mixing layer biased the (open full item for complete abstract)

Committee: Mo Samimy (Advisor) Subjects:

Master of Sciences (Engineering), Case Western Reserve University, 2012, EMC - Aerospace Engineering

The knowledge of the flow field in microchannels is becoming increasingly important with the advent of the ionic wind pump and other microscale heat removal devices. The understanding of this flow field will lead to more effective and improved designs. Non-intrusive microscale particle image velocimetry (PIV) utilizing a microscopic objective lens is used to obtain the velocity field in microchannels. The scales of these channels are similar to those encountered in such devices as the ionic wind pump. Microchannels with dimensions ranging from 0.8 mm to 2 mm are used. Computational fluid dynamics (CFD) models are used to replicate each test, with varying inlet conditions and mesh densities. The CFD flow fields are compared to the PIV results for validation purposes, with relative errors between CFD and PIV typically between 2% and 10%. The agreement between the experimental data and computational results ranged from acceptable to excellent, validating this method. The channel with lowest aspect ratio consistently showed the largest agreement between experimental and numerical values.

Committee: Jaikrishnan R. Kadambi PhD (Advisor); J. Iwan D. Alexander PhD (Committee Member); Vikas Prakash PhD (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science (MS), Ohio University, 2013, Mechanical Engineering (Engineering and Technology)

In this study I investigate the changes in the mechanical properties of trabecular bone due to altered loading. The bone samples come from porcine mandibular condyles of treated and untreated pigs from a previous study. The treated animals wore one of two kinds of occlusal splints which presumably altered the loading on the mandibular condyle. This study uses micro-CT images of the mandibular condyles to render a finite element mesh of the trabecular structure. Uniaxial compression was then simulated with finite element analysis to determine the apparent modulus of the bone samples. It was found that one of the splinting treatments significantly reduced the apparent modulus and bone volume fraction in the central region of the mandibular condyle. This study also used experimental uniaxial compression tests of fresh bone samples to validate the finite element model. It was found that there was 30% agreement between the finite element model and the experimental results for the apparent modulus in the anterior-posterior, and medial-lateral directions.

Committee: John Cotton (Advisor) Subjects: Biomechanics