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Ghods, MasoudEffect of Convection Associated with Cross-section Change during Directional Solidification of Binary Alloys on Dendritic Array Morphology and Macrosegregation
Doctor of Engineering, Cleveland State University, 2017, Washkewicz College of Engineering
This dissertation explores the role of different types of convection on macrosegregation and on dendritic array morphology of two aluminum alloys directionally solidified through cylindrical graphite molds having both cross-section decrease and increase. Al- 19 wt. % Cu and Al-7 wt. % Si alloys were directionally solidified at two growth speed of 10 and 29.1 µm s-1 and examined for longitudinal and radial macrosegregation, and for primary dendrite spacing and dendrite trunk diameter. Directional solidification of these alloys through constant cross-section showed clustering of primary dendrites and parabolic-shaped radial macrosegregation profile, indicative of “steepling convection” in the mushy-zone. The degree of radial macrosegregation increased with decreased growth speed. The Al- 19 wt. % Cu samples, grown under similar conditions as Al-7 wt. % Si, showed more radial macrosegregation because of more intense “stepling convection” caused by their one order of magnitude larger coefficient of solutal expansion. Positive macrosegregation right before, followed by negative macrosegregation right after an abrupt cross-section decrease (from 9.5 mm diameter to 3.2 mm diameter), were observed in both alloys; this is because of the combined effect of thermosolutal convection and area-change-driven shrinkage flow in the contraction region. The degree of macrosegregation was found to be higher in the Al- 19 wt. % Cu samples. Strong area-change-driven shrinkage flow changes the parabolic-shape radial macrosegregation in the larger diameter section before contraction to “S-shaped” profile. But in the smaller diameter section after the contraction very low degree of radial macrosegregation was found. The samples solidified through an abrupt cross-section increase (from 3.2 mm diameter to 9.5 mm diameter) showed negative macrosegregation right after the cross-section increase on the expansion platform. During the transition to steady-state after the expansion, radial macrosegregation profile in locations close to the expansion was found to be “S-shaped”. This is attributed to the redistribution of solute-rich liquid ahead of the mushy-zone as it transitions from the narrow portion below into the large diameter portion above. Solutal remelting and fragmentation of dendrite branches, and floating of these fragmented pieces appear to be responsible for spurious grains formation in Al- 19 wt. % Cu samples after the cross-section expansion. New grain formation was not observed in Al-7 wt. % Si in similar locations; it is believed that this is due to the sinking of the fragmented dendrite branches in this alloy. Experimentally observed radial and axial macrosegregations agree well with the results obtained from the numerical simulations carried out by Dr. Mark Lauer and Prof. David R. Poirier at the University of Arizona. Trunk Diameter (TD) of dendritic array appears to respond more readily to the changing growth conditions as compared to the Nearest Neighbor Spacing (NNS) of primary dendrites.

Committee:

Surendra Tewari, Ph.D. (Advisor); Jorge Gatica, Ph.D. (Committee Member); Orhan Talu, Ph.D. (Committee Member); Rolf Lustig, Ph.D. (Committee Member); Kiril Streletzky, Ph.D. (Committee Member)

Subjects:

Aerospace Materials; Automotive Materials; Chemical Engineering; Condensed Matter Physics; Engineering; Fluid Dynamics; High Temperature Physics; Materials Science; Metallurgy

Keywords:

Directional Solidification; Natural Convection; Fluid Flow; Binary Alloys; Macrosegregation; Dendritic Array; Dendrite Morphology; Solutal Remelting; Thermosolutal Convection; Aluminum Alloy; Cross section Change

Rose, David HarryA Cumulative Damage Approach to Modeling Atmospheric Corrosion of Steel
Doctor of Philosophy (Ph.D.), University of Dayton, 2014, Materials Engineering
Past attempts to develop models that predict atmospheric corrosion rates used statistical regression, “power-law”, or other approaches that result in linear or simple nonlinear corrosion rate predictions. Such models were calibrated by statistically comparing corrosion test results to predictions based upon long-term (e.g., annual) deposition measurements of chloride aerosols and/or SO2. Relative humidity, if explicitly considered, was only used to define the amount of time during the year when conditions were thought to be favorable for corrosion. Most models ignored temperature effects but those that do only consider annual averages. A new approach was constructed to predict corrosion rates using the concept of cumulative damage. This new model is analogous to some types of fatigue models and is based upon the Eyring equation, which was originally developed to predict the dependence of chemical reaction rates on levels of the presumed acceleration factors. The model makes hourly weight loss predictions, which when added together makes longer-term “cumulative” predictions. Principal advantage of using hourly predictions is that the effects of diurnal and seasonal temperature cycles and related changes to relative humidity are explicitly considered. The stochastic nature of atmospheric contaminants is considered as well. An inverse modeling approach using Monte Carlo simulations was used to fit various candidate models to proxy environmental characterization data representing conditions at corrosion test sites. Proxy data (measured elsewhere and for other purposes) was used to infer the stochastic environmental severity at sites where corrosion tests were conducted. Such data included hourly SO2 and ozone data obtained from the Environmental Protection Agency’s Air Quality System database, longer-term chloride deposition data from the National Atmospheric Deposition Program’s on-line database, and hourly weather data from the U.S. Air Force’s 14th Weather Squadron. Proxy data was used so that if this current research proved successful, follow-on work could lead to a practical methodology that design engineers could employ to make realistic predictions without having to explicitly characterize the environment at a location of interest. Cumulative predictions made using such data were statistically compared to quarterly corrosion test results that came from a DoD Strategic Environmental Research and Development Program (SERDP) funded effort and other related programs that used the same testing protocols. Billions of simulations were conducted whereby coefficients employed by the candidate model were randomly varied and the individual predictions statistically compared to test measurements in order to identify the most accurate model. Each candidate model was calibrated by considering hourly data for an entire year at multiple locations in order to quantify interactions between acceleration factors. The degree of fit between the model results and test measurements at the calibration sites was very high (R2=~ 0.99). When the optimum model was applied to locations where corrosion tests were conducted but not used for calibration, the fit was not quite as good, but was still quite high (R2=~0.86). Analyses were conducted to identify ways to further improve accuracy, thus laying the framework for future efforts.

Committee:

Douglas Hansen, Ph.D. (Advisor)

Subjects:

Aerospace Materials; Automotive Materials; Materials Science

Keywords:

atmospheric corrosion; cumulative damage; mass loss; modeling; predictions; environmental severity; climate zones; surf zones; urban pollution; Monte Carlo simulations

Chen, De-ShiouSliding mode observers for automotive alternator
Doctor of Philosophy, The Ohio State University, 1998, Mechanical Engineering

Estimator development for synchronous rectification of the automotive alternator is a desirable approach for estimating alternator's back electromotive forces (EMFs) without a direct mechanical sensor of the rotor position. Recent theoretical studies show that estimation of the back EMF may be observed based on system's phase current model by sensing electrical variables (AC phase currents and DC bus voltage) of the synchronous rectifier. Observer design of the back EMF estimation has been developed for constant engine speed.

In this work, we are interested in nonlinear observer design of the back EMF estimation for the real case of variable engine speed. Initial back EMF estimate can be obtained from a first-order sliding mode observer (SMO) based on the phase current model. A fourth-order nonlinear asymptotic observer (NAO), complemented by the dynamics of the back EMF with time-varying frequency and amplitude, is then incorporated into the observer design for chattering reduction. Since the cost of required phase current sensors may be prohibitive, the most applicable approach in real implementation by measuring DC current of the synchronous rectifier is carried out in the dissertation. It is shown that the DC link current consists of sequential "windows" with partial information of the phase currents, hence, the cascaded NAO is responsible not only for the purpose of chattering reduction but also for necessarily accomplishing the process of estimation. Stability analyses of the proposed estimators are considered for most linear and time-varying cases. The stability of the NAO without speed information is substantiated by both numerical and experimental results.

Prospective estimation algorithms for the case of battery current measurements are investigated. Theoretical study indicates that the convergence of the proposed LAO may be provided by high gain inputs. Since the order of the LAO/NAO for the battery current case is one order higher than that of the link current measurements, it is hardly to find moderate values of the input gains for the real-time sampled-data systems. Technical difficulties in implementation of such high order discrete-time nonlinear estimators have been discussed. Directions of further investigations have been provided.

Committee:

Vadim I. Utkin (Advisor)

Subjects:

Automotive Materials; Electrical Engineering; Energy; Mechanical Engineering

Balagurunathan, JayakishanInvestigation of Ignition Delay Times of Conventional (JP-8) and Synthetic (S-8) Jet Fuels: A Shock Tube Study
Master of Science (M.S.), University of Dayton, 2012, Mechanical Engineering
The global depletion of petroleum-based fuels has led the world to more closely examine alternate fuels. Therefore, alternate fuels produced from feedstocks such as coal, soybeans, palm oil or switch grass through methods such as coal liquefaction, biomass gasification, and Fischer-Tropsch synthesis have been tested. Among these techniques, fuels generated using Fischer-Tropsch technologies are of interest because they produce clean burning hydrocarbons similar to those found in commercial fuels. Therefore, in this study the Fischer-Tropsch derived S-8 fuel was evaluated as a drop-in replacement for the jet fuel JP-8. The jet fuel JP-8 is comprised of n-, iso- and cyclo- alkanes as well as aromatics while the S-8 fuel is primarily comprised of n- and iso- alkanes. The composition of the fuel affects its ignition characteristics chemically and physically by either advancement or delay of time to ignition. Since this study focused on the chemical effects, the fuels were completely pre-vaporized and pre-mixed. A high pressure, high temperature heated single pulse shock tube was used for this study. The shock tube is an established experimental tool used to obtain ignition delay data behind reflected shock waves under operating conditions relevant to modern engines. The experiments were conducted over a temperature range of 1000-1600 K, a pressure of 19±2 atm, equivalence ratios of 0.5, 1 and 3, within a dwell time of 7.6±0.2 ms and an argon dilution of 93% (v/v). Ignition delay times were measured using the signal from the pressure transducer on the end plate with guidance from the optical diagnostic signal. Along with JP-8 and S-8, the ignition delay of n-heptane was also studied. N-heptane was chosen to represent the n-alkanes in the fuels for this study since it was present in both fuels and also to prove the fact that the n-alkanes were rate controlling. The results indicate that both S-8 and JP-8 fuels have similar ignition delays at corresponding equivalence ratios. The fuel-rich mixtures ignited faster at lower temperatures (<1150 K) and the fuel-lean mixtures ignited faster at higher temperatures (>1150 K). In the transition period between lower to higher temperatures (~1100-1200 K), the equivalence ratio had no significant effect on the ignition delay time. The results also show that the ignition delay time measurements of S-8 and JP-8 fuels are similar to the ignition delay of n-heptane at the equivalence ratio of Φ=0.5 and thereby indicate that the n-alkanes present in these fuels controlled the ignition under these conditions. The ignition delay results of S-8 and JP-8 at Φ=3.0 from this study were also compared to prior work (Kahandawala et al., 2008) on 2-methylheptane and n-heptane/toluene (80/20 liquid vol.%), respectively and found to be indistinguishable. This data serves to extend the gas phase ignition delay database for both JP-8 and S-8 and is the first known data taken for both these fuels at higher temperatures (>1000 K) for an equivalence ratio of 3.0 with argon as the diluent gas.

Committee:

Sukh Sidhu, Dr (Committee Chair); Philip Taylor, Dr (Committee Member); Moshan Kahandawala, Dr (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Alternative Energy; Automotive Engineering; Automotive Materials; Chemical Engineering; Chemistry; Energy; Engineering; Environmental Engineering; Mechanical Engineering; Petroleum Engineering; Technology

Keywords:

Ignition delay; shock tube; S-8; JP-8; Jet fuels; Fuel characteristics; heated shock tube; Fischer-Tropsch; Alternate fuels; alkanes; synthetic fuel; fuel; iso-alkanes; jayakishan balagurunathan

Hu, YiranIdentification and State Estimation for Linear Parameter Varying Systems with Application to Battery Management System Design
Doctor of Philosophy, The Ohio State University, 2010, Electrical and Computer Engineering

In this dissertation, the identification and state estimation for linear parameter varying (LPV) systems as well as their applications to battery management system design are investigated. First, two complete LPV system identification procedures are described. One procedure uses a layered optimization process while the other uses a subspace based method. Both methods provide theoretically sound and practical processes under which realistic LPV system identification problems can be solved. Secondly, controller and observer design techniques for LPV systems are examined. In particular, the stability conditions in the form of parameter dependent linear matrix inequalities (LMI) that result from the applications of the standard Lyapunov stability theory and other advanced techniques such as L2 and H to LPV systems are discussed in detail. Also discussed are the some of the techniques for solving these LMIs. Lastly, because real systems often contain parametric uncertainty, the use of input to state stability to characterize closed loop performance of controllers or state estimator under such condition is also reviewed.

The tools developed for LPV systems are then applied to solve the problems of model identification and state of charge (SoC) estimation for battery cells. The model identification problem is tackled using both identification schemes so that differences in performance and effectiveness between the methods can be compared and contrasted. A SoC estimator based on LPV system state estimation techniques is then designed using the model identified. Because parametric uncertainty is inherent in the estimator designed, the stability and performance of the estimator is analyzed using the notion of input to state stability. Experimental data is then used to illustrate the efficacy of this method. The goal of these applications is to show the relevance of the LPV structure and techniques to problems in battery management system design, so that research will be done to solve other problems in this area under the same framework.

Committee:

Steve Yurkovich, PhD (Advisor); Giorgio Rizzoni, PhD (Committee Member); Yann Guzennec, PhD (Committee Member)

Subjects:

Automotive Materials; Electrical Engineering

Keywords:

LPV; system identification; battery management; battery modeling; state of charge estimation

Kuruvilla, MithunAn Understanding of the Quasi-static Behavior, High Cycle Fatigue and Final Fracture Behavior of a Titanium (Ti- 4 Al-2.5 V-1.5 Fe-0.25 O2) Alloy
Master of Science, University of Akron, 2008, Mechanical Engineering

Titanium, which is referred as a “wonder metal” has been in use for structural application for more than 50 years both in the form of commercially pure titanium and alloys. The wide range of mechanical properties exhibited by titanium led to the development of various alloys tailored for specific application in areas spanning aerospace to sports. The innovatively engineered titanium alloy ATI 425TM is an emerging high performance, high strength alloy and a viable replacement to the work horse and most commercially popular titanium alloy Ti-6Al-4V. This newly emerged alloy offers the inherent advantage of being receptive to mechanical deformation by cold working. Initially this alloy was developed and put forth for use as armor plate for ballistic protection. This alloy also shows promise for use in aerospace-related applications. In this thesis report is presented and discussed the final fracture behavior of the alloy deformed under both quasi static and cyclic fatigue loading conditions, highlighting the role of product form in governing the mechanical deformation and fracture behavior. Samples of the alloy were prepared from both rod stock and sheet stock, and deformed with stress axis both parallel and perpendicular to the longitudinal direction for the sheet stock and along the longitudinal axis for the rod stock.

The intrinsic influence of processing on microstructure of the rod revealed alpha grains of varying size and shape being well distributed through the transformed beta matrix. The hardness measurements were consistent and the macrohardness was found to be about half the value of the microhardness. Tensile properties of this alloy are comparable with the commercial alloy Ti-6Al-4V, within the limits of experimental scatter. The tensile deformed fracture surface was macroscopically rough and microscopically, reminiscent of locally ductile and brittle failure mechanisms. The influence of intrinsic microstructural features of the alloy product and nature of loading on final fracture behavior is discussed. The high cycle fatigue resistance of the chosen titanium alloy revealed a trend shown by most non- ferrous metallic materials. The final fracture behavior of the alloy under cyclic loading conditions showed differences in the nature and volume fraction of the features with maximum stress at a given load ratio.

The processing on the sheet stock of both orientations resulted in alpha plus beta microstructure. The microhardness and macrohardness data reveals the alloy to be harder in the transverse orientation than in the longitudinal orientation. The tensile properties of the sheet stock with transverse orientation, when compared to the commercial alloy Ti-6Al-4V were observed to be better than sheet stock with longitudinal orientation. The tensile fracture surface of the alloy sheet along the longitudinal orientation revealed at the macroscopic level a fairly rough transgranular region and at microscopic level a healthy population of microscopic voids and shallow dimples of varying size and shape. For the transverse test specimen, the tensile fracture surface was macroscopically rough and globally at an inclination to the far field stress axis and microscopically it was rough and covered with a healthy population of voids of varying and dimples of varying size and shape. The high cycle fatigue resistance of the chosen titanium alloy revealed that the transverse oriented specimens showed more fatigue resistance compared to the longitudinal ones. Cyclic fatigue fracture surfaces revealed differences in the nature and volume fraction of the features with maximum stress at a given load ratio. The region of crack initiation and early crack growth and stable crack growth was essentially flat and transgranular.

Committee:

Dr. Tirumalai S. Srivatsan, PhD (Advisor)

Subjects:

Aerospace Materials; Automotive Materials; Biomedical Research; Engineering; Materials Science; Mechanical Engineering; Metallurgy

Keywords:

Titanium Alloy; ATI 425; Tension; High Cycle Fatigue

Anozie, Uchechukwu ChamberlinMicroencapsulation of Soluble Sulfur by Calcium Alginate
Master of Science, University of Akron, 2012, Chemical Engineering

The migration of compounding ingredients to the surface of cured or uncured rubber tends to be one of the contributing factors towards the properties imparted on a rubber article such as the making of a multi-ply article like belts or tires. The effect from the migration of the compounding ingredients may or may not be detrimental to the performance of the rubber article. For instance, there are specific situations where the migration of compounding ingredients like antioxidants or waxes to the surface of a rubber compound may be beneficial to act in protecting the rubber from ozone aging. However, there are other instances where the migration of compounding ingredients harmful to the properties of the rubber compound. One of such compounding ingredients is sulfur, which can act to decrease the tackiness of rubber and hinder the formation of multi-ply articles like a tire. Therefore, there is a need to prevent the migration and formation of excess compounding ingredients like sulfur on the surface of rubber.

Microencapsulation of compounding ingredients may be used as one of the methods to prevent the migration of compounds like sulfur which was the primary area of focus. Microencapsulation of sulfur by using primarily alginate, served as the mechanism used to prevent the migration of sulfur to the surface of rubber. The microencapsulated sulfur beads produced had a number frequency distribution with 87% having a bead size less than 150 µm and the lower percentage accounting for larger bead sizes. In the 87% of the bead distribution, 44.3% accounted for bead sizes with a size range from 50 to 100 µm while 24.7% and 18.0% accounted for bead sizes with a size range from 0 to 50 µm and 100 to 150 µm respectively. The bulk of the lower percentage was in the size range from 150 to 200 µm with a value of 9.3%. Beads produced had a high percentage (> 80%) of sulfur encapsulated. These microencapsulated sulfur beads were compared with ordinary rubbermaker’s sulfur and insoluble sulfur to distinguish their effects in the compounding formulation during rubber testing. The rubber testing involved tensile study and a sulfur blooming study. The results from the sulfur blooming study suggested that microencapsulated soluble sulfur functioned better than ordinary rubbermaker’s sulfur to prevent sulfur blooming at the tested temperatures (100¿¿¿¿C and 120¿¿¿¿C). The results from the study also suggested that microencapsulated soluble sulfur performed relatively better than insoluble sulfur at the 120¿¿¿¿C temperature; however, a relatively better result was obtained for insoluble sulfur in comparison with microencapsulated soluble sulfur at the 100¿¿¿¿C temperature.

The tensile study on the other hand, indicated that both ordinary rubbermaker’s sulfur and insoluble sulfur achieved better results than microencapsulated soluble sulfur. The lower result obtained for microencapsulated sulfur was attributed to the microencapsulated soluble sulfur bead characteristics (size, shape, etc.) and the interaction of the beads in the rubber matrix. These properties might have been influential in the lower results achieved for microencapsulated soluble sulfur in addition to the crosslink density of the cured rubber compound. The results obtained from the research were useful to guide the future developments on the microencapsulation of soluble sulfur.

Committee:

Lu-Kwang Ju, Dr. (Advisor); George Chase, Dr. (Committee Member); Michael Cheung, Dr. (Committee Member)

Subjects:

Automotive Materials; Chemical Engineering; Engineering; Materials Science; Polymers

Keywords:

Microencapsulation; rubber compounding; sulfur blooms; curatives; alginate; vegetable oil; fillers; scorch safety

Javorsky, Joseph FrankObserving the Main Effects of Automotive Primers when Bonding to Polyvinylchloride
Master of Science in Mechanical Engineering, University of Toledo, 2012, Mechanical Engineering

The targeted facility is one that supplies window panels for automotive companies. Much focus of the research relies heavily on bonding various substrates to glass. While the majority of the research lies in this area, there are some business applications, such as bonding stainless steel to Polyvinylchloride (PVC). This application is commonly seen on the outside of side windows on high-end model vehicles.

Multiple studies were performed to gain further understanding when bonding PVC to glass in order to provide the strongest bond in the shortest amount of time focusing on primer characteristics. All of these experiments focused on glass to PVC bonding. However, there is no information that focuses on bonding PVC to stainless steel. Current processes are in line with individual automotive standards, but more needs to be understood about this process in order to improve the process to keep up with competition.

The research found that glass outperformed stainless steel, but the molding process may need to be redesigned in order to compare the two substrates directly. Generally, hot and humid conditions, non-shaken primer, as well as a thick primer path and high preheat can all positively impact the travel distance observed. Obtaining high amounts of plastic cohesive failure depends more upon the bonded substrate, as many optimal factor levels were different.

Committee:

Matthew Franchetti, PhD (Committee Chair); Hongyan Zhang, PhD (Committee Member); Tim Stansfield, PhD (Committee Member)

Subjects:

Automotive Materials; Mechanical Engineering; Statistics

Keywords:

Polyvinylchloride; PVC; Taguchi; Stainless steel; glass; primer; cohesive; Optimal; automotive

Gnanasekar, Vignesh KumarEvaluation of Thermal Stress in Carbon/Glass Hybrid and Glass Nanocomposite under Resistive Heating
Master of Science (M.S.), University of Dayton, 2015, Civil Engineering
Resistive heating of nanocomposite material is proposed for use in many applications because of its light weight and low current requirements. When the nanocomposites are resistively heated, thermal stresses starts arising in it due to mismatch of CTE between the fiber and matrix of the nanocomposite. A nanocomposite material can withstand only limited thermal stress when it is resistively heated. If the thermal load is too high, or combined with other external loads, the nanocomposite can fail by means of delamination, crack formation, warpage and other related modes. Hence, studying the thermal stress that develops in nanocomposites upon resistive heating will help in preventing otherwise unanticipated failures. The objective of this effort was to develop and experimentally validate a Finite Element Method model for evaluation of the thermal stress arising in nanocomposite material upon resistive heating. In order to fill the technology gap of predicting thermal stress in resistively heated nanofiber composites, a finite element method (FEM) model was created. This model was created using ABAQUS® software. To verify the results of the model, the experimental method of hole-drilling was adopted. The nanocomposite considered for the research were a carbon/glass hybrid with epoxy resin and a glass/epoxy composite reinforced with CNT Buckypaper. The experiment was based on the principle of redistribution of stress when the hole is drilled in the composite and the relieved strain is measured by a strain gage rosette. The strain release corresponds to the thermal stress that was present before the drilling the hole. The thermal stress results of hole-drilling method were compared with the FEM model result, validating the model and analysis results. The verified FEM model can be used to predict thermal stresses arising in nanocomposites and preventing failure when the nanocomposite is resistive heated and externally loaded.

Committee:

Thomas Whitney (Advisor)

Subjects:

Aerospace Materials; Automotive Materials; Civil Engineering; Engineering; Materials Science; Nanotechnology

Keywords:

CNT bucky paper; resistive heating; nanocomposites; hole drilling method; thermal stress measurement; resistive heating deicing; finite element method

Nunez Moran, Emerson OsvaldoEvaluation of the Localized Corrosion Resistance of 21Cr Stainless Steels
Master of Science, The Ohio State University, 2010, Materials Science and Engineering
Ferritic stainless steels have good corrosion resistance properties and lower cost than austenitic steels due to the lack of nickel. However, they have a lower formability than that of austenitics, and they show brittleness at low temperatures, near 475°C, and of welds. Pohang Steel Company (POSCO) has interest in a 21% Cr ferritic stainless steel, which is a concentration that is relatively unexplored. Pitting corrosion of stainless steels is associated with surface defects and heterogeneities in the matrix, in particular inclusions, however, there is little information about the initiation sites in clean steels, with low S content. Therefore, it is of interest to investigate where the most susceptible sites for pitting initiation are located, and the role they play. The corrosion resistance of the ferritic alloys was evaluated and compared to the performance of austenitic SS304 steel using crevice corrosion tests and cyclic polarization tests in chloride solution to determine the pitting and repassivation potentials of the alloys. The role that inclusions play during pitting was evaluated for the ferritic stainless steels through a chemical attack experiment where the alloys were exposed to an acidic chloride solution and the progression of the attack was assessed at defined inclusions and discrete time intervals. The pitting potential (Epit) distribution of the ferritic alloys shows values ranging from 100 mV to 450 mV higher than those observed on SS304, indicating a higher resistance to pit initiation for the ferritic steels. In the crevice corrosion test, SS304 showed higher repassivation potentials (Erep) than the ferritic steels and in the pitting corrosion test the Erep values were higher for the ferritic steels. In both cases, however, the difference in Erep was about 100 mV. The differences in Erep between crevice and pitting may be caused by a strong dependence of Erep on the charge density in the low charge density region associated to pitting. The attack under a crevice former has larger dimensions than a pit, and thus the crevice repassivation potential might be different than that for pits. The higher repassivation potential for deep crevices found for SS304 indicates a better resistance to localized corrosion propagation. The combination of this result with the higher pitting potentials for the ferritic stainless steels suggests that the localized corrosion resistance of the ferritic steels is about the same as for SS304. The inclusions present in the ferritic stainless steels acted as pit initiation sites, due to their cathodic behavior compared to the metal matrix, promoting the dissolution of the metal matrix surrounding them.

Committee:

Gerald Frankel (Advisor); Rudolph Buchheit (Committee Member)

Subjects:

Automotive Materials; Engineering; Materials Science; Metallurgy

Keywords:

Corrosion; pitting; NMI; Stainless steel; ferritic; inclusion

Turner, Andrew JosephLow-Velocity Impact Behavior of Sandwich Panels with 3D Printed Polymer Core Structures
Master of Science in Mechanical Engineering (MSME), Wright State University, 2017, Mechanical Engineering
Sandwich panel structures are widely used in aerospace, marine, and automotive applications because of their high flexural stiffness, strength-to-weight ratio, good vibration damping, and low through-thickness thermal conductivity. These structures consist of solid face sheets and low-density cellular core structures, which are often based upon honeycomb topologies. The recent progress of additive manufacturing (AM) (popularly known as 3D printing) processes has allowed lattice configurations to be designed with improved thermal-mechanical properties. The aim of this work is to design and print lattice truss structures (LTS) keeping in mind the flexible nature of AM. Several 3D printed core structures were created using polymeric material and were tested under low-velocity impact loads. Different unit-cell configurations were compared to aluminum honeycomb cores that are tested under the same conditions. An impact machine was designed and fabricated following the ASTM D7136 Standard to correctly capture the impact response. The absorption energy as well as the failure mechanisms of lattice cells under such loads are investigated. The differences in energy-absorption capabilities were captured by integrating the load-displacement curve found from the impact response. Similar manufacturing and sandwich-panel-fabrication processes must be used to accurately compare the impact responses. It is observed that selective placement of vertical support struts in the unit-cell results in an increase in the absorption energy of the sandwich panels. Other unit-cell configurations can be designed with different arrangements of vertical struts into the well-known body centered cubic (BCC) LTS for further improvements in absorption energy capabilities.

Committee:

Ahsan Mian, Ph.D. (Advisor); Raghavan Srinivasan, Ph.D., P.E. (Committee Member); Joseph Slater, Ph.D., P.E. (Committee Member)

Subjects:

Automotive Materials; Engineering; Experiments; Mechanical Engineering; Polymers

Keywords:

Additive manufacturing; 3D Printing; Sandwich structures; Energy absorption; Low-velocity impact

Bates, Griffin MichaelCharacterizing the Cold Temperature Performance of Guayule (Pathenium argetnatum) Natural Rubber and Improving Processing of Guayule and Agronomic Practices of Taraxacum kok-saghyz
Master of Science, The Ohio State University, 2015, Food, Agricultural and Biological Engineering
Natural rubber (NR) is a vital commodity for modern economies with an expected global demand of 17 MT by 2025. This growth also will coincide with an expected supply shortfall of 1.5-3.0 MT by 2020. Guayule (Parthenium argenatum) is being investigated as a domestic source of NR due to its high molecular weight rubber content and its ability to grow in semiarid climates within the United States. Previous research has shown the ductility of guayule rubber particles fractured at -196°C compared to hevea particles which suffer shear fracture. In order to further promote guayule, the cold temperature flexibility of guayule was characterized using dynamic mechanical analysis in both green (uncompounded) and compounded latex and dry rubber samples. When compared to Hevea, Guayule NR has a lower glass transition temperature, storage modulus, and loss modulus, stiffness, and dynamic viscosity at -100°C which are evidence of greater flexibility under extreme cold conditions. There is also a correlation between the removal of protein content in both Hevea and Guayule to increased flexibility, as well as an increase of flexibility in Hevea through the removal of gel content. Membrane-removal from the rubber particles, in both species, increases flexibility. These characteristics prove the utility of Guayule and promote the continued research and cultivation of this vital commodity. Green guayule’s cold temperature flexibility was shown to be transferable to compounded latex samples, however the recipe was a major factor as to how much guayule’s cold temperature advantage can be translated to finish products. In dry rubber samples, there was little to no difference between hevea and guayule at -100°C, except that guayule may be able to use less filler to attain similar properties as hevea requires. In processing guayule latex, fine particles from leaf matter are a prohibitive factor for latex quality since guayule leaves do not abscise naturally. This requires mechanical or chemical defoliation that can be cost-prohibitive or decrease latex quality further. It was shown that exposure to N2(l) of less than one second and a swift impact is enough to quickly defoliate guayule shrub without significantly decreasing extractable latex quantities in fresh shrub. While small branches were more sensitive to this exposure, larger branches were able to withstand the exposure with little repercussions on the extractable latex quantities. Another alternative natural rubber source, Taraxacum kok-saghyz (referred to as TK; also known as Buckeye Gold, Kazak dandelion, and Russian dandelion) is being developed as a domestic source of rubber, but best agronomic practices must be established. By placing fresh August or November harvested roots in 4°C cold storage with humidity can increase the concentration of rubber in the roots over a period of 30 to 60 days. This ability did not occur in roots less than 7g fresh weight and June-harvested roots. This study shows that TK can be stored for extended periods the fact of which is vital for continuous production facilities necessary to advance TK as a viable source of domestic rubber. A planting density studied was carried out by planting densities of 1.24, 2.47, 4.94, and 9.88 million plants/ha in the Spring of 2013 and harvesting half in late October 2013 and the following May (2014). The October-harvested roots had greater plant retention the number of plants harvested divided by the number of transplanted plants, than the May-harvested roots. The October-harvested roots had higher root mass and higher overall extractable rubber per plot than the May-harvested plots. If post-harvest storage is considered as well, the 1.24 million plants/ha density could be the most advantageous planting density with a potential of 2,720kg dry rubber/ha/year.

Committee:

Katrina Cornish, PhD (Advisor); Yebo Li, PhD (Committee Member); Michel Frederick, PhD (Committee Member)

Subjects:

Aerospace Materials; Agricultural Engineering; Agriculture; Automotive Materials; Engineering; Experiments; Low Temperature Physics; Materials Science; Sustainability

Keywords:

Natural Rubber; Polymers; Alternative Rubber; Guayule; Parthenium argentatum; Taraxacum kok-saghyz; Sustainablility; Renewable; Domestic; Agriculture; Agronomics; Materials Engineering; Kazakh dandelion; Cold temperature behavior

Peer, Andrea JPerformance Testing and Modeling of Ultra-High Strength Steel and Complex Stack-Up Resistance Spot Welds
Master of Science, The Ohio State University, 2017, Materials Science and Engineering
Hot stamped boron steels, such as Usibor® 1500, have been increasingly used in automotive structural components for light-weighting and impact resistance. Classified as an ultra-high strength steel, these alloys have superior strength with tensile strengths exceeding 1500 MPa. The rapid heating and cooling thermal cycle during resistance spot welding can significantly alter the martensitic base metal microstructure, resulting in formation of coarse-grained and subcritical heat-affected zones (CGHAZ and SCHAZ) with inferior mechanical properties. The martensitic CGHAZ is adjacent to the weld nugget and experiences the most time above the AC3, which allows for austenite grain growth. The SCHAZ is next to the unaffected base metal and does not reach the AC1¬ during welding, thus the base metal microstructure is over-tempered into cementite and ferrite. The present research aims at developing the fundamental knowledge of plastic deformation and fracture behaviors of ultra-high strength steel resistance spot welds. As a resistance spot weld comprises highly inhomogeneous microstructure, the overall research approach is based on studying the local (or microstructure-dependent) mechanical properties for individual regions in the weld as well as their interactions with weld geometry on the deformation behavior. Specifically, optimal welding parameters are determined to produce welds of appropriate nugget diameter for 2T Usibor 1500 with a gauge thickness of 1.5 mm. Micro-hardness mapping and metallographic analysis allow for characterization of the weld metal, CGHAZ, SCHAZ, and base metal of the spot weld. Quasi-static tensile testing with digital image correlation (DIC) is used to determine the local stress-strain behaviors of each region using bulk microstructural samples created in a Gleeble® thermal-mechanical simulator. Conventional and innovative resistance spot weld mechanical testing methods are used to generate more knowledge on the deformation of joints under various loading conditions. Sectioned tensile shear testing and single-sided wedge testing procedures have been established to use 2-D DIC for in situ observations of local deformation on the exposed weld cross-section during testing. A mechanical model, developed using Abaqus finite element analysis (FEA) code by incorporating the local constitutive behaviors of RSW joints, is used to better understand the effect of weld nugget profiles on the stress state present during loading. The FEA model is validated by comparing the simulated strain fields to the experimentally measured strain fields. The knowledge generated in this study can help improve the accuracy of predicting spot weld fracture of ultra-high strength steels in the automotive industry. Particularly, the fine-resolution, coupon-scale model developed in this research will be useful for implementation into coarse-resolution, full-scale models for crash simulation and optimization of vehicle components.

Committee:

Wei Zhang, PhD (Advisor); Menachem Kimchi (Advisor); David Phillips, PhD (Committee Member)

Subjects:

Automotive Engineering; Automotive Materials; Engineering; Materials Science; Metallurgy; Transportation

Keywords:

Welding; Resistance Spot Welding; Automotive; Mechanical Testing; Finite Element Analysis; Mechanical Properties; Metallurgy; Crash Simulation;

Gingerich, Mark BryantJoining Carbon Fiber and Aluminum with Ultrasonic Additive Manufacturing
Master of Science, The Ohio State University, 2016, Mechanical Engineering
Due to increasing emphasis on lightweighting to increase fuel efficiency, integration of carbon fiber reinforced polymers (CFRP) with metal structures is necessary. Current adhesive and mechanical fastening methods used for joining CFRP to metals are not ideal due to poor mechanical properties and incompatibility with current manufacturing infrastructure. Consequently, new joining techniques are needed for increasing the use of CFRP. In this research project, a method of creating joints between CFRP and 6061-H18 aluminum was developed by using ultrasonic additive manufacturing (UAM). The UAM process was used to embed dry carbon fiber tows within an aluminum matrix, creating a mechanical joint between the two materials. The joints were then integrated with additional CF fabrics and epoxy, forming a fully integrated CF-Al structure. This technique was used to create CF-Al joints for tensile, cross tensile, and three-point-bend testing. Mechanical test results showed that the UAM constructed joints had superior strength when compared to adhesive single lap joints. Throughout the UAM joint manufacturing process, experimental observations paired with FEA were used to help solve issues with foil tearing, which is a common problem experienced when materials are embedded with UAM.

Committee:

Marcelo Dapino (Advisor); Anthony Luscher (Committee Member)

Subjects:

Aerospace Engineering; Automotive Engineering; Automotive Materials; Engineering; Experiments; Materials Science; Polymers

Keywords:

UAM; ultrasonic additive manufacturing; CFRP to metal joining; automotive joining; aluminum; carbon fiber; ultrasonic consolidation; hybrid transition structures; adhesive benchmarking; carbon fiber integration

Viggiano, Rocco PInvestigations into High Surface Area and Hierarchical Phase Segregated Network Structures
Doctor of Philosophy, Case Western Reserve University, 2015, Macromolecular Science and Engineering
Aerogels are an interesting class of materials that possess many exotic and extreme properties. These properties are developed as the gel network is produced from solution. As the gel develops, it builds a hierarchical structure, possessing architectures at different size scales through molecular and macro-scale interactions. Once the solvent is removed, and the resultant aerogel is produced, the hierarchical nature of the material produces many desirable properties including: extremely high porosities (greater than 90% pore volume)[1], extremely low thermal conductivities (10-30 mW/m-k)[1], very low densities (as low as 0.002 g/cm3)[2], low refractive indices (as low as 1.01),[3] low dielectric constants (between 1.0 and 1.5),[4] high surface areas,[5,6] and the slowest speed of sound through a solid material. The first chapter of this thesis deals with the structure/property relationships of polymer/clay aerogels interfused with uniformly distributed air bubbles were examined. Through the incorporation of a polyelectrolyte in a montmorillonite (MMT) clay solution, the viscosity was systematically changed by the addition of ions with different charges. The bubbles were achieved via high speed mixing and were stabilized through the use of the surfactant sodium dodecyl sulfate (SDS). As the charge of the ion increased from +1 (Na+ ions) to +2 (Ca2+ ions) to finally +3 (Al3+ ions), the modulus of the resultant aerogels increased. The foamed polymer/clay aerogels showed a reduction in thermal conductivity while retaining similar mechanical properties to unfoamed polymer/clay aerogels. The most promising composition was one which contained 5% MMT clay/5% poly(vinyl alcohol)/0.5% xanthum gum/0.5% SDS/0.2% Al2(SO4)3·6(H2O) possessing a density of 0.083 g/cm3, an average modulus of 3.0 MPa, and a thermal conductivity of 41 mW/m·K. The second project investigated the feasibility of incorporating ground recycled polyurethane (PU) foam into clay/polymer aerogels. This was demonstrated and a range of compositions were prepared and characterized to determine the effect of variation in the formulations on density and mechanical properties of the resulting materials. The study followed a modified combinatorial approach. Initially, experiments were performed in water using either sodium exchanged montmorillonite or laponite clay, poly(vinyl alcohol) (PVOH) solution as the polymer binder, and the recycled PU foam. Freezing and freeze-drying the aqueous gels produced aerogels, which were characterized through density and mechanical testing, scanning electron microscopy, and thermal gravimetric analysis. The study was expanded by exploring alternative binder chemistries, including the use of an alginate polymer in place of the PVOH, or adding a polyisocyanate as across-linking agent for PVOH. The effect of recycled PU foam content, clay type and level, and binder type and level on mechanical properties of the aerogels were determined. The goal of the third project was to determine if lignin could be converted into foam-like aerogels using a well-established and environmentally benign freeze drying process. Interest in lignin as a bio-resource has been gaining popularity in recent years, as it is currently viewed by most industries as a waste product that in most cases is simply burned as a fuel source. The use of lignin in a polymer/clay aerogel offers the potential for a high value-added foam-like material potentially usurping the use of traditional petroleum derived foams in some applications. The present work demonstrates that lignin/clay and lignin/alginate aerogel samples can possess compressive moduli as high as 36.0 MPa. The final project addresses a fundamental material property concern associated with polyimide aerogels. Polyimide aerogels possess low dielectric constants, low thermal conductivities, high porosity, flexibility and low densities with outstanding mechanical properties. However, polyimide aerogels will undergo thermally induced shrinkage at temperatures far below their glass transition temperatures (Tg) or their onset of decomposition temperatures. Attempts to minimize thermal shrinkage were successful when a rigid filler, such as cellulose nanocrystals (CNCs), were introduced into the polyimide backbone. As an alternative to using rigid fillers, it was proposed that the incorporation of bulky, space filling moieties into the polymer backbone would also provide an effective route to reduce thermal shrinkage. An array of 20 polyimide aerogels were synthesized from 3,3’4,4’-biphenyltetracarboxylic dianhydride (BPDA) and 4,4’-oxydianiline (ODA) and in some cases BPDA and a combination of ODA and 9,9’-bis(4-aminophenyl) fluorene (BAPF). The aerogels were cross-linked with 1,3,5-benzenetricarbonyl trichloride (BTC). The polymer concentration, n-value and molar concentration of ODA and BAPF were varied. The resultant aerogels were fully characterized and were subjected to isothermal heating at 150 °C and 200 °C for up to 500 hours. It was observed that the samples containing BAPF possessed the lowest thermal shrinkages. Reductions in thermal shrinkage of around 20% were observed in samples containing the highest molar concentrations of BAPF.

Committee:

David Schiraldi, Ph.D. (Advisor); Mary Ann Meador, Ph.D. (Advisor); Gary Wnek, Ph.D. (Committee Member); Eric Baer, Ph.D. (Committee Member)

Subjects:

Aerospace Materials; Automotive Materials; Chemistry; Engineering; Experiments; Inorganic Chemistry; Materials Science; Organic Chemistry; Polymer Chemistry; Polymers

Keywords:

Aerogel, High Surface Area, Low Thermal Conductivity, Montmorillonite Clay, Polyvinyl alcohol, Polyurethane Foam, Lignin, Polyimide, Gel, Network, Cross-Linking, Ice Templating, Freeze-Drying, Lyophilization, Supercritical Fluid Extraction

Chen, Meng-HsienA STUDY OF SELECTIVE SURFACE AND INTERNAL OXIDATION OF ADVANCED HIGH STRENGTH STEEL GRADES
Doctor of Philosophy, Case Western Reserve University, 2014, Materials Science and Engineering
Advanced high-strength steels (AHSS) have been widely used in automotive industry to improve safety and fuel economy. However, unintentional selective oxidation of alloying elements of AHSS during the thermal cycles employed on a continuous galvanizing line (CGL) complicates the coating process. Amongst the observed effects, external oxides can cause incomplete reactive wetting, resulting in bare spot defects in the zinc coating. This study focuses on developing and validating &#x201c;oxidation maps&#x201d; to define regions of selective oxidation for alloying elements in PO2-T space. Oxidation maps use CALPHAD method in combination with the Wagner&#x2019;s model to determine regions where no oxidation, internal oxidation or external oxidation will occur. Experiments were carried out in an attempt to validate the predictions. Three types of AHSS grade steels, with variation in Mn, Si, Al contents, were used for experiments to validate the oxidation maps. Samples of selected steels were subjected to four different simulated CGL thermal cycles with two heating rates and two hold times, that bracket much of the range expected in industrial practice. Experiments were also undertaken for two of the steels under much higher dew point annealing conditions to probe the predicted boundary between external and internal oxidation. Samples were characterized by SEM, AES, XPS, and TEM to determine the oxide phases as well as the oxidation modes. Analysis results demonstrated that the formation of oxide phase on or in each steel is consistent with the thermodynamic modeling. A calculated Ellingham diagram clearly illustrates the formation sequence of oxide phases for the steels studied. For the prediction of oxidation mode, the oxidation maps are generally consistent with the analysis result. Inconsistency was observed only in one circumstance, and this is attributed to the highly heterogeneous surface caused by cold rolling. Otherwise, a kinetic model was studied to simulate the amount of atoms diffusing across steel surface and incorporated into the oxide(s). The number of oxide particles of a given size formed on a selected area was also consistent with predictions.

Committee:

James McGuffin-Cawley (Advisor); Mark De Guire (Committee Member); Frank Ernst (Committee Member); Jay Mann, Jr. (Committee Member)

Subjects:

Automotive Materials; Engineering; Materials Science; Metallurgy

Keywords:

CALPHAD; AHSS; advanced high strength steel; selective oxidation; oxidation map; CGL; galvanizing

Salaani, Mohamed KamelDevelopment and validation of a vehicle model for the National Advanced Driving Simulator
Doctor of Philosophy, The Ohio State University, 1996, Mechanical Engineering

A computational efficient advanced mathematical model of a passenger vehicle dynamics is developed for the National Advanced Driving Simulator (NADS). This research advanced high fidelity modeling techniques using the multi-body dynamics formulations, in particular, the Real Time Recursive Dynamics (RTRD). The suspensions have been modeled accurately where the comprehensive nonlinear characteristics were met. Comprehensive vehicle subsystems have been modeled that include tire forces, wheel kinematics, aerodynamic forces, brake system, and kinematic steering system. The computational speed has been achieved, while accuracy has been preserved in the context of the broad scope of simulation applications.

The simulation results are validated using experimental field testing performed in this research. The results show that the simulation predicted very well the physics of vehicle dynamics. The steady state gains up to the limit indicated accurate predictions of understeer behavior. The transient response comparisons show good agreement in terms of timing of the transient events and peak levels of the variables which are indicative of limit performance conditions. The lateral transfer function show reasonable agreement which gives some credibility to the composite lateral/directional dynamics. The vehicle's ride gains show good predictions of vehicle natural frequencies and amplitude attenuation of road disturbance input.

Committee:

Dennis Guenther (Advisor)

Subjects:

Automotive Materials; Mechanical Engineering

Terzak, John CharlesModeling of Microvascular Shape Memory Composites
Master of Science in Engineering, Youngstown State University, 2013, Department of Mechanical and Industrial Engineering
This work investigates the adaptive and morphing properties of SMCs based on a shape memory polymer (SMP) and a microvascular arrangement of shape memory alloys (SMAs). Here, the microvascular SMA phase has been subjected to a two-way shape memory effect (SME) process, in order to fully control the actuation properties of the SMC. It has been observed that the two-way trained SMA successfully induces a morphing performance on the SMC during a fluid heating-cooling cycle. The initial results suggest that the actuation behavior of the SMC strongly depends on the microvascular fluid heating rate as well as on the temperature difference between the glass transition temperature of the SMP and the activation temperature of the SMA. Analytical and Finite Element Method (FEM) analysis on the microvascular SMC has also been performed. The results suggest that the FEA analysis offers a better prediction of the thermo-mechanical behavior of the SMC. It has been observed that whilst the FEA successfully predicts the thermal profile of the SMC, the mechanical modeling seems to require a degree of amendment. Here, the FEA has predicted a deflection 20% higher than those experimentally recorded. Although a refinement is needed on the mechanical modeling of the FEA analysis, the current FEA work certainly provides the elementary design parameters for future optimizations of morphing structures based on SMC.

Committee:

Pedro Cortes (Advisor); Hazel Marie (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Automotive Engineering; Automotive Materials; Chemical Engineering; Materials Science; Mechanical Engineering

Keywords:

Shape Memory Effect; Shape Memory Composite; vascular thermal network; Shape Memory Alloy; Shape Memory Polymer; hybrid composites; morphing structures

Hoover, Robert R.New Method for Coating Nickel with Ultrathin Platinum Films
MS, Kent State University, 2010, College of Arts and Sciences / Department of Chemistry
An atomic layer deposition (ALD) technique for applying very thin platinum coatings onto nickel substrates is presented. In this research, a removable nickel rotating disk electrode was used as the substrate for a process involving MeCpPtMe3 and H2, both of which were in the gas phase when exposed to the substrate. The substrate was exposed to the two aforementioned compounds sequentially. Ultra pure N2 was used to remove each component before introducing the next one into the chamber. This process of alternately exposing the nickel disk to MeCpPtMe3 and H2 (with N2 in between) was repeated for specified numbers of times in order to produce films of various thicknesses. Electrochemical properties of the coatings were tested using rotating disk electrode geometry. On several occasions, the total amount of Pt applied was determined in order to assess the economic feasibility of potential scale up.

Committee:

Yuriy Tolmachev, PhD (Advisor)

Subjects:

Analytical Chemistry; Automotive Materials; Chemical Engineering; Chemistry; Energy; Environmental Engineering; Materials Science; Molecules

Keywords:

ALD; Pt; oxygen reduction

Hilty, Devin R.An Experimental Investigation of Spin Power Losses of Planetary Gear Sets
Master of Science, The Ohio State University, 2010, Mechanical Engineering

Planetary gears are used commonly in many power transmission systems in automotive, rotorcraft, industrial, and energy applications. Powertrain efficiency concerns in these industries create the need to understand the mechanisms of power losses within planetary gear systems. Most of the published work in this field, however, has been limited to fixed-center spur and helical gear pairs. An extensive set of experiments is conducted in this research study to investigate the mechanisms of spin power loss caused by planetary gear sets, in an attempt to help fill the void in the literature.

A test set-up was designed and developed to spin a single-stage, unloaded planetary gear set in various hardware configurations within a wide range of carrier speeds. The measurement system included a high-resolution torque sensor to measure torque loss of the gear set used to determine the corresponding spin power loss. Repeatability of the test set-up as well as the test procedure was demonstrated within wide ranges of speed and oil temperature.

A test matrix was defined and executed specifically to measure total spin loss as well as the contributions of its main components, namely drag loss of the sun gear, drag loss of the carrier assembly, pocketing losses at the sun-planet meshes, pocketing losses at the ring-planet meshes, viscous planet bearing losses, and planet bearing losses due to centrifugal forces. Multiple novel schemes to estimate the contributions of these components of power losses were developed by using the data from tests defined by the test matrix. Fidelity of these schemes was tested by comparing them to each other. Based on these calculations, major components of power losses were identified and rank ordered. Impact of the rotational speed and oil temperature on each component was also quantified.

Committee:

Ahmet Kahraman, PhD (Advisor); Gary Kinzel, PhD (Committee Member)

Subjects:

Automotive Materials; Energy; Engineering; Experiments; Mechanical Engineering; Transportation

Keywords:

planetary gears; efficiency; power loss; transmission efficiency; gears; gear design; planetary gear efficiency; planetary gear power loss

Nguyen, The MinhA Novel Semi-Active Magnetorheological Mount for Vibration Isolation
Doctor of Philosophy in Engineering, University of Toledo, 2009, Mechanical Engineering

In recent years, the higher price of fossil fuels and green house effects has been the motivating factors for the automotive industry to introduce more efficient vehicles. Today evolution in automobiles is mostly to reduce fuel consumption and emissions. Variable cylinder management has been employed in V6 & V8 engines to allow the vehicles to operate with only 3 or 4 active cylinders. Hybrid technologies including hybrid electric and emerging hydraulic hybrid equip the vehicles with additional power sources which work at higher efficiency than that of internal combustion engines. The proven advantages of the hybrid vehicles or variable cylinder management also come with challenging problem of noise, vibration and harshness (NVH). This issue has to be properly addressed in order for the technologies to find consumer acceptance.

The NVH in modern vehicles is mainly due to the involvement of multiple power sources working in different modes and the switching among them. This feature can lead to shock and vibration over a wide range of frequencies. It has been proven that passive vibration isolators, e.g. elastomeric and hydraulic, are not sufficient to deal with this problem. Active mounts are effective, but they are expensive and can lead to stability problems. Research has shown that semi-active vibration isolators are as effective as active mounts while being significantly less expensive

In this study, a novel shock and vibration isolator in the form of a magnetorheological (MR) mount is introduced. MR fluids are smart fluids which respond to magnetic fields. Using these fluids it is possible to transform a passive hydraulic vibration isolator to a semi-active device one. The semi-active MR mount presented in this dissertation is unique because it utilizes the MR fluid in two configurations flow (or valve) and squeeze modes to mitigate shock and vibration over a wide range of frequencies.

The new mount was designed following a thorough literature review of the semi-active and MR vibration isolation. A mathematical model of the mount was developed to represent the vibration isolation behavior of the system. The analytical model was numerically solved and simulated in MATLAB®. Simulation results were used to predict the performance of the mount and to evaluate the effect of design parameters on the mount behavior. A prototype MR mount was built based on the analytical model. The mount was experimentally evaluated. The experimental data was used to verify the model in predicting the mount characteristics. This study provided a fundamental understanding on the behavior of MR fluid in vibration isolation devices. The mount demonstrates effectiveness of the flow and squeeze modes when they are activated individually and in combination. The results of this research can lead to developing effective isolation devices for many different applications including hybrid and alternative fuel vehicles.

Committee:

Mohammad Elahinia, PhD (Advisor); Walter Olson, PhD (Committee Member); Nagi Naganathan, PhD (Committee Member); Maria Coleman, PhD (Committee Member); Abdollah Afjeh, PhD (Committee Member)

Subjects:

Automotive Materials; Engineering; Experiments; Mechanical Engineering

Keywords:

Noise and vibration isolation; magnetorheological fluid; semi-active isolators; flow mode; squeeze mode

Olson, Garrett WestonExperiments on the High-Power and High-Temperature Performance of Gear Contacts
Master of Science, The Ohio State University, 2012, Mechanical Engineering
In this study, gear contact tests were performed using a recently developed test methodology capable of both high-power (pitch-line velocities up to 50 m/s and pinion torques up to 450 N-m) and high-temperature (oil inlet temperatures up to 150C) operating conditions. Test specimens and operating conditions were chosen in order to simulate high-power automotive and aerospace applications. Automotive test specimens were made from a typical automotive transmission gear steel, SAE 4118M, at surface roughnesses typical of hard ground gears. Aerospace test specimens were made out of a high performance (high-temperature) proprietary gear steel. These aerospace specimens were either chemically polished or super-finished following grinding to achieve roughness amplitudes more than 10 times smoother than typical ground surfaces. Throughout each test interim inspections were used to identify and monitor failure modes. Experimental testing for automotive applications is shown to consistently produce contact fatigue failures in the form of micro-pitting and macro-pitting. Tests were suspended when macro-pits exceeded the test methodologies pre-determined failure criteria. Experimental testing for aerospace applications is shown to be absent of any contact fatigue failures due to the extremely smooth contact surfaces. The primary mode of contact failure in aerospace tests is observed to be scuffing.

Committee:

Ahmet Kahraman (Advisor); Gary Kinzel (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Automotive Engineering; Automotive Materials; Engineering; Mechanical Engineering

Keywords:

gears; gear contacts; high-power; high-temperature; contact fatigue; pitting; scuffing

Yadav, Ajay D.Process Analysis and Design in Stamping and Sheet Hydroforming
Doctor of Philosophy, The Ohio State University, 2008, Industrial and Systems Engineering

This thesis presents initial attempts to simulate the sheet hydroforming process using Finite Element (FE) methods. Sheet hydroforming with punch (SHF-P) process offers great potential for low and medium volume production, especially for forming (a) lightweight materials such as Al- and Mg- alloys and (b) thin gage high strength steels (HSS). Sheet hydroforming has found limited applications and is thus still a relatively new forming process. Therefore, there is very little experience-based knowledge of process parameters (namely forming pressure, blank holder tonnage) and tool design in sheet hydroforming. For wide application of this technology, a design methodology to implement a robust SHF-P process needs to be developed. There is a need for a fundamental understanding of the influence of process and tool design variables on hydroformed part quality. This thesis addresses issues unique to sheet hydroforming technology, namely, (a) selection of forming (pot) pressure, (b) excessive sheet bulging and tearing at large forming pressures, and (c) methods to avoid leaking of pressurizing medium during forming. Through process simulation and collaborative efforts with an industrial sponsor, the influence of process and tool design variables on part quality in SHF-P of axisymmetric punch shapes (cylindrical and conical punch) is investigated.

In stamping and sheet hydroforming, variation in incoming sheet coil properties is a common problem for stamping plants, especially with (a) newer light weight materials for automotive applications (aluminum-, magnesium- alloys) and (b) thin gage high strength steels. Even though incoming sheet coil may meet tensile test specifications, high scrap rate is often observed in production due to inconsistent material behavior. Thus, tensile test specifications may not be adequate to characterize sheet material behavior in production stamping/hydroforming operations. There is a strong need for a discriminating method for testing incoming sheet material formability. The sheet bulge test emulates biaxial deformation conditions commonly seen in production operations. This test is increasingly being applied by the European automotive industry, especially for obtaining reliable sheet material flow stress data that is essential for accurate process simulation. This thesis presents a new 'inverse-analysis' methodology for calculating flow stress curves at room temperature, using the biaxial sheet bulge test. This approach overcomes limitations of previously used closed-form membrane theory equations and exhibits great potential for elevated temperature bulge test application.

To verify the developed methodologies presented in this thesis, selected case studies are presented, to (a) demonstrate the successful application of finite element (FE) simulation in tool design, process sequence design and springback reduction in stamping and sheet hydroforming and, (b) validate the developed methodology for automation/standardization of tool and process sequence design procedure and recording of existing design guidelines in transfer die stamping.

Committee:

Taylan Altan, PhD (Advisor); Gary L. Kinzel, PhD (Committee Member); Jerald R. Brevick, PhD (Committee Member); Donald M. Terndrup, PhD (Committee Member)

Subjects:

Automotive Materials; Industrial Engineering; Mechanical Engineering

Keywords:

sheet metal forming; sheet hydroforming; process simulation; material characterization

Montello, Aaron DavidAn Experimental Investigation of Water Droplet Growth, Deformation Dynamics and Detachment in a Non-Reacting PEM Fuel Cell via Fluorescence Photometry
Master of Science, The Ohio State University, 2008, Mechanical Engineering

While the concept of fuel cells has been around for more than 100 years, they have long been considered too expensive and not well refined enough for mainstream application. With the combined pressures of decreasing world oil supplies as well as growing concerns for the role carbon dioxide emissions are playing to cause climate change, PEM fuel cell technology has reemerged as a potential power source for automotive transportation. Thanks to significant advances in material technologies, fuel cell system costs have reduced while performance has significantly increased. There still exist various cost issues, as well as a wide variety of technical barriers preventing broad based adoption of the technology. One of these key technical barriers is low system power density, due in part to a restriction of the rate that fuel can be forced through the system. This restriction is a result of the limitation in the rate of removal of product water from the system.

It has been well documented that water production in fuel cells occurs in discrete locations, resulting in the formation and growth of discrete droplets within the gas flow channels (GFCs) along the gas diffusion layer (GDL) surface. There have been few experimental efforts aimed at understanding the dynamic interaction of such water droplets with the crossing air flow however. The first portion of this research uses a simulated fuel cell GFC with three transparent walls in conjunction with a high speed fluorescence photometry system to capture videos of dynamically deforming droplets. In viewing such videos it is noted that the droplets undergo vibratory deformation patterns. The video information is then processed and analyzed in Matlab, resulting in the formulation of plots indicating the dominant horizontal and vertical deformation frequency components over the range of sizes of droplets from formation to detachment. The system is also used to characterize droplet detachment size at a variety of channel air velocities.

There have been a fair number of experimental research efforts attempting to aid in the water removal process, however it is believed that more effective, simpler solutions exist than those that have been tried. Using a solenoid valve fixed near the channel air exit, it is possible to introduce a small amount of pulsed air flow in addition to the predominant unidirectional flow. A wide range of solenoid excitation frequencies are tested for one of the flow velocities analyzed in the first portion of the work, and it is found that certain excitation conditions allow for critical droplet size reductions of greater than 20%. It is believed that this behavior should correspond with improved water efflux characteristics and this technique is believed to have promise for future fuel cell operational improvement.

Committee:

Yann Guezennec, PhD (Advisor); Giorgio Rizzoni, PhD (Committee Member); Junmin Wang, PhD (Committee Member)

Subjects:

Automotive Materials; Chemical Engineering; Engineering; Experiments; Fluid Dynamics; Hydrology; Mechanical Engineering; Optics; Scientific Imaging; Transportation

Keywords:

PEM fuel cell; experimental; water management; water droplet dynamics; GDL; GFC; variable air flow; two-phase flow; visualization; fluorescence photometry; video processing

Rodriguez, Alvaro A.Corrosion inhibition mechanism of a surfactant admixture on carbon steel alloy ASTM A36 [UNS K02600] coated with a high performance UV-cured coating
Doctor of Philosophy, University of Akron, 2016, Chemical Engineering
Several studies have been published describing the corrosion inhibition effectiveness of surfactant admixtures by measuring the ability of surfactant molecules to physically adsorb onto metal surfaces. However, the effects of these admixtures have not been previously studied on coated metal surfaces to determine their corrosion inhibition mechanism. While corrosion protective coatings isolate exposed metal surfaces by forming a barrier between a substrate and the electrolyte, their performance is highly dependent on their interaction with their immediate environment. During the winter season in Snowbelt areas where chloride roadway deicers are greatly employed, coated metal surfaces in vehicles are constantly exposed to harsh and changing environments making them susceptible to failure. In order to extend the service life of these exposed coated surfaces, additional treatment by surfactant admixtures is regarded as an effective corrosion prevention strategy. In this work, the corrosion mechanism of surfactant admixtures on coated metal panels is evaluated by understanding the interaction of the liquid-solid interface. Despite the numerous mechanisms of inhibition behavior, it is hypothesized in this study that the contributions from inhibition solution systems create a protective layer over substrates by the formation of multi layers from aggregation or adsorption of surfactants. Furthermore, this study will help understand the relationship of the surface of corrosion protective coatings and the interaction with its environment. Electrochemical impedance spectroscopy (EIS) is applied to evaluate the corrosion performance of a high performance, low VOC, two component polyurethane enamel and a high performance UV-cured coating system on carbon steel alloy A36 under immersion testing of sodium chloride solutions of surfactant admixtures. This electrochemical technique permits the evaluation of the properties of the coating system by monitoring its degradation with respect to time by following changes in the impedance spectra. Data were recorded at room temperature by measuring the water uptake into the coating in the presence and absence of surfactant in 0.6 M NaCl solutions. The surface of the coated metal sample was evaluated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) validating the formation of a barrier in the interface of the substrate and the coating system. Furthermore, the affinity of surfactant admixtures on the polyurethane enamel and the UV-cured coated metal surfaces can be quantified by measuring the wettability of the surface via contact angle measurements. Surface tension theory and dynamic fluid properties will illustrate the ability of surfactants to either form a layer or adsorb into the pores of the coating system. Changes in the dynamic contact angle of surfactant admixtures on coated surfaces with respect to time elucidate the effect of surface roughness, heterogeneity, capillary imbibition and swelling on these fluid systems. Inhibition efficiency results on bare metal surfaces from accelerated corrosion testing (ASTM B117) showed that salt neutralizer solutions are alloy specific and concentration dependent; while laboratory testing results demonstrated the effect of the properties of these solutions by correlating critical wash concentration, static contact angle, chemical structure, and effective adsorption with inhibition efficiency. Quantitative and qualitative information gathered in this study provide the means for understanding the role of the kinetics of surfactant admixtures adsorption on the corrosion protection resistance of a high performance polyurethane coating and a high performance UV-cured coating system. Moreover, it may further aid in the design of corrosion mitigation systems by determining what properties of surfactant admixtures and coatings provide the best corrosion protection.

Committee:

Chelsea Monty, Dr. (Advisor); Scott Lillard, Dr. (Committee Member); Gang Cheng, Dr. (Committee Member); Christopher Miller, Dr. (Committee Member); John Senko, Dr. (Committee Member)

Subjects:

Automotive Materials; Chemical Engineering; Engineering; Materials Science; Physical Chemistry

Keywords:

UV-cured coating systems; salt neutralizers; surfactants; corrosion inhibition; corrosion protective coatings; department of transportation; snow and ice control; electrochemical impedance spectroscopy; wetting kinetics;imbibition; spreading

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