Master of Science, University of Akron, 2010, Civil Engineering

A vibration-based testing methodology is presented that assesses fatigue behavior of material for metallic structure. To minimize the testing duration, the test setup is designed for a base-excited multiple-specimen arrangement driven in a high-frequency resonant mode, which allows completion of fatigue testing in an accelerated period. A high performance electro-dynamic exciter (shaker) is used to generate harmonic oscillation of cantilever beam specimens, which are clasped on the shaker armature with specially-designed clamp fixtures. The shaker operates in closed-loop control with dynamic specimen response feedback provided by a scanning laser vibrometer. A test coordinator function is developed to synchronize the shaker controller and the laser vibrometer, and to complete the closed-loop scheme: the test coordinator monitors structural health of the test specimens throughout the test period, recognizes change in specimen dynamic behavior due to fatigue crack initiation, terminates test progression, and acquires test data in an orderly manner. Topological design is completed by constructing an analytical model and performing finite element analysis for the specimen and fixture geometry such that peak stress does not occur at the clamping fixture attachment points. Experimental stress evaluation is conducted to verify the specimen stress predictions. A successful application of the experimental methodology is demonstrated by validation tests with aluminum specimens subjected to fully-reversed bending stress.

Committee: Gun Jin Yun Dr. (Advisor); Craig C. Menzemer Dr. (Committee Member); Wieslaw K. Binienda Dr. (Committee Member) Subjects: Engineering

Master of Science in Engineering, Youngstown State University, 2018, Department of Mechanical, Industrial and Manufacturing Engineering

The objective of this research is to determine if surface finish influences the mechanical properties of cast heat treated aluminum (A356-T6). Binder jetting of sand allows for complex molds to be designed and printed to decrease the amount of time, cost and material. This project is separated into three phases. First phase of the project is the development of a benchmark casting and evaluation of surface roughness. In this phase, the surface finish of several angles of print orientation were compared. Certain angles produced a very noticeable stair step feature. Second phase of the project characterizes the static tensile and fatigue properties of A356-T6 cast flat bars from molds of four print orientation angles (0°, 5°, 15°, 30°). Lastly, the third phase of the project is fluid penetrant inspection (FPI) testing. The intent of this phase is to determine if stair step features would affect the outcome of this common nondestructive evaluation process.

Committee: Brett Conner PhD (Advisor); Jason Walker PhD (Committee Member); Virgil Solomon PhD (Committee Member) Subjects: Mathematics; Mechanical Engineering

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2022, Materials Science and Engineering

Additive Manufacturing (AM), particularly laser powder bed fusion, is being studied for use in critical component applications. Tensile and fatigue testing shows differences when built using different laser powers. However, when fabricated in an as-printed geometry, the gauge sections of the two specimens are different and experience different thermal behavior. This work explores microhardness, microstructure size, Niobium segregation, and porosity from samples made with varying laser power and different build geometry sizes representative of the gauge sections in the tensile and fatigue bars. Results show that microhardness varies spatially across the sample. Smaller diameter metallographic coupons (fatigue diameter) have a coarser microstructure and lower microhardness than the larger diameter (tensile diameter) when built using the same parameters. Therefore, the fatigue and tensile properties are not comparing the same material structure. Understanding the effect of build geometry on microstructure provides insight towards consistency in AM mechanical properties testing strategies.

Committee: Henry D. Young Ph.D. (Committee Co-Chair); Joy Gockel Ph.D. (Committee Co-Chair); Onome Scott-Emuakpor Ph.D. (Committee Member) Subjects: Engineering; Materials Science

Master of Science, The Ohio State University, 1971, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1966, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Sciences (Engineering), Case Western Reserve University, 2022, Materials Science and Engineering

The effects of changes in process parameters, heat treatment, build orientation, and resulting defects on fatigue behavior of selective laser melting-processed AlSi10Mg have been determined. Samples were prepared under distinct P-V parameters and heat treatments for the following classifications: A- nominal with SR+HIP+T6, B- large defects with SR+HIP+T6, G- small to medium defects with SR+HIP+T6, D- many defects with SR+HIP+T6, E- large defects with SR+T6, and F- small to medium defects with SR+T6. Fatigue crack growth (FCG) testing of bend bars and high cycle fatigue (HCF) fatigue testing of cylindrical samples occurred at a stress ratio R = 0.1 and 20 Hz according to appropriate ASTM standards. This is reviewed along with ASTM-standardized tension testing of cylindrical samples. Increased defects typically reduced UTS, ductility, and fracture toughness particularly in the Z orientation. The S-N performances of X/Y orientation were improved or similar to the Z orientation in HCF as a result of having smaller or similar fatigue-initiating defect sizes, that were quantified for all failed S-N samples. HIP-processing generally reduced fatigue-initiating defects sizes and improved most S-N performances. Compared to SLM AlSi10Mg from literature, the nominal (A) build had an increased HCF performance. HCF sample life was estimated by using fracture surface defect measurements and FCG data obtained for those process conditions.

Committee: John Lewandowski (Committee Chair); Sunniva Collins (Committee Member); Clare Rimnac (Committee Member) Subjects: Materials Science

Master of Science (MS), Ohio University, 2020, Mechanical Engineering (Engineering and Technology)

Fatigue failures are sudden and catastrophic, and for critical parts must be prevented through proper design. Fatigue testing of materials yields data critical for proper design but takes large spans of testing time to complete with conventional methods. Therefore, high speed fatigue testing that produces quality data is advantageous for reducing costs and time. However, it has been shown that testing speeds may affect material performance, both in static tensile testing and dynamic fatigue testing. The effect of strain rate on material performance in static tensile testing and how it relates to fatigue testing performance at commensurate strain rates was the primary objective for this thesis work for sheet Ti-6Al-4V and Inconel 718. Implementing a vibration-driven, fully reversed bending fatigue test protocol leveraging high speed testing capability, a comparable forced displacement bending fatigue test protocol, and a high speed tensile test protocol implementing Digital Image Correlation (DIC), stress versus strain data and S-N curve data was acquired to examine two strain-rates of fatigue and tensile testing. Higher ultimate tensile strengths were observed in high strain rate tests as compared to low strain rate tests, 4.23% higher for Ti-6Al-4V and 1.91% for Inconel 718. Ti-6Al-4V exhibited higher fatigue strength in high speed tests than low speed, but Inconel 718 exhibited lower fatigue strength at high speeds as compared to low speeds.

Committee: Timothy Cyders Dr. (Advisor); Brian Wisner Dr. (Committee Member); Young David Dr. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Experiments; Mechanical Engineering; Systems Design

Master of Science in Mechanical Engineering (MSME), Wright State University, 2019, Mechanical Engineering

Additive manufacturing (AM) produces rough surfaces that are detrimental to the mechanical performance of the part. In this work, downward-facing surfaces were fabricated in alloy 718 using laser powder bed fusion and investigated with surface characterization and axial fatigue testing. Coupons with downward-facing surfaces at 45°, 60°, and 75° and flat axial fatigue bars with as-built and machined holes were built. Both specimens were fabricated with three levels of downskin laser power and the coupons with three levels of downskin laser speed. Surface characterization showed roughness increased as the downward-facing angle decreased. Fatigue testing with digital image correlation showed localized strain on the downskin as-built surfaces with deep notches and the fully machined specimens had ≥ 4 times longer life comparatively. Surface roughness is a critical factor in AM and this research gives insight to understand the influence of processing parameters and downward-facing angle on fatigue performance and build tolerances.

Committee: Joy Gockel Ph.D. (Advisor); Onome Scott-Emuakpor Ph.D. (Committee Member); Nathan Klingbeil Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2019, Mechanical Engineering

In this study, a new state-of-the-art gear contact durability test machine is developed to eliminate some key limitations, issues and inconveniences associated with conventional FZG machines. Based on lessons learned from prior in-house studies using conventional FZG machines, a number of requirements are specified. A new four-square concept is designed and fabricated to gain various advantages with respect to foot-print, temperature regulation, and long-lasting auxiliary components. The mechanical layout and out-of-the-loop torque application methodology are described along with the heat management and lubrication systems. Various new safety provisions are highlighted, in addition to a streamlined interim gear inspection procedure during long-cycle contact fatigue tests performed on these new machines. For demonstration purposes, the proposed machines are used to conduct an example contact fatigue test program to evaluate a stress-life curve of ground spur gears made of a typical automotive gear steel. The test procedures, test conditions and the test specimens are described. Various results containing digital images of the gear teeth, surface wear and roughness progression over the fatigue life of the gears are detailed. A detailed statistical analysis is presented to define a stress-life curve and confidence intervals. This example fatigue study confirms the suitability of the new machines to perform high-fidelity gear contact fatigue experiments.

Committee: Ahmet Kahraman (Advisor); David Talbot (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Materials Engineering

In practice, adjacent preform sandwich cores are joined with a simple butt joint without special precautions. When molded, this gap is filled with resin and creates a resin rich area. Stress risers will be amplified under cyclic load, and consequently, the serviceability of the structure will be affected. Designers and researchers are aware of this problem; however, quantifying this effect and its intensity and consequence on the service life of the structures has not yet been developed. Despite pervious findings, limited experimental data backed by a comprehensive root cause failure analysis is available for sandwich under axial static, fatigue and post-fatigue. If such a comprehensive experimental characterization is conducted, specifically understanding the nature of the damage, intensity, and residual strength, then a valid multi-scale damage model could be generated to predict the material state and fatigue life of similar composite structures with/without core joints under in-plane static and fatigue load. This research study characterized the effect of scarf and butt core joints in foam core sandwich structures under in-plane static and fatigue loads (R=0.1 and R= -1). Post-Fatigue tensile tests were also performed to predict the residual strength of such structures. Nondestructive Evaluation Techniques were used to locate the stress concentrations and damage creation. A logical blend of experimental and analytical prediction of the service life of composite sandwich structures is carried out. The testing protocol and the S-N curves provided in this work could be reproducible and extrapolated to any kind of core material. This research study will benefit composite engineers and joint designers in both academia and industry to better apprehend the influence of core joints and its consequence on the functionality of sandwich structures.

Committee: Elias Toubia (Advisor); Paul Murray (Committee Member); Thomas Whitney (Committee Member); Youssef Raffoul (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Civil Engineering; Composition; Design; Engineering; Materials Science; Mechanical Engineering; Polymers

PhD, University of Cincinnati, 2017, Engineering and Applied Science: Mechanical Engineering

Fatigue failure is a major reason behind the failure of mechanical components and machine parts. In turbine engines and related applications, the components are subjected to cyclic loading at elevated temperatures. Superalloys have high strength and environmental resistance to perform under extreme high temperatures and stress conditions. Improvement in the strength, fatigue life, and/or temperature capabilities of these superalloys will yield huge economic benefits. To address these challenges, surface treatment techniques are implemented to improve the fatigue behavior of currently used superalloys at elevated temperatures. This study investigates Ultrasonic Nano-crystal Surface Modification (UNSM) and Laser Shock Peening (LSP) as techniques to improve strength and fatigue behavior of ATI 718 Plus (718Plus) at room and elevated temperatures. The effect of temperature and strain rate on the strength, ductility, and failure behavior of 718Plus was investigated. The results showed that with the increase of temperature at slow strain rate, there is a small reduction in the yield strength, a large drop in ductility, and a change in fracture mode from ductile transgranular to brittle intergranular cracking. Analysis of the microstructure showed that the driving mechanism at higher temperatures and slower strain rates is oxygen-induced intergranular cracking, a dynamic embrittlement mechanism and that the d precipitates on the grain boundaries are facilitators. Increase of strain rate at 704 °C caused a small increase in the yield strength, a huge increase in the ductility, and a change in fracture mode from brittle to ductile failure. This showed that the driving mechanism at higher strain rates was Portevin–Le Chatelier effect. Finally, 718Plus has superior fatigue behavior at its operation temperature (650 °C) compared to room temperature due to the strengthening of the ?' precipitates which increased its endurance limit by ~20% (~145 MPa). The repetitive strikes (open full item for complete abstract)

Committee: Vijay Vasudevan Ph.D. (Committee Chair); Woo Kyun Kim Ph.D. (Committee Member); Yijun Liu Ph.D. (Committee Member); Dong Qian Ph.D. (Committee Member); Jing Shi Ph.D. (Committee Member) Subjects: Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 1973, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, Case Western Reserve University, 2015, Materials Science and Engineering

Al-Mg 5xxx alloys are desirable in a wide array of structural applications that require a weldable alloy with good corrosion resistance. However, significant changes in the mechanical properties have been shown to occur after both short-term high temperature (e.g. 175°C, < 100 hours) and long-term low temperature (e.g. 60°C, 1000's hrs) laboratory thermal exposures. Commercially available 5083-H116, 5456-H116 and 5083-H131 alloy plates were thermally exposed to various low and intermediate temperatures for times in excess of 20,000 hrs. Significant changes to the strength and fatigue crack growth behavior have been observed after such exposures. In particular, the longitudinal splitting in the short-transverse (ST) direction has been exhibited during fatigue crack growth of L-T samples tested in laboratory air after sufficient time and temperature exposure combinations. In order to directly examine environmental effects on cracking in the ST plane, slow strain rate tensile tests have been conducted in the S-T orientation in various environments (e.g. Lab Air, Dry, and Corrosive). These tests showed significant reductions in ductility and time to failure depending upon the degree of sensitization and type of environment. In order to quantify these effects in more details, environmentally enhanced cracking experiments using J-based fracture mechanics tests were conducted in similar environments on fatigue-precracked samples in the S-T orientation. The evolution of properties (i.e. fracture/fatigue) and the effects of microstructural features (e.g. grain boundary segregation, grain boundary precipitation, grain orientation and misorientation, etc.) and environmentally enhanced cracking are provided along with the effects of various remediation treatments.

Committee: John Lewandowski (Advisor); Henry Holroyd (Committee Member); Rimnac Clare (Committee Member); Schwam David (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Doctor of Philosophy, University of Akron, 2015, Mechanical Engineering

This dissertation is divided into two categories based upon lubrication functionality and its application. The categories are: Dry film lubrication and Fluid film lubrication with thin film coatings. Thin film coatings examined in this work were deposited using closed field unbalanced magnetron sputtering and RF-DC coupled magnetron sputtering systems. In Dry/Solid film lubrication, the mechanical, structural and tribological properties of two Molybdenum disulphide (MoS2) based coatings are examined and evaluated. Among the two coatings, one coating is doped with Ti (Ti-MoS2) and the other is a combination of metal, lubricant and oxide (Sb2O3/Au - MoS2). These coatings are known to provide low friction in vacuum environments. The goal of this work was to evaluate friction and wear performance of MoS2 doped coatings in unidirectional and reciprocating sliding contact under different environmental conditions. Sliding contact results showed friction and wear dependence on temperature and humidity. The formation and removal of transfer films and the recrystallization and reorientation of basal layers on the steel counterface was observed as the mechanism for low friction. Structural analysis revealed a relationship between the microstructural properties and tribological performance. It was also observed that the addition of dopants (Ti, Au, Sb2O3) improved the mechanical properties as compared to pure MoS2 coatings. Further, the rolling contact performance of the coatings was measured on a five ball on rod tribometer and a Thrust bearing tribometer under vacuum and air environments. The rolling contact experiments indicated that life of the rolling components depend on the amount of material present between the contacts. Fluid film lubrication with thin film coatings investigates the possibilities to improve the performance and durability of tribological components when oils and thin films are synergistically coupled. In this work, the ability of a Diamond L (open full item for complete abstract)

Committee: Gary Doll (Advisor) Subjects: Aerospace Materials; Engineering; Experiments; Materials Science; Mechanical Engineering

PhD, University of Cincinnati, 2002, Engineering : Engineering Mechanics

The posterior cruciate ligament (PCL) is the primary restraint to posterior translation and is a secondary restraint to varus, valgus and external rotation.[12, 32, 43, 60] PCL injuries increase posterior translation and impair a person's ability to perform daily activities.[59, 67, 100] If left untreated, degenerative changes will appear earlier in the injured knee than in the contralateral knee.[17, 79, 82] A variety of surgical procedures have been used in an attempt to restore normal posterior translation. Some procedures have been unable to restore posterior translation,[48, 77, 111, 127] while others have been unable to maintain normal posterior translation[65, 85, 90]. The failure to control posterior translation has been attributed to graft elongation.[48, 81, 85] In an attempt to prevent graft elongation, two-bundle reconstructions have been investigated[65, 81, 119] and have shown promising initial results. However, the resistance to posterior translation is unknown. The purpose of this research was to investigate the ability of one and two-bundle PCL reconstructions to resist posterior translation during cyclic fatigue testing. The femoral attachment of the one-bundle graft and one bundle (AL2) of all two-bundle grafts were located within the PCL's anterolateral band, which is named for its anterior femoral insertion and its lateral tibial insertion. The second bundle was placed posterior to the AL2 bundle in one of three locations that varied in their depth within the notch: shallow (S), intermediate (I), and deep (D). The specimens were cycled from near full extension to 120 degrees of flexion with 100 N applied posterior force. The knees were cycled until the tension in both bundles was 50 N or less. The two-bundle reconstructions did not provide better resistance to posterior translation than the one-bundle reconstruction for a 2.5-mm posterior translation increase. The AL2-I reconstruction resisted the return of posterior translation for significantl (open full item for complete abstract)

Committee: Dr. Edward S. Grood (Advisor) Subjects: Engineering, Biomedical

Master of Science (MS), Ohio University, 2002, Mechanical Engineering (Engineering and Technology)

Multiaxial Fatigue Testing Machine

Committee: Hajrudin Pasic PhD (Advisor) Subjects: Computer Science; Electrical Engineering

Master of Science (MS), Ohio University, 2002, Mechanical Engineering (Engineering and Technology)

Multiaxial Fatigue Testing Machine

Committee: Hajrudin Pasic (Advisor) Subjects: Mechanical Engineering

Master of Science (MS), Ohio University, 2000, Mechanical Engineering (Engineering)

Torsion fatigue system for mechanical characterization of materials

Committee: Hajrudin Pasic (Advisor) Subjects: Engineering, Mechanical

Master of Science (M.S.), University of Dayton, 2010, Mechanical Engineering

It has been observed that the life limiting fatigue behavior in numerous superalloys is dominated by small crack growth behavior. While environmental effects on crack growth behavior of Ni-base superalloys are well documented within the literature, the published research is largely limited to long crack behavior due to the difficulty of measuring small cracks in a vacuum chamber. A testing capability for optical measurement of small cracks under ultra-high vacuum and at elevated temperatures has been developed. Optical measurement capabilities have been evaluated on a lab air machine to determine crack measurement accuracy. Vacuum tests were then run at 650°C on a sub-solvus IN100 specimen to quantify the effect of vacuum on the propagation life within the small crack regime. The effectiveness of this test capability and the role of environment on small crack growth behavior will be discussed.

Committee: Robert Brockman PhD (Advisor); Steven Donaldson PhD (Committee Member); Gerald Shaughnessy (Committee Member) Subjects: Materials Science; Mechanical Engineering