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Leque, NicholasDevelopment of an Experimental Methodology for Evaluation of Gear Contact Fatigue under High-Power and High-Temperature Conditions
Master of Science, The Ohio State University, 2011, Mechanical Engineering
Contact fatigue failures in the form of pitting or micro-pitting have been a perennial problem in power transmission applications. These failures are dictated by a large number of parameters including loading conditions, gear geometry and tooth modifications, kinematics (rolling and sliding velocities), lubricant parameters (viscosity, pressure-viscosity behavior), and material parameters (material type, hardness, case depth, residual stresses). As such, theoretical treatment of contact fatigue failures has been rather challenging, directing the focus to the experimental investigation of the problem. Most of the experimental gear pitting studies to date were limited to low-speed and low-temperature operating conditions. This study aims at developing a methodology for evaluating the contact fatigue lives of gears under high-speed (pitch-line velocities up to 50 m/s), high-stress (contact stresses up to 2 GPa) and high-temperature (oil inlet temperatures up to 150C). Specifications of a test machine concept that meets these requirements are defined and two test machines are designed and procured for this purpose. Gear test specimens that result in pits consistently are developed with the other competing failures (wear, scuffing, tooth breakage), as well as the high vibration conditions, avoided. Preliminary high-speed tests are presented at the end, representing both automotive and aerospace conditions to show that pitting and micro-pitting failures can be produced with the proposed methodology.

Committee:

Ahmet Kahraman, PhD (Advisor); Carlos Castro, PhD (Committee Member)

Subjects:

Engineering; Mechanical Engineering

Keywords:

Gears; fatigue life; pitting; micro-pitting; high-speed; high-temperature; aerospace; automotive

Miller, MaxAn Integrated Experimental and Simulation Study on Ultrasonic Nano-Crystal Surface Modification
MS, University of Cincinnati, 2013, Engineering and Applied Science: Mechanical Engineering
Ultrasonic Nano-Crystal Surface Modification (UNSM) is a relatively new material processing technology to enhance the operating service lives, or fatigue life, of engineering components. There is an increasing interest in extending this technology to metal parts such as aircraft engine turbine blades, compressor blades and medical implants such as spinal rods. In this process a ball made with tungsten carbide generates 20 - 40 KHz strikes of a few hundred Newton on the specimen surface. It works as a cold forging process; however the small ball that works itself across the specimen surface has a dynamic load added to the normal static load. The total striking force, feed, ball radius, amplitude of dynamic load and speed can vary to yield different results. UNSM induces severe plastic deformation and deep compressive residual stresses to increase surface hardness, improve surface roughness, and introduce nano-crystallization near the specimen surface. Currently there is no systematic approach to predict the material response under UNSM. Therefore the objective of this thesis is to develop a process model for predicting the material response as a result of the UNSM process. Before developing the model, experimental data is extracted from two UNSM treated coupons, one of Ti-6Al-4V and the other IN718 SPF. First a MATLAB code is developed to define the displacement history of the carbide ball on the surface of the specimen during the UNSM process. For titanium alloy (Ti-6Al-4V) a temperature, pressure, and rate dependent constitutive material model for is established to account for the high strain rates associated with UNSM. A semi-implicit forward tangent modulus algorithm is developed to implement the material and damage model, and this is linked with the FEM software LS-DYNA through a user-defined material subroutine. We use the Johnson Cook material model already within the LS-DYNA software to simulate IN718 SPF. The residual stress obtained from the simulation is compared and verified with experimental results. To further understand the UNSM process, the residual stress results are compared with Laser Shock Peening (LSP) to note the differences.

Committee:

Dong Qian, Ph.D. (Committee Chair); Seetha Ramaiah Mannava, Ph.D. (Committee Member); Vijay Vasudevan, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

residual stress;Material Model;Ultrasonic Nano-Crystal Surface Modification;Laser Shock Peening;material processing;fatigue life

Colin, Julie AnneDeformation History and Load Sequence Effects on Cumulative Fatigue Damage and Life Predictions
Doctor of Philosophy in Engineering, University of Toledo, 2009, Mechanical Engineering

Fatigue loading seldom involves constant amplitude loading. This is especially true in the cooling systems of nuclear power plants, typically made of stainless steel, where thermal fluctuations and water turbulent flow create variable amplitude loads, with presence of mean stresses and overloads. These complex loading sequences lead to the formation of networks of microcracks (crazing) that can propagate. As stainless steel is a material with strong deformation history effects and phase transformation resulting from plastic straining, such load sequence and variable amplitude loading effects are significant to its fatigue behavior and life predictions.

The goal of this study was to investigate the effects of cyclic deformation on fatigue behavior of stainless steel 304L as a deformation history sensitive material and determine how to quantify and accumulate fatigue damage to enable life predictions under variable amplitude loading conditions for such materials. A comprehensive experimental program including testing under fully-reversed, as well as mean stress and/or mean strain conditions, with initial or periodic overloads, along with step testing and random loading histories was conducted on two grades of stainless steel 304L, under both strain-controlled and load-controlled conditions. To facilitate comparisons with a material without deformation history effects, similar tests were also carried out on aluminum 7075-T6.

Experimental results are discussed, including peculiarities observed with stainless steel behavior, such as a phenomenon, referred to as secondary hardening characterized by a continuous increase in the stress response in a strain-controlled test and often leading to runout fatigue life. Possible mechanisms for secondary hardening observed in some tests are also discussed. The behavior of aluminum is shown not to be affected by preloading, whereas the behavior of stainless steel is greatly influenced by prior loading. Mean stress relaxation in strain control and ratcheting in load control and their influence on fatigue life are discussed. Some unusual mean strain test results are presented for stainless steel 304L, where in spite of mean stress relaxation fatigue lives were significantly longer than fully-reversed tests. Prestraining indicated no effect on either deformation or fatigue behavior of aluminum, while it induced considerable hardening in stainless steel 304L and led to different results on fatigue life, depending on the test control mode.

In step tests for stainless steel 304L, strong hardening induced by the first step of a high-low sequence significantly affects the fatigue behavior, depending on the test control mode used. For periodic overload tests of stainless steel 340L, hardening due to the overloads was progressive throughout life and more significant than in high-low step tests. For aluminum, no effect on deformation behavior was observed due to periodic overloads. However, the direction of the overloads was found to affect fatigue life, as tensile overloads led to longer lives, while compressive overloads led to shorter lives. Deformation and fatigue behaviors under random loading conditions are also presented and discussed for the two materials.

The applicability of a common cumulative damage rule, the linear damage rule, is assessed for the two types of material, and for various loading conditions. While the linear damage rule associated with a strain-life or stress-life curve is shown to be fairly accurate for life predictions for aluminum, it is shown to poorly represent the behavior of stainless steel, especially in prestrained and high-low step tests, in load control. In order to account for prior deformation effects and achieve accurate fatigue life predictions for stainless steel, parameters including both stress and strain terms are required. The Smith-Watson-Topper and Fatemi-Socie approaches, as such parameters, are shown to correlate most test data fairly accurately.

For damage accumulation under variable amplitude loading, the linear damage rule associated with strain-life or stress-life curves can lead to inaccurate fatigue life predictions, especially for materials presenting strong deformation memory effect, such as stainless steel 304L. The inadequacy of this method is typically attributed to the linear damage rule itself. On the contrary, this study demonstrates that damage accumulation using the linear damage rule can be accurate, provided that the linear damage rule is used in conjunction with parameters including both stress and strain terms. By including both loading history and response of the material in damage quantification, shortcomings of the commonly used linear damage rule approach can be circumvented in an effective manner.

In addition, cracking behavior was also analyzed under various loading conditions. Results on microcrack initiation and propagation are presented in relation to deformation and fatigue behaviors of the materials. Microcracks were observed to form during the first few percent of life, indicating that most of the fatigue life of smooth specimens is spent in microcrack formation and growth. Analyses of fractured specimens showed that microcrack formation and growth is dependent on the loading history, and less important in aluminum than stainless steel 304L, due to the higher toughness of this latter material.

Committee:

Ali Fatemi, PhD (Advisor); Mohamed Samir Hefzy, PhD (Committee Member); Yong Gan, PhD (Committee Member); Efstrafios Nikolaidis, PhD (Committee Member); Douglas Nims, PhD (Committee Member)

Subjects:

Engineering; Mechanical Engineering

Keywords:

Aluminum 7075-T6; Stainless Steel 304L; Cyclic Hardening; Deformation History Effect; Pre-hardening;Mean Stress; Fatigue Life Prediction; Load Sequence Effect; Overload Effect; Variable Amplitude Loading

Singh, GulshanEffective Simulation and Optimization of a Laser Peening Process
Doctor of Philosophy (PhD), Wright State University, 2009, Engineering PhD

Laser peening (LP) is a surface enhancement technique that has been applied to improve fatigue and corrosion properties of metals. The ability to use a high energy laser pulse to generate shock waves, inducing a compressive residual stress field in metallic materials, has applications in multiple fields such as turbomachinery, airframe structures, and medical appliances. In the past, researchers have investigated the effects of LP parameters experimentally and performed a limited number of simulations on simple geometries. However, monitoring the dynamic, intricate relationships of peened materials experimentally is time consuming, expensive, and challenging.

With increasing applications of LP on complex geometries, these limited experimental and simulation capabilities are not sufficient for an effective LP process design. Due to high speed, dynamic process parameters, it is difficult to achieve a consistent residual stress field in each treatment and constrain detrimental effects. With increased computer speed as well as increased sophistication in non-linear finite element analysis software, it is now possible to develop simulations that can consider several LP parameters.

In this research, a finite element simulation capability of the LP process is developed. These simulations are validated with the available experimental results. Based on the validated model, simplifications to complex models are developed. These models include quarter symmetric 3D model, a cylindrical coupon, a parametric plate, and a bending coupon model. The developed models can perform simulations incorporating the LP process parameters, such as pressure pulse properties, spot properties, number of shots, locations, sequences, overlapping configurations, and complex geometries. These models are employed in parametric investigations and residual stress profile optimization at single and multiple locations.

In parametric investigations, quarter symmetric 3D model is used to investigate temporal variations of pressure pulse, pressure magnitude, and shot shape and size. The LP optimization problem is divided into two parts: single and multiple locations peening optimization. The single-location peening optimization problems have mixed design variables and multiple optimal solutions. In the optimization literature, many researchers have solved problems involving mixed variables or multiple optima, but it is difficult to find multiple solutions for mixed-variable problems. A mixed-variable Niche Particle Swarm Optimization (MNPSO) is proposed that incorporates a mixed-variable handling technique and a niching technique to solve the problem.

Designing an optimal residual stress profile for multiple-location peening is a challenging task due to the computational cost and the nonlinear behavior of LP. A Progressive Multifidelity Optimization Strategy (PMOS) is proposed to solve the problem. The three-stage PMOS, combines low- and high- fidelity simulations and respective surrogate models and a mixed-variable handling strategy. This strategy employs comparatively low computational-intensity models in the first two stages to locate the design space that may contain the optimal solution. The third stage employs high fidelity simulation and surrogate models to determine the optimal solution. The overall objective of this research is to employ finite element simulations and effective optimization techniques to achieve optimal residual stress fields.

Committee:

Ramana Grandhi, PhD (Advisor); Allan Clauer, PhD (Committee Member); Robert Brockman, PhD (Committee Member); Nathan Klingbeil, PhD (Committee Member); Ravi Penmetsa, PhD (Committee Member); David Stargel, PhD (Other); Kristina Langer, PhD (Other)

Subjects:

Engineering

Keywords:

laser shock peening; residual stress; fatigue life; design optimization; finite element analysis

Godbole, ChinmayThe Influence of Reinforcement on Microstructure, Hardness, Tensile Deformation, Cyclic Fatigue and Final Fracture behavior of two Magnesium Alloys
Master of Science in Engineering, University of Akron, 2011, Mechanical Engineering

The application of Metal Matrix composites (MMC) spans over a wide range of structural applications owing to its improved mechanical properties namely high specific modulus and high strength to weight ratio when compared to their monolithic metal counterparts. Magnesium having a low density of 1.73 gm/cm3 is approximately two thirds of that of aluminum, one fourth of zinc, and one fifth of steel, allows it offer a very high specific strength among conventional engineering alloys.

Three Magnesium alloys based nano reinforced metal matrix composite were fabricated using solidification technique followed by hot extrusion. Magnesium alloy AZ31 was reinforced with alumina particulate (Al2O3p) and carbon nanotubes separately to produce (1) AZ31/1.5 vol% Al2O3 and (2) AZ31/1.0 vol% CNT composites. 3 wt% aluminum was added to AZ91 Mg alloy and reinforced with alumina particulate to synthesize (3) AZ (12)1/1.5 vol% Al2O3 nanocomposite. The test specimens of the composites and the monolithic alloys were precision machined and conformed to the standards specified in ASTM E8/E466. The samples were deformed in tension under strain controlled loading at rate of 0.0001s-1 to obtain the tensile properties. Stress amplitude controlled high cycle cyclic fatigue was carried over a range of maximum stress, at frequency of 5 Hz and at load ratios of 0.1 and -1. The number of cycles to failure were recorded. In this thesis report the effect of reinforcement and processing on the microstructure modification, hardness, tensile properties, stress controlled high cycle fatigue response and micro mechanics of final fracture behavior of the magnesium alloy composite is neatly presented discussed and compared with their unreinforced monolithic alloy counterparts. The elastic modulus, yield strength, ultimate tensile strength of the reinforced magnesium alloys were compared to the unreinforced counterpart. The ductility quantified by elongation to failure over 0.5 inches (12.7 mm) gage length of the test specimen and reduction in cross-section area of the composite were compared to the monolithic alloy. A comparison of fatigue response of the reinforced magnesium alloys with unreinforced counterparts were done to observe improvement in cyclic fatigue life at load ratio of 0.1 and – 1. The key mechanisms responsible for the superior cyclic fatigue and tensile behavior of the composite are discussed.

Committee:

Tirumalai Srivatsan, Dr (Advisor); Craig Menzemer, Dr (Committee Member); Amit Prakash, Dr (Committee Member)

Subjects:

Materials Science; Mechanical Engineering

Keywords:

Magnesium alloy; aluminum oxide; particulate reinforcement; metal matrix composite; microstructure; hardness; tensile response; cyclic fatigue life; fracture

Lavvafi, HosseinEFFECTS OF LASER MACHINING ON STRUCTURE AND FATIGUE OF 316LVM BIOMEDICAL WIRES
Doctor of Philosophy, Case Western Reserve University, 2013, Materials Science and Engineering
Recent advances in minimally invasive surgical techniques and an increasing need to miniaturize medical devices has led to a surge in developing advanced manufacturing techniques. In order to meet the functional needs of such small devices as cardiovascular stents, guide wires, and needles, the use of new materials and delicate geometries has increased creating a new challenge for manufacturing and machining. Some applications often include fine details that are impossible to achieve with rotary tool machining. Laser machining is one tool harnessing an enormous potential for the manufacture of such finely detailed devices as well as providing a means for improving the local material effects as a result of processing. However, thermal damage caused by laser machining can affect the performance of the components. As devices continue shrinking in size, there is a greater need for “athermal” manufacturing methods that have no adverse effect on performance. In this study, Nd:YAG and femtosecond lasers with different pulse widths were used to machine AISI 316LVM biomedical grade wires. The mechanical behavior of these materials were evaluated in uniaxial tension, and in cyclic strain-controlled fatigue with the use of a flex tester operated to provide fully reversed bending fatigue. All the fatigue testing was conducted in air over a range of cyclic strains to determine both the high-cycle and low-cycle fatigue regimes. The effects of laser input energy and pulse width on surface quality, heat affected zone (HAZ), and subsequent mechanical response are reported Baseline fatigue data on 316LVM wires in the annealed and hard conditions revealed that the hard wires exhibited better high cycle fatigue behavior than exhibited by the annealed wires. However, the low cycle fatigue behavior of the annealed wires was better than that obtained on the hard wires. This was successfully modeled using the Coffin-Manson-Basquin approach. Mixed results were obtained on the fatigue behavior of laser-treated wires. Low power Nd:YAG laser-treated 316LVM annealed wires exhibited better fatigue performance in both high cycle fatigue and low cycle fatigue compared to the annealed 316LVM wires. In contrast, high power Nd:YAG laser-treated annealed wires exhibited poorer fatigue performance in both high cycle and low cycle fatigue. Nd:YAG laser-treated 316LVM hard wires exhibited poorer fatigue performance in both high cycle fatigue and low cycle fatigue compared to the 316LVM hard wires. The femtosecond laser-machined annealed wires exhibited better fatigue life in both high cycle and low cycle fatigue compared to the annealed wires. In contrast, the femtosecond laser-machined hard wires exhibited lower fatigue life in both the high cycle fatigue and low cycle fatigue regimes compared to hard wires. Attempts at modeling the fatigue behavior of the laser-treated wires was unsuccessful using the Coffin-Manson-Basquin approach, likely due to localized surface conditions that dominated the fatigue behavior of the laser-treated wires.

Committee:

John J. Lewandowski, PhD (Committee Chair); David Schwam, PhD (Committee Member); Gerhard Welsch, PhD (Committee Member); Malcolm Cooke, PhD (Committee Member)

Subjects:

Materials Science

Keywords:

316LVM; medical device; laser machining; microfabrication; flex bending fatigue; femtosecond laser; stent; Nd:YAG nanosecond laser; Coffin-Manson-Basquin; fatigue-life; heat exchanger; heat-affected zone

Wertz, John NicholasAn Energy-Based Experimental-Analytical Torsional Fatigue Life-Prediction Method
Master of Science, The Ohio State University, 2010, Aero/Astro Engineering
An energy-based cycle-dependent fatigue life prediction framework for the calculation of torsional fatigue life and remaining life has been developed. The framework for this fatigue prediction method is developed in accordance with previously developed energy-based axial and bending fatigue life prediction approaches, which state: the total strain energy density accumulated during both a monotonic fracture event and cyclic processes is the same material property, where each can be determined by measuring the area beneath the monotonic true stress-strain curve and the area within a hysteresis loop, respectively. The energy-based fatigue life prediction framework is composed of the following entities: (1) the development of a shear fatigue testing procedure capable of assessing cyclic plastic strain energy density accumulation in a pure shear stress state and (2) the incorporation of an energy-based fatigue life calculation scheme to determine the remaining fatigue life of in-service gas turbine materials subjected to pure shear fatigue. Validation of the improved theory was attempted but failed due to undesired axial loading occurring during testing. Future work was proposed to address the issues.

Committee:

Herman Shen, PhD (Advisor); Jack McNamara, PhD (Committee Member); Tommy George, PhD (Other); Onome Scott-Emuakpor, PhD (Other)

Subjects:

Aerospace Materials; Engineering; Experiments; Mechanical Engineering; Mechanics

Keywords:

energy-based torsional fatigue life-prediction shear method

Tarar, Wasim AkramA New Finite Element Procedure for Fatigue Life Prediction and High Strain Rate Assessment of Cold Worked Advanced High Strength Steel
Doctor of Philosophy, The Ohio State University, 2008, Mechanical Engineering
This dissertation presents a new finite element procedure for fatigue life prediction and high strain rate assessment of cold worked Advanced High Strength Steel (AHSS). The first part of this research is related to the development of a new finite element procedure from an energy-based fatigue life prediction framework previously developed for prediction of axial, bending and multi-axial fatigue life. The framework for the prediction of fatigue life via energy analysis consists of constitutive laws which correlate the cyclic energy to the amount of energy required to fracture a material. In this study, the energy expressions that construct the new constitutive laws are integrated into a minimum potential energy formulation to develop new finite elements for fatigue life prediction for structural components subjected to axial, bending and multi-axial cyclic loads. The comparison of finite element method (FEM) results to the existing experimental fatigue data verifies the new finite element method for fatigue life prediction. The final output of this finite element analysis is in the form of number of cycles to failure for each element. The performance of the fatigue finite element is demonstrated by the fatigue life predictions from Al 6061-T6 and Ti-6Al-4V. In addition to developing new fatigue finite elements, a new equivalent stress expression and a new finite element procedure for multiaxail fatigue life prediction are also proposed. The new procedure is applicable to biaxial as well as multiaxial fatigue applications. The second part of this research is related to the development of LSDYNA material model for vehicle crash simulation based on high strain rate assessment of cold worked AHSS. In order to simulate actual crash using software like LSDYNA, it is desirable to have accurate stress/strain data for materials. The material models available in the literature ignore the effect of cold working on the material and present data only for flat sheets. In this research, the cold worked AHSS with curved cross-section is tested at strain rates of 1000 (in/in)/s and the data is used to develop a corresponding LSDYNA material model for vehicle crash simulation.

Committee:

Dr. M.-H. Herman Shen (Advisor); Dr. Brian Harper (Committee Co-Chair); Dr. Noriko Katsube (Committee Member); Dr. John Yu (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Fatigue; Life Cycles; Finite Element Methods; Material Models

Bathini, UdaykarA Study of Microstructure, Tensile Deformation, Cyclic Fatigue and Final Fracture Behavior of Commercially Pure Titanium and a Titanium Alloy
Master of Science in Engineering, University of Akron, 2010, Civil Engineering

Rapid industrial growth and advances in the domains of engineering and related technologies during the last fifty years have led to the extensive use of traditional metals and their alloy counterparts. Titanium is one such metal which has gained wide popularity in the aerospace and defense related applications owing to a wide range of impressive mechanical properties like excellent specific strength (σUTS/ρ), stiffness, corrosion and erosion resistance, fracture toughness and capability to withstand significant temperature variations.

Two materials, namely commercial purity titanium (Grade 2), referred to henceforth as Ti- CP (Grade 2) and the “work-horse” alloy Ti-6Al-4V have been chosen for this research study. The intrinsic influence of material composition and test specimen orientation on the tensile and fatigue behavior for both Ti- CP (Grade 2) and Ti-6Al-4V have been discussed. Samples of both Ti- CP (Grade 2) and Ti-6Al-4V were prepared from the as-provided plate stock along both the longitudinal and transverse orientations. The specimens were then deformed to failure in uniaxial tension for the tensile tests and cyclically deformed at different values of maximum stress at constant load ratio of 0.1 for the high cycle fatigue tests. The microstructure, tensile properties, resultant fracture behavior of the two materials is presented in the light of results obtained from the uniaxial tensile tests. The conjoint influence of intrinsic microstructural features, nature of loading and specimen properties on the tensile properties is discussed. Also, the macroscopic fracture mode, the intrinsic features on the fatigue fracture surface and the role of applied stress-microstructural feature interactions in governing failure for the cyclic fatigue properties for both the materials under study Ti- CP (Grade 2) and the “work-horse” alloy Ti-6Al-4V have been discussed in detail.

Careful study of the microstructure for Ti-CP (Grade 2) material at a low magnification revealed the primary alpha (α) grains to be intermingled with small pockets of beta (β) grains. Observation at the higher allowable magnifications of the optical microscope revealed very fine alpha (α) phase lamellae located within the beta (β) grain. The microhardness and macrohardness measurements were consistent through the sheet specimen for Ti- CP (Grade 2) and slightly lower compared to Ti-6Al-4V. However, the macrohardness was marginally higher than the microhardness resulting from the presence of a large volume fraction of the soft alpha phase. The hardness values when plotted reveal marginal spatial variability. Tensile fracture of Ti-CP (Grade 2) was at an inclination to the far field tensile stress axis for both longitudinal and transverse orientations. The overload region revealed a combination of fine microscopic cracks, microscopic voids of varying size and randomly distributed through the surface, and a large population of shallow dimples, features reminiscent of locally brittle and ductile failure mechanisms. The maximum stress (σmaximum) versus fatigue life (Nf) characteristics shown by this material is quite different from those non-ferrous metals that exhibit a well-defined endurance limit. When compared at equal values of maximum stress at a load ratio of 0.1, the fatigue life of the transverse specimen is noticeably greater than the longitudinal counterpart. At equivalent values of maximum elastic strain, the transverse specimens revealed noticeably improved fatigue life as compared one-on-one to the longitudinal counterparts.

Careful observations of the Ti-6Al-4V alloy microstructure over a range of magnifications spanning very low to high magnification revealed a duplex microstructure consisting of the near equiaxed alpha (α) and transformed beta (β) phases. The primary near equiaxed shaped alpha (α) grains (light in color) was well distributed in a lamellar matrix with transformed beta (dark in color). The microhardness and macrohardness values recorded for the Ti-6Al-4V alloy reveal it to be harder than the commercially pure (Grade 2) material. However, for the Ti-6Al-4V alloy the microhardness is noticeably higher than the corresponding macrohardness value that can be ascribed to the presence of a population of processing-related artifacts and the hard beta-phase. Tensile fracture of the Ti-6Al-4V alloy was macroscopically rough and essentially normal to the far field stress axis for the longitudinal orientation and cup-and-cone morphology for the transverse orientation. However, microscopically, the surface was rough and covered with a population of macroscopic and fine microscopic cracks, voids of varying size, a population of shallow dimples of varying size and shape, features reminiscent of locally brittle and ductile failure mechanisms. When compared at equal values of maximum stress at a load ratio of 0.1, there is a marginal to no influence of microstructure on high cycle fatigue life of both orientations of the alloy.

Committee:

Anil Patnaik, Dr. (Advisor)

Subjects:

Civil Engineering; Materials Science

Keywords:

Titanium Alloy; Commercially Pure Titanium; Microstructure, Tensile Properties; Tensile Fracture; Titanium; Materials tests; Cyclic tests; Fatigue life; Fracture