Mechanical Engineering Commons^™

Locally Optimized Covariance Kriging For Non-Stationary System Responses, Daniel Lee Clark Jr.

Browse all Theses and Dissertations

In this thesis, the Locally-Optimized Covariance (LOC) Kriging method is developed. This method represents a flexible surrogate modeling approach for approximating a non-stationary Kriging covariance structures for deterministic responses. The non-stationary covariance structure is approximated by aggregating multiple stationary localities. The aforementioned localities are determined to be statistically significant utilizing the Non-Stationary Identification Test. This methodology is applied to various demonstration problems including simple one and two-dimensional analytical cases, a deterministic fatigue and creep life model, and a five-dimensional fluid-structural interaction problem. The practical significance of LOC-Kriging is discussed in detail and is directly compared to stationary Kriging considering computational …

Elucidating The Role Of Microstructure, Texture, And Microtexture On The Dwell Fatigue Response Of Ti-6al-4v, Alec Mitchell Blankenship

Browse all Theses and Dissertations

Ambient temperature dwell sensitivity is known to be deleterious to the fatigue response of near-alpha titanium alloys. Dwell fatigue refers to the presence of a sustained hold at peak stress as opposed to the continuous variation of normal cyclic fatigue loading. This reduction in failure life-times from dwell loading is attributed to early crack nucleation and faster crack propagation. The degradation is the result of plastic anisotropy on the microstructural scale along with tendency of titanium alloys to creep at low temperatures at stresses well below the 0.2% offset yield strength. Despite being the most widely used titanium alloy, Ti-6Al-4V …

Methodology For Analysis Of Stress, Creep, And Fatigue Behavior Of Compliant Mechanisms, Joshua Allen Crews

Doctoral Dissertations

"A methodology is developed for analyzing stress within homogeneous and metallic-reinforced, fixed-free compliant segments and small-length flexural pivots. Boundary conditions related to the inclusion of metallic reinforcing components within a polymer compliant segment are investigated. The analysis method outlined herein relies on key outputs from the pseudo-rigid-body models (PRBMs). A method is presented for the redesign of compliant mechanisms to include metallic reinforcement to reduce stress while maintaining force-deflection behavior. Examples are provided in which a compliant segment is redesigned to include metallic reinforcement by using the stress equations developed from the PRBM. The effect of bonding between the polymer …

Fatigue Performance Of Glass Fiber/Epoxy Composite At Low Temperature, Prajakta Govande 2817401530, Dominic R. Cross, Kwek Tze Tan

Williams Honors College, Honors Research Projects

Due to technological advancement in the manufacturing methods of composites, these materials find a plethora of applications which include but are not limited to wind energy projects in the form of turbine blades. These blades at times are exposed to temperatures as low as -40ᵒC. Therefore, there is a need to study low-temperature effects on such materials under different loading scenarios. This study investigates the possibility of utilizing MAC/GMC as a simulation tool to match trends of mechanical properties such as fatigue performance and stiffness variation of a given Glass fiber/Epoxy composite at 23ᵒC (room temperature) and -40 ᵒC, under …

Finite Element Analysis And Topology Optimization Of Differential Case And Control Arm For Static And Fatigue Loading, Pankaj N. Kalan

Dissertations, Master's Theses and Master's Reports

Optimization of the automobile components can result in a significant decrease in vehicle weight, increase in fuel efficiency and reduction in environmental damage. For example, the lightweight vehicle production will save over 4.4×109 GJ of energy and 4.1×108 tons of CO2 over a 10 year period, compared to the current non-light weight vehicles. This equates to 890 billion miles or 42 billion gallons of gas savings (Wu 2016). This study evaluates the weight reduction possible by using manual and automatic (using Optistruct software) topology optimization processes. Optimization of a vehicle differential case done in this study shows that a weight …

Electromechanical Coupling Behavior Of Dielectric Elastomer Transducers, Jianyou Zhou

Electronic Thesis and Dissertation Repository

Dielectric elastomer transducers with large deformation, high energy output, light weight and low cost have been drawing great interest from both the research and industry communities, and shown potential for versatile applications in biomimetics, dynamics, robotics and energy harvesting. However, in addition to multiple failure modes such as electrical breakdown, electromechanical instability, loss-of-tension and fatigue, the performance of dielectric elastomer transducers are also strongly influenced by the hyperelastic and viscoelastic properties of the material. Also, the interplay among these material properties and the failure modes is rather difficult to predict. Therefore, in order to provide guidelines for the optimal design …

Modeling Of Environmentally Assisted Fatigue Crack Growth Behavior, Sree Phani Chandar Reddy

Dissertations

The formation of fatigue cracks and their propagation due to cyclic loading in metals have been a concern for more than hundred years. Since fatigue failure were first reported by the railroad industry in 1840s, tremendous progress has been achieved in understanding fatigue behavior of metals. But fatigue damage is still a concern due to its complex dependency on various environmental variable like humidity, temperature, time and corrosive environment. Although numerous theories and models have been proposed in the past, the effects of environment on fatigue crack growth (FCG) is not completely understood. This dissertation aims to shed light on …

Face Sheet/Core Debonding In Sandwich Composites Under Static And Fatigue Loading, Manjinder Singh Warriach

Wayne State University Dissertations

Delamination growth due to face sheet/core debonding is a major concern due to its inherent weakness in sandwich composites which can be exacerbated due to the presence of flaws. In this research work The primary objective of this research was to characterize the delamination crack growth behavior in E-glass face sheet/polyurethane foam core sandwich composite with pre-existing initial delamination crack at a face sheet/core interface under static and fatigue for mode I and mixed mode loading. For mode I static loading two types of delamination experiments, namely T-peel test and wedge test were implemented to evaluate fracture toughness in polyurethane …

Degradation And Fatigue Involving Dissipated Processes, Md Liakat Ali

LSU Doctoral Dissertations

Irreversible material degradation due to cyclic mechanical loading is investigated utilizing the concept of thermodynamic entropy, plastic strain energy, and temperature slope measurement. Uniaxial tension-compression and fully-reversed bending fatigue tests are performed over a wide range of loading conditions with metallic and composite materials subject to both constant- and variable-amplitude loading. A methodology is developed for the estimation of the fatigue fracture entropy (FFE) and fatigue toughness of metallic specimens in a rapid fashion. It is found that the FFE and the fatigue toughness of each material tested are within a small band. The value of FFE is found to …

Implementation Of Analytical Fatigue Models Into Opensim To Predict The Effects Of Fatigue On Anterior Cruciate Ligament Loading, Michael A. Samann

Mechanical & Aerospace Engineering Theses & Dissertations

The anterior cruciate ligament (ACL) provides stability to the knee joint while performing activities such as a side step cut. Neuromuscular fatigue, a reduction in muscle force producing capabilities, alters lower extremity mechanics while performing a side step cut and may increase the risk of ACL injury, particularly in females. Musculoskeletal modeling allows for the measurement of muscle forces, which are difficult to measure in-vivo. Therefore, musculoskeletal modeling, may improve our understanding of the effects of neuromuscular fatigue on muscle force production and loading of the ACL. Therefore, the purpose of this study was to develop a musculoskeletal model which …

Prediction Of Tribological Behavior Of Candidate Materials For Rotor Seals, John W. Franzino, Will F. Michul

Materials Engineering

To reduce high costs associated with manufacturing and testing materials for rotor seals, a procedure needs to be developed to quickly and accurately test candidate materials as they are released. The test should reduce the amount of fabrication required and model working conditions in order to accurately assess the tribological behavior of candidate materials. A possible solution was examined that utilized a rig meant to model operational stresses and wear. Compression modulus data was then taken in order to quantify the accumulation of damage due to microcracking, the primary mode of failure, through a damage index parameter. Testing results concluded …

A Practical Tool For The Determination Of Surface Stresses In Railroad Bearings With Different Contact Geometries And Load Conditions Using Finite Element Analysis, Michael A. Mason

Theses and Dissertations

The connection between contact geometry and fatigue in tapered roller bearings utilized in the railroad environment is still of interest. Roller bearings for railroad applications are typically precision ground with crowned contact geometries to prevent edge loading of components. This normally results in completely elastic Hertzian contact stresses under standard railcar loads. However, under extreme load conditions, detrimental edge loading has been known to occur. It is proposed to develop a tool, using finite element analysis, that can be utilized to optimize complex raceway crown geometries for severe applications.

A successful implementation of this tool is presented and validated using …

An Experimental Investigation Of Corrosion Fatigue Life Via Thermographic Method, Richard Wayne Purvis

LSU Master's Theses

The effect of prior corrosion fatigue damage on the thermographic response of 1018 low carbon steel is investigated. Specimens were subject to rotating bending fatigue at 38 Hz loading frequency while being exposed to a 3.5% NaCl and distilled water solution. Some specimens were subject to corrosion fatigue for part of their fatigue life and then their thermographic response measured under fatigue in air at 62 Hz loading frequency. Fatigue tests in air with thermographic measurement were performed as a comparison. It was observed that the initial temperature rise after corrosion fatigue fits the previously proposed model for air fatigue, …

Using A Sleep And Activity Monitor To Operationalize Fatigue Risk Management, Vanessa Bégat Seitz

LSU Master's Theses

When a person continues to work despite being fatigued, an accident may occur or productivity may decrease. Reducing fatigue related accidents is complicated due to the subjective nature and pervasiveness of the feeling of fatigue. Because finding one universal definition or measure of fatigue is problematic, fatigue is typically measured by a combination of factors such as amount of sleep obtained, physical or cognitive work performed, or sleepiness which can then be related back to a measure of performance. Until recently, sleep measurement was restricted to a lab setting; however, with the emergence of actigraph devices, it is now possible …

Energy Dissipation And Entropy Generation During The Fatigue Degradation: Application To Health Monitoring Of Composites, Ali Kahirdeh

LSU Doctoral Dissertations

In this dissertation, an experimental approach for characterizing energy dissipation and degradation evolution in a woven Epoxy/Glass (G10/FR4) laminate subjected to fully reversed bending fatigue test is presented. Infrared thermography and acoustic emission are utilized to characterize the degradation progression. The results show similar evolutionary response indicating the presence of three degradation stages. The effect of the surface cooling on the fatigue life of the laminates is investigated both experimentally and analytically. The results show that the life of the laminate is highly dependent on the temperature and that surface cooling can significantly increase the fatigue life of the laminate. …

Trampoline And Bungee Fatigue-Test Machine, Andy Brock, Christopher D'Elia, Ryan Murphy

Mechanical Engineering

JumpSport, a Saratoga based recreational and fitness trampoline company, sponsored this senior project team towards the development of a fatigue-testing machine. The goal of this project was to iterate the previous machine JumpSport used for bungee cord, spring, and trampoline fatigue testing. Since minimal study had been conducted on these specific bungee cords, the fixture was designed to confirm the theoretical correlations for rubber and perform the final tests according to a strict protocol. Operating with a specific test protocol in mind will allow the data from multiple tests to be combined and analyzed statistically. With a design concept in …

Rebounder Fatigue Test Machine, Caroline Reeves, Will Robertson, Ethan Flory

Mechanical Engineering

JumpSport, a company that designs and sells trampolines and trampoline accessories, has sponsored this senior project team to design, build, and test a trampoline fatigue test machine. The machine must simulate a person jumping on the trampoline to test the life of JumpSport’s fitness trampolines and kids’ trampolines. Partway through the design process, the objectives were altered and this senior project team was tasked with merging with another Cal Poly senior project group to create an all-inclusive test machine to accommodate both full-trampoline testing and individual bungee cord testing.

The final design is centered on a slider crank linkage driven …

Effect Of Total Awake Time On Drivers' Performance And Evaluation Of Training Intervention To Mitigate Effects Of Total Awake Time On Drivers' Performance, Abd Malek Abdul Hamid

Open Access Dissertations

Driving while sleepy, drowsy or fatigued are leading contributors to road crashes. Sleepiness, drowsiness and fatigue usually occur at the end of a prolonged period of time during which an individual has been awake. Although these factors have been heavily researched, it is not clear how one of their primary causes, a prolonged total awake time (TAT), might affect driving skills such as hazard anticipation, hazard mitigation and attention maintenance, three skills that are crucial for safe driving.

The first experiment investigated how these three driving skills are affected by prolonged TAT, and if so to what extent. Forty-eight participants …

A Hybrid Constitutive Model For Creep, Fatigue, And Creep-Fatigue Damage, Calvin Stewart

Electronic Theses and Dissertations

In the combustion zone of industrial- and aero- gas turbines, thermomechanical fatigue (TMF) is the dominant damage mechanism. Thermomechanical fatigue is a coupling of independent creep, fatigue, and oxidation damage mechanisms that interact and accelerate microstructural degradation. A mixture of intergranular cracking due to creep, transgranular cracking due to fatigue, and surface embrittlement due to oxidation is often observed in gas turbine components removed from service. The current maintenance scheme for gas turbines is to remove components from service when any criteria (elongation, stress-rupture, crack length, etc.) exceed the designed maximum allowable. Experimental, theoretical, and numerical analyses are performed to …

Thermomechanical Fatigue Life Prediction Of Notched 304 Stainless Steel, Justin Karl

Electronic Theses and Dissertations

The behavior of materials as they are subjected to combined thermal and mechanical fatigue loads is an area of research that carries great significance in a number of engineering applications. Power generation, petrochemical, and aerospace industries operate machinery with expensive components that undergo repeated applications of force while simultaneously being exposed to variable temperature working fluids. A case of considerable importance is found in steam turbines, which subject blades to cyclic loads from rotation as well as the passing of heated gases. The complex strain and temperature histories from this type of operation, combined with the geometric profile of the …

Creep-Fatigue Crack Initiation And Propagation Of A Notched Stainless Steel, Scott Keller

Electronic Theses and Dissertations

Premature failures of vital gas turbine components, such as blades and vanes, have been the result of increasing demands of power generation facilities. As power needs fluctuate throughout the day, operators are quickly firing up gas turbines as a means of providing instant power. Traditionally, these engines run at constant operating conditions; however, contemporary operating conditions call for these engines to be applied on an “as necessary” basis. The result of the cyclic startup and shutdown of gas turbines has led to a phenomenon known as creep-fatigue (CF). A coupling of two primary failure mechanisms in gas turbines, CF conditions …

Development And Validation Of Probabilistic Fatigue Models Containing Out-Life Suspensions, Noel S. Murray

Electronic Theses and Dissertations

Author's abstract: In the area of reliability engineering it is necessary to be confident that a component or system of components will not fail under use for safety and cost reasons. One major mechanism of failure to a mechanical component is fatigue. This is the repetitious motion of loading and unloading of the material, typically below the ultimate tensile strength of the material, which ultimately leads to a catastrophic failure. To ensure this does not happen, engineers design components based on tests to determine the life of these components. These tests are typically conducted on a bench type tester in …

The Effect Of Cryogenic Treatment On The Fatigue Life Of Chrome Silicon Steel Compression Springs, Debra Lynn Smith

Dissertations (1934 -)

The purpose of this dissertation is to explore the effect of cryogenic treatment on the fatigue life of compression springs. Product manufacturers are constantly searching for ways to make their products last longer. This dissertation addresses three questions: (1) What is the effect of cryogenic treatment on the fatigue life of chrome silicon steel compression springs? Does the life increase, decrease, or remain the same? (2) What is the effect of cryogenic treatment on the Percent Load Loss (Stress Relaxation) of chrome silicon steel compression springs? (3) What are the possible changes in the material that cause these effects?

The …

Fatigue Testing And Computational Analysis Of A Spinal Implant, Timothy Helton

Electronic Theses and Dissertations

The following study investigates the fatigue behavior of a spinal implant developed by Synthes, Inc. to provide stability and off load pressure from the discs in the lumbar region. The installation process for the StenoFix design utilizes plastic deformations to customize the device to each individual patient, but also has potential to degrade fatigue behavior. Physical testing of two titanium alloys, Ti-6Al-7Nb and Ti-15Mo, was conducted on hydraulic test frames and compared to computational simulations which were carried out for the following scenarios: cyclic excitation following plastic deformation; variation of material property definition; variation of loading location; and three modifications …

Thermodynamic Approach To Fatigue Failure Analysis In Metals And Composite Materials, Mehdi Naderi Abadi

LSU Doctoral Dissertations

Fatigue is a dissipative process and must obey the laws of thermodynamics. In general, it can be hypothesized that the degradation of machinery components is a consequence of irreversible thermodynamic processes that disorder a component, and that degradation is a time dependent phenomenon with increasing disorder. This suggests that entropy —a fundamental parameter in thermodynamics that characterizes disorder— offers a natural measure of component degradation. The majority of the existing methods for prediction of fatigue are limited to the study of a single fatigue mode, i.e., bending or torsion or tension-compression. Further, the variability in the duty cycle in a …

Plasticity And Damage In Bimodal Grain Size Al-5083: Microstructural Finite Element, Steven Nelson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Bimodal and nanocrystalline aluminum alloys are being investigated as stronger replacements for conventional polycrystalline aluminum alloys. Higher strengths are achieved by reducing the grain size of a metal; however, as the grain size is reduced the ductility diminishes. One solution that limits this decrease in ductility is the addition of a few microcrystalline grains into a nanocrystalline alloy, creating a bimodal microstructure that offers a better balance of strength and ductility. Two- and three-dimensional microstructural finite element (FE) simulations of monotonic and fatigue failures in Al-5083 having bimodal grain structures are conducted. To reduce the computational time and facilitate the …

Fatigue Life Analysis Of T-38 Aileron Lever Using A Continuum Damage Approach, James D. Gyllenskog

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

In a recent investigation conducted by the United States Air Force, the mechanical failure of the aileron lever, manufactured from 2014-T6 aluminum, caused the fatal mishap of a T-38 trainer aircraft. In general the locations of cracks are unknown and must be determined by simulation. In this study we propose to use a continuum damage modeling approach to determine the degradation and damage in a material as the number of cycles of loading increases. This approach successfully predicts the location of crack initiation, propagation path, and propagation rate. A stress-based model in conjunction with the successive initiation technique is utilized. …

Performance Analysis And Life Prediction For Small Wind Turbine Blades: A Wood Laminate Case Study, Christopher James Nosti

Master's Theses

A detailed study of the fatigue life of wooden wind turbine blades for a new 10 kilowatt system was undertaken. A numerical model of the blades was created using the technical software package MATLAB in order to estimate the maximum stress occurring within the blade in response to changes in wind velocities based on a wind profile approximating the location where these turbines are expected to operate. The material properties of the wooden laminate were measured using an Instron tensile test machine and were found to be in line with published values. In parallel with this effort, a three dimensional …

Manufacture, Characterization, And Application Of Multiwall Carbon Nanotube Composite Crylonitrile-Butadiene-Styrene, Daniel Ray Bortz

University of Kentucky Master's Theses

Carbon nanotubes have been studied for nearly two decades and their amazing properties continue to spur intense investigation in the area of polymer composites. In terms of potential commercialization, mutiwall carbon nanotubes (MWCNTs) are currently the most prevalent and economically viable form of nanotubes. Uncovering innovative means to take full advantage of their properties remains a fundamental issue. In this thesis, viability of their use to reinforce polymeric systems is reported. Acrylonitrilebutadiene- styrene (ABS) was used as the host matrix. MWCNTs were introduced to the ABS matrix via melt compounding. The resulting composite was thoroughly rheologically, thermally, and mechanically characterized. …

Fracture Toughness, Crack-Growth-Rate And Creep Studies Of Alloy 276, Joydepp Pal

UNLV Theses, Dissertations, Professional Papers, and Capstones

Austenitic nickel-base Alloy 276 had been proposed to be a candidate structural material within the purview of the nuclear hydrogen initiative program. A mechanistic understanding of high temperature tensile deformation of this alloy has already been presented in an earlier investigation. The current investigation has been focused on the evaluation of crack-growth behavior, fracture toughness, stress-corrosion-cracking and creep deformation of this alloy as functions of different metallurgical and mechanical variables. The results of crack-growth study under cyclic loading indicate that this alloy exhibited greater cracking tendency with increasing temperature at a constant load ratio (R). However, the effect of temperature …