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Full-Text Articles in Mechanical Engineering

Thermodynamic Approach To Fatigue Failure Analysis In Metals And Composite Materials, Mehdi Naderi Abadi Jan 2011

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 ...


On The Thermodynamics Of Degradation, Mehdi Amir Darehbidi Jan 2011

On The Thermodynamics Of Degradation, Mehdi Amir Darehbidi

LSU Doctoral Dissertations

All materials when subjected to fatigue loading are prone to failure if the number of cycles exceeds a certain level. Prediction of the number of cycles to failure is, therefore, of utmost importance in nearly all engineering applications. The existing methods for evaluating the fatigue life are tedious, expensive, and extremely time consuming as fatigue often takes many thousands to millions of cycles until failure occurs. Therefore, methods that can readily estimate the number of cycles to failure are highly desirable. In this work, innovative solutions to fatigue problems are presented and their practical significance is discussed. The premise of ...


Fabrication And Property Study Of Plasma Sprayed Alumina Coatings And Magnetron Sputtered Multilayers, Ranran Liu Jan 2011

Fabrication And Property Study Of Plasma Sprayed Alumina Coatings And Magnetron Sputtered Multilayers, Ranran Liu

LSU Doctoral Dissertations

In this study, air or atmospheric plasma spraying (APS), one of thermal spraying processes, was used to produce alumina coatings and single splats. Nanoindentation technique was used to measure the mechanical properties, such as hardness and elastic modulus, of APS alumina coatings and single splats. The detailed procedures to calculate elastic modulus and hardness, and testing parameters for nanoindentation have been provided. This study revealed that the phase combination of α-Al2O3 and γ-Al2O3 played an important role in the scattering distribution of nanoindentation results on APS alumina coatings. In addition, nanoindentation technique was used to predict the phase information of ...


Molecular Dynamics Simulation Studies Of Surface-Stress Effects In Metallic Nanostructures, Jijun Lao Jan 2011

Molecular Dynamics Simulation Studies Of Surface-Stress Effects In Metallic Nanostructures, Jijun Lao

LSU Doctoral Dissertations

Using molecular dynamics (MD) simulations we investigate the surface-stress-induced structural transformations and pseudoelastic behavior in palladium (Pd) crystalline nanowires. For a <100> initial crystal orientation our studies indicate that the surface stress can cause Pd nanowires to spontaneously undergo structural changes with characteristics that are determined by the wire cross-sectional area. Specifically, when the cross-sectional area is below 2.18nm x 2.18nm the wire changes spontaneously its crystal structure from the initial fcc structure to a body-centered-tetragonal (bct) structure. In wires of larger cross-sectional area (i.e., 2.57nm x 2.57nm) the structural transformation is achieved via a spontaneous ...


Small Footprint High Flow Rate Microdevice For Rare Target Cell Capture, Taehyun Park Jan 2011

Small Footprint High Flow Rate Microdevice For Rare Target Cell Capture, Taehyun Park

LSU Doctoral Dissertations

A novel high flow rate cell capture design was introduced to overcome the limitations of the current technologies or methods for rare target cell capture. Even though the rare target cell capture using BioMEMS technology has great potential for cancer diagnosis, previous rare cell capture research could not overcome the limitations of low flow rate or low recovery rate. Rare cell research requires precise sample preparation for accurate results. A new method of preparation for a single or a precise number of target cell was introduced. Current sample preparation methods which are not suitable for rare cell research, such as ...


Embedded Piezoelectric Fiber Composite Sensors For Applications In Composite Structures, Hari Prasad Konka Jan 2011

Embedded Piezoelectric Fiber Composite Sensors For Applications In Composite Structures, Hari Prasad Konka

LSU Doctoral Dissertations

Health monitoring of the composite structures is an important issue that must be addressed. Embedded sensors could be an effective way to monitor the health of composite structures continuously and which could also avoid the catastrophic failures of composite structures. Piezoelectric-fiber-composite sensors (PFCS) made from micro-sized Lead Zirconate Titanate (PZT) fibers have great advantages over the traditional bulk PZT sensors for embedded sensor applications. PFCS as an embedded sensor will be an ideal choice to continuously monitor the stress/strain levels and health conditions of composites. This work presents a critical study on using PFCS as an effective embedded sensor ...


A Biomimic Self-Healing Shape Memory Polymer Based Syntactic Foam For Smart Structural Composites, Jones Nji Jan 2011

A Biomimic Self-Healing Shape Memory Polymer Based Syntactic Foam For Smart Structural Composites, Jones Nji

LSU Doctoral Dissertations

This study explored the development of a new self-healing Polystyrene Shape Memory Polymer (PSMP) based syntactic foam for service life extension in structural polymeric composites. The objective was to self-heal structural-length scale damage in an autonomous, efficient, timely and repeatable manner at the molecular-length scale. Self-healing is achieved through a novel two step close-then-heal (CTH) self-healing scheme, designed to mimic the natural biological process of wound healing in humans. A new methodology to fabricate three-dimensional (3-D) fiber reinforced shape memory polymer syntactic foam for structural applications was developed. The effect of impact energy on the ability for the 3-D fiber ...