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Retrospective Theses and Dissertations

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Full-Text Articles in Applied Mechanics

Experimental Observations Of Shear Band Nucleation And Propagation In A Bulk Metallic Glass Using Wedge-Like Cylindrical Indentation , Antonia Maki Antoniou Jan 2006

Experimental Observations Of Shear Band Nucleation And Propagation In A Bulk Metallic Glass Using Wedge-Like Cylindrical Indentation , Antonia Maki Antoniou

Retrospective Theses and Dissertations

Bulk metallic glasses (BMGs), or amorphous metal alloys, have a unique combination of properties such as high strength, large elastic strain limit (up to 2%), corrosion resistance and formability. These unique properties make them candidates for precision mechanical elements, hinge supports, contact surfaces as well as miniaturized systems (MEMS). However, their limited ductility hinders further realizations of their industrial potential. Under uniaxial tension tests, metallic glass fails in a brittle manner with unstable propagation of a single shear band. There is a need to understand the conditions for shear band nucleation and propagation in order to achieve a superior material ...


Synergy Between Chemical Dissolution And Mechanical Abrasion During Chemical Mechanical Polishing Of Copper , Wei Che Jan 2005

Synergy Between Chemical Dissolution And Mechanical Abrasion During Chemical Mechanical Polishing Of Copper , Wei Che

Retrospective Theses and Dissertations

Chemical mechanical planarization (CMP) is a mainstream semiconductor processing method for achieving local and global wafer planarization. However, the CMP process fundamentals are poorly understood, and thereby inhibit migratability of lab-scale experiments to production processes. This work addresses the synergistic role of chemical dissolution rate (CDR) and mechanical abrasion rate (MAR) on the material removal mechanisms during CMP process.;A set of nano-wear experiments on elecro-plated copper surfaces are conducted with systematic exposure to active slurry. Initial results of in situ wear test in chemically active slurry showed an increased material removal rate (MRR) relative to a dry wear test ...


A Numerical Approach To Model And Predict The Energy Absorption And Crush Mechanics Within A Long-Fiber Composite Crush Tube , Leon Pickett Jr. Jan 2005

A Numerical Approach To Model And Predict The Energy Absorption And Crush Mechanics Within A Long-Fiber Composite Crush Tube , Leon Pickett Jr.

Retrospective Theses and Dissertations

Past research has conclusively shown that long fiber structural composites possess superior specific energy absorption characteristics as compared to steel and aluminum structures. However, destructive physical testing of composites is very costly and time consuming. As a result, numerical solutions are desirable as an alternative to experimental testing. Up until this point, very little numerical work has been successful in predicting the energy absorption of composite crush structures. This research investigates the ability to use commercially available numerical modeling tools to approximate the energy absorption capability of long-fiber composite crush tubes. This study is significant because it provides a preliminary ...


Fatigue Life Investigation Of Solid And Hollow Rollers In Pure Rolling Contact , Wisam M. Abu Jadayil Jan 2005

Fatigue Life Investigation Of Solid And Hollow Rollers In Pure Rolling Contact , Wisam M. Abu Jadayil

Retrospective Theses and Dissertations

Solid and hollow cylindrical rollers in pure rolling contact have been modeled using the finite element package, ABAQUS, to study the stress distribution and the resulting deformations in the rollers' bodies when the two rollers are subjected to a pure normal loading or to a combined normal and tangential loading. The tangential loading is one third of the normal loading value. Then the Ioannides-Harris fatigue life model for rolling bearings has been applied on the ABAQUS numerical results to investigate the fatigue life of the solid and hollow rollers. Using the fatigue life of the solid rollers as the reference ...


Stochastic Models For Material Removal Rate (Mrr) In Chemical Mechanical Planarization (Cmp) Process , Changxue Wang Jan 2004

Stochastic Models For Material Removal Rate (Mrr) In Chemical Mechanical Planarization (Cmp) Process , Changxue Wang

Retrospective Theses and Dissertations

Most of the previous work related to the prediction of the material removal rate (MRR) in CMP process to date has been concerned with the ideal case, wherein there is no randomness associated with either the pad or the slurry. In the work of this dissertation, we investigated the material removal rate (MRR) by taking some of the randomness into account, including randomly varying pad asperity heights and/or randomly varying slurry particle sizes.;The MRR decay phenomenon as well as the MRR variation on the slurry particle size distribution has gained more and more attention in CMP industry. However ...


Effects Of Material Microstructure And Surface Geometry On Ultrasonic Scattering And Flaw Detection , Yanming Guo Jan 2003

Effects Of Material Microstructure And Surface Geometry On Ultrasonic Scattering And Flaw Detection , Yanming Guo

Retrospective Theses and Dissertations

This dissertation studies the effect of two practical attributes of structural materials on ultrasonic inspection. The effects of the material microstructure of polycrystalline aluminum alloys on propagating ultrasonic waves and the effects of surface curvature and roughness on ultrasonic scattering and flaw detectability are both addressed.;The relationships between ultrasonic properties (velocity, attenuation, and backscattering) and the microstructure are studied both experimentally and theoretically for rolled aluminum samples with highly elongated grains. Attenuation measurements show a very small anisotropy, whereas backscattering measurements show a very high anisotropy. Existing theories and related extensions are able to explain these physical phenomena. Three ...


Statistical Signal Processing For Mechanical Systems , Li Wen Jan 2003

Statistical Signal Processing For Mechanical Systems , Li Wen

Retrospective Theses and Dissertations

Random processes such as temperature and acoustic noise are found in all types of mechanical systems. Knowledge of these processes can lead to improved design and detection methods related to faulty operation. The goal of this dissertation is to contribute to the knowledge base of such processes. Specifically, we address statistical signal processing methods that are appropriate and consistent relative to the physics of these systems. Two generic problems associated with random signal measurements from mechanical systems are addressed.;Random processes associated with mechanical systems usually have complex spectral structure containing both continuous and line spectral components. Accordingly, they are ...


Hybrid Finite-Volume/Transported Pdf Method For The Simulation Of Turbulent Reactive Flows , Venkatramanan Raman Jan 2003

Hybrid Finite-Volume/Transported Pdf Method For The Simulation Of Turbulent Reactive Flows , Venkatramanan Raman

Retrospective Theses and Dissertations

A novel computational scheme is formulated for simulating turbulent reactive flows in complex geometries with detailed chemical kinetics. A Probability Density Function (PDF) based method that handles the scalar transport equation is coupled with an existing Finite Volume (FV) Reynolds-Averaged Navier-Stokes (RANS) flow solver. The PDF formulation leads to closed chemical source terms and facilitates the use of detailed chemical mechanisms without approximations. The particle-based PDF scheme is modified to handle complex geometries and grid structures. Grid-independent particle evolution schemes that scale linearly with the problem size are implemented in the Monte-Carlo PDF solver. A novel algorithm, in situ adaptive ...


Interactive Stress Re-Analysis In Virtual Reality , Kurt Anthony Chipperfield Jan 2002

Interactive Stress Re-Analysis In Virtual Reality , Kurt Anthony Chipperfield

Retrospective Theses and Dissertations

This research combines virtual reality with fast stress re-analysis/approximation methods, meshless stress analysis, and free-form deformation (FFD) to produce a virtual design environment that allows interactive stress re-analysis. The interactive stress re-analysis program allows designers to visualize the initial stresses in their design, then modify the design while watching the stresses update as the design is changed.;The primary objective of this research is to find the best stress re-analysis method for use in the virtual design environment. The pre-conditioned conjugate gradient (PCG) iterative method is compared with respect to accuracy and speed with the combined approximation (CA) method ...


Extraction Methods For Multidirectional Driving Point Accelerance And Transfer Point Accelerance Matrices , Jianrong Dong Jan 2000

Extraction Methods For Multidirectional Driving Point Accelerance And Transfer Point Accelerance Matrices , Jianrong Dong

Retrospective Theses and Dissertations

To experimentally determine the multidirectional driving point and transfer accelerance matrices is a difficult task that has remained unsolved for 30 years. These matrices relate both linear and rotational degrees of freedom in three dimensions. The direct measurement of dynamic moments and rotational accelerations is very difficult. Little work exists on the subject and none includes so many DOF's. Besides, it is assumed that any test attachment is rigid and none used angular accelerometers to measure the angular acceleration;Various errors in substructure testing are studied. The study reveals that the interface DOF deficiency error is the most catastrophic ...


Ultrasonic Beam Models In Anisotropic Media , Matthias Rudolph Jan 1999

Ultrasonic Beam Models In Anisotropic Media , Matthias Rudolph

Retrospective Theses and Dissertations

This dissertation models the sound fields produced by ultrasonic transducers for immersion inspections where the sound fields pass through general curved interfaces into a general anisotropic material;The foundations for these models are discussed, including slowness surfaces for anisotropic materials and the reflection/transmission of plane waves at a planar fluid/anisotropic solid interface;Three beam models are developed. Two of these models---the boundary diffraction wave model and the multi-Gaussian model---rely on the paraxial approximation, resulting in models that are computationally very efficient. As a consequence, those models can be used to conduct parametric studies in a highly effective manner ...


Backscattering And Attenuation During The Propagation Of Ultrasonic Waves In Duplex Titanium Alloys , Paul Donald Panetta Jan 1999

Backscattering And Attenuation During The Propagation Of Ultrasonic Waves In Duplex Titanium Alloys , Paul Donald Panetta

Retrospective Theses and Dissertations

This dissertation reports results from studies of the interactions between the microstructure/macrostructure of titanium alloys and propagating ultrasonic waves. Attention is focused on the interactions which cause backscattering and attenuation. Experimental studies will be reported which show that the phase aberration contribution to attenuation does not remove energy from the propagating beam, and a physical picture is developed. A simple ray model which encompasses the ideas presented in the physical picture is used to predict attenuation for propagation in single phase materials with elongated grains. In addition, a general theory for attenuation that includes some degree of multiple scattering ...


Development Of An Empirical Model Of Human Sweating And A Semi-Empirical Model Of Human Thermoregulation , Jennifer Jane Walker Jan 1999

Development Of An Empirical Model Of Human Sweating And A Semi-Empirical Model Of Human Thermoregulation , Jennifer Jane Walker

Retrospective Theses and Dissertations

The physiology of the human thermoregulatory response to changes in environment and work load has been studied from the perspective of both the physiologist and the engineer. Both fields have brought certain skills and tools to the effort. An effort to bring together the understanding gained from these two perspectives has been lacking. In this work a model for the sweat response and a model for the thermoregulatory response to changes in room temperature were developed. These models were developed using the modeling tools of engineering and the knowledge contained in past experimental data;An empirical model of the sweat ...


Chip-Controlled 3-D Complex Cutting Tool Insert Design And Virtual Manufacturing Simulation , Shizhuang Luo Jan 1999

Chip-Controlled 3-D Complex Cutting Tool Insert Design And Virtual Manufacturing Simulation , Shizhuang Luo

Retrospective Theses and Dissertations

Designing suitable tools for the turning operation is of vital interest to manufacturers. The tool inserts used nowadays adopt complex geometric shapes. A question facing many manufacturers is how to effectively design complex shaped tool inserts and how to prove the validity of such design. One of the important criteria for selecting inserts is the ability to control chip formation and chip breaking;The research work described in this dissertation attempted to bring innovation into the cutting tool insert design process by using feature-based modeling and by proposing a predictive chip model and integrating it into the design process. Such ...


A Three-Dimensional, Dynamic Model Of The Human Body For Lifting Motions , Jason Clay Gillette Jan 1999

A Three-Dimensional, Dynamic Model Of The Human Body For Lifting Motions , Jason Clay Gillette

Retrospective Theses and Dissertations

Lower back pain is prevalent in society and manual lifting has been linked as one potential cause of these types of injuries. Therefore, the 3dLift biomechanical model was developed in this research with the goal of quantitatively analyzing lifting motions. The model divided the body into fifteen segments that were connected by fourteen anatomical joints. During experimental trials, a volunteer subject lifted an object using four different lifting combinations: symmetric leglifts, asymmetric leglifts, symmetric backlifts, and asymmetric backlifts. In order to individualize the 3dLift model, anthropometric parameters were estimated using measurements taken on the subject. During the lifting trials, the ...


Finite Element Modeling Of Transient Ultrasonic Waves In Linear Viscoelastic Media , Paul Andrew Stucky Jan 1998

Finite Element Modeling Of Transient Ultrasonic Waves In Linear Viscoelastic Media , Paul Andrew Stucky

Retrospective Theses and Dissertations

Linear viscoelasticity offers a minimal framework within which to construct a causal model for wave propagation in absorptive media. Viscoelastic media are often described as media with memory, that is, the present state of stress is dependent on the present strain and the complete time history of strain weighted by time convolution with an appropriate time-dependent stress relaxation modulus. An axisymmetric, displacement based finite element method for modeling pulsed ultrasonic waves in linear, homogeneous viscoelastic media is developed that does not require storage of the complete time history of displacement at every node. This is accomplished by modeling the stress ...


Thermal Stresses In Axially Symmetric Fracture Mechanics Problems For Bodies With An External Crack , Janice Sue Pawloski Jan 1998

Thermal Stresses In Axially Symmetric Fracture Mechanics Problems For Bodies With An External Crack , Janice Sue Pawloski

Retrospective Theses and Dissertations

The method of integral transforms is used in this work to solve for both the temperature distribution and the stress function for several axially symmetric fracture mechanics problems. The problems considered are symmetric in temperature and stresses with respect to the plane of the crack. Due to the mixed boundary conditions in the plane of the crack, this method leads to two sets of dual integral equations. One of these is a result of solving the conduction problem, and the other occurs in the solution of the thermoelastic problem;In this work, the problem of determining stress intensity factors for ...


Methodology Development Of An Engineering Design Expert System Utilizing A Modular Knowledge-Base Inference Process , Steven John Winter Jan 1998

Methodology Development Of An Engineering Design Expert System Utilizing A Modular Knowledge-Base Inference Process , Steven John Winter

Retrospective Theses and Dissertations

Methodology development was conducted to incorporate a modular knowledge-base representation into an expert system engineering design application. The objective for using multidisciplinary methodologies in defining a design system was to develop a system framework that would be applicable to a wide range of engineering applications. The technique of "knowledge clustering" was used to construct a general decision tree for all factual information relating to the design application. This construction combined the design process surface knowledge and specific application depth knowledge. Utilization of both levels of knowledge created a system capable of processing multiple controlling tasks including; organizing factual information relative ...


Boundary Element Strategies And Discretized Green's Functions: Applications In Composite Materials And Wave Mechanics , Lingyun Pan Jan 1997

Boundary Element Strategies And Discretized Green's Functions: Applications In Composite Materials And Wave Mechanics , Lingyun Pan

Retrospective Theses and Dissertations

In this thesis, it is explicitly shown that the exact Green's function and the unknown boundary variables on the boundary, in a given boundary value problem (BVP), satisfy the same boundary integral equation (BIE) but with a different known vector. Indeed, it is made explicit here that in using the BIE method to solve a given boundary value problem, one has in fact constructed the Green's function for the domain. This observation provides a way to construct a library of numerical approximations to exact Green's functions (discretized Green's functions) for problems for which analytical Green's ...


The Dynamics Of Liquids In Moving Containers: Numerical Models For Viscous Unsteady Free Surface Flows , Adonis C. Kassinos Jan 1997

The Dynamics Of Liquids In Moving Containers: Numerical Models For Viscous Unsteady Free Surface Flows , Adonis C. Kassinos

Retrospective Theses and Dissertations

The transportation and control of liquid masses poses a problem of immense practical interest. Slosh forces generated by the motion of the liquid can easily interfere with the safe operation of the vehicle. The successful design and execution of such operations depends upon not only the understanding, but also the ability to predict the dynamic behavior of liquids in moving containers;The numerical simulation of liquid sloshing in moving containers is considered in this study. Numerical models are developed and applied to both two and three dimensional flows. The motion of the vehicle can be quite general, given by the ...


Planning Fatigue Experiments And Analyzing Fatigue Data With The Random Fatigue-Limit Model And Modified Sudden Death Tests , Francis Garcia Pascual Jan 1997

Planning Fatigue Experiments And Analyzing Fatigue Data With The Random Fatigue-Limit Model And Modified Sudden Death Tests , Francis Garcia Pascual

Retrospective Theses and Dissertations

In this research, we address important issues faced by researchers in fatigue testing. We suggest a practical model to describe the relationship between fatigue life and applied stress, illustrate the corresponding data analysis methods, and study test plans under this model. We also present test plans that provide a systematic and efficient use of a limited number of test positions. These methods emphasize the importance of accuracy in the study of fatigue life while recognizing physical realities and resource limitations;In a fatigue-limit model, test units tested below the fatigue limit (also known as the threshold stress) theoretically will never ...


The Effect Of Stiffener Parameters On The Farfield Sound Radiation From Composite Beams: Experiment And Theory , Julie Cathleen Slaughter Jan 1997

The Effect Of Stiffener Parameters On The Farfield Sound Radiation From Composite Beams: Experiment And Theory , Julie Cathleen Slaughter

Retrospective Theses and Dissertations

The effects of spatial and material variations on farfield sound radiation from carbon/epoxy composite beams were investigated. Specifically, the geometry of a single stiffener of carbon/epoxy embedded in a beam, periodically spaced stiffeners along the length of a beam, and single stiffeners of different materials embedded in beams were all investigated. Because of a lack of methods to sufficiently model the details of spatially varying material properties, experimental data were used to identify important parameters that needed to be included in a model. Vibration testing was performed for three frequency ranges: 500 Hz to 1500 Hz, 1500 Hz ...


Operating Characteristics Of A Hydrogen-Oxygen-Fueled Roller Engine , James E. Ettaro Jan 1997

Operating Characteristics Of A Hydrogen-Oxygen-Fueled Roller Engine , James E. Ettaro

Retrospective Theses and Dissertations

The use of carbon based fuels for energy production is resulting in severe global environmental damage. Hydrogen has been identified as the ultimate, universal fuel that could eliminate this problem. In order to implement a hydrogen infrastructure advances in hydrogen technology must continue to occur (Padro 1996);Engines fueled by hydrogen gas combusted in a combustion chamber with air produce oxides of nitrogen. These oxides of nitrogen are responsible for photochemical smog, health and environmental problems. On the other hand, hydrogen combusted in pure oxygen would eliminate the formation of the oxides of nitrogen (de Boer & Hulet, 1980). Modern engine designs, however, cannot effectively convert the energy of stoichiometric hydrogen-oxygen combustion into useable power;In this research, a ...


Numerical Solution Of Inverse Problems In Nondestructive Evaluation Using The Boundary Element Method And Multivariate Adaptive Regression Splines , Sinniah Balakrishnan Jan 1996

Numerical Solution Of Inverse Problems In Nondestructive Evaluation Using The Boundary Element Method And Multivariate Adaptive Regression Splines , Sinniah Balakrishnan

Retrospective Theses and Dissertations

Flaw identification is an important inverse problem that underlies techniques for nondestructive evaluation (NDE). In this study, a known steady state thermal field is used to identify multiple flaws in a material. The problem is to determine locations and sizes of the multiple flaws if the number of flaws and the temperature at certain probe locations on the boundary are known. The boundary element method (BEM) is used as a computational tool in this task;Earlier work in this area has dealt with the case of a single flaw, while we address the case of multiple flaws. The identification of ...


Variants Of Asymptotic Extremes , Chih-Yao Liu Jan 1996

Variants Of Asymptotic Extremes , Chih-Yao Liu

Retrospective Theses and Dissertations

In this dissertation, we study two variants of asymptotic extremes, with the first exploiting Daniels' "covering circle", and the second exploiting a certain variant of it. The first topic concerns geometric tolerancing, for gauging the quality of either the assembly of two manufactured planar parts, or the conformance of a single such planar part to its jig. Minimax point-to-point discrepancy and the corresponding plate misalignment are studied asymptotically in n, using the notion of random covering circle, in the case of circular normal and circular uniform error. The second topic concerns certain asymptotic distributions related to game values, for k ...


The Effect Of Rib Attachment Properties On Structural Acoustics , Matthew Scott Carney Jan 1996

The Effect Of Rib Attachment Properties On Structural Acoustics , Matthew Scott Carney

Retrospective Theses and Dissertations

Sound Pressure measurements were taken of several 2.44m long thin beams which had 0.635cm wide t-ribs centered on them. The beams were excited by a chirp signal with the frequency range of 500Hz to 1500Hz. Two rib attachment methods were used on the beams. One group of beams were machined out of thick stock to the geometry of a rib welded to a beam to ensure that the rib and attachment were one continuous media. The other group of beams had ribs that were welded on. Fillets from the welding process were subjected to heat-treatment and machining to ...


Finite Element Modeling Of Ultrasonic Wave Propagation With Application To Acoustic Microscopy , Tianji Xue Jan 1996

Finite Element Modeling Of Ultrasonic Wave Propagation With Application To Acoustic Microscopy , Tianji Xue

Retrospective Theses and Dissertations

The development of NDE techniques and the accurate interpretation of measurement signals require a firm understanding of the physical process of energy/defect interactions. This in turn demands an accurate model for the propagation of ultrasonic waves in acoustic and elastic media. Analytical approaches are restricted due to the arbitrary geometries of the discontinuities involved. In this work, a comprehensive numerical model based on the finite element method is developed to simulate ultrasonic wave propagation in ultrasonic NDE systems with emphasis on application to acoustic microscopy;Starting from the governing equations of dynamic elasticity, semi-discretized finite element equations in the ...


A Compliant Model For Estimation And Optimization Of Damping In Vibrating Structures , Thomas Jeffrey Thompson Jan 1995

A Compliant Model For Estimation And Optimization Of Damping In Vibrating Structures , Thomas Jeffrey Thompson

Retrospective Theses and Dissertations

Proposed future space missions involve large structures which must maintain precise dimensional tolerances even during dynamic maneuvers. In order to attenuate disturbances in the many modes of vibration of such a structure, active and passive vibration control are proposed. The passive control is to be achieved by placing viscous or viscoelastic members or materials within a structure in order to absorb energy. Ascertaining the best combination of locations for such treatments is difficult due to the large number of cases, each of which requires computationally expensive complex eigenvalue analyses of a finite element model to compute modal damping values;In ...


Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson Jan 1995

Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson

Retrospective Theses and Dissertations

High stress in a crucial instrument part can cause failure. Stress detection is one of the aims of nondestructive testing. The velocity change of acoustic waves can be used to detect stress in a material. An acoustic microscope is an instrument which induces and detects acoustic waves and in one mode of operation, is able to measure the velocity of acoustic surface waves. It does this over a very small area and is capable of high spatial resolution;One of the challenges in the measurement of stress is the achievement of high spatial resolution. Since the stress induced velocity shifts ...


Quo Vadis - A Framework For Intelligent Routing In Large Communication Networks , Armin Robert Mikler Jan 1995

Quo Vadis - A Framework For Intelligent Routing In Large Communication Networks , Armin Robert Mikler

Retrospective Theses and Dissertations

Modern communication networks contain hundreds if not thousands of interconnected nodes. Traffic management mechanisms must be able to support a cost-effective, responsive, flexible, robust, customer-oriented high speed communication environment while minimizing the overhead associated with management functions. Conventional traffic management mechanisms for routing and congestion control algorithms entail tremendous resource overhead in storage and update of network state information;Quo Vadis is an evolving framework for intelligent traffic management in very large communication networks. It is designed to exploit topological properties of large networks as well as their spatio-temporal dynamics to optimize multiple performance criteria through cooperation among nodes in ...