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Articles 1  30 of 113
FullText Articles in Mechanical Engineering
Experimental Observations Of Shear Band Nucleation And Propagation In A Bulk Metallic Glass Using WedgeLike Cylindrical Indentation , Antonia Maki Antoniou
Experimental Observations Of Shear Band Nucleation And Propagation In A Bulk Metallic Glass Using WedgeLike 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 ...
A Numerical Approach To Model And Predict The Energy Absorption And Crush Mechanics Within A LongFiber Composite Crush Tube , Leon Pickett Jr.
A Numerical Approach To Model And Predict The Energy Absorption And Crush Mechanics Within A LongFiber 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 longfiber composite crush tubes. This study is significant because it provides a preliminary ...
Ultrasonic System Models And Measurements , Ana Lilia LopezSanchez
Ultrasonic System Models And Measurements , Ana Lilia LopezSanchez
Retrospective Theses and Dissertations
In this work ultrasonic models and measurements are used to characterize a number of the important elements of an ultrasonic measurement system as well as the entire system. Ultrasonic measurement models for predicting the response from reference reflectors are described, including a new ultrasonic measurement model recently developed to simulate the ultrasonic response of an infinitely long cylindrical cavity. The reference reflectors considered include spherical pores, flatbottom holes and sidedrilled holes, which are commonly used in nondestructive evaluation studies. These reflectors are employed in a series of modeling/experimental studies to assess where approximate and more exact scattering models are ...
Ultrasonic Guided Waves In Composite Plates: A Study Of Interface Bond Condition And Material Properties Determination With Broadband Focused AirCoupled Ultrasounds , Sorin Vasile Teles
Ultrasonic Guided Waves In Composite Plates: A Study Of Interface Bond Condition And Material Properties Determination With Broadband Focused AirCoupled Ultrasounds , Sorin Vasile Teles
Retrospective Theses and Dissertations
This work is focused on two important aspects of the study of the composite materials: characterization of interface bonding in layered composites and evaluation of elastic material properties in aircoupled experiments.;The characterization of interface condition in a layered composite is critical to understand the behavior of the material under various stress situations. A closed disbond, alternatively known as zerovolume disbond or " kissingdisbond" (KSD) is difficult to detection by conventional normalincidence ultrasonic nondestructive evaluation (NDE) methods. Such undetected defect may be dangerous because it can produce a significant decrease in structural integrity or lead to a catastrophic failure under certain ...
Stochastic Models For Material Removal Rate (Mrr) In Chemical Mechanical Planarization (Cmp) Process , Changxue Wang
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 ...
Statistical Signal Processing For Mechanical Systems , Li Wen
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 ...
Effects Of Material Microstructure And Surface Geometry On Ultrasonic Scattering And Flaw Detection , Yanming Guo
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 ...
Electromechanical Characterization Of Ultrasonic Nde Systems , Changjiu Dang
Electromechanical Characterization Of Ultrasonic Nde Systems , Changjiu Dang
Retrospective Theses and Dissertations
An ultrasonic nondestructive evaluation (NDE) measurement system is a complex collection of many elements such as the pulser/receiver, the cabling, the transducers, and the material configuration being tested. To completely model an ultrasonic measurement system, a system model, called the electroacoustic measurement (EAM) model , was developed. This model allows one to analyze the measurement system at many different levels, ranging from individual details to the entire system itself. The EAM model has been implemented in software using the MATLAB development environment such that one has control over the specification of the detailed system components. On the other hand, the ...
LayUp Characterization And Elastic Property Determination In Composite Laminates , Dong Fei
LayUp Characterization And Elastic Property Determination In Composite Laminates , Dong Fei
Retrospective Theses and Dissertations
This dissertation focuses on two important nondestructive evaluation and materials characterization problems related to composite laminates: ply layup characterization and elastic property determination. For ply layup characterization, we have developed a shear wave transmission technique to effectively detect ply layup errors in composite laminates. The effects of fiber orientation on normalincident shear waves propagating through a composite laminate have been investigated both theoretically and experimentally. To facilitate rotation, EMATs (electromagnetic acoustic transducers) were used to generate and receive the shear waves. It was found that the transmitted shear waves when the EMAT transmitter and receiver were perpendicular to each other ...
Extraction Methods For Multidirectional Driving Point Accelerance And Transfer Point Accelerance Matrices , Jianrong Dong
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
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 modelsthe boundary diffraction wave model and the multiGaussian modelrely 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 ...
A ThreeDimensional, Dynamic Model Of The Human Body For Lifting Motions , Jason Clay Gillette
A ThreeDimensional, 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 ...
Nonlinear And Hysteretic Magnetomechanical Model For Magnetostrictive Transducers , Marcelo Jorge Dapino
Nonlinear And Hysteretic Magnetomechanical Model For Magnetostrictive Transducers , Marcelo Jorge Dapino
Retrospective Theses and Dissertations
The growing interest on magnetostrictive materials for generation of strains and forces in smart structure systems motivates the development of increasingly accurate models of the performance of these materials as used in transducers. The proposed magnetomechanical model provides a characterization of the material magnetization as well as the strain and force output by a transducer in response to quasistatic applied magnetic fields. The model is built in three steps. In the first, the mean field model for ferromagnetic hysteresis originally developed by Jiles and Atherton is used to compute the magnetization arising from the application of magnetic fields. While this ...
Thermal Stresses In Axially Symmetric Fracture Mechanics Problems For Bodies With An External Crack , Janice Sue Pawloski
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 KnowledgeBase Inference Process , Steven John Winter
Methodology Development Of An Engineering Design Expert System Utilizing A Modular KnowledgeBase Inference Process , Steven John Winter
Retrospective Theses and Dissertations
Methodology development was conducted to incorporate a modular knowledgebase 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 ...
Sensitivity Boundary Integral Equations With Applications In Engineering Mechanics , Daming Zhang
Sensitivity Boundary Integral Equations With Applications In Engineering Mechanics , Daming Zhang
Retrospective Theses and Dissertations
In sensitivity analysis for problems involving thin domains or domains with cracks, conventional boundary integral equations must be supplemented and/or replaced by hypersingular ones. This is due to the fact that the conventional equations become nearlydegenerate for thin domains and actually degenerate for cracks. Such degenerate character follows from the close proximity to each other, or actual coincidence, of two defining surfaces in each case. Hypersingular boundary integral equations for sensitivity analysis are developed in two forms in this thesis, using a global regularization and a local regularization. The regularizations are facilitated by observing that the singularity order of ...
Interaction Of Acoustic Beam With Elastic Structures , Han Zhang
Interaction Of Acoustic Beam With Elastic Structures , Han Zhang
Retrospective Theses and Dissertations
This thesis describes experiments and calculations performed on the interaction of acoustic beams in water and air with planar and cylindrical elastic structures. Ultrasonic reflection measurements have been used to elucidate the phenomena of guided wave generation and reradiation by selecting beam incidence at, or near, phasematching conditions. Under these circumstances reasonant mode conversion of accoustic wave to guided wave mode energy can occur. This interaction has been studied in rubbercoated steel, aluminum, plexiglas, and graphiteepoxy composite. The acoustic coupling media used in these experiments has been either water or air;Some theoretical modeling has also been undertaken to explain ...
Boundary Element Strategies And Discretized Green's Functions: Applications In Composite Materials And Wave Mechanics , Lingyun Pan
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 Effect Of Stiffener Parameters On The Farfield Sound Radiation From Composite Beams: Experiment And Theory , Julie Cathleen Slaughter
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 ...
A Method For Determining Mixed Mode Stress Intensity Factors Using Strain Gage Data , Gregory Roger Swanson
A Method For Determining Mixed Mode Stress Intensity Factors Using Strain Gage Data , Gregory Roger Swanson
Retrospective Theses and Dissertations
An experimental method for determining mixed mode stress intensity factors, crack tip location, and crack tip orientation using strain gage data near the crack tip is developed. From the strain gage data and the relative location of the strain gages to each other the location of the crack tip and its orientation relative to the strain gages is derived along with the mixed mode stress intensity factors. The method is based on an iterative linear least squares fit to generalized Westergaard equations that describe the strain field near a crack tip;The method is applied to numerical data generated from ...
Design, Analysis, And Modeling Of Giant Magnetostrictuve Transducers , Frederick Theodore Calkins
Design, Analysis, And Modeling Of Giant Magnetostrictuve Transducers , Frederick Theodore Calkins
Retrospective Theses and Dissertations
The increased use of giant magnetostrictive, TerfenolD transducers in a wide variety of applications has led to a need for greater understanding of the materials performance. This dissertation attempts to add to the TerfenolD transducer body of knowledge by providing an indepth analysis and modeling of an experimental transducer. A description of the magnetostriction process related to TerfenolD includes a discussion of material properties, production methods, and the effect of mechanical stress, magnetization, and temperature on the material performance. The understanding of the TerfenolD material performance provides the basis for an analysis of the performance of a TerfenolD transducer. Issues ...
Numerical Solution Of Inverse Problems In Nondestructive Evaluation Using The Boundary Element Method And Multivariate Adaptive Regression Splines , Sinniah Balakrishnan
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 ...
The Effect Of Rib Attachment Properties On Structural Acoustics , Matthew Scott Carney
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 tribs 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 heattreatment and machining to ...
The Rules For The Exchange And Analysis Of Dynamic Information In Structural Vibration , Paulo Sergio Varoto
The Rules For The Exchange And Analysis Of Dynamic Information In Structural Vibration , Paulo Sergio Varoto
Retrospective Theses and Dissertations
Modern machines are often composed of components that are designed and manufactured by a number of suppliers and are expected to operate successfully over a wide range of dynamic environments when assembled. Two examples are either a satellite attached to a launch vehicle at several points or a brake assembly attached to an automobile. The main question is "What information is needed to define a suitable dynamic test environment that will ensure that components will function properly when assembled?";Vibration test tailoring is a name that is often given to the process of trying to develop adequate test specifications and ...
Ultrasonic Transducer Characterization And Transducer Beam Modeling For Applications In Nondestructive Evaluation , Terence Peter Lerch
Ultrasonic Transducer Characterization And Transducer Beam Modeling For Applications In Nondestructive Evaluation , Terence Peter Lerch
Retrospective Theses and Dissertations
In this work, analytic models have been developed for two different nondestructive evaluation (NDE) applications: the characterization of spherically focused ultrasonic immersion transducers, and the prediction of the radiated wave fields of a variety of commonly used ultrasonic transducers;When a spherically focused probe is correctly and completely characterized, its corresponding theoretical model can accurately predict the experimentally measured structure of its incident wave field. A new and efficient method for completely characterizing a spherically focused transducer and its accompanying measurement system is described. Predicted responses that make use of this method are shown to correspond very well to measured ...
Fracture Of An Infinitely Large Elastic Plate Containing A Curved Crack , YuiChuin Shiah
Fracture Of An Infinitely Large Elastic Plate Containing A Curved Crack , YuiChuin Shiah
Retrospective Theses and Dissertations
Both of the problems of inplane fracture and outofplane transverse flexure of an infinitely large isotropic plate containing a circular arc crack is solved using the complex variable method. A new conformal mapping function is introduced to transform the contour surface of a circular arc crack to a unit circle. Through this mapping function, direct stress integration is performed along the unit circle for various loading conditions. After Cauchy integrals are taken for each term in the boundary equations, the complex stress functions corresponding to the specified loading conditions are determined. Without using the limiting process, the obtained solutions can ...
Ultrasonic Scattering From Decorated Grain Boundaries , John Mittleman
Ultrasonic Scattering From Decorated Grain Boundaries , John Mittleman
Retrospective Theses and Dissertations
The microstructure of polycrystalline materials is manipulated in many ways to create materials with superior engineering properties. Alloying pure materials, for example, can alter crystallographic structure to strengthen or stiffen the material, but when impurities collect along grain boundaries, the material may become embrittled. This undesirable condition is generally associated with improper heat treatment during fabrication, but it may also occur during the service life of alloys exposed to penetrating radiation or severe thermal conditions. This dissertation studies scattering from decorated grain boundaries theoretically and experimentally, and ties results for isolated scatterers to grain noise measurements on materials composed entirely ...
Minimizing The Radiated Sound Power With Minimal Structural Modification , Daniel Henry Kruger
Minimizing The Radiated Sound Power With Minimal Structural Modification , Daniel Henry Kruger
Retrospective Theses and Dissertations
In cases where a structure's excitation cannot be altered, the sound radiation from the structure must be minimized by modifying the structure within given design constraints. This dissertation considers minimizing sound radiated by an existing structure with minimal changes to the structure itself. To accomplish this the sound power radiated by a structure was written as a function of the normal surface velocity using the boundary element method. The feasibility of reducing radiated sound power with small patches of constrained layer damping material is proved. Small patches of constrained layer damping material are placed on the structure to effectively ...
Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson
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 ...
Ultrasonic Nondestructive Evaluation Techniques And The Effects Of Fiber Architecture On Mechanical Performance In MultiDirectionally Reinforced Textile Composites , Richard Douglas Hale
Ultrasonic Nondestructive Evaluation Techniques And The Effects Of Fiber Architecture On Mechanical Performance In MultiDirectionally Reinforced Textile Composites , Richard Douglas Hale
Retrospective Theses and Dissertations
Constant load stress rupture tests were performed on alloy 908. The test matrix used varied oxygen concentration, applied load, temperature, and percent cold work. The effect of modifying surface residual stresses on intergranular oxidation and cracking was examined using constant strain Cring tests;The mechanism for high temperature intergranular fracture in alloy 908 is stress assisted intergranular oxidation cracking. A direct correlation between percent intergranular fracture and oxygen concentration was observed. This result was comparable to the oxidation assisted, intergranular fracture behavior of alloy 718. Internal oxidation, for temperatures at or near 650∘ C and under an applied tensile stress ...