At micrometer length scales of material removal, size effect is observed in mechanical micro-cutting where the energy per unit volume i.e. specific cutting energy increases nonlinearly as the uncut chip thickness is reduced from several hundred microns to a few microns (or less). There is no consensus in the literature on the cutting mechanism that causes this size effect. Noticeable discrepancy is also observed in the surface roughness produced at small feeds in micro-turning between the theoretical and the measured roughness. To date, there has been little effort made to develop a detailed process model for micro-cutting to accurately predict the size effect in specific cutting energy, and to develop a fundamental understanding of surface generation at the low feeds typical of micro-cutting processes. The main objective of this thesis is therefore to develop a predictive process model of micro-cutting of ductile metals that is capable of accurately predicting the size effect in specific cutting energy based on strain gradient based material strengthening considerations. In addition, this thesis attempts to explain the discrepancy between the theoretical and measured surface roughness at small feeds in micro-turning via a model that accounts for the size effect due to material strengthening. A coupled thermo-mechanical finite element model formulation incorporating strain gradient plasticity is developed to simulate orthogonal micro-cutting process. The thermo-mechanical model is experimentally validated in orthogonal micro-cutting of a strain rate insensitive aluminum alloy Al5083-H116. The model is then used to analyze the contributions of two major material strengthening factors to the size effect in specific cutting energy: strain gradient and temperature. The effects of cutting edge radius on the specific cutting energy and its role relative to the material length scale arising from strain gradient plasticity are also examined. A surface roughness model for micro-turning that incorporates the effects of kinematic roughness, cutting edge roughness and surface roughening due to plastic side flow is developed and shown to explain the observed discrepancy between the theoretical and measured surface roughness in micro-cutting. In addition, the model is found to accurately capture the increase in surface roughness at very low feeds.

The effect of silicon doping on the strain in c-plane InN films grown on c-plane GaN by plasma-assisted molecular beam epitaxy is investigated. Strain is measured by x-ray reciprocal space mapping and Raman spectroscopy. The silicon doping concentration of our sample is about 1018 cm-3 by Hall measurement. Relation between the strain and the silicon concentration is obtained. To understand the increase in tensile stress caused by Si doping is discussed in terms of a crystallite coalescence model.

This work investigates the influence of gate-induced floating body effect (GIFBE) on negative bias temperature instability (NBTI) in partial depleted silicon-on-insulator p-type metal-oxide-semiconductor field effect transistors (PD-SOI p-MOSFETs). The results indicate GIFBE causes a reduction in the electrical oxide field, leading to an underestimate of NBTI degradation. This can be attributed to the electrons tunneling from the process-induced partial n+ poly gate, and at higher voltages is dominated by the proposed anode electron injection (AEI) model. Moreover, when introducing the mechanical strain to PD-SOI p-MOSFETs result in decreasing the NBTI degradation for BC and FB devices, because increase of effective mass of hole and barrier height to decrease the probability of reaction of NBTI. The degradation of NBTI on FB device less than BC device because of strain-induced band gap narrowing to substrate and p+ poly gate, resulting in the rising of rate of impact ionization in AEI model to increase the accumulation of electrons on body. After that, giving the drain voltage in NBTI stress, the threshold voltage, Vth, shift decreases as drain voltage (VD) rising within the stress condition of VD= -1V. This phenomenon can be attributed to the shorter effective reaction time of hole and Si-H bonds after applying drain voltage during NBTI stress. However, beyond the condition at VD= -1V, the Vth shift rises as the drain voltage increasing. This behavior is resulted from the self-heating effect induced by the higher stress VD to increase the degradation of NBTI.

In this study, ultrafine-grained commercial purity AA1050 aluminum was produced by equal channel angular extrusion (ECAE).Annealing at 250¢J was able to give a grain size of 0.59£gm. Specimens were compressed along different ECAE axis under a strain rate of 7.1¡Ñ10-4 s-1at room temperature. Compression tests were also performed under 5¡Ñ10-5 s-1, 7.1¡Ñ10-4 s-1 ,and 10-1 s-1 strain rates at 100¢J,150¢J ,and 175¢J. Surface morphology of specimens was observed by optical and scanning electron microscopes to study the generation of shear bands. Texture within shear bands was analyzed by electron backscattered diffraction (EBSD). The present research found that, different compression direction has little effect on the generation of shear bands. Increasing compression temperature and decreasing strain rates have the effect of decreasing the degree of strain localization of shear bands. Shear band deformation is compatible with the uniform deformation occurred outside shear bands. Texture change within shear bands is rotated about an axis perpendicular to the specimen surface, and strengthens the texture component.

When an aluminum alloy plate after rolling, non-uniform residual stress distributions existed inside the plate and defects, such as edge wave, middle wave, of the plate will be induced. Usually, a levelling process will be adopted to modify the plate flatness. By numerically simulating the tension levelling process, the purpose of this thesis is to understand the final dimensions and the residual stress distribution of the aluminum plate subjected to the tension levelling process. This study used the finite element method as the basic theory of the numerical simulation. A 3-D model of a cold-rolled plate with a side wave, subjected to tension levelling process was constructed. Then, the effects of the variations of the tensile ratio and residual stress distribution after rolled on the residual stress distribution after levelling and the improvement of flatness were studied. The simulation results showed that in the wave region, the tension levelling process could eliminate more than 90% of the residual stress, in the flat region was up to 80%.Also, after leveling, the residual stress distribution in the flat region was more uniform than the wave region. After-rolled residual stresses at the wave region affected the final peak position of the wave and the stress eliminated ratio of the wave region, but showed no significant effect on the final plate width and the residual strains. After-rolled residual stresses at the flat region affected the stress elimination ratio of the flat region only. The tensile ratio would affect the plate flatness, the plate width, stress elimination ratio, and the maximum residual stress. The higher of the tensile ratio, the more flatness of the plate would be obtained, but the higher residual strain would be induced and caused the lesser range of available plate.

Disuse of weight bearing bones has been shown to cause bone loss. This poses a health concern for people exposed to microgravity, such as astronauts. Animal studies are used to study factors related to bone loss and countermeasures to prevent bone loss. This study used a hindlimb unloaded (HU) rat model to simulate microgravity and a muscle stimulation countermeasure to simulate resistive exercise. Uniaxial strain gages were implanted on the antero-medial aspect of the proximal tibia to measure the mechanical strain during a typical exercise session. In a separate but parallel study, the exercise was shown to be an effective countermeasure to disuse related bone loss. The current study sought to understand the loading of the bone during the exercise. To determine if the strain response changes during a protocol using this countermeasure, strains were measured on a group of weight bearing animals and a group that were hind limb unloaded and received the countermeasure for 21 days. Strain magnitudes and rates were considered and related to torques at the ankle joint. No significant differences in strain magnitudes were noted between the baseline control group and the hindlimb unloaded group that received the countermeasure. The two kinds of contractions used in an exercise session are isometric and eccentric. The isometric contractions are used to adjust the stimulation equipment for the eccentric contractions, which constitute the exercise. Peak strain levels during the isometric contractions ranged from 900 to 2200 microstrain while the eccentric were 38% lower and ranged from 600 to 1400. Eccentric strain rates were 62% lower than the isometric contractions strain rates. These results indicate that the strain environment during the isometric contractions may be causing more of the osteogenic response than the eccentric contractions, which have previously been thought to be the primary part of the countermeasure.

Mounting evidence suggests that the normal biomechanical state of arteries may include a nearly equibiaxial intramural stress, and that arteries tend to undergo rapid and dramatic remodeling when perturbed from this normal state. Technical developments in the early 1980s and late 1990s enabled in vitro and ex vivo studies, respectively, of isolated perfused microvessels, and it is clear that they share many similarities in behavior with arteries. To date, however, there has been no systematic study of the effects of biaxial loading on the biomechanical behavior of arterioles. In this project, we describe a modification to a prior in vitro arteriole test system that allowed us to investigate the role of altered axial stretch on the passive, myogenic, and fully contracted biaxial behavior of isolated rat cremaster arterioles. We show that axial stretches from 85% to 110% of normal values induce modest changes in the measured circumferential and axial stress-stretch behavior and similarly in traditional measures of distensibility and myogenic index. Nevertheless, altered axial stretch has a dramatic affect on the biaxial state of stress and it appears that near equibiaxial stress occur at axial stretches larger than those used previously. Whereas this finding will not affect prior estimates of material and functional behavior, it may have important implications for the design of long-term ex vivo and in vivo studies wherein vessel growth and remodeling are critical.

This thesis research synthesizes a new class of composite materials and investigates their properties, performance, and potential applications. The new materials that are multi-phase and multifunctional are considered for use in car cooling systems, internal combustion engine waste-heat-power generators, and engine crack healing which are major problems plaguing the auto industry. This research uses primarily experimental approaches to study the magnetocaloric compound, Ge5Si2Ge2 (GSG), that has large strain effects. Such a material was formed into a composite using Al as a substrate. The newly developed composite, GSG-Al, is the first material of its kind that possesses self-healing effects in cracks. X-ray diffraction was used to determine the crystal structures that existed within the material. It is found that the sintering process used to create the composite caused the formation of GdAlGe that is a magnetic compound with a high Curie temperature. The GSG-Al has a wide variety of crystal structures, ranging from face centered cubic for aluminum phases to monoclinic and orthorhombic phases for GSG. The discovery of GdAlGe confirmed that alpha-ThSi-type tetragonal and YAlGe-type orthorhombic crystal structures existed. Transmission electron microscopy (TEM) was used to analyze the wear debris collected during tribo-testing. The debris were also analyzed using energy-dispersive X-ray spectroscopy (EDS) for chemical analysis. The GSG-Al was put through tribological studies at several different temperatures to determine the thermal effects on the composite. The GSG-Al, although found to be ductile, showed high resistance to wear when compared to a common aluminum alloy, Al 6061-T651. The wear rate decreased with increasing temperature when the temperature was increased from the room temperature to 150 degrees C. Results showed that with GSG, the composite did not show cracking common in Al alloys. This was due to the unique thermal expansion properties of the GSG-Al. The phase transformation induced a significant volume expansion in the material and thus a giant strain effect. This research opens new approaches in energy conversion and improving efficiency of automobile engines. The composite developed here is important for future scientific investigation in the area of multifunctional materials as well as materials that exhibit self-healing tendencies.

New measuring methods continue to be developed in the field of wind anemometry for various environments subject to low-speed and high-speed flows, turbulent-present flows, and ideal and non-ideal flows. As a result, anemometry has taken different avenues for these environments from the traditional cup model to sonar, hot-wire, and recent developments with sphere anemometers. Several measurement methods have modeled the air drag force as a quadratic function of the corresponding wind speed. Furthermore, by incorporating non-drag fluid forces in addition to the main drag force, a dynamic set of equations of motion for the deflection and strain of a spherical anemometer's beam can be derived. By utilizing the equations of motion to develop a direct relationship to a measurable parameter, such as strain, an approximation for wind speed based on a measurement is available. These ODE's for the strain model can then be used to relate directly the fluid speed (wind) to the strain along the beam’s length. The spherical anemometer introduced by the German researcher Holling presents the opportunity to incorporate the theoretical cantilevered Euler-Bernoulli beam with a spherical mass tip to develop a deflection and wind relationship driven by cross-area of the spherical mass and constriction of the shaft or the beam's bending properties. The application of Hamilton's principle and separation of variables to the Lagrangian Mechanics of an Euler-Bernoulli beam results in the equations of motion for the deflection of the beam as a second order partial differential equation (PDE). The boundary conditions of our beam's motion are influenced by the applied fluid forces of a relative drag force and the added mass and buoyancy of the sphere. Strain gauges will provide measurements in a practical but non-intrusive method and thus the concept of a measuring strain gauge is simulated. Young's Modulus creates a relationship between deflection and strain of an Euler-Bernoulli system and thus a strain and wind relation can be modeled as an ODE. This theoretical sphere anemometer's second order ODE allows for analysis of the linear and non-linear accuracies of the motion of this dynamic system at conventional high speed conditions.

In our research, aluminum (1050) was deformed by plane strain compression (PSC) up to 65% reduction. The total deformation conditions include four temperatures (from 150oC to 300oC) and two strain rates (5¡Ñ10-2s-1 and 5¡Ñ10-4s-1). After the deformation, the specimens were examined by TEM for observing the morphology of the microstructures and measuring various parameters, which includes the sizes and aspect ratios of dislocation cells, as well as the distribution of misorientation angles for dislocation walls. At last, the proportions of GNBs and IDBs were tried to be determined.