Although a considerable amount of research exists on geometrical aspects of 5-axis flank milling, the dynamics of this efficient milling operation have not yet been given proper attention. In particular, investigating machining chatter in 5-axis flank milling remains as an open problem in the literature. The axial depth of cut in this operation is typically quite large, which makes it prone to machining chatter. In this thesis, chatter in 5-axis flank milling is studied by developing analytical methods of examining vibration stability, generating numerical simulations of the process, and conducting experimental investigations. The typical application of 5-axis milling includes the machining of thermal resistant steel alloys at low cutting speeds, where the process damping dominates the machining vibration. The results of experimental study in this thesis showed that the effect of process damping is even stronger in flank milling due to the long axial engagement. Accordingly, the first part of the thesis is devoted to studying process damping, and in the second part, the modeling of chatter in flank milling is presented. Linear and nonlinear models have been reported in the literature that account for process damping. Although linear models are easier to implement in predicting stability limits, they could lead to misinterpretation of the actual status of the cut. On the other hand, nonlinear damping models are difficult to implement for stability estimation analytically, yet they allow the prediction of “finite amplitude stability” from time domain simulations. This phenomenon of “finite amplitude stability” has been demonstrated in the literature using numerical simulations. In this thesis, that phenomenon is investigated experimentally. The experimental work focuses on uninterrupted cutting, in particular plunge turning, to avoid unduly complications associated with transient vibration. The experiments confirm that, because of the nonlinearity of the process damping, the transition from fully stable to fully unstable cutting occurs gradually over a range of width of cut. The experimental investigation is followed by developing a new formulation for process damping based on the indentation force model. Then, the presented formulation is used to compute the stability lobes in plunge turning, taking into account the effect of nonlinear process damping. The developed lobes could be established for different amplitudes of vibration. This is a departure from the traditional notion that the stability lobes represent a single boundary between fully stable and fully unstable cutting conditions. Moreover, the process damping model is integrated into the Multi-Frequency Solution and the Semi Discretization Method to establish the stability lobes in milling. The basic formulations are presented along with comparisons between the two approaches, using examples from the literature. A non-shallow cut is employed in the comparisons. Assessing the performance of the two methods is conducted using time domain simulations. It is shown that the Semi Discretization Method provides accurate results over the whole tested range of cutting speed, whereas higher harmonics are required to achieve the same accuracy when applying the Multi Frequency Solution at low speeds. Semi Discretization method is modified further to calculate the stability lobes in flank milling with tools with helical teeth. In addition to the tool helix angle and long axial immersion, the effect of instantaneous chip thickness on the cutting force coefficients is considered in the modified formulation of Semi Discretization as well. Considering the effect of chip thickness variation on the cutting force coefficients is even more important in the modeling of 5-axis flank milling, where the feedrate, and consequently the chip thickness, varies at each cutter location. It also varies along the tool axis due to the additional rotary and tilt axis. In addition to the feedrate, the tool and workpiece engagement geometry varies at each cutter location as well. The actual feedrate at each cutter location is calculated by the dynamic processing of the toolpath. The tool and workpiece engagement geometry is calculated analytically using the parametric formulation of grazing surface at the previous and current passes. After calculating the instantaneous chip thickness and tool/workpiece engagement geometry, they are integrated into the Semi Discretization Method in 5-axis flank milling to examine the stability of vibration at each cutter location. While the presented chatter analysis results in establishing stability lobes in 3-axis flank milling, it results in developing a novel approach in presenting the stability of the cut in 5-axis flank milling. The new approach, namely “stability maps”, determines the unstable cutter locations of the toolpath at each spindle speed. The accuracy of established 3-axis flank milling stability lobes and 5-axis stability maps is verified by conducting a set of cutting experiments and numerical simulations.

Designing horizontal-axis wind turbine (HAWT) blades to achieve satisfactory levels of performance starts with knowledge of the aerodynamic forces acting on the blades. In this thesis, HAWT blade design is studied from the aspect of aerodynamic view and the basic principles of the aerodynamic behaviors of HAWTs are investigated. Blade-element momentum theory (BEM) known as also strip theory, which is the current mainstay of aerodynamic design and analysis of HAWT blades, is used for HAWT blade design in this thesis. Firstly, blade design procedure for an optimum rotor according to BEM theory is performed. Then designed blade shape is modified such that modified blade will be lightly loaded regarding the highly loaded of the designed blade and power prediction of modified blade is analyzed. When the designed blade shape is modified, it is seen that the power extracted from the wind is reduced about 10% and the length of modified blade is increased about 5% for the same required power. BLADESIGN which is a user-interface computer program for HAWT blade design is written. It gives blade geometry parameters (chord-length and twist distributions) and design conditions (design tip-speed ratio, design power coefficient and rotor diameter) for the following inputs / power required from a turbine, number of blades, design wind velocity and blade profile type (airfoil type). The program can be used by anyone who may not be intimately concerned with the concepts of blade design procedure and the results taken from the program can be used for further studies.

No description available.

The goal of this academic project was to study the effects of different variables on the damage progression around a central hole in carbon fiber composite coupon specimens. The tracked variables included the type of layup, stress ratio, stress levels, and damage mechanisms observed in each specimen. In-situ x-ray of the individual laminates recorded the extent of damage, mostly longitudinal splitting, as a function of the cycle count. The following lay-ups were included in the experiment: [45/90/-45/02/45/02/-45/0]s, [±5/65/(±5)2/-65/±5]s, and [±5/65/(±5)2/-65/5/65]s. More specifically, the objective of this study was to determine the stress levels at which detectable damage started to develop. The researchers chose to apply 50,000 cycles at each stress level and once damage was detected, the stress level was typically raised by 34.5 MPa (5 KSI), and then cycled another 50,000 cycles until damage exceeding 1.27 cm (0.50") in length was observed. Once the damage exceeded 1.27 cm (0.50"), cycling was continued to 1,000,000 cycles. Upon completion of the fatigue cycling, each specimen's residual strength was determined. The damage length versus stress level was plotted as a way to compare damage onset stresses and growth as a function of lay-up and stress ratio.

Includes bibliographical references (leaves 228-257). / xxii, 257 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Aims to determine the impact of maternal undernutrition during late gestation and during the periconceptional and gestational periods on fetal growth, fetal blood pressure and the fetal hypothalamo-pituitary adrenal axis in the sheep. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physiology, 2001

Maintenance of normal health requires an intact stress system capable of mounting the metabolic, autonomic, behavioural and motor responses required for coping with or avoiding physiological and pathological challenges. The neuroendocrine component of this response principally involves the hypothalamic-pituitary-adrenal (HPA) and sympatho-adrenomedullary (SAM) axes. Impaired regulation of these axes has been implicated in the pathogenesis and expression of numerous disease states, however, it has proved very difficult to reproducibly activate the HPA and SAM axes and no single test exists that can reliably and safely be used to study these systems in man. Carbon dioxide (CO2) is the principal regulator of respiration, acid-base balance and behavioural-state arousal in humans. Paradigms of CO2 inhalation have been used in psychiatric research to investigate panic and anxiety disorders, but evaluation of other components of the stress response to CO2 has not previously been performed. I hypothesised that a single breath of 35% CO2 would be a simple and reliable tool for the evaluation of the stress response in humans. A single breath of four doses of CO2 (5%, 25%, 35% and 50%) was administered to 9 healthy volunteers in a randomised, single blind fashion. Subjective symptoms of anxiety increased in a dose-dependent manner. Inhalation of a single breath of 35% CO2 stimulated significant ACTH (p = 0.006), noradrenaline (p < 0.0001), cortisol (p = 0.02) and prolactin (p = 0.002) release. It also provoked an acute pressor response and an associated bradycardia (p < 0.0001 for both). No significant habituation of psychological, HPA or cardiovascular responses was seen when this dose was repeated after one week (n = 10) or 6 months (n = 5). It was apparent that a single breath of 35% CO2 reliably and safely produced SAM and HPA axis activation and further studies were then undertaken to assess the mechanism by which the observed responses occurred and its potential clinical implications. Administration of naltrexone (an opiate antagonist) to 10 normal volunteers disinhibited the HPA axis (p < 0.0004), whilst administration of metyrapone (a cortisol synthesis inhibitor) significantly reduced baseline cortisol (p < 0.03) levels. However, this alteration in HPA axis activity had no effect on either cardiovascular or psychological responses. Further, in a study of 8 breastfeeding mothers (a state associated with physiological suppression of the HPA axis) suckling significantly reduced plasma cortisol levels compared with control (p = 0.002) and bottle-feeders (p = 0.003). Despite this cortisol, systolic blood pressure (SBP), heart rate and psychological responses to 35% CO2 were not affected

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 114-134).

Thesis (Ph. D.)--Michigan State University. Dept. of Zoology & Environmental Toxicology, 2008. / Title from PDF t.p. (viewed on Mar. 30, 2009) Includes bibliographical references. Also issued in print.

Thesis (Ph.D.) -- University of Adelaide, School of Paediatrics and Reproductive Health, Discipline of Obstetrics and Gynaecology, 2008. / "March 2008" Bibliography: leaves xxvi-xliii. Also available in print form.

Thesis (Ph. D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Vita. "December 2006" Includes bibliographical references.