Material failures in heat exchangers are often closely tied to events associated with the conditions of service and operating parameters. These events can generally be attributed to adverse load application and higher than optimum operating temperatures that could lead to changes in the microstructure of the materials and fatigue failure of the component. However, fatigue failure in heat exchangers is usually associated with the presence of a biaxial stress condition. Two nonparallel forces create a two-dimensional stress field at the free surface of the structural element where the process and mechanism of fatigue failure normally initiate. An experimental investigation was conduct6d to evaluate the biaxial fatigue behavior of commercially pure titanium Ti-50A (Grade 2) and low-alloy titanium Ti-Code 12 (Grade 12) heat exchanger materials. The biaxial state of stress was composed of an axial stress and a superimposed torsional stress, applied in a thin-wall tubular specimen machined from titanium tubing. Torsional stress was applied independently using a torsion machine and a torque fixer assembly devised as part of this study. After applying the desired torsion, the torsionally stressed specimen was mounted on a closed-loop electrohydraulic machine for the application of axial cyclic loading. A minimum of four tests were conducted for each of three alternating stress levels at both high and low torsional stresses. The biaxial fatigue test under load control condition was done under fully reversed cycles equivalent to a biaxiality ratio of -1. These test parameters were determined from an analytical formulation based on Mohr's circle. The results are presented in terms of the various measured or calculated quantities versus number of cycles to fracture. Biaxial fatigue curves were drawn through the experimental points corresponding to Weibull's mean life criterion. The four data points exhibit scatter that appears to be related to the applied stress amplitude. It was also found that a correlation exists between the magnitude of applied cyclic biaxial stress and fatigue life to failure. In addition, the results have been discussed taking existing failure criteria into account. / Graduation date: 1985

Graduation date: 1996

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 126-127).

Thesis (Ph. D.)--Oregon Graduate Center, 1982.

Graduation date: 1993

Ti-6Al-2Sn-4Zr-2Mo-0.1Si specimens were shaped by repeated cycles of heating (to 954 °C) and hammer or press forging followed by a solution anneal that varied from 968 to 998 °C. The coupons were originally extracted from billets forged below the beta trans us ( 1009 °C) and slow cooled to ambient temperature. Macroscopic and microstructural banding is observed in some forged and solution annealed coupons, that consists of regions of elongated primary alpha. More significant banding is observed subsequent to annealing at lower temperatures (968 °C), whereas much less microstructural banding is present after annealing at higher temperatures (998 °C). About the same level of banding is observed in hammer forged and press forged coupons. The observation of these bands is significant since they may lead to inhomogeneous mechanical properties. Specifically, at least some types of banding are reported to affect the high temperature creep properties of this alloy. The origin of these bands was therefore researched. Classically, banding in Ti-6242-0.1Si has been regarded as a result of adiabatic shear, chill zone formation or compositional inhomogeneity. High and low magnification metallography, electron microprobe analysis and microhardness tests were performed on forged and annealed specimens in this investigation. The composition inside the bands appears identical to that outside of the bands. The fraction of primary alpha is also found to be identical. The bands have higher microhardness. These results suggest that the bands are not related to composition gradients. The bands also do not appear to be a result of adiabatic shear or other localized deformation. The bands of this study appear to originate from the elongated primary alpha microstructure of the forged billet (from which test coupons were extracted). The deformation of the extracted coupon may be neither fully homogeneous nor sufficiently substantial and the coupon is only partly statically restored after a solution anneal. Areas not fully restored appear as "bands" with elongated primary alpha, that are remnant of the starting billet microstructure. Therefore, a source of banding in Ti-6242-0.1Si alloy, additional to the classic sources, is evident. This type of banding is likely removed by relatively high solution treatment temperatures and perhaps greater plastic deformation during forging. / Graduation date: 1992

Anodized aluminium oxide may be chemically treated to yield a uniform self-organized distribution of pores with a specific pore diameter. The thickness of in-house anodized alumina and its pore size can be modified by changing the electrolyte, the temperature of the electrolyte, the time of anodization and the potential over the anodized plates.  In this thesis, a method for anodized aluminium oxide (AAO) was optimized for creating custom-made porous alumina membranes and coating them with TiO2 and polyethylene glycol (PEG). The purpose of finding a method to create porous alumina oxide with specific pore diameters was to eventually use these membranes for use in contact with human living tissue, allowing wanted nutrients and fluid to pass in and out.      SEM images showed that a reproducible method has been established for the membrane production, where the pore diameter is ~ 300nm and the thickness of the oxide is approximately 100µm. The SEM images also showed that the pores are stable and uniform over the entire aluminum plate where they are initially produced.      As a test for biocompatibility, the membranes were implanted into the hipbone of pigs. The histology test showed fibrosis around the location where the membranes were placed. An observation during the extraction was swollenness in the surrounding tissue, which indicates inflammation around the implant. In this respect, the membranes cannot be used for the purpose intended.

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In this study, we deposit titanium dioxide (TiO2) as gate oxide on thin film transistor (TFT) by liquid phase deposition (LPD) on the amorphous silicon (a-Si) and polycrystalline silicon (poly-Si) substrates. After depositing LPD-TiO2 film, we use to fabricate TFT device. In our experiment, we do some measurement about physical, chemical and electrical properties for LPD-TiO2 film and discussed with them. the TiO2 film morphology and thickness was characterized by scanning electron microscopy ( SEM ), structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and chemical properties was characterized by X-ray photoelectron spectroscopy (XPS),and electrical properties was characterized by leakage current: current-voltage (B1500A) and dielectric constant: capacitance-voltage (E4280A). In TFT device study, we complete measurement about physical, chemical and electrical properties for LPD-TiO2 films. The LPD-TiO2 film was used as TFT device, We complete mask manufacture, mesa structure definition, deposit TiO2 thin film, gate definition, photolithography and ICP- etching. Ion implantation is carrying out.