This work investigated cathodic disbonding of an unpigmented phenalkamine-cured epoxy coating on mild steel, EC, exposed to 3.5 wt.% NaCl solution. Scanning Acoustic Microscopy (SAM), Scanning Kelvin Probe (SKP), Electrochemical Impedance Spectroscopy (EIS) and optical microscopy have been combined to conduct this study. Several factors affecting the cathodic disbonding process: Film thickness, Cation mobility, Electrolyte concentration, Temperature, Paint composition, Polarisation and Open circuit potential, have been investigated. SAM results show that the disbonding of EC with a linear scribe spreads outwards from the defect with blisters forming at the anodes (as shown in SKP potential maps) within the disbond. The disbonded region does not correspond to complete adhesion loss as verified by peel-testing. Semi-immersion tests show that disbonding under full- and semi-immersion conditions have similar behaviours and both follow parabolic kinetics indicating the disbonding is likely to be controlled by a transport process along the coating/metal interface. An intact epoxy coated mild steel panel coupled with bare mild steel shows that the cathodic reaction beneath the coating obeys Tafel law. A mathematical model simulating cathodic disbonding which produces realistic potential files and shows the oxygen reduction is mostly located near the disbond mouth has been developed.

Thesis (Ph. D.)--University of Wyoming, 2007. / Title from PDF title page (viewed on Nov. 7, 2008). Includes bibliographical references (p. 86-88).

Excerpt: A 57-year-old horticulturist is working on a ladder leaned up against a tree trunk when the ladder slips, causing her to fall six feet onto concrete. Her right foot and ankle sustain the force of the fall; she is in excruciating pain and unable to bear weight on the foot. She is immediately transported to a local emergency department for evaluation.

No description available.

Wasserstoff-induzierte Schäden sind ein verbreitetes Problem in verschiedenen Anwendungen von Metallen. In dieser Arbeit wurde Wasserstoff-induzierte Rissbildung in Eisen untersucht. Die Proben wurden elektrochemisch mit Wasserstoff beladen. Diese Beladung führt zu Rissen in den Eisenproben und Blistern auf deren Oberfläche, wenn Risse oberflächennah lokalisiert sind. Als Triebkraft der Rissbildung wurde der hohe Wasserstoffdruck in den Rissen gefolgert. Dieser Druck wurde durch eine Kombination aus Ausgasexperimenten und Dichtemessungen bestimmt. Die Mikrostruktur, die Risse und Blister umgibt, wurde mit Elektronenmikroskopie untersucht. Dafür wurden Rissflächen durch Zugversuche freigelegt. Oxidische Einschlüsse konnten als Ausgangspunkt für Risse ausgemacht werden. Mit Transmissionselektronenmikroskopie wurden duktile Merkmale in der Nähe von Rissen sichtbar. Ein Mechanismus für die Riss- und Blisterbildung wurde vorgeschlagen.

Thesis (Ph. D.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (M.S.)--Western Washington University, 2010. / Includes bibliographical references (leaves 59-61). Also issued online.

With the development of hydrogen fuel cell technology continuing to advance, rapid characterization of membranes is increasingly important for design purposes. Pressurized blister testing has been suggested as an accelerated characterization alternative to traditional relative humidity (RH) cycling tests, and is the focus of this project. Prior efforts to determine the stress state present in the pressurized membrane blister test, however, have required constitutive properties of the membrane (Young's modulus and Poisson's ratio), along with Hencky's classic model for circular membrane stresses. Herein we describe an analysis method and computer vision imaging technique that are capable of determining the stress state in a pressurized circular membrane based solely on simple equilibrium equations and geometric considerations. This analysis method is applied to an image of the blister during testing, and the only additional required data is the pressure at the time the image was taken. By pressurizing circular blisters, an equi-biaxial, mechanical stress state is induced, simulating membrane stresses experienced during fuel cell operation as humidity levels fluctuate. The analysis leverages membrane theory and the axisymmetric geometry to determine the stress state from a profile image of the inflated blister. As a check for the method, an elastomer with known constitutive properties was analyzed using both the previous Hencky's solution method, as well as the new computer vision imaging method. The comparison of stress calculation results show that the two methods agree within 5 percent. A primary mechanism of membrane failure through mechanical stressors is the growth of local defects (usually chemically induced) due to the cyclic equi-biaxial stress state. In order to better understand and characterize the effect of disparate initial defects on CCM, two primary methods to defect membranes were introduced. The first was a compression against sandpaper method meant to simulate GDL compression, and the second was a targeted method using a hypodermic needle to initiate a defect at a central location on the membrane prior to pressurization. Observing the pressure decay in these defected blisters as compared to undefected tests showed that, while undefected samples did not experience pressure decay until failure, defected samples began showing signs of leaking through pressurization cycle profiles and steady state pressures achieved. Pressure data showed that samples tended to lose pressure more quickly with increasing initial defect severity. Undefected samples exhibited no pressure loss until the moment of failure, which was often catastrophic and instantaneous. Sandpaper defected samples exhibited a slow decay in cycle steady state pressure throughout tests, with no increase in cycle pressurization time. Needle samples showed a slow decay in cycle steady state pressure as well as an increase in time for the cycles to reach steady state. The needle defects were the most locally severe and thus the pressure decay indicators were most significant out of all the samples tested. The blister test method rapidly cycles mechanical stresses in a CCM, and elucidates signs of leaking that correlate to flaw development in recorded pressure data. With further development, it might serve as a robust method to quickly test flaw growth rate and development in CCM samples. / Master of Science / Fuel cells are a technology used to supply energy to many sources. In fuel cells, the membrane can limit the lifetime of the entire cell, as the membrane separates the reactant gases allowing the generation of power. If that membrane develops holes or cracks, the fuel cell won't be able to generate as much power, and cell replacement is costly in time and money. Thus, it is important to develop robust membranes to avoid loss in efficiency as much as possible. The research here focuses on rapidly testing how long these membranes last, so that membrane performance can be appropriately ranked, leading to faster technological improvements. We developed two main methods for use in combination with existing blister pressurization equipment; an image-based method that can determine the forces in the membrane, and a novel method to defect membranes before testing. The first method uses a code-based approach to process the image of the blister profile and return stresses. The second method defects the blister before testing so the growth of the defect can be observed over time. Leaking characteristics in the blister were identified in several tests, and the severity of the defects was determined from this information. Thus, the development of the defects can be monitored through these leak characteristics.

The ability to accurately measure surface and interfacial energies affects our understanding of friction, wear, bonding and adhesion. Although there are accurate ways to measure the surface energies of liquids, the surface energies of solids have been harder to characterize. In order to broaden the knowledge of adhesion of solids, a modification to the constrained blister test is proposed. Most of the previous work on constrained blisters has examined the debonding of the blister from the surface underneath as pressure is applied from below. In this thesis, the contact of the constrained blister with the flat surface above it is considered. In addition, the blister is given specified boundary conditions at its outer radius, which has a fixed value. Three models of the blister behavior are considered: linear plate, nonlinear plate, and membrane. The contact of the blister with the substrate above it is modeled with no adhesion, the JKR-type of adhesion, and the DMT-type of adhesion. Several substrate heights are considered, along with several values for the work of adhesion in the JKR analysis, and several combinations of force magnitude and gap size in the DMT analysis. The effect of adhesion on the contact radius is investigated. Sometimes the contact radius changes discontinuously as the pressure is increased or decreased. Results from the three models of blister behavior and the different models of adhesion are compared. / Master of Science

Bridge decks are commonly subjected to harsh environmental conditions that often lead to serious corrosion problems triggered by blisters under the hot mix asphalt bridge deck surfacing and secretly evolving during weather exposure until damage is often detected too late. Blisters may form under both the waterproofing dense mastic asphalt layer or under the waterproofing membrane which is often applied as additional water protection under the mastic asphalt (MA). One of the main technical issues is the formation of blisters under the membrane and asphalt-covered concrete structures caused by a complex mechanism governed by bottom-up pressure and loss of adhesion. A linear viscoelastic finite-element model was developed to simulate time-dependent blister growth in a dense mastic asphalt layer under uniformly applied pressure with and without temperature and pressure fluctuation. A finite element model was developed using ABAQUS with linear viscoelastic properties and validated with a closed form solution from first-order shear-deformation theory for thick plates. In addition, the blister test was conducted on different samples of MA in the laboratory and digital image correlation measurement technique was used to capture the three-dimensional vertical deflection of the MA over time. It was found that the blister may grow continuously under repeated loading conditions over subsequent days. With respect to blistering under waterproofing membranes, mechanical elastic modeling and experimental investigations were performed for three different types of membranes under in-plane stress state. The orthotropic mechanical behavior of a polymer modified bitumen membrane (PBM) was determined from biaxial test data. Finally, blister tests by applying controlled pressure between orthotropic PBMs and concrete plates were performed for studying the elliptical adhesive blister propagation using digital 3D image correlation. The energy calculated from elliptical blister propagation was found comparable to the adhesive fracture energy from standard peeling tests for similar types of PBMs. This indicates that the peeling test assists to evaluate and rank the adhesive properties of different types of membranes with respect to blister formation at room temperature without conducting time consuming and complicated pressurized blister propagation tests using digital 3D image correlation. / <p>QC 20130625</p>