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Asphalt’s fatigue and modulus characteristics play an important role in pavement design. Ultimately they govern the required thickness of asphalt to structurally support heavy vehicles. The thickness of the asphalt layer is a major contributor to the cost of construction. In New Zealand, the design of structural asphalt layers has been a problem for some time and gives rise to two areas of concern. First, the present fatigue failure criterion, the Shell fatigue transfer function, which has been adopted from overseas, not only underestimates the fatigue life of the country’s asphalts, but does not accurately characterise the fatigue behaviour of our local asphalt mixes. Consequently, asphalt thicknesses are overdesigned. Second, asphalt’s fatigue behaviour is influenced by numerous factors and therefore can be difficult to characterise. The primary objective of this thesis is to develop fatigue and modulus models, by carrying out fatigue and modulus tests, to characterise the behaviour of two typical New Zealand structural asphalts. Both resilient and stiffness moduli tests were performed at a range of temperatures and loading rates developing moduli master curves, which predict the asphalt’s modulus for any pavement temperature and vehicle speed. A general full factorial experiment was carried out utilising the four-point flexural beam fatigue test. Tests were carried out at different strain levels, temperatures, and loading rates. An analysis of variance showed that the impacts of strain amplitude, temperature, binder type, the interaction of strain amplitude and temperature, and the interaction of strain amplitude and binder type have a significant effect on fatigue behaviour. The developed models, which account for temperature effects give the pavement engineer the ability to undergo a more accurate assessment of fatigue damage than at present for different climatic temperatures demonstrated by using an incremental damage analysis approach. The research shows that with such characterisation for the given pavement’s design life, thinner and less expensive roads can be constructed in New Zealand.

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Approved for public release; distribution is unlimited / The US Navy is currently developing a new family of high-strength , low-alloy steels which derive a significant portion of their strength from copper precipitation. These highly weldable steels require little or no preheat. resulting in substantial cost savings. The first of these steels. HSLA-80, has been certified for ship construction, but recent studies have indicated some susceptibility to stress relief cracking in weldments. HSLA-100, a modification of HSLA-80, is now being considered for several higher-strength naval structures. Stress-relief cracking has not been studied previously in this steel and is the subject of investigation in this work. The steel weldments were loaded below their yield strength, heated to temperatures of 550°-650° C, and permitted to stress relieve for one hour. At all temperatures, the steel exhibited susceptibility to stress relief cracking in certain stress ranges. Optical and scanning electron microscopy exhibited intergranular cracking which always traversed the coarse-grained region of the heat-affected zone. Auger and transmission electron microscopy indicated high concentrations of alloying elements at the grain boundaries. Stress-relief cracking was associated with the diffusion of alloying elements to the prior austenite grain boundaries. / http://archive.org/details/stressreliefcrac00mcnu / Captain, Canadian Forces

The invention of electric arc welding revolutionized the steel construction industry, but also brought some problems when the welded region has inferior properties compared to the plate metal. A major cause of brittle failure was identi ed as hydrogen embrittlement of the weld zone, although a comprehensive understanding of this phenomenon is not, even now, available. Hydrogen in solution in the weld zone is found in arc welds, due to the intense conditions in the welding arc. There is invariably a sufficient source in the form of moisture and hydrocarbon residue to give a few parts-per-million (ppm) by mass of hydrogen in the weld pool, which is a sufficient concentration to bring the possibility of hydrogen cold cracking in the completed weld. Hydrogen is significantly mobile in steels at room temperature, which is certainly why a few ppm of hydrogen can concentrate on a microscopic scale and initiate cracks, but also means that on a macroscopic scale there is hydrogen dispersion, which can relieve the cracking risk or place hydrogen in hydrogen cracking susceptible regions. The understanding of solubility and mobility of hydrogen in steels of different compositions and microstructures is therefore paramount. The question investigated in this work is whether the characteristics of the weld hydrogen cracking tendency can be explained by the features of weld hydrogen transport, especially when steel selection is a variable. Plate steel ranging from a 0.22%C pearlitic steel to a 0.05%C thermo-mechanically controlled-rolled and accelerated-cooled (TMCR-AC) high strength low alloy (HSLA) steel with no pearlite, plus a 0.4%C non-plate steel, were included in the experimental program. Welds were made with rutile ux-cored-wire (R-FCW) at two hydrogen levels, together with rutile shielded-metal-arc (R-SMA) welds. In order to investigate the di usion rates, a novel experiment has been devised. The welded plate has been milled away at an angle from the underside of the weld to provide increasing distances between the fusion boundary and the plate under-surface. The formation of hydrogen bubbles in glycerol enabled the measurements of the time dependent diffusion distances. The results clearly show a square root time correlation, as expected from the Fickian mechanism and enabled the calculation of diffusion coefficients for different steels. A nearly four fold difference was found between the steels, with the fastest hydrogen movement in the TMCR-AC steel. To reveal the initial distribution of hydrogen some samples were frozen immediately after welding and machined under liquid nitrogen. This test ruled-out any signi cant hydrogen dispersion during the deposition of the weld and during the cooling down period. The experimental data were interpreted using a new numerical computer model, based on random jumps of hydrogen between equivalent lattice sites. It is shown that this numerical model gives identical results to the analytical Fickian approach, but has the advantage that it can be used for any boundary shape. When this model has been applied to the experimental data, some unexpected features have been found. The amount of hydrogen emerging at surfaces distant to the weld was higher than expected from a concentration-driven mechanism; suggesting that a di erent transport mechanism should be applied. The numerical model has also indicated a discontinuity in the hydrogen concentration at the fusion boundary. It is a consequence of the model that hydrogen solubilities and di usivities are inversely related properties of the metal; a feature which is supported by experimental evidence. The tendency of hydrogen cracking to appear in the weld metal rather than in the heat-a ected-zone (HAZ) can thus be explained by higher di usivity of hydrogen in the plate metal. It appears that there is a relationship between the diffusivity and the microstructure, particularly when the content and form of carbon is considered.

Call number: LD2668 .T4 1986 M34 / Master of Science / Civil Engineering

The objective of this work was to study the effect of supercritical water on coke formed on ZSM-5 during its use as a dodecane cracking catalyst. ZSM-5 coking was quantified at different reaction times, finding that the presence of supercritical water reduced coke formation by an order of magnitude or more. Coked samples were analyzed using several methods, including temperature programmed oxidation (TPO), attenuated total reflectance infrared (ATR-IR) spectroscopy, carbon-13 nuclear magnetic resonance (13C NMR), diffuse reflectance ultraviolet-visible spectroscopy (DR-UV-vis) and UV-Raman. Coked produced in the absence of SCW was formed by polycyclic aromatic hydrocarbons (PAHs) with more than 4 aromatic rings containing alkyl side chains. Coke produced in the presence of SCW was formed by aromatics with 1 to 3 aromatic rings. The characteristics of coke formed in the absence of water on ZSM-5 that had been pretreated in SCW were intermediate to those of coke formed on fresh ZSM-5 in the presence and absence of water, suggesting that the presence of water influences coke properties. It was also verified that SCW can decrease coke formation due to its effect on Bronsted acidity of the catalyst and ability to promote coke gasification. The effect of coke deposits produced in the presence and absence of SCW on the rate of ethanol dehydration, a model reaction studied under diffusion-controlled conditions, indicated that SCD/SWC coke deactivated less the catalyst than SCD coke.

La fissuration à chaud par liquation peut se produire dans la zone affectée thermiquement lors du soudage. Deux facteurs influent ce phénomène : les contraintes thermiques dues au gradient de température et la perte potentielle de ductilité due à la présence d'un film liquide aux joints de grains en fonction de leur composition chimique. Des essais de ductilité à chaud (Gleeble) ont été utilisés pour étudier l'effet combiné de la teneur en bore et du temps de maintien sur la chute de la ductilité dans la plage de température de liquation pour l’acier inoxydable austénitique de type 316L. Il est démontré que les teneurs en bore élevées et les temps de maintien courts favorisent la perte de ductilité dans cette plage de température. En complément la spectrométrie de masse à ionisation secondaire a été utilisée pour tenter de corréler les variations de ductilité à la distribution du bore aux joints de grains. D'autres essais de fissuration à chaud en soudage (Varestraint, PVR) ont été effectués pour confirmer l'influence de la teneur en bore sur la sensibilité à la fissuration de l’acier 316L. Les résultats indiquent que des fissures apparaissent sur toutes les éprouvettes et que le chargement mécanique externe minimal pour créer les fissures de liquation diminue avec la teneur en bore. Plus la teneur en bore est élevée, plus le matériau est donc sensible à la fissuration à chaud par liquation. Un critère de fissuration à chaud par liquation a été déterminé en se basant sur les résultats des essais de ductilité à chaud et la simulation des essais de soudage. / Liquation cracking may occur in the heat-affected zone during welding. Two factors influence this phenomenon: the tensile stresses generated during welding and the potential loss of ductility due to the presence of a liquid film at grain boundaries depending on their chemical composition. Gleeble hot ductility tests have been used to study the combined effect of boron content and holding time on ductility drop in the liquation temperature range of a 316L type austenitic stainless steel. It is shown that high boron contents and short holding times promote the loss of ductility in this temperature range. Secondary ion mass spectrometry has been used inattempt to correlate mechanical results to boron distribution either at grain boundaries or in the bulk. Other hot cracking tests (Varestraint, PVR) have been performed to confirm the influence of boron content on hot cracking sensitivity of AISI 316L stainless steels during welding. Results indicate that cracks appear on all specimens and that the minimum external mechanical loading for liquation cracking decreases with boron content. The higher the boron content is, the more the specimen exhibits tendency to hot cracking. A liquation hot cracking criterion has been determined, based on the results of the hot ductility tests and the simulation of welding tests.

As more services and workflows are moved into computerized systems the number of accounts a person has to be aware of is on steady increase. Today the average user is likely to have more than 25 accounts for different services used on a daily basis that all need authentication. The dominant authentication mechanism used today is still password authentication. In an attempt to satisfy the requirements of different password creation policies and to recall all passwords when needed users tend to rely on different strategies for password creation. These strategies may all seem to provide adequate security, and they may do, but the reality is that they differ tremendously in terms of how time consuming it is to crack passwords generated with the different strategies. By conducting interviews with domain experts different password creation strategies are discussed and pseudo algorithms for cracking passwords are constructed. Based on mutual definitions of the classes and a predefined word list the cost for cracking passwords generated by different strategies are explored. Major findings indicate that strategies based on phrases are at the top of the list. Using a strategy to create a seemingly random password based on a logical phrase, where only the first letter from each word is used, tends in some cases to be the best of choice. An example is to turn the phrase “this password is the greatest of them all” into “tpitgota” instead of using the phrase “goodword” to create an 8 character long password. However, if the phrase contains words not usually found in common dictionaries the best strategy seems instead to be utilizing character substitution as in turning the phrase “my dog Krillex is cool” into “myDoGkriLLExiscooL”.