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Creep is a time-dependent deformation of materials under stress at elevated temperatures. The phenomenon of creep allows materials to plastically deform gradually over time, even at stress levels below its yield point or below its transformation temperature. The issues involving creep are especially significant for magnesium alloys, since they are susceptible to creep deformation from temperatures as low as 100 ºC, which inhibits their potential application in areas such as automotive engines. The University of Canterbury has developed a significant level of experience and infrastructure in the field of Electron Backscatter Diffraction (EBSD). EBSD allows microstructures to be characterized by imaging the crystal structure and its crystallographic orientation at a given point on a specimen surface, whereby the process can be automated to construct a crystallographic “orientation map” of a specimen surface. In light of this, the creep of magnesium and its alloys was studied using a novel technique, in which a conventional tensile creep test was interrupted at periodic intervals, and the EBSD was used to acquire the crystallographic orientation maps repeatedly on a same surface location at each interruption stages. This technique allows simultaneous measurement of the rate of creep deformation and the evolution of the specimen microstructure at various stages of creep, bringing further insight into the deformation mechanisms involved. This thesis summarizes the study of the microstructural and crystallographic texture evolution during creep of pure magnesium and a creep resistant magnesium alloy Mg- 8.5Al-1Ca-0.3Sr. Pure magnesium exhibit a conventional “power-law” type creep, and although its creep properties are well established in the past literatures, there has been little in terms of reconciliation between the observed creep rates and the underlying deformation mechanisms. The alloy Mg-8.5Al-1Ca-0.3Sr, on the other hand, is a modern die casting alloy used in the automotive industry for engine and gearbox applications, and despite its superior creep resistance, little is known about the microstructural contributions to its creep properties. This research was conducted to provide a link between the creep properties, observed microstructures, and theories of creep deformation by the use of advanced microscopy techniques. For the first time, the detailed, sequential microstructural development of magnesium and its alloys during creep has been revealed.

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The object of this research is to investigate the rate of soil creep and. its controlling variables at Killhope basin in Upper Weardale (Northern Pennines). The experimental work was designed to trace the movement of soil. Five sites were selected for study (three on peaty soils and two on mineral soils). At each site a set of four different instruments (an Anderson's tube, a Young's pit, wooden pillars and Rashidian's instrument)were used to measure creep rates for 18 months. To investigate which variables control this process, soil samples from sampling sites were used for quantitative analysis. The results of this study indicate: 1. Annual linear rates of soil creep varied from 0.58 mm to 1.52 mm.2. A strong relationship between creep rate and soil moisture content and its fluctuations.3. Higher creep rates for organic soils than for mineral soils.4. Non-exponential decline of rate of movement with depth.5. No evidence for the influence of slope angle on creep rate.6. The small differences in values recorded by different instruments show that the Rashidian technique was sufficiently accurate and useful for monitoring seasonal soil creep.

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Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Bibliography: leaves 517-527.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 162-165). Also available via the Internet.

Mid-temperature creep deformation in the range of 600 to 850°C is assuming greater importance in Ni-based superalloys. This is because the design operating temperature of the combustion cycle is increasing as the new generations turbofan engines become more efficient. The temperature at the rim of turbine disks and the root of turbine blades can be in this critical range of temperatures for significant portions of the mission cycle, leading to a complex time-dependent mode of plasticity called "microtwinning"'. Unfortunately this kind of coupled displacive-diffusive deformation mechanism is not yet well understood, and even the range of temperatures and stresses where microtwinning occurs is not clearly defined. This work explores the fundamentals of this phenomenon, from the kinetics of microtwinning to its influence on the mechanical behaviour of the material. To achieve this objective, coupled computational-experimental studies have been carried out. First, the contribution of microtwinning mechanism to the creep deformation of a single crystal superalloy is studied. The accumulated creep strain computed from quantitative stereology of the tested samples supports the role of this mechanism in conferring plastic deformation. Second, the chemical composition of the microtwins is analysed by means of atomic-resolution characterisation techniques (APT and TEM). Segregation of Î3'-stabilisers to the growing faults is found to be crucial for the understanding of the creep mechanisms in this range of temperatures. Third, a model for diffusion-controlled growth of microtwins is proposed and used to recover the experimental creep strain rates. This then provides the basis for a thermodynamically consistent constitutive model developed on the basis of crystal plasticity theory. The constitutive model is subsequently implemented into a finite element code to study the activation of the different plastic mechanisms within single crystal and polycrystalline aggregates depending on the crystal orientation. With the support of this model, a relation between the rotations of the crystal and the creep life of the different crystal orientations is established. The numerical and experimental results ultimately reveal the critical role of the microtwinning on the asymmetric behaviour of the alloy and thus, its influence on the mechanical performance.