Shape and size of rocks are important physical characteristics of aggregates used in engineering and for interpretation of the genesis of naturally occurring sediment. Several image processing programs are available for measure the size and shape of various types of objects. The accuracy and reproducibility of results of a new imaging method and new matlab based 3D imaging program has been studied. 3D results are obtained by coupling two images of particles one of their largest and one of the smallest projected areas. The accuracy of results depends on the focal length used for imaging as well as the positioning of particles in the view field.

Thesis advisor: Mark D. Behn / Ice sheet flow is strongly controlled by the conditions at the ice-bed interface. While these processes are hard to observe directly, comparisons between numerical modeling and ice surface observations can be used to indirectly infer subglacial processes. Specifically, seasonal summer speed up near the margin of the Greenland Ice Sheet (GIS) has been linked to the presence of subglacial water. For decades, the Glen flow law has been the most widely-accepted constitutive relation for modeling ice flow. However, while the Glen law captures the temperature-dependent, nonlinear viscosity of ice, it does not explicitly incorporate ice grain size, which has been shown in laboratory experiments to influence ice rheology. To compensate for the lack of explicit grain size dependence, ice sheet models often utilize an “enhancement factor” that modifies the flow law to better match observations, but does not provide insight into the physical processes at play. Using a grain size sensitive rheology that incorporates grain size evolution due to dynamic recrystallization and grain growth, I model the effects of seasonal variations of subglacial hydrology in a 2-D vertical cross-section of ice flow on both annual and inter-annual timescales. The presence of subglacial water reduces the frictional coupling between the ice and the bed. Here I simulate the presence of water at the ice-bed interface during the melt season using patches of free-slip and explore a range of patch sizes and geometries to investigate their role in modulating ice surface velocities and grain size within the ice. I compare modeled winter and summer surface velocities to observations taken on the western margin of the GIS and find that realistic surface velocities are achievable using agrain size sensitive flow law without the introduction of an enhancement factor. Further, the grain size of the internal ice responds on an inter-annual timescale to these seasonal forcings at the bed, potentially leading to long-term changes in surface velocities. / Thesis (MS) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

The Latin American steel making company Ternium S.A. aims to develop and produce a new type of advanced high strength steel (AHSS) in which the main alloying elements are carbon, aluminium, manganese, and silicon. The present work is the first phase of the development project and it involves casting and characterization of four steel compositions with varying amounts of the aforementioned elements. The results revealed that the Mn-content had a large impact on the development of hard phases during solidification. A steel with a Mn-content of 2 %wt. had almost completely transformed to pearlite during cooling, while a steel with a 4 %wt. Mn-content consisted of primarily martensite and retained austenite. Only the impact of the Mn-content is evaluated. The columnar grain size for two of the four steel compositions were in the range of 20-30 mm, which is similar to those observed from continuous casting. This indicate that the heat transfer rate was slow enough to allow these grains to grow. Measurements during casting showed an initial cooling rate of 10-20°C/min at a distance of 10 mm inside the ingot, which is much slower than the surface cooling rate during continuous casting (100-150°C/min). It was assumed that the cooling rate was similar for all castings since the methodology was identical. However, the steel used for cooling rate measurements was not characterized, why a correlation between cooling rate and composition could not be obtained. A heat transfer model was developed to gain further knowledge of the solidification process. As a reference to the heat transfer model, a eutectic Bi-42Sn alloy was cast with temperaturemonitoring using a casting setup identical to that of the steel castings. A similar cooling rate tothe Bi-42Sn reference casting was obtained where the cooling was faster from above of the ingot than below. Thus, the last part of the metal to solidify during the simulation was situated in the lower half of the ingot. This provides a model for testing future steel compositions.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20336号 / 工博第4273号 / 新制||工||1662(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 松原 英一郎, 教授 乾 晴行 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Nanotechnology offers significant opportunities in providing solutions to existing engineering problems as well as breakthroughs in new fields of science and technology. In order to fully realize benefits from such initiatives, nanomanufacturing methods must be developed to integrate enabling constructs into commercial mainstream. Even though significant advances have been made, widespread industrialization in many areas remains limited. Manufacturing methods, therefore, must continually be developed to bridge gaps between nanoscience discovery and commercialization. A promising technology for integration of top-down nanomanufacturing yet to receive full industrialization is equal channel angular pressing, a process transforming metallic materials into nanostructured or ultraine grained materials with significantly improved performance characteristics. To bridge the gap between process potential and actual manufacturing output, a prototype top-down nanomanufacturing system identified as indexing equal channel angular pressing (IX-ECAP) was developed. The unit was designed to capitalize on opportunities of transforming spent or scrap engineering elements into key engineering commodities. A manufacturing system was constructed to impose severe plastic deformation via simple shear in an equal channel angular pressing die on 1100 and 4043 aluminum welding rods. 1/4 fraction factorial split-plot experiments assessed significance of five predictors on the response, microhardness, for the 4043 alloy. Predictor variables included temperature, number of passes, pressing speed, back pressure, and vibration. Main effects were studied employing a resolution III design. Multiple linear regression was used for model development. Initial studies were performed using continuous processing followed by contingency designs involving discrete variable length work pieces. IX-ECAP offered a viable solution in severe plastic deformation processing. Discrete variable length work piece pressing proved very successful. With three passes through the system, 4043 processed material experienced an 88.88% increase in microhardness, 203.4% increase in converted yield strength, and a 98.5% reduction in theoretical final grain size to 103 nanometers using the Hall-Petch relation. The process factor, number of passes, was statistically significant at the 95% confidence level; whereas, temperature was significant at the 90% confidence level. Limitations of system components precluded completion of studies involving continuous pressing. Proposed system redesigns, however, will ensure mainstream commercialization of continuous length work piece processing.

The present study develops a phenomenological adaptation to an internal state variable (ISV) model that incorporates the influence of dynamic recrystallization (DRX) in a material’s evolving microstructure and flow stress response. During metal forming and joining processes that promote internal heat distributions and large strains, microstructural processes often occur that result in a transformation of the evolving microstructure away from the base distribution. In an effort to lower the stored energy accumulated in the material’s lattice and grain structure, the deformed material may undergo a type of dynamic recovery process, such as DRX. In this study, the ISV model’s flow stress output is modified to include a phenomenological DRX softening and hardening term internal to the isotropic hardening rate ISV. The flow stress thus directly includes the influence of microstructure evolution. The evolving grain size is modeled such that an inverse relation exists between strain hardening and average grain size.

The present study focuses on the evolving microstructure of Mg alloy AZ31. The material is subjected to channel die compression at room temperature to simulate a reduction stage in the rolling process. Samples are annealed to provoke recovery, static recrystallization, and grain growth. Annealing is carried out at three temperatures for times ranging from 10s to 10,000s. The material’s response is exhibited through the use of data collection methods such as microhardness, optical microscopy, and electron backscatter diffraction (EBSD). Methodology behind experimentation and data collection techniques are documented in detail. Conclusions are made about the effects of the compression and annealing processes on the material’s microstructure. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) model is introduced, and a simple recrystallization kinetics plot is attempted.

Tropical latitudes play an important role in global climate as they export moisture and energy pole-ward. Recent tests of predictive climate models against Holocene paleoclimate data show discrepancies between predicted and observed values in Tropical regions. Terrestrial paleoclimate records could help resolve these discrepancies by all allowing for better understand of the sensitive ocean-atmosphere climate dynamics in the tropics and by providing additional information from a diverse source of proxies. The Caribbean is an ideal location for study as its climate is influenced by both the Atlantic and Pacific Oceans. However, there are relatively few sources of paleoclimate proxies in this region due to its archipelagic nature. If Caribbean climate is to be thoroughly investigated, additional environments and climate proxies need to be investigated. As coastal systems are ubiquitous throughout the Caribbean, they are ideal for investigation of Holocene paleoclimate in this region. However, they can be ephemeral on millennial timescales making them challenging to use in paleoclimate analysis. This dissertation discusses new methods and basins that facilitate the study of these systems. Several important contributions have been made by this thesis. (1) Core scanning XRF data, when examined with additional proxies such as foraminifera, can be used to infer shifts in regional precipitation patterns in a coastal setting. Though these methods have been used before in deep basins, this represents the first use of core scanning XRF in a littoral setting. (2) The evolution of sinkhole sedimentation is reliant on both the morphology of the sinkhole and water level within the feature. This thesis shows that coastal systems are a viable source of paleoclimate information and which can hold valuable information for reconstructing climate. / Thesis / Master of Science (MSc)

High performance cutting tools are essential in many industry areas. Cemented carbides (WC-Co) are common materials used for these applications due to the excellent mechanical properties. The mechanical properties of the material are manly dependent on the WC grain size distribution.To be able to tailor the material properties it is important to be able to characterize and control the WC grain size.In this study a quantitative method for WC grain size distribution measurements has been developed using the automated electron backscatter diffraction (EBSD) technique. The EBSD system was optimized for a fast and accurate measurement. Using the method approximately 2000-3000 WC grains can be measured in approximately 25 minutes. This will give reliable statistics and information about the material.The method was used to compare materials produced with three different milling methods; traditional 30l ball mill, method A and B. Two WC raw materials with different initial particle sizes, one coarser and one finer, was milled aiming for similar grain sizes in the sintered structure. The results showed some tendency for a larger fraction of large grains in the materials produced using the ball mill compared to the materials produced with method A and B. The difference between the milling methods was larger using a raw material with a coarser initial particle size.The developed quantitative method was successfully used to compare grain size distributions of different materials in a fast and quantitative way. The differences between the materials were small and materials with similar grain size distribution and mechanical properties could be produced using both the traditional ball mill method and method A and B.

A new laboratory permeameter was developed for measuring the hydraulic conductivity of gravels ranging from 0.1 to 2 m/s. The release of pneumatic pressure applied to the test specimen induces an underdamped oscillatory response of the water level above the permeameter, similar to an underdamped in situ slug test response in monitoring wells. A closed form model was derived to calibrate the hydraulic minor losses in the permeameter and the hydraulic conductivity of the specimen by performing tests without and with a specimen. The majority of each test series performed on individual specimens produced hydraulic conductivity values within 10% of the average, which is very small for such a measurement. Tests were performed using the permeameter on a collection of subrounded and angular gravels prepared to measured grain size distributions and porosities. The surface area was determined by evaluating the shape and angularity using a method developed in this research and these parameters were used with the measured tortuosity and hydraulic conductivity, to back calculate the packing factor of the Kozeny-Carman equation. The results show that the packing factor for the gravels and materials tested is proportional to the tortuosity cubed. These results provide a valuable update to the Kozeny-Carman equation for predicting the hydraulic conductivity of gravels. Field slug interference tests were performed in pairs of monitoring wells installed at the same elevation in a floodplain deposit of silty sand in Dedham MA. Slug tests were performed in one of the wells while the response was monitored simultaneously in both wells. The measured responses were both analyzed by modifying the KGS model of Hyder et al. (1994) to consider the wellbore storage and filter packs effects. This modification was found to produce estimates of hydraulic conductivity based on the slugged well response that compared well with that estimated based on the observation well's response. Calibrated hydraulic conductivities for the pairs of wells tested ranged from 4x10-6 to 1.5x10-5 m/s and specific storage ranged from 2x10-5 to 7x10-4 m-1.