This report is to investigate the use of fracture mechanics parameters (fracture toughness, specific work of fracture) to characterize comminution process. Comminution is a very important industrial process and is extremely low in efficiency. Establishment of a crushing index based on fracture mechanics principles is of great significance for improved machine design and enhanced efficiency. Single particle fracture study has been reviewed because it is considered the most elementary process in and provides the basis for comminution. <p>Rock fragmentation can be best described by fracture mechanics principles and concepts. The most fundamental concept in fracture mechanics is fracture toughness. Extensive review has been done on the fracture toughness application to rock fragmentation problems, and has found it has not been successfully used in comminution process. Further study is necessary to investigate the link between comminution and fracture toughens. Interrelation of fracture. toughness with other rock properties has been studied. Loading rate effects on fracture toughness has also been reviewed. <p>Fracture toughness testing for rock materials has also been studied. The SCB (Semi-Circular Bend specimen) method has been selected for its sound analytical background and ease of operation. A experimental proposal is made based upon the survey results. Single particle fracture is proposed to be conducted on the Allis-Chalmers High Energy Crush Test System, which, compared with other test apparatus, more closely simulates the actual crushers. Detailed procedures on how to use the test system has been given in the report. / Master of Science

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A multiscale continuum model for fragmentation in ductile metals was developed, motivated by structure-property relationships obtained from lower length scale and numerical simulations. Fragmentation occurs during high strain rate deformation as the result of widespread internal damage in the form of void or crack nucleation, growth, and coalescence. The connection between internal damage structures and fragmentation was determined through Molecular Dynamics (MD) simulations of high rate deformation in copper, iron, and iron-carbon alloys. The fragmentation metric of interest in this study is the fragment size, which is represented in MD simulations by the fragment length scale, or the solid volume per surface area ratio. Three deformation modes of varying stress triaxialities, plane strain tension, equibiaxial expansion, and isotropic expansion, provide a range of damage growth behavior allowing the fragment length scale to be correlated to damage structures under different conditions. Modified Embedded Atom Method (MEAM) potentials for the materials enable the representation of damage (and newly created free surfaces) under the extreme conditions. Continuum, nonhomogeneous percolation simulations establish a criterion for fragmentation based on internal damage structure. The continuum percolation simulations are motivated by void size and shape information taken from experimental fracture surfaces of an aluminum 7085 alloy. The combination of the percolation based fragmentation criterion and MD motivated fragmentation model yields a framework for the multiscale modeling of fragmentation.

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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Forest fragmentation is a ubiquitous consequence of anthropogenic land-use change, yet its effects on ecosystem processes and biogenic carbon (C) cycling remain unclear, especially belowground. Forest edges, or the boundary of forest and non-forest land cover, experience altered environmental conditions that affect soil biogeochemical cycling and microbial communities. Urbanization can further alter forest soil dynamics and may interact with perturbations at the forest edge in complex, nonlinear ways. Though soils comprise over 40 % of the global forest C sink, the net effects of interacting global change drivers (e.g., rising temperatures, fragmentation, urbanization) are largely unknown, introducing large uncertainties into estimates of soil C fluxes and our understanding of soil ecology. I co-designed and implemented an observational field campaign of forest edges along an urbanization gradient in Massachusetts to characterize soil C cycling and its drivers from the forest edge to the interior. I use field measurements of soil temperature, moisture and C efflux as CO2, or soil respiration, to find diverging trends in soil C losses at urban and rural forest edges. I find that urban soil respiration rates are less sensitive to rising temperatures than rural soils and that urban edges are even less sensitive than their interior counterparts. I then perform a holistic characterization of soil properties and microbial activity to explore the effects of multiple, simultaneous environmental perturbations on forest edge soils. I report that soil C content does not reflect diverging trends in soil C efflux between rural and urban sites and, instead, is generally lower at the forest edge, suggesting a decoupling between edge soil C pools and fluxes. I also report that soil properties often mediated by human activity, such as pH, temperature, and trace element concentrations, broadly predict soil C dynamics from edge to interior across the urbanization gradient. Finally, I conduct a meta-analysis of published studies on forest edge soil C cycling and its drivers and interpret the findings through a lens of broader global change. I demonstrate that soil conditions converge at the forest edge across the globe, where soils are hotter, drier, and less acidic than the forest interior. I find limited investigation of soil C fluxes and substantial variability in edge soil C stocks, and I conclude that forest edges are not direct analogs for global change experiments. My dissertation demonstrates that soil C cycling is significantly altered by both forest fragmentation and urbanization. I highlight the need for further study both in situ at the forest edge and through multi-factor manipulation experiments to improve our understanding of an increasingly fragmented and urbanized forest landscape.

<p> The mass spectra of disubstituted 1,4-dithiane, 1,4-oxathiane, and 1,4-oxaselenane, as well as the mass spectra of some disubstituted bicyclic and tricyclic sulfur and selenium compounds, were studied. The exact composition of the major ions of many of these compounds was determined. Fragmentation mechanisms are proposed to account for the major peaks in their spectra.</p> / Thesis / Master of Science (MSc)

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