Theses and Dissertations at Montana State University (MSU)
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Item Micromechanical analysis of energy expenditure in snow fracture(Montana State University - Bozeman, College of Engineering, 2017) LeBaron, Anthony Michael; Chairperson, Graduate Committee: Daniel MillerA microstructure-based evaluation of snow combining experimental and analytical approaches was performed. Shear tests were performed on both homogeneous and layered samples of un-notched snow. Force and displacement during loading were recorded. Immediately after testing, small subsamples of snow were subjected to micro-CT scanning to capture 3D microstructure details. Microstructure was then modeled as a grain-bond network. The grain-bond network was subject to minimum energy fracture path calculations as well as discrete element modeling. The discrete element model showed good agreement with experiments. Taken together, results from models and experiments show a widespread damage accumulation process in snow. A large fracture process zone (FPZ) is observed, even in samples with weak layers. Evidence indicates that even in snow avalanches, there is likely significant energy dissipation within the slab.Item A computational model of two-phase, turbulent atmospheric boundary layers containing blowing snow(Montana State University - Bozeman, College of Engineering, 1991) Liston, Glen EddyItem Use of mixture theory to represent a cohesive elastic-viscoplastic material(Montana State University - Bozeman, College of Engineering, 1997) Barber, Michael JamesThe analysis of material properties depends upon detailed information of the physical, geometric, and chemical properties of the materials. Relating these properties to a set of mathematical models is the principle objective of mechanics. Mixtures of materials made up of several constituents require special consideration since the constituent behavior must be reconciled with the overall behavior of the mixture. Mathematical models and their validity must be established to represent these materials. This thesis establishes a methodology whereby a logical sequence of considerations may be followed to represent complex mixtures adequately. Several existing theories of mechanics are assimilated into a cohesive theory to demonstrate the validity of the mathematical model used to represent mixtures. A structured development of the second law of thermodynamics is constructed to allow additional constraint equations which will restrict the form of new parameters. An example of a wood-snow mixture is used to show how the analysis is to be completed. Laboratory tests were run to use as a means of constructing the values of the new constitutive parameters. Proposed ways of including more constituents and spatial dimensions suggested.Item A structural theory for the deformation of snow(Montana State University - Bozeman, College of Engineering, 1977) St. Lawrence, William FrancisItem A continuum mixture theory with an application to turbulent snow, air flows and sedimentation(Montana State University - Bozeman, College of Engineering, 1986) Decker, Rand AlanItem A constitutive equation for snow subjected to long-duration small strain-rates(Montana State University - Bozeman, College of Engineering, 1982) Dandekar, Bhushan WasudeoItem Nonequilibrium thermodynamics of temperature gradient metamorphism in snow(Montana State University - Bozeman, College of Engineering, 2013) Staron, Patrick Joseph; Chairperson, Graduate Committee: Edward E. AdamsIn the presence of a sufficient temperature gradient, snow evolves from an isotropic network of ice crystals to a transversely isotropic system of depth hoar chains. This morphology is often the weak layer responsible for full depth avalanches. Previous research primarily focused on quantifying the conditions necessary to produce depth hoar. Limited work has been performed to determine the underlying reason for the microstructural changes. Using entropy production rates derived from nonequilibrium thermodynamics, this research shows that depth hoar forms as a result of the snow progressing naturally toward thermal equilibrium. Laboratory experiments were undertaken to examine the evolution of snow microstructure at the macro scale under nonequilibrium thermal conditions. Snow samples with similar initial microstructure were subjected to either a fixed temperature gradient or fixed heat input. The metamorphism for both sets of boundary conditions produced similar depth hoar chains with comparable increases in effective thermal conductivity. Examination of the Gibbs free energy and entropy production rates showed that all metamorphic changes were driven by the system evolving to facilitate equilibrium in the snow or the surroundings. This behavior was dictated by the second law of thermodynamics. An existing numerical model was modified to examine depth hoar formation at the grain scale. Entropy production rate relations were developed for an open system of ice and water vapor. This analysis showed that heat conduction in the bonds had the highest specific entropy production rate, indicating they were the most inefficient part of the snow system. As the metamorphism advanced, the increase in bond size enhanced the conduction pathways through the snow, making the system more efficient at transferring heat. This spontaneous microstructural evolution moved the system and the surroundings toward equilibrium by reducing the local temperature gradients over the bonds and increasing the entropy production rate density. The employment of nonequilibrium thermodynamics determined that the need to reach equilibrium was the underlying force that drives the evolution of snow microstructure. This research also expanded the relevance of nonequilibrium thermodynamics by applying it to a complicated, but well bounded, natural problem.