Browsing College of Engineering and Mines (CEM) by Subject "Materials science"
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A Mechanical Evaluation Of Alaskan White SpruceThis project serves to demonstrate the usefulness of Alaskan White Spruce as a construction material. This is done through the development of allowable strength values for design purposes. Such values allow engineers to design structures using Alaskan White Spruce, increasing the usefulness of the wood species.<p> The mechanical properties of Alaskan White Spruce are investigated. Summaries of the mechanical properties and of subsequently developed allowable structural design values are given. Included are discussions of the Alaskan White Spruce species, general wood behavior, mechanical testing of wood, statistical data analysis, and allowable property development. Results are compared against the work of other researchers. Appendices of test data are given.<p> Test results and subsequent data analysis indicate Alaskan White Spruce possesses strength similar to Douglas-Fir/Larch lumber and higher strength than Spruce/Pine/Fir type lumbers. This indicates that Alaskan White Spruce may have considerable worth as a construction material. <p>
Experimental And Numerical Study Of Sonic Wave Propagation In Freezing Sand And SiltA numerical model for delineating the temperature-velocity relationship of freezing porous media and soil is developed in Matlab based on Leclaire's Biot-type three-phase theory. Leclaire's theory gives lower sonic velocities than the experimental results because it does not take into consideration the effect of the solid-ice frame when water is freezing. To take the solid-ice effective frame into account, the average bulk and shear moduli estimation are modified with a proposed procedure. The modification gives higher P-wave and S-wave velocities that fit experimental data well. A comprehensive suite of physical and acoustic laboratory experiments are conducted on artificial sands, sand-clay mixtures and Fairbanks silts to investigate the temperature-velocity relationship during the freezing process and the effects of grain size and fine clay content. A Multi-channel ultrasonic scanning system (MUSS) is designed, installed and programmed for the experimental computerized ultrasonic tomography (CUST) study. The inward and outward freezing process and freezing front development in Fairbanks silt samples are observed using computerized ultrasonic tomography (CUST) in the laboratory. The experiments generate sonic wave velocity and temperature distribution during the freezing process. The freezing front is clearly identified in the CUST as a function of time and temperature. Comprehensive numerical finite element method (FEM) simulations, which account for the conduction in porous media, the latent heat effect and the nonlinear thermal properties of soil, are performed on the inward and outward freezing process of Fairbanks silt based on the experimental conditions. In conjunction with the temperature-velocity model developed in the study, sonic wave velocity tomograms are generated. The results are comparable with those obtained by CUST. The study indicates that CUST is an effective method for studying freezing processes and has potential for indirect measurement of unfrozen water content variations in the soil without interfering with the freezing process.
Experimental Investigations Of Fluid Dynamic And Thermal Performance Of NanofluidsThe goal of this research was to investigate the fluid dynamic and thermal performance of various nanofluids. Nanofluids are dispersions of metallic nanometer size particles (<100 nm) into the base fluids. The choice of base fluid is an ethylene or propylene glycol and water mixture in cold regions. Initially the rheological characterization of copper oxide (CuO) nanofluids in water and in propylene glycol was performed. Results revealed that higher concentrations of CuO nanoparticles (5 to 15%) in water exhibited time-independent pseudoplastic and shear-thinning behavior. Lower concentrations (1 to 6%) of CuO nanofluids in propylene glycol revealed that these nanofluids behaved as Newtonian fluids. Both nanofluids showed that viscosity decreased exponentially with increase in temperature. Subsequent correlations for viscosities as a function of volume concentration and temperature were developed. Effects of different thermophysical properties on the Prandtl number of CuO, silicon dioxide (SiO2) and aluminum oxide (A12O 3) nanofluids were investigated. Results showed that the Prandtl number increased with increasing volume concentrations, which in turn increased the heat transfer coefficients of the nanofluids. Various nanofluids were compared for their heat transfer rates based on the Mouromtseff number, which is a Figure of Merit for heat transfer fluids. From this analysis, the optimal concentrations of nanoparticles in base fluids were found for CuO-water nanofluids. Experiments were performed to investigate the convective heat transfer enhancement and pressure loss of CuO, SiO2 and A12O 3 nanofluids in the turbulent regime. The increases in heat transfer coefficient by nanofluids for various volume concentrations compared to the base fluid were determined. Pressure loss was observed to increase with nanoparticle volume concentration. It was observed that an increase in particle diameter increased the heat transfer coefficient. Calculations showed that application of nanofluids in heat exchangers in buildings could result in volumetric flow reduction, reduction in the mass flow rate and size, and pumping power savings. Experiments on a diesel electric generator with nanofluids showed a reduction of cogeneration efficiency due to the decrease in specific heat compared to the base fluids. However, it was found that the efficiency of the waste heat recovery heat exchanger increased for nanofluids.
Nanotribological Characterization Of Dynamic SurfacesThis dissertation research includes three fundamental areas: utilizing an atomic force microscope (AFM) to study the nanomechanical and tribological properties, to understand friction and wear at nanometer length, and to study wear mechanisms of boride coatings for biological applications. This was the first time that an AFM was used to study the nanomechanical and tribological properties and the performance of the materials. The AFM enables detailed investigation of the wear modes at multi-length scales as well as the surface mechanical properties. Surface analysis using an AFM included the surface texture, profile of indents, wear tracks, and wear scars. The friction force microscope (FFM) revealed the relationship between surface texture and frictional properties, thus contributing to the fundamental understanding of nanotribology. A new wear model was proposed. Also, hardening was discovered under the indents. The multi-scale wear study was focused on fundamental wear mechanisms. New wear modes, different than the traditional ones, were proposed. In this research, nanocracks and other damage (hardening and plastic flow) were found at different scales. Boride coatings on refractory metals were investigated for biological applications. Tribological performance of these coatings was studied in dry and wet (biofluid) conditions. It was found that boron plays an important role in forming amorphous and crystalline wear debris.