A finite element analysis approach is used to determine the susceptibility to wrinkles for thin sheets with clamped ends when subjected to tensile loading. The model problem chosen to do this analysis is the stretching of a thin sheet with clamped-ends. In the preliminary analysis, a stress analysis of thin sheets is done to study the stresses that develop under these boundary conditions. The analysis shows that there is a stretch-induced compressive stress in the transverse direction to the applied load that causes wrinkles. Then, the parametric study is conducted to determine the effect of aspect ratio and strain on the compressive stress. Based on the results of the parametric study, a critical strain value for each aspect ratio is determined for which the corresponding compressive stress is zero. Further buckling analysis is performed to find the buckling modes of the model problem that shows a limit of aspect ratio below which buckling is not possible under given conditions. Finally, post-buckling analysis shows the nature of wrinkles observed in the model problem for different aspect ratios. / text

Granitic rocks usually exhibit strongly anisotropy due to pre-existing microcracks induced by long-term geological loadings. The understanding of anisotropy in mechanical properties of rocks is critical to a variety of rock engineering applications. In this thesis, the anisotropy of tension-related failure parameters involving tensile strength, flexural strength and Mode-I fracture toughness/fracture energy of Barre granite is investigated under a wide range of loading rates. Three sets of dynamic experimental methodologies have been developed using the modified split Hopkinson pressure bar system; Brazilian test to determine the tensile strength; semi-circular bend method to determine the flexural strength; and notched semi-circular bend method to determine the Mode-I fracture toughness and fracture energy. For all three tests, a simple quasi-static data analysis is employed to deduce the mechanical properties; the methodology is assessed critically against the isotropic Laurentian granite. It is shown that if dynamic force balance is achieved in SHPB, it is reasonable to use quasi-static formulas. The dynamic force balance is obtained by the pulse shaper technique. To study the anisotropy of these properties, rock blocks are cored and labeled using the three principal directions of Barre granite to form six sample groups. For samples in the same orientation group, the measured strengths/toughness shows clear loading rate dependence. More importantly, a loading rate dependence of the strengths/toughness anisotropy of Barre granite has been first observed: the anisotropy diminishes with the increase of loading rate. The reason for the strengths/toughness anisotropy can be understood with reference to the preferentially oriented microcracks sets; and the rate dependence of this anisotropy is qualitatively explained with the microcracks interaction. Two models abstracted from microscopic photographs are constructed to interpret the rate dependence of the fracture toughness anisotropy in terms of the crack/microcracks interaction. The experimentally observed rate dependence of the anisotropy is successfully reproduced.

Granitic rocks usually exhibit strongly anisotropy due to pre-existing microcracks induced by long-term geological loadings. The understanding of anisotropy in mechanical properties of rocks is critical to a variety of rock engineering applications. In this thesis, the anisotropy of tension-related failure parameters involving tensile strength, flexural strength and Mode-I fracture toughness/fracture energy of Barre granite is investigated under a wide range of loading rates. Three sets of dynamic experimental methodologies have been developed using the modified split Hopkinson pressure bar system; Brazilian test to determine the tensile strength; semi-circular bend method to determine the flexural strength; and notched semi-circular bend method to determine the Mode-I fracture toughness and fracture energy. For all three tests, a simple quasi-static data analysis is employed to deduce the mechanical properties; the methodology is assessed critically against the isotropic Laurentian granite. It is shown that if dynamic force balance is achieved in SHPB, it is reasonable to use quasi-static formulas. The dynamic force balance is obtained by the pulse shaper technique. To study the anisotropy of these properties, rock blocks are cored and labeled using the three principal directions of Barre granite to form six sample groups. For samples in the same orientation group, the measured strengths/toughness shows clear loading rate dependence. More importantly, a loading rate dependence of the strengths/toughness anisotropy of Barre granite has been first observed: the anisotropy diminishes with the increase of loading rate. The reason for the strengths/toughness anisotropy can be understood with reference to the preferentially oriented microcracks sets; and the rate dependence of this anisotropy is qualitatively explained with the microcracks interaction. Two models abstracted from microscopic photographs are constructed to interpret the rate dependence of the fracture toughness anisotropy in terms of the crack/microcracks interaction. The experimentally observed rate dependence of the anisotropy is successfully reproduced.

The implementation of technologies such as aluminum powder metallurgy (P/M) can be used in the automobile industry to have potential economic and environmental advantages. This technology to produce vehicle components can offer the combination of weight savings due to the low density of aluminum and material and machining savings via near net shape processing attributes. In an effort to expand the scope of application for aluminum P/M, considerable research has emphasized the development of new alloys and composites. One such alloy is P/M 2324, an aluminum-copper-magnesium alloy developed to have increased mechanical properties over the standard aluminum P/M alloys of the AC2014 type. The objective of this work was to undertake a comprehensive study on the effects of hot deformation on the emerging alloy P/M 2324 as well as the alloy with a SiC addition. Here, a forgeability study of these alloys and its wrought counterpart AA2024 was completed. To

TiNi shape memory alloys (SMAs) have been extensively used in various applications. The great interest in TiNi alloys is due to its unique shape memory and superelasticity effects, along with its superior wear and dent resistance. Shape memory and superelastic effects are due to a reversible martensitic transformation that can be induced either thermally or mechanically. In this study, indentation tests at different temperatures, loads and strain rates have been performed on superelastic TiNi alloy. Deformation characteristics of superelastic TiNi under indentation have been compared to AISI 304 steel as a conventional material. Also, in-situ optical microscopy tests with interrupted heating have been employed in order to gain an insight into the coupled deformation and reversible martensitic transformation behaviour of TiNi SMAs under tensile loads. An understanding of the impacts of strain rate and temperature on the deformation behaviour of TiNi SMAs under localized compressive loads has been proposed.

No description available.

The most widely accepted approach to long-term storage of nuclear waste is to design and construct a deep geological repository, where the geological environment acts as a natural barrier to radio nuclide migration. Sedimentary rocks, particularly argillaceous formations, are being investigated by many countries because of favorable isolating qualities (laterally continuous and low permeability) and the ability of self-sealing of fractures. Underground construction creates a damage zone around the excavation. The depth away from the excavation surface of the damage zone depends on the rock mass properties, the stress field, and the construction method. This research investigates the fracture development process in sedimentary rocks and evaluates continuum modelling methods to predict the damage zone dimensions. At the laboratory scale, a complete classification system for samples of carbonate and siliciclastic rocks has been developed, with geotechnical considerations, which when applied narrows the variability of the mechanical properties. Using this system, crack initiation (CI) shows the most uniform range in each class, particularly for mud rocks. Tensile strength was found to be higher for the Brazilian method than Direct method of testing. Brazilian reduction to Direct values was found to be rock type dependent. Laboratory testing results are also influenced by the orientation of bedding. Bedding and other structures were also found to influence the excavation behaviour as observed at the Niagara Tunnel Project in a mudstone and in excavations in the Quintner limestone of Switzerland. The conceptual stages of damage development and the potential fracture networks in sedimentary rocks are used to summarize the understanding of excavation damage developed in this thesis. Using a continuum based modelling approach, a set of predictive damage depth curves were developed for the different excavation damage zones. This approach was found to be most sensitive to the tensile strength used as an input. Back analysis of the Niagara Tunnel Project and forward prediction of the excavation damage around a shaft in the Queenston Formation are used to illustrate the importance of this research. The prediction methods were also applied to cut-off design analysis. This research has enhanced the understanding of excavation damage development in sedimentary rocks and provided a methodology to predict the dimensions of the excavation damage zones using a continuum based approach. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2014-01-29 16:08:58.022

No description available.

Aramid fiber reinforced polymer (AFRP) composite materials show promise for prestressed concrete bridge applications. However, there are still some knowledge gaps due to lack of sufficient data to assess the long-term performance and therefore sustainability of beams prestressed with AFRP composite materials. The objective of this research is to effectively characterize the material properties based on the short-term and long-term characteristics of AFRP bars. Tensile, creep-rupture, and relaxation tests are experimentally conducted using AFRP bars to validate testing procedures and expand an existing limited database. Previous results from tensile tests show that the stress-strain behavior of Arapree® AFRP bars is linear until failure with tensile strength of approximately 210 ksi (1448 MPa) and strain of 2.1%. For the creep-rupture tests, three specimens are tested and monitored at four different load levels (50, 60, 75 and 85% of maximum tensile strength) throughout a period of 14 days (short-term evaluation) and 42 days (long-term evaluation). From these tests, it is expected that for a 100-year life span, 55% of the ultimate load, Fu, must be applied as an initial stress to obtain a long-term residual strength of 0.80 Fu. For the relaxation tests, six specimens at four different strain levels (50, 60, 75 and 85% of maximum tensile strain) are tested and monitored throughout a period of 14 days and 42 days. Relaxation loss profiles of the AFRP bars are developed based on the experimental data collected from prestressed AFRP bars, which have been less well understood given lack of sufficient experimental data. Overall, the results of this study provide more insight as to the reliability and potential long-term performance of AFRP bars embedded within prestressed bridge structures.

With the increasing requirements for higher strength materials with high electrical conductivity, a lot of interest has been paid to develop Cu-based composites in the last 25 years. These composites have superior tensile strength, combined with good electrical conductivity, to that exhibited by pure Cu and conventional Cu alloys. To date, much of the research carried out on this composite has focused on the mechanical and electrical properties of the as processed material. However, there is a basic lack of understanding of the way in which the properties may change or degrade during service. Without this knowledge, these composites cannot be fully and safely exploited. Thus the objective of this study was to investigate the thermo-mechanical behaviour of a Cu-Cr composite, and the nature and extent of any damage mechanisms occurring within the composite over a wide range of experimental conditions. Neutron diffraction was used to investigate the deformation behaviour of the individual phases in the composite and their interaction through elastic and plastic loading at room temperature. For the composite, a fairly good agreement was observed in the phase strains predicted by the Eshelby theory and measured by neutron diffraction. In-situ tensile tests in the SEM were also performed to study the damage mechanism of the composite. Tensile and creep tests were carried out in air and in vacuum over a wide range of temperatures. To provide data for comparison with the composite material, pure Cu specimens were tested whenever possible. Creep resistance increases significantly with the introduction of Cr fibres into Cu. The higher creep rate of the composite in air than in vacuum is due to the gradual decrease of the cross-sectional area of the matrix due to increasing thickness of the oxide layer. Damage characteristics and distributions were found to be similar during tensile and creep testing.