As the world’s population increases, the demand for energy also grows. The strain on our limited resources of fossil fuels is unsustainable in the long term. An alternative, renewable method of energy generation must be implemented. Solar energy has good potential as an environmentally sound, unlimited energy source, but solar devices are not yet able to efficiently store energy for later use. A device has been proposed which uses direct sunlight to split water into hydrogen and oxygen. The hydrogen can then be harvested and stored as fuel, solving the question of how to effectively store energy generated during times of peak sunlight for use when sunlight levels are low. The prototype device incorporates arrays of doped silicon microwires which function as light absorbers and current-carriers, driving the chemical reactions that evolve hydrogen from water. This work aims to quantify and characterize the reduction in microwire resistivity that is achievable through application of silicon’s piezoresistive properties. Silicon displays a change in electrical resistance as a function of applied mechanical strain. This electromechanical effect has been studied extensively in bulk and top-down (etched) microstructures, but studies on microstructures grown bottom-up have been limited. A simple method is presented for piezoresistive characterization of individual, released, bottom-up silicon microwires. It is shown that these n-type microwires display a consistent negative piezoresistive response which increases in magnitude with increasing doping concentration. It was found that harnessing the piezoresistive response of moderately-doped (∼10^17 cm^−3) n-type wires allowed for a maximum observed reduction in resistivity of 49%, which translated to a 1% reduction in overall system resistance of a prototype unit cell of the artificial photosynthesis device, if all other components therein remained unchanged. / February 2015

This project is centred on an ongoing trailer component failure problem at the STEELBRO New Zealand Ltd due to cracks. In this research the problem has been systematically approached using ANSYS finite element analysis software. The approach involves investigation of the problem and structural analysis of the trailer subjected to two types of service conditions. The service conditions are simulated in ANSYS which involved CAD and finite element modelling of the trailer, and then the finite element model is validated experimentally by strain gauges and geometrically by ANSYS element shape checking capability. The finite element model subjected to static structural analysis confirmed the crack locations and indicated the cause of the failure. Further fatigue analysis on one of the loading condition revealed it’s potential to cause failure at the crack locations. Finally, this research concludes with a proposal of revised component design to overcome the failure at the crack locations and recommendations for further analysis on the trailer.

Deformational properties of soil, in terms of modulus and damping, exert a great influence on seismic response of soil sites. However, these properties for sands containing some portion of fines particles have not been systematically addressed. In addition, simultaneous modelling of the modulus and damping behaviour of soils during cyclic loading is desirable. This study presents an experimental and computational investigation into the deformational properties of sands containing fines content in the context of site response analysis. The experimental investigation is carried on sandy soils sourced from Christchurch, New Zealand using a dynamic triaxial apparatus while the computational aspect is based on the framework of total-stress one-dimensional (1D) cyclic behaviour of soil. The experimental investigation focused on a systematic study on the deformational behaviour of sand with different amounts of fines content (particle diameter ≤ 75µm) under drained conditions. The silty sands were prepared by mixing clean sand with three different percentages of fines content. A series of bender element tests at small-strain range and stress-controlled dynamic triaxial tests at medium to high-strain ranges were conducted on samples of clean sand and silty sand. This allowed measurements of linear and nonlinear deformational properties of the same specimen for a wide strain range. The testing program was designed to quantify the effects of void ratio and fines content on the low-strain stiffness of the silty sand as well as on the nonlinear stress-strain relationship and corresponding shear modulus and damping properties as a function of cyclic shear strains. Shear wave velocity, Vs, and maximum shear modulus, Gmax, of silty sand was shown to be significantly smaller than the respective values for clean sands measured at the same void ratio, e, or same relative density, Dr. However, the test results showed that the difference in the level of nonlinearity between clean sand and silty sands was small. For loose samples prepared at an identical relative density, the behaviour of clean sand was slightly less nonlinear as compared to sandy soils with higher fines content. This difference in the nonlinear behaviour of clean sand and sandy soils was negligible for dense soils. Furthermore, no systematic influence of fines content on the material damping curve was observed for sands with fines content FC = 0 to 30%. In order to normalize the effects of fines on moduli of sands, equivalent granular void ratio, e*, was employed. This was done through quantifying the participation of fines content in the force transfer chain of the sand matrix. As such, a unified framework for modelling of the variability of shear wave velocity, Vs, (or shear modulus, Gmax) with void ratio was achieved for clean sands and sands with fines, irrespective of their fines content. Furthermore, modelling of the cyclic stress-strain behaviour based on this experimental program was investigated. The modelling effort focused on developing a simple constitutive model which simultaneously models the soil modulus and damping relationships with shear strains observed in laboratory tests. The backbone curve of the cyclic model was adopted based on a modified version of Kondner and Zelasko (MKZ) hyperbolic function, with a curvature coefficient, a. In order to simulate the hysteretic cycles, the conventional Masing rules (Pyke 1979) were revised. The parameter n, in the Masing’s criteria was assumed to be a function of material damping, h, measured in the laboratory. As such the modulus and damping produced by the numerical model could match the stress-strain behaviour observed in the laboratory over the course of this study. It was shown that the Masing parameter n, is strain-dependent and generally takes values of n ≤ 2. The model was then verified through element test simulations under different cyclic loadings. It was shown that the model could accurately simulate the modulus and the damping simultaneously. The model was then incorporated within the OpenSees computational platform and was used to scrutinize the effects of damping on one-dimensional seismic site response analysis. For this purpose, several strong motion stations which recorded the Canterbury earthquake sequence were selected. The soil profiles were modelled as semi-infinite horizontally layered deposits overlying a uniform half-space subjected to vertically propagating shear waves. The advantages and limitations of the nonlinear model in terms of simulating soil nonlinearity and associated material damping were further scrutinized. It was shown that generally, the conventional Masing criteria unconservatively may underestimate some response parameters such as spectral accelerations. This was shown to be due to larger hysteretic damping modelled by using conventional Masing criteria. In addition, maximum shear strains within the soil profiles were also computed smaller in comparison to the values calculated by the proposed model. Further analyses were performed to study the simulation of backbone curve beyond the strain ranges addressed in the experimental phase of this study. A key issue that was identified was that relying only on the modulus reduction curves to simulate the stress-strain behaviour of soil may not capture the actual soil strength at larger strains. Hence, strength properties of the soil layer should also be incorporated to accurately simulate the backbone curve.

No description available.

Zirconium and its alloys are used extensively in the nuclear industry. In the Canadian Deuterium Uranium reactor, the primary containment in the primary coolant system is composed of Zr-2.5wt%Nb in the form of a pressure tube. The permissible chemical composition of Zr-2.5wt%Nb for use in the pressure tube in nuclear reactors is dictated by ASTMB353. Oxygen and iron are the highest content controlled elements in the standard alloy, after zirconium and niobium. Oxygen is an alpha-stabilizer, and diffuses preferentially to the alpha phase, leading to a well established increase in the yield strength of the alpha phase. Iron is a beta-stabilizer, and is concentrated in the beta phase, as well as near alpha-beta grain boundaries. While the mechanical properties of standard Zr-2.5wt%Nb alloy are well understood, there is a dearth of knowledge on the individual effect of these alloying additions, especially at non-standard concentrations. Additionally, the experimental evidence that does exist does not directly take into account the two-phase nature of the alloy, or the effect of impurities on specific deformation modes. Notably absent is experimental evidence on the effect of interstitial impurities on twinning in the hexagonal close-packed alpha phase. This work seeks to complement the present understanding of these phenomena. Mechanical tests have been performed on three specially prepared Zr-2.5wt%Nb alloys to clarify the contributions of oxygen and iron to Zr-2.5wt%Nb deformation properties. Traditional mechanical measurements were complemented by in situ and ex situ diffraction measurements. Tests were performed at a range of temperatures (77K - 673K) and strain rates (quasi-static to 10^-2/s). Increasing oxygen content from 1176wppm to 3300wppm increases the macroscopic yield stress at room temperature, and results in a transition in work hardening behaviour at low strain rates. Increasing iron content from 547wppm to 1080wppm has no effect on the macroscopic yield stress, but increases the work hardening rate at room temperature. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-10-11 20:06:57.655

I present physical shear-box experiments investigating the relationship between geometrical properties of shear zones and mechanical properties of deformed rocks. Experimental methodology is also examined critically and new materials for analogue modelling of shear localization are presented. First, I tested experimentally whether meaningful rheological information can be deduced from finite geometrical shear zone data. The results predict characteristic geometrical responses for certain end-member materials. However, it will be difficult to constrain such responses in the field. In the second part physical controls on deformation in the shear box are analysed for Newtonian and power-law fluids and an elastoviscoplastic strain-softening material. Since models always represent simplifications of the natural problem, it is essential to understand fully the physics of a given simulation. I show that displacement boundary conditions, model geometry, and rheology control shear zone geometry. Practical applications of the shear box for modelling natural shear localization and limitations of isothermal physical models with displacement boundary conditions in general are discussed. In the third part, new data on the rheology of highly-filled silicone polymers are introduced. Since dynamic similarity must be satisfied in analogue models to permit scaled, quantitative simulations of deformation processes, the choice of suitable rock analogues is critical for physical experiments. In particular, we address the problem of designing power-law fluids to model rocks deforming by dislocation creep. We found that highly-filled polymers have complex rheologies. Hence, such materials must be used with care in analogue modelling and only for certain experimental stress-strain rate conditions. Finally, I investigated whether fault network geometry and topography of brittle strike-slip faults are influenced by the degree of compaction of the host rock. Analogue shear experiments with loose and dense sand imply that the degree of sediment compaction may be a governing factor in the evolution of fault network structure and topography along strike-slip faults in sedimentary basins. Therefore, models of strike-slip faults should consider potential volume changes of deformed rocks.

A research project at Linnaeus University focuses on optimizing theadhesives joints between wood and glass, with the aim of obtain stiffcomponents that can act as a load and stabilizing elements and still betransparent. But there is, however, still a lack of knowledge regarding theadhesive materials which need to be further investigated. This thesis focused on testing six different adhesives in relaxation and todetermine the viscosity (η) and modulus of elastic (MOE, E). Viscosity andMOE are then used in combination in a standard linear solid model (SLS)describing the viscoelasticity mathematically. Figures and tables are used topresent the results and the evaluation. The so determined parameters can beused in e.g. finite element models for the design of load bearing timber glasscomposites.

This research focuses on the spall properties of aluminum-magnesium (Al-Mg)alloys.Aluminum alloy 5083 (Al 5083) was used as a model alloy for the work performed in this study. Al-Mg alloys represent a light-weight and corrosion resistant alloy system often used in armor plating. It is desirable to process armor plate material to yield a microstructure that provides maximum resistance to spall failure due to blast and projectile impacts. The blast and impact resistance has often been quantified based on the measurement of the spall strength and the Hugoniot elastic limit (HEL). The spall properties of Al-Mg alloys were measured for four different microstructural states resultant from varying processing conditions. The four microstructures include: (a) textured grain structure from a rolled Al 5083-H116 plate, (b) sub-micron grain structure produced using equi-channel angular pressing (ECAP),(c) equiaxed grain structure, and (d) precipitation hardened microstucture from an Al-9wt.% Mg alloy. The overall results show that grain size is not the most dominant microstructural feature affecting spall strength in aluminum alloys, when the impact conditions are the same. Texture, especially if brittle inclusions align along the grains, appears to have the most dominant effect resulting in decreased spall strength. Furthermore, one-dimensional modeling shows that the inclusion size and distribution is the controlling factor for void formation during spalling. Grain size does affect the decompression rate dependence of each microstructure, whereby smaller grain sizes result in a larger power law exponent for fits of spall strength versus decompression rate. Unlike the spall strength, the HEL shows an increasing trend with decreased grain size, as would be expected from a Hall-Petch type effect, indicating that a smaller grain size is best for penetration resistance. Samples processed using ECAP alone provide the best combination of spall strength and HEL and therefore the most promise for improved blast and penetration resistance of aluminum-magnesium alloy armor plates.

Strain detecting with carbon nanotube (CNT) networks is one of the encouraging findings in sensor technologies. Two types of CNT based films are available for strain detection, namely CNT composite films and CNT films. Configurations of the CNT networks in these films can be made into random and aligned distributions. Understanding of fundamental knowledge regarding piezoresistive response in CNT networks in particular of the CNT film is not quite available, and this is the motivation of the present thesis. In this thesis, piezoresistive response of CNT networks under in-plane straining was studies in details first. Based on the stick percolation model, the relation between the density and conductance in CNT networks (with randomly distributed) was established and then the models which describe the relation between the density and piezoresistive sensitivity and the relation between density and piezoresistive linearity, respectively, were developed. After that, fabrication of CNT networks with aligned distributions was studied. Likewise, the models as developed for CNT network with random distributions were developed for ones with aligned distributions. Finally, modeling of the stress transfer between the nanotubes and polymer matrix was studied. This study has led to the following conclusions: (1) piezoresistive response in CNT networks of the CNT film follows the stick percolation model with the critical exponent coefficient (α) in the model being 1.938; (2) it is feasible to fabricate aligned CNT networks of varying densities with the technique which combines the spray deposition and externally applied magnetic field; (3) the configuration of CNT networks, in addition to their density, was a primary factor governing their piezoresistive response; (4) slipping occurs at the interface between the nanotube and polymer matrix when the films are subject to in-plane straining. The contributions of this study are: (1) the knowledge along with a percolation model for piezoresistive response of CNT networks of the CNT film, (2) a fabrication technique to align CNT networks of the CNT film, and (3) the knowledge along with a model for interaction between the CNT and polymer substrate in the CNT film.

In this work, three aluminum sheet alloys, AA5754, AA5182 and AA6111, which are prime candidates for replacing mild steel in automobile structures, are tested in tension at quasi-static and high strain rates. <br /><br /> In order to characterize the constitutive response of AA5754, AA5182 and AA6111 at high strain rates, tensile experiments were carried out at strain rates between 600 s^-1 and 1500 s^-1, and at temperatures between ambient and 300??C, using a tensile split Hopkinson bar (TSHB) apparatus. As part of this research, the apparatus was modified in order to provide an improved means of gripping the sheet specimens. Quasi-static experiments also were conducted using an Instron machine. <br /><br /> The experimental data was fit to the Johnson-Cook and Zerilli-Armstrong constitutive models for all three alloys. The resulting fits were evaluated by numerically simulating the tensile experiments conducted using a finite element approach.