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<p>Masonry is one of the most commonly used materials in building construction throughout the world. Unreinforced masonry (URM) walls typically have very low flexural capacities and tend to posses brittle failure modes. Due to brittle nature of URM walls, it is critical to predict the behaviour of the wall when exposed to extreme out of plane loadings such as blast loads. An effective way to enhance the ability of unreinforced masonry walls to withstand blast loads and consequently to limit the amount of wall damage is imposing arching mechanism on the wall. Since carrying out physical experiments to study the response of URM walls subjected to blast load is both dangerous and expensive, finite element modeling has become more attractive to researchers. In this research, an unreinforced one-way arching wall is simulated using the finite element program LS-DYNA and its behaviour subjected blast loading is studied. The model is constructed based on the data recorded earlier during a physical blast experiment. Close agreement was observed between the numerical and experimental results which validated the developed model. A sensitivity study is then performed where the influence of variation of some input parameters such as mortar strength, coefficients of friction, scaled distance, boundary condition, wall height and the effect of two-way arching action on the wall’s response is evaluated. The most influential parameters in this study found to be the scaled distance, wall height and two-way arching action. Smaller scaled distances result in high deflection and as the scaled distance increases the maximum deflection decreases. The wall height also significantly affect the wall’s response to blast loads, i.e. the taller the wall the larger the maximum displacement. It is also concluded that two-way arching action can significantly reduce the wall’s maximum deflection.</p> / Master of Applied Science (MASc)

Several efforts have been made in the past half century to characterize the behavior of brain tissue under different modes of loading and deformation rates; however each developed model has been associated with limitations. This dissertation aims at addressing the non-linear and rate dependent behavior of brain tissue specially in high strain rates (above 100 s-1) that represents the loading conditions occurring in blast induced neurotrauma (BINT) and development of a universal constitutive model for brain tissue that describes the tissue mechanical behavior from medium to high loading rates.. In order to evaluate the nature of nonlinearity of brain tissue, bovine brain samples (n=30) were tested under shear stress-relaxation loading with medium strain rate of 10 s-1 at strain levels ranging from 2% to 40% and the isochronous stress strain curves at 0,1 s and 10 s after the peak force formed. This approach enabled verification of the applicability of the quasilinear viscoelastic (QLV) theory to brain tissue and derivation of its elastic function based on the physics of the material rather than relying solely on curve fitting. The results confirmed that the QLV theory is an acceptable approximation for engineering shear strain levels below 40% that is beyond the level of axonal injury and the shape of the instantaneous elastic response was determined to be a 5th order odd polynomial with instantaneous linear shear modulus of 3.48±0.18 kPa. To investigate the rate dependent behavior of brain tissue at high strain rates, a novel experimental setup was developed and bovine brain samples (n=25) were tested at strain rates of 90, 120, 500, 600 and 800 s-1 and the resulting deformation and shear force were recorded. The stress-strain relationships showed significant rate dependency at high rates and was characterized using a QLV model with a 739 s-1 decay rate and validated with finite element analysis. The results showed the brain instantaneous elastic response can be modeled with a 3rd order odd polynomial and the instantaneous linear shear modulus was 19.2±1.1 kPa. A universal constitutive model was developed by combining the models developed for medium and high rate deformations and based on the QLV theory, in which the relaxation function has 5 time constants for 5 orders of magnitude in time (from 1 ms to 10 s) and therefore, is capable of predicting the brain tissue behavior in a wide range of deformation rates. Although the universal model presented in this study was developed based on only shear tests and the material parameters could not be found uniquely, by comparing the results of this study with previously available data in the literature under tension unique material parameters were determined for a 5 parameter generalized Rivlin elastic function (C10=3.208±0.602 kPa, C01=4.191±1.074 kPa, C11=79.898±18.974 kPa, C20=-37.093±7.273 kPa, C02=-37.712±5.678 kPa). The universal constitutive model for brain tissue presented in this dissertation is capable of characterizing the brain tissue behavior under large deformation in a wide range of strain rates and can be used in computational modeling of Traumatic Brain Injury (TBI) to predict injuries that result from falls and sports to automotive accidents and BINT. / Mechanical Engineering

Compared to materials with a straight geometry, materials with a corrugated architecture have shown potential to improve ductility without sacrificing strength due to the unbending of the corrugation during loading. The purpose of this research was to study the effect of geometric and material parameters on the stress-strain response of materials with a corrugated geometry and understand what controls the unbending process and under what conditions improved ductility was achievable. This involved studying isolated corrugations and corrugation reinforced composites under tensile and transverse compressive loading by performing parametric studies using Finite Element Modeling (FEM) simulations. These simulations showed that improvements in ductility are directly related to the degree of corrugation present and can be attributed to an initial bending dominated process. The unbending of the corrugation leads to an evolving geometry which causes the material to strengthen and ultimately delays necking. For corrugated composites, it was found that there is significant interplay between the properties of the components and the geometry of the corrugation. To obtain a benefit in ductility through corrugation, the matrix must have sufficiently high work hardening to accommodate the unbending corrugation without itself necking, but also have sufficiently low flow stress relative to the reinforcement yield strength to prevent the corrugation from stretching instead of unbending. Also, if the boost in work hardening from unbending occurs too early, no gain in ductility is achieved. In addition to these findings, tools for predicting the strength and ductility of these materials were developed, including an analytical model for the isolated corrugations and a series of benefit maps and surfaces for the corrugated composites. These tools proved to be fairly effective. Finally, the FEM findings were compared to experimental stress-strain curves and strain maps for validation and showed relatively good qualitative agreement. / Thesis / Doctor of Philosophy (PhD) / It is uncommon to find a material that possesses both high strength as well as the ability to elongate a lot without failing. One way to achieve this combination of properties is to use a wavy or corrugated structure that provides increased elongation when loaded due to the straightening of the corrugation. The purpose of this thesis was to study how materials which possess a wavy or corrugated geometry behave when they are subjected to a stretching load. This research utilized computer simulations and simple experimental testing to evaluate both isolated corrugations and corrugations embedded in another material. It was found that the amount of improvement in elongation is dependent on the initial amount of waviness. Also, whether a material shows improved elongation depends on whether the corrugation is able to unbend, which in turn depends on the corrugation geometry and the relative mechanical properties of the two materials.