Over the past decades, bulk metallic glasses (BMGs) have attracted extensive interests because of their unique physical and chemical properties such as good corrosion resistance, larger elastic elongation limit and high strength and hardness. They are also seen as the potential material for micro-electro-mechanical systems (MEMS). However, despite many extraordinary properties in BMGs, BMGs might be difficult to be made into MEMS, different from thin film metallic glasses (TFMGs). Compared with BMGs, few studies have been carried out on TFMGs and their application for MEMS. In this study, efforts have been made to study the properties of multilayered TFMGs. The multilayer thin film selected in this thesis is amorphous/nanocrystalline nanolaminate systems. The micro-pillars of multilayered TFMGs with diameter of 1 £gm are fabricated by using focus ion beam (FIB) and tested in microcompression at room temperature. On nano-indentation test, the phenomenon of strain burst decreases by way of multilayer system. It means that the multilayer system can retard the shear band propagation initiated from the amorphous layers. Under the microcompression test, the deformation of both ZrCu (100 nm)/Cu (50 nm) and ZrCu (100 nm)/Cu (10 nm) multilayer micro-pillars are still dominated by the emission of shear bands in a manner of strain burst to release the energy, but the ZrCu (100 nm)/Cu (100 nm) multilayer thin films reveal continuous deformation and smooth stress-strain curve with no strain burst. First, the sufficient thick of copper layer can absorb more energy from shear deformation of amorphous layer. Second, the copper layer exhibits plastic flow along the transverse direction under the iso-stress deformation. The transverse plastic flow acts as a shear force at interface causing non-stress concentration at amorphous layer. It means that the amorphous layer can be deformed to large plastic strain without stress concentration, causing a homogeneous deformation. According to these two deformation mechanisms, it is possible that the ZrCu (100 nm)/Cu (100 nm) multilayer thin film is better system for improving the ductility of amorphous alloy with a good strength.

The fingerprint of deformation in materials at large strains and at high strain rates is the formation of adiabatic shear bands. Adiabatic shear bands lead to unexpected failure of materials during service. This study investigated the possibility of eliminating adiabatic shear bands from materials subjected to severe deformation at high strain rates by post impact heat treatment. Five groups of cylindrical AISI 4340 steel samples were impacted using the Direct Impact Hopkinson Pressure Bar (DIHPB) developed at the University of Manitoba. Selected impacted samples with distinct transformed shear bands were soaked at 350⁰C to 850⁰C for periods ranging from 30 minutes to 4 hours to investigate how temperature and time affects the properties and structure of the shear bands. Annealing the shear bands at 350⁰C resulted in an increase in hardness of the shear bands and the surrounding material outside the shear bands regardless of the heat treatment before impact, amount of deformation, and the time of annealing. Significant decrease in hardness of the shear bands occurred after post impact annealing at 650⁰C for 30 minutes and 2 hours. Hardness of the shear bands reduced to the same level as that of the impacted material outside the shear bands. However, the initial path of the shear bands in the impacted steel samples could be traced through a “signature” left after the annealing. Post-impact annealing of the steel samples at 750⁰C and 850⁰C resulted in a homogenous microstructure with no trace of the shear bands. The “signatures” which were used to trace the path of the shear bands in impacted samples annealed at 650⁰C disappeared and the hardness across the samples became uniform. The observations from this study show that adiabatic shear bands in typical steel can be eliminated by annealing heat treatment. The temperature of annealing is the most critical parameter and the annealing should be performed above 650⁰C.

Submarine landslides, commonly triggered by earthquakes, significantly affect tsunami wave heights. Subaerial landslides can also generate tsunamis (if the land flows into a body of water) and may be catastrophic in nature, causing human casualties and direct property damage. This work focuses on landslides associated with shear band that develops beneath the slipping mass. Accordingly, we consider a landslide as a dynamic process when a shear band emerges along the potential failure surface. Within this band, the shear strength decreases due to the softening behaviour of the particulate material. Material above the band moves downwards, causing the band to propagate dynamically. This already produces a landslide velocity before the slide reaches the post-failure stage and begins separating from the substrata and generating tsunami. However, existing models of tsunamigenic landslides assume zero initial slide velocity. Previous analyses of the catastrophic shear band propagation in slopes of normally- and over-consolidated sediments have shown that a relatively short initial failure zone is sufficient to cause a full-scale landslide. For the shear band to propagate, the energy produced in the body by an incremental propagation of the shear band must exceed the energy required for the propagation. This consideration separates the shear band growth into progressive (stable) and catastrophic (dynamic) stages and treats the band growth as a true physical process rather than an instantaneously appearing discontinuity. This work considers a dynamic shear band problem formulated within the framework of the Palmer and Rice’s [1973] approach. We obtain the exact, closed-form solution for the shear band and landslide velocities as well as for the spatial and temporal distributions of strain and material velocity. This solution assesses when the slide fails due to the limiting condition near the propagating tip of the shear band. We also obtain a simple asymptotic solution, which is compared to the exact solution. In the case of submerged slopes, the obtained solutions are used in landslide and tsunami height analyses. Our results suggest that the conventional static approach to the slope stability analysis leads to a significant underestimation of the slide size (volume). In most cases, the volumes of catastrophic slides are roughly twice the volumes of progressive slides. For submerged slides, this dynamic effect further manifests itself in increasing the tsunami magnitude compared to the static case.

In this experimental, we use ECAE with route BC to produce the ultrafine-grain Al and use different annealing temperature to get grain size at 0.4

Since the first discovery of amorphous alloys in 1960, researchers have explored many unique mechanical, magnetic, and optical characteristics of such materials for potential applications. Up to now, well-developed processes, such as rapid quenching, sputtering, evaporation, pulse laser deposition, etc, have been applied for different applications in micro-electro-mechanical systems (MEMS). Due to the lack of ordered structure, amorphous alloys can bear a high stress in the elastic region. Their plastic deformation stability is also of interest and has been widely studied. The shear-band characteristic, a kind of inhomogeneous deformation mechanism, dominates the deformation after yielding at room temperature. While a shear band nucleate, its propagation usually cannot be arrested or stopped. In other words, the occurrence of matured shear bands needs to be prevented. There are two major approaches in this aspect. The first is to increase the material yield strength so as to delay the shear band nucleation. Another is to incorporate intrinsic or extrinsic particles so as to absorb the kinetic energy of shear bands in the amorphous matrix. In this study, we utilize three strategies to control the propagation of shear bands in thin film metallic glasses (TFMGs): sub-Tg annealing, the addition of strong element in solute form, and the introduction of strong nanocrystalline layers. For sub-Tg annealing, the base alloy system is Zr69Cu31, with a base film hardness of 5.1 GPa measured by nanoindentation. After annealing, the hardness exhibits ~30% increase. Without the occurrence of the phase transformation, as confirmed by X-ray diffraction, the possible reaction during sub-Tg annealing is attributed to structural relaxation, not crystallization. The full width at half maximum of the X-ray peak exhibits a decreasing trend in the using X-ray and transmission electron microscopy diffraction, meaning the excess free volumes forming during vapor-to-solid deposition process would be annihilated by localized atomic re-arrangement. Moreover, the formation of medium-ordering-range clusters was confirmed utilizing high-resolution transmission electronic microscopy. The denser amorphous structure leads to the increment of hardness. For the addition of Ta in Zr55Cu31Ti14, sputtering provides a wide glass forming range with solubility of Ta approaching ~75 at%. With increasing Ta content, the elastic modulus and hardness increase slowly. A steep rise occurs at ~50 at% of Ta. Up to 75 at% of Ta, the elastic modulus and hardness approaches 140 GPa and 10.0 GPa, respectively (100% increment). Up to now, Ta-rich TFMGs exhibit the highest elastic modulus and hardness among all amorphous alloys fabricated using vapor deposition techniques. The irregular increase is attributed to the formation of Ta-Ta bonding. A large quantity of Ta bonds would lead to the formation of Ta-rich nanoclusters, drastically decreasing the strain rate while shear band propagates under nanoindentation and microcompression tests. The introduction of nanocrystalline Ta layers can not only effectively enhance the yield strength but also serve as the absorber for the kinetic energy of shear bands, revealing ductility in the microcompression test.

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On the toughening of bulk metallic glasses (BMGs), successful results in the phase-separated Zr63.8Ni16.2Cu15Al5 BMG have achieved compressive ductility over 15% through the computational-thermodynamic approach. In this study, the phase-separated Zr63.8Ni16.2Cu15Al5 BMG was compressed to nominal strains of 3%, 7%, and 10% at low strain rates (~10-4 s-1) and the results demonstrated that the BMG exhibited apparent uniform deformation initially, followed by visible local shear bands development. Afterwards, a single shear along the principal shear plane was soon developed and mainly dominated the whole deformation process. The principal shear contributed more than 2/3 of the overall plastic strain until failure. It was also found that the local shear strain varied along the principal shear plane and decreased monotonically from the shear band initiation site. Subsequently, in-situ compression experiments were conducted to monitor the change of sample shape during deformation in order to properly correlate with the stress-strain curve. The observed images showed that there was a one-to-one correspondence between the intermittent sample sliding and flow serration in the plastic region of stress-strain curve. Further investigations on flow serration were conducted on the Pd40Ni40P20 BMG through the compression experiments equipped with high-sensitivity strain gauges directly attached to two opposite sides of the test sample. There was an accompanied displacement burst when a shear band starts to propagate during deformation and this displacement burst would be accurately captured by the high-sensitivity strain gauges. Based on the displacement-time profile for one serration, shear-band propagating speed can be estimated and found to be insensitive to the applied strain rates (or the applied crosshead speeds). The disappearance of flow serration at high strain rates should be a result that the signal of displacement burst was overwhelmed by the applied strain rate. Using the shear strain rate data, the measured viscosity within a propagating shear band was found to be relatively low, which is in similar to the viscosity values reported in the supercooled liquid region during homogeneous deformation. In comparison with shear band propagation in the brittle Mg58Cu31Y6Nd5 and Au49Ag5.5Pd2.3Cu26.9Si16.3, moderately ductile Cu50Zr43Al7 and Pd40Ni40P20, and highly ductile phased-separated Zr63.8Ni16.2Cu15Al5 systems, the ductility of BMGs appears to be closely related to the dynamics during shear band propagation. The more ductile in nature the metallic glass is, the slower the shear band propagating speed would become. We also made attempts to investigate the shear band propagation in the porous Mo particles reinforced Mg58Cu28.5Gd11Ag2.5 bulk metallic glass composites (BMGCs) with up to 10% compressive failure strain. It was found that flow serration was absent in the stress-strain curve. Using high-sensitivity strain gauges, no distinct displacement burst was detected in the displacement-time profile. The diappearance of flow serration for the current porous Mo particles reinforced Mg58Cu28.5Gd11Ag2.5 BMGC is apparently associated with the lack of long-range shear band propagagtion. By employing the approach of separating the homogeneous amorphous matrix into many individual compartments, only short-range shear band propgagation is possible in the current Mg-based BMGC. An effective free spacing considering the spacing between two porous Mo particles and porous Mo particle size was applied to interpret the development of shear band propagation and is a useful indicator for the design of BMGC with high ductility.

There is currently an interest in optimizing the structural design to improve materials' strength to weight ratio or improve stiffness for energy absorption. As such, cellular structures are continuously studied and improved. However, it is a well-known fact in the literature that one primary mechanism of failure of a honeycomb is the formation of shear bands. The impacts of these shear bands bring many questions and unknowns, especially when the cellular structures are created with the increasingly popular manufacturing technique of 3D printing. Therefore, understanding the deformations in 3D printed honeycomb structures is necessary to explain the behavior of materials generated through new additive manufacturing techniques and further the knowledge of the deformation localization and, consequently, formations of shear bands in the deformation process of cellular structures.In the first phase of this work, samples with a unit cell regular hexagonal honeycomb format were designed and manufactured using masked-stereolithography (M-SLA). After the curing process, the samples were prepared with a paint application in the format of speckle, and DIC was realized in a compression experiment to identify and analyze the presence of high strain regions indicating the presence of shear bands. A second phase was then conducted, aiming to consider the control and manipulation of the shear band through the utilization of relief holes. The results demonstrated that adding incisions in specific parts of the polymeric honeycomb makes it possible to change its strain spread through the shear band and change its toughness.

Surface fault rupture poses a serious threat to infrastructure in many seismically active regions, but knowledge about the factors which control the likelihood of surface displacement is limited. Current probabilistic frameworks rely only on fault mechanism and moment magnitude to predict the probability of rupture to the ground surface. However, recent work has shown that there may be other parameters which also deserve consideration. For example, statistical analyses have demonstrated that variation in near surface material stiffness may significantly affect the probability of surface rupture over reverse faults. In addition, numerical investigations indicate that the rupture history of native soil deposits also greatly influences the nature of rupture propagation. Given that evidence exists which suggests multiple variables are at work, this study aimed to improve our understanding of which are most critical for predicting surface fault rupture hazard. We sought to generate physical evidence concerning the impact of near surface soil stiffness, soil type, and rupture history on fault rupture propagation. A 3 meter long by 1 meter wide fault box apparatus was constructed to simulate idealized reverse fault rupture oriented at 45° beneath 60cm of soil. Relatively large dimensions were chosen so that shear wave velocity measurements could be taken directly without interference from the walls of the apparatus. Experiments were conducted on loose sand, dense sand, stiff clay, and soft clay. The same sand was used for both the dense and loose sand experiments and is identified as Monterey #2/16. The clay was a scale model mixture of San Francisco Bay Mud and consisted of kaolinite, bentonite, class C fly ash, and water. Separate batches of clay were mixed with differing final water contents for the stiff and soft clay experiments. In each case, the fault box was filled to 60 cm and rupture was driven to the surface in two phases. The first phase represented an undisturbed native soil deposit with no existing shear band. The second simulated repeat rupture along a pre-existing shear band. The results indicate that increasing material stiffness promotes rupture propagation in both sand and clay. When disturbed soil is re-ruptured, surface rupture occurred much more readily in all materials. Overall, the presence of a pre-existing shear band was shown to have the greatest impact on the likelihood of surface rupture, though both material stiffness and type were also found to have a strong influence as well. The fault box experiments support the findings from previous work as well as shed new light on which parameters are most critical for accurate surface rupture predictions.

The initiation and propagation of adiabatic shear bands is analyzed numerically for an impulsively loaded thick-walled steel tube. A circumferential V-notch located at the outer surface of the center of the tube provides a stress concentration. The material is modeled as strain hardening, strain-rate hardening and thermal softening. The dynamic loading conditions considered are pure torsion, axial pressure combined with torsion, and internal pressure combined with torsion. Because of the stress concentration, a shear band will first initiate in an element adjoining the notch tip and propagate radially inwards through the thickness of the tube. The speed of propagation and the amount of energy required to drive a shear band through the material are calculated. The effects of the pressure preload and the depth of the notch are studied. Also, the influence of thermal softening is investigated by modeling it after a relation proposed by Zhou et al. <i>[Vita removed July 18, 2008 CK/GMc 2/2/2012]<i> / Master of Science