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No description available.

No description available.

No description available.

No description available.

In the laser-induced cavitation (LIC) technique, a vapor-gas cavity is generated in water, or a soft material by focusing an intense laser pulse into the sample. The high-strain-rate mechanical properties of these samples can be investigated through a real-time size measurement of the expanding cavity bubble. Although this LIC technique has been applied to multiple research fields such as mechanical, biological and medical areas. It is possible to simplify and improve this LIC method by introducing optical-fibers. In this approach, we propose to employ an optical-fiber to deliver the intense laser pulse to an arbitrary position of an optical opaque specimen. At the same time, we also attempt to generate LIC at one end of the optical-fiber. This optical-fiber based LIC is achieved by dip-coating of the laser absorbing film on the fiber end. Thus, the film can absorb the laser pulse and generate LIC within the sample. In this study, the development of the coating material, the introduction of the optical-fiber into the existing LIC system, and the optical-fiber based LIC experiments are performed to characterize high-strain-rate mechanical properties of soft materials. We investigate the coating conditions and verify the consistency of the ablation based on the optimized coating materials. By conducting LIC experiments with gelatin samples, the feasibility of developed LIC method is investigated, LIC events are successfully formed at the fiber end which is inserted into the sample, and the rapid expanding dynamics are imaged with ultrafast stroboscopic microscopy. Using the multiple-exposure images, the expanding speeds and maximum cavity sizes are quantified to provide high-strain-rate characteristics of the soft materials. The inconsistency of the cavitation behavior resulted by the fluctuation of the coating condition and the high power intense laser conducting optical-fiber destruction can be improved by developing new coating method and new protective coating on the fiber end in the future.

<p>Tension and compression experiments have been carried out on a series of Mg-Y alloys with Y content up to 1.3 at.%, in a range of temperatures between 4.2K and 298K, to study the effect of Yttrium on mechanical properties and strain hardening. The alloys show strong difference in the hardening behavior under tension and compression attributed to the effect of texture. The yield strength scales with concentration of the solute as cⁿ, where c is the concentration of the solute in atomic percent and n~2/3. The results suggest that in addition to the atomic size and modulus misfit effects, the valence may be responsible for the enhanced strengthening of Y in Mg. Strain rate sensitivity measurements carried out under tension and compression reveal that Mg-Y alloys show decreasing SRS with increasing Y content at 298K and exhibit a negative SRS in highly concentrated alloys. At low temperatures the alloys show positive SRS increased with Y content. Texture measurements suggest that increasing Y content in alloys decreases the amount of basal component and enhances non-basal orientations. The reduced yield asymmetry between tension and compression observed in higher Y content alloys is being attributed to the weakening of the basal texture.</p> / Master of Applied Science (MASc)

The split Hopkinson bar test is the most commonly used method for determining material properties at high rates of strain. The theory governing the specifics of Hopkinson bar testing has been around for decades. It has only been the last decade or so, however, that significant data processing advancements have been made. It is the intent of this thesis to offer the insight of its author towards new advancements. The split Hopkinson bar apparatus consists of two long slender bars that sandwich a short cylindrical specimen between them. By striking the end of a bar, a compressive stress wave is generated that immediately begins to traverse towards the specimen. Upon arrival at the specimen, the wave partially reflects back towards the impact end. The remainder of the wave transmits through the specimen and into the second bar, causing irreversible plastic deformation in the specimen. It is shown that the reflected and transmitted waves are proportional to the specimen's strain rate and stress, respectively. Specimen strain can be determined by integrating the strain rate. By monitoring the strains in the two bars, specimen stress-strain properties can be calculated. Several factors influence the accuracy of the results, including longitudinal wave dispersion, impedance mismatch of the bars with the specimens, and transducer properties, among others. A particular area of advancement is a new technique to determine the bars dispersive nature, and hence reducing the distorting effects. By implementing numerical procedures, precise alignment of the strain pulses is facilitated. It is shown that by choosing specimen dimensions based on their impedance, the transmitted stress signal-to-noise ratio can be improved by as much as 25dB. An in depth discussion of realistic expectations of strain gages is presented, along with closed form solutions validating any claims. The effect of windowing on the actual strains is developed by analyzing the convolution of a rectangular window with the impact pulse. The thesis concludes with a statistical evaluation of test results. Several recommendations are then made for pursuing new areas of continual research. / Master of Science

Dynamically recrystallized quartz microstructures preserved in contact aureoles allow for stress and strain rate estimates associated with penetrative deformation of rocks surrounding pluton margins. Microstructural analysis of the Harkless quartzites surrounding the western margin of Papoose Flat pluton indicates that recrystallization occurred by grain boundary migration with mean recrystallized grain size ranging from 86-225 µm. The application of three calibrated piezometers results in differential stress estimates between ~11 and ~29 MPa. Published wet-quartzite dislocation creep flow laws combined with deformation temperature, water fugacity, and differential stress estimates infer strain rates that range from 1.2 x 10⁻¹⁴ s⁻¹ to 2.3 x 10⁻¹² s⁻¹. In order to analyze 3D subsurface fault geometry along map-pattern curves (salients and recesses), a structure contour map of the Moine thrust, extending from the North Coast southwards to the Dundonnel area, was constructed from 1:50,000 scale British Geological Survey (BGS) maps by correlating between elevation control points constrained by the intersection of the fault trace with topographic contours. The structure contour map indicates significant lateral variation in fault geometry along the Moine thrust, with recesses associated with antiformal corrugations in the subsurface and salients characterized by planar geometries or broad synformal corrugations. Additionally, structure contour maps constructed on the Glencoul thrust, as depicted by original BGS maps confirms that the thrust segments to the NE and SW of Loch Glencoul are part of the same structure, rather than different structures separated by a lateral ramp as shown on more recent BGS maps. / Master of Science

Free-Fall Penetrometer (FFP) testing is an easy and rapid test procedure for seabed sediment characterization favorable to conventional geotechnical testing mainly due to its cost-effectiveness. Yet, FFP testing results are interpreted using empirical correlations, but difficulties arise to understand soil behavior under the high-strain rate (HSR) loading effects during rapid FFP penetration. The numerical simulation of FFP-soil interaction is also challenging. This study aims to numerically analyze FFP testing of saturated loose sands using the particle-based Material Point Method (MPM). The numerical analysis was conducted by simulating calibration chamber FFP tests on saturated loose quartz sand. The numerical results using quasi-static properties resulted in a reaction of the sand softer than the actual calibration chamber test. This implied the necessity of considering HSR effects. After performing parametric analyses, it was concluded that dilation plays an important role in the response of sand-water mixtures. Comparison of dry and saturated simulations showed that FFP penetration increases when the soil is dry and tends to develop a general bearing capacity failure mechanism. This is because the pore water increases the stiffness of the system and due to the increased strength that develops in saturated dilative sands when negative pore pressures develop. Local bearing failure mechanism is observed in all saturated simulations. Finally, numerical CPT (quasi-static) and FFP tests were used to examine the strain rate coefficient used in practice (K); and a consistent range between 1 to 1.5 was obtained. / Master of Science / Accurate characterization of seabed sediments is crucial to understand sediment mobilization processes and to solve nearshore engineering problems such as scouring around offshore structures. Its portability, low testing effort, and repeatability make FreeFall Penetrometer (FFP) testing a highly cost-effective sediment characterization test. Nevertheless, due to the complex penetration mechanism of FFPs in soils (e.g., high-strain rate effects due to rapid FFP loading), converting FFP output into practical information is complicated, and it heavily relies on empirical correlations. This thesis presents a numerical analysis of FFP testing on saturated sand using the Material Point Method. First, the simulation results were compared with laboratory tests. Later, a parametric study was performed to understand the effect of different material parameters on the FFP response and to highlight in a simplified manner the effects of rapid loading on the sand behavior. Additional simulations in dry sand (without water) revealed that dry conditions provide larger FFP penetrations than saturated ones for the same material parameters. Lastly, the strain rate coefficient, which is a parameter required in one of the most common empirical methods for converting FFP output into geotechnical parameters, was back-calculated. The results were consistent with values used in practice for similar conditions.