Browsing by Subject "deformation"
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Item An Abrupt Transition in the Mechanical Response of the Upper Crust to Transpression Along the Queen Charlotte Fault(2015-05) Trehu, Anne M.; Scheidhauer, Maren; Rohr, Kristin M. M.; Tikoff, Basil; Walton, Maureen A. L.; Gulick, Sean P. S.; Roland, Emily C.; Walton, Maureen A. L.; Gulick, Sean P. S.The Queen Charlotte Fault (QCF) is a major strike-slip fault that forms the boundary between the Pacific and North American plates from 51 degrees to 58 degrees N. Near 53.2 degrees N, the angle of oblique convergence predicted by the Mid-Ocean Ridge VELocity (MORVEL) interplate pole of rotation decreases from > 15 degrees in the south to < 15 degrees in the north. South of 53.2 degrees N, the convergent component of plate motion results in the formation of a 40 km wide terrace on the Pacific plate west of QCF and earthquakes with thrust mechanisms (including the 2012 Haida Gwaii earthquake sequence) are observed. North of 53.2 degrees N, in the primary rupture zone of the M 8.1 strike-slip earthquake of 1949, the linear terrace disappears, and topography of the continental slope west of the QCF is characterized by a complex pattern of ridges and basins that trend obliquely to the primary trace of the QCF. Deformation within the Pacific plate appears to occur primarily through strike-slip faulting with a minor thrust component on secondary synthetic faults. The orientations of these secondary faults, as determined from seismic reflection and bathymetric data, are consistent with the reactivation of faults originally formed as ridge-parallel normal faults and as thrust faults formed parallel to the QCF south of the bend at 53.2 degrees N and subsequently translated to the north. We suggest that an oblique convergence angle of 15 degrees represents a critical threshold separating distinct crustal responses to transpression. This result is consistent with theoretical and analog strain models of transpressive plate boundaries. The sharpness of this transition along the QCF, in contrast to purely continental transform boundaries, may be facilitated by the relatively simple structure of oceanic crust and the presence of pre-existing, optimally oriented faults in the young Pacific plate.Item Characterization of Acoustic Softening of Aluminum 6061 Within a Plasticity Framework(University of Texas at Austin, 2014) Mao, Q.; Coutris, N.; Fadel, G.Ultrasonic additive manufacturing (UAM) is a rapid prototyping technology that features a metal joining process through ultrasonic welding. The bonding mechanisms and mechanics of UAM have been investigated for decades. Meanwhile, the plastic deformations of metals were extensively studied by many researchers for their significant roles in bond formation. However, most of these research efforts considered solely the surface frictional effects on plastic deformation whereas the volumetric effects of ultrasound were rarely considered. This paper investigates the effects of ultrasound on deformation of Aluminum 6061 through experimental studies and highlights the volumetric effects of ultrasound, i.e. the “acoustic softening”: a stress reduction on the stress-strain relation of Aluminum 6061 upon application of ultrasounds. Based on observations obtained from a designed experimental setup, a phenomenological model is proposed to characterize the acoustic softening effects in terms of the ultrasonic intensities. Additionally, by modifying Hockett’s plasticity model, a plasticity frame work is established to characterize the deformation of Aluminum 6061 in UAM. The acoustic softening model is then incorporated into the plasticity framework. The complete model is then validated by comparing its predictions with experimental measurements.Item Deformation Post-Processing of Additive Manufacturing Components(University of Texas at Austin, 2013) Crane, N.B.; Lusk, C.P.; Nussbaum, J.; Consuegra Reyes, Y.Parts produced by additive manufacturing (AM) often require post processing to improve surface finish and mechanical properties. However, little attention has been given to including deformation in the post processing. Deformation post-processing can address some part size, manufacturing cost, and geometry limitations of 3D printing. Additionally, it could be used to create 3D surfaces using planar manufacturing processes (such as printed circuit board manufacturing). The challenge of deformation post-processing is the design of the correct fabrication state to produce the desired final state and the accurate deformation of the parts to the desired final state. This paper demonstrates the geometric capability, potential applications, and methods for accurately and repeatedly deforming the initial geometry to the desired configuration using features in the parts.Item Heat Sources within the Greenland Ice Sheet: Dissipation, Temperate Paleo-Firn and Cryo-Hydrologic Warming(2015-02) Luthi, M. P.; Ryser, C.; Andrews, L. C.; Catania, G. A.; Funk, M.; Hawley, R. L.; Hoffman, M. J.; Neumann, T. A.; Andrews, L. C.; Catania, G. A.Ice temperature profiles from the Greenland Ice Sheet contain information on the deformation history, past climates and recent warming. We present full-depth temperature profiles from two drill sites on a flow line passing through Swiss Camp, West Greenland. Numerical modeling reveals that ice temperatures are considerably higher than would be expected from heat diffusion and dissipation alone. The possible causes for this extra heat are evaluated using a Lagrangian heat flow model. The model results reveal that the observations can be explained with a combination of different processes: enhanced dissipation (strain heating) in ice-age ice, temperate paleo-firn, and cryo-hydrologic warming in deep crevasses.Item Identification of Crucial Parameters in a Mathematical Multiscale Model of Glioblastoma Growth(2014-01) Schuetz, Tina A.; Mang, Andreas; Becker, Stefan; Toma, Alina; Buzug, Thorsten M.; Mang, AndreasGlioblastomas are highly malignant brain tumours. Mathematical models and their analysis provide a tool to support the understanding of the development of these tumours as well as the design of more effective treatment strategies. We have previously developed a multiscale model of glioblastoma progression that covers processes on the cellular and molecular scale. Here, we present a novel nutrient-dependent multiscale sensitivity analysis of this model that helps to identify those reaction parameters of the molecular interaction network that influence the tumour progression on the cellular scale the most. In particular, those parameters are identified that essentially determine tumour expansion and could be therefore used as potential therapy targets. As indicators for the success of a potential therapy target, a deceleration of the tumour expansion and a reduction of the tumour volume are employed. From the results, it can be concluded that no single parameter variation results in a less aggressive tumour. However, it can be shown that a few combined perturbations of two systematically selected parameters cause a slow-down of the tumour expansion velocity accompanied with a decrease of the tumour volume. Those parameters are primarily linked to the reactions that involve the microRNA-451 and the thereof regulated protein MO25.Item Letter to H.B. Stenzel from E.H. Sellards on 1933-05-09(1933-05-09) Sellards, E.H.Item Modeling of Crack Propagation in 2D Brittle Finite Lattice Structures Assisted by Additive Manufacturing(University of Texas at Austin, 2017) Wu, Yan; Yang, LiThe failure characteristics of lattice structures are of significant importance in various lightweight applications such as aerospace and biomedicine. In this study, several 2D lattice structures with different number of unit cells that represent different geometrical characteristics and deformation mechanisms were investigated for their fracture behaviors. The fracture characteristic of the cellular samples was studied experimentally through tensile testing. The fracture propagation patterns of different lattice designs were investigated by high-speed camera, and consequently analyzed via analytical model in order to evaluate the effect of finite unit cells on the fracture characteristics of these cellular structures. The results were further compared with the classic cellular fracture theory by Gibson and Ashby. The comparison results suggest that for small number of unit cells designs the homogenized fracture model does not provide accurate crack propagation predictions.Item Natural Strain in Glacial and Diapric Rock Salt with Emphasis on Oakwood Dome, East Texas(1983) Jackson, M. P. A.In Part I, structural styles in the gravity-driven, ductile-flow processes of glaciers and diapirs are analyzed. Salt glaciers flow under minute differential stress when dampened by rainfall. Thus, the concentration of water in diapiric rock salt is of paramount importance to predicting creep rates in a repository medium. Natural strain rates for rock salt vary enormously from 10^8/s to 10^16/s; the slowest rates are those for average diapiric uplift. Contrary to widespread generalization, structural attitudes in dome-salt mines are predominantly moderate to steep, rather than vertical. In the proposed model, diapiric folds are triggered by (1) shear stresses induced by upward flow, (2) shear stresses induced by boundary effects of the salt source layer, and (3) normal stresses induced by convergent flow. Folding in salt stocks follows the similar-fold model although many folds appear to have been initiated by buckling. Closed interference structures are sheath folds formed by intense constriction of originally gentle fold culminations and depressions. Construction of plunge-isogon maps from mapped linear structures allows the flow directions of diapiric salt to be deduced. Part II describes the results of geometric analysis and strain analysis of salt core from Oakwood Dome. The core has penetrated the hinge zone and lower limb of an inclined overturned antiform, which probably represents a salt tongue that has spread outward from the diapir center. Structural evidence indicates severe truncation of the diapir crest, probably by groundwater dissolution during cap-rock formation. The uppermost 2 meters of rock salt recrystallized in the presence of water. Consideration of homologous temperatures and present maximum erosion rates suggests that the salt recrystallized at least 3 million years ago at depths 400 meters greater than present. All the strains recorded in Oakwood halite are of the flattening type. The ratio of flattening to constriction increases upward, whereas the strain intensity decreases upward, perhaps in transition to an originally "neutral" zone in the diapir, since removed by dissolution. The orientations of maximum-extension directions in rock salt vary widely.Item Numerical Analysis of Thermal Stress and Deformation in Multi-Layer Laser Metal Deposition Processes(University of Texas at Austin, 2013-08-16) Liu, Heng; Sparks, Todd E.; Liou, Frank W.; Dietrich, David M.Direct metal deposition (DMD) has gained increasing attention in the area of rapid manufacturing and repairing. This process involves extremely high thermal gradients and heat and cooling rate, resulting in residual stresses and distortion. This paper presents a 3D sequentially coupled thermo-mechanical finite element model to predict residual stresses and deformations. The temperature distribution, thermal stress field and geometry deformation across domain are illustrated. The effect of deposition parameters on residual stress and deflections are also explored. A set of validation experiments for mechanical effects were conducted using laser displacement sensor. The comparisons between the simulated and experimental results show good agreement.Item Pseudo Jahn-Teller Effect In The Origin Of Enhanced Flexoelectricity(2015-01) Bersuker, Issac B.; Bersuker, Issac B.The controversy between the theory and experiment in explaining the origin of enhanced flexoelectricity is removed by taking into account the pseudo Jahn-Teller effect (PJTE) which, under certain conditions, creates local dipolar distortions of dynamic nature, resonating between two or more equivalent orientations. The latter become nonequivalent under a strain gradient thus producing enhanced flexoelectricity: it is much easier to orient ready-made dipoles than to polarize an ionic solid. For BaTiO3, the obtained earlier numerical data for the adiabatic potential energy surface in the space of dipolar displacements in the Ti centers were used to estimate the flexoelectric coefficient integral in the paraelectric phase in a one-dimensional model with the strain gradient along the [111] direction: integral = -0.43 X 10(-6) Cm-1. This eliminates the huge contradiction between the experimental data of integral similar to mu Cm-1 for this case and the theoretical predictions (without the PJTE) of 3-4 orders-of-magnitude smaller values. Enhanced flexoelectricity is thus expected in solids with a sufficient density of centers that have PJTE induced dipolar instabilities. It explains also the origin of enhanced flexoelectricity observed in other solids, noticeable containing Nb perovskite centers which are known to have a PJTE instability, similar to that of Ti centers. The SrTiO3 crystal as a virtual ferroelectric in which the strain gradient eases the condition of PJTE polar instability is also discussed. (C) 2015 AIP Publishing LLC.Item RESIDUAL STRESS AND DEFORMATION ANALYSIS OF INCONEL 718 ACROSS VARYING OVERHANGS IN LASER POWDER BLOWN DIRECTED ENERGY DEPOSITION(University of Texas at Austin, 2023) Hernandez, A.J.; Garcia, D.; Watanabe, K.I.; Gradl, P.R.; Wheeler, K.; Hafiychuk, Halyna; Wicker, R.B.; Medina, F.Any metal that is subjected to rapid heat and cooling will undergo the development of residual stresses. As they experience intense temperature fluctuations, this will consequently alter the way the material will behave. This issue proves to be of great concern within additive manufacturing. That said, the presence of temperature fluctuations is more prominent in Directed energy deposition (DED), whereas other methods of manufacturing are more prominent in the pre- or post- printing process. This in turn means the deformation, as well as the redistribution of the residual stresses within pieces, are subject to variance by several process parameters set during a print. By using the Inconel 718 alloy feedstock in RPMI’s Laser Powder Directed Energy Deposition (LP-DED) printer, a series of coupons with four different overhang angles and laser power outputs will determine how these changes thermo-mechanically affect the prints through the use of FEA simulations and scans.Item Shear-Wave Splitting and Mantle Flow Beneath the Colorado Plateau and its Boundary with the Great Basin(2008-10) Wang, Xinling L.; Ni, James F.; Aster, Richard; Sandvol, Eric; Wilson, David; Sine, Christopher; Grand, Stephen P.; Baldridge, W. Scott; Wilson, David; Sine, Christopher; Grand, Stephen P.Shear-wave splitting measurements from SKS and SKKS phases show fast polarization azimuths that are subparallel to North American absolute plate motion within the central Rio Grande Rift (RGR) and Colorado Plateau (CP) through to the western rim of the CP, with anisotropy beneath the CP and central RGR showing a remarkably consistent pattern with a mean fast azimuth of 4 degrees +/- degrees 6 E of N. Approaching the rim from the southeast, fast anisotropic directions become north-northeast-south-southwest (NNE-SSW), rotate counter clockwise to north-south in the CP-GB transition, and then to NNW-SSE in the western Great Basin ( GB). This change is coincident with uppermost mantle S-wave velocity perturbations that vary from +4% beneath the western CP and the eastern edge of the Marysvale volcanic field to about -8% beneath the GB. Corresponding delay times average 1.5 sec beneath the central CP, decrease to approximately 0.8 sec near the CP-GB transition, and increase to about 1.2 sec beneath the GB. For the central CP, we suggest anisotropy predominantly controlled by North American plate motion above the asthenosphere. The observed pattern of westward-rotating anisotropy from the western CP through the CP-GB transition may be influenced to asthenospheric flow around a CP lithospheric keel and/or by vertical flow arising from edge-driven small-scale convection. The anisotropic transition from the CP to the GB thus marks a first-order change from absolute plate motion dominated lithosphere-asthenosphere shear to a new regime controlled by regional flow processes. The NNW-SSE anisotropic fast directions of split SKS waves in the eastern GB area are part of a broad circular pattern of seismic anisotropic fast direction in the central GB that has recently been hypothesized to be due to toroidal flow around the sinking Juan de Fuca-Gorda slab.Item The Internal Structure of Model and Natural Salt Domes(1985) Jackson, M. P. A.To enhance our understanding of the internal structure of salt stocks, we conducted 30 centrifuge experiments that produced hundreds of model diapirs under artificial acceleration generally equivalent to 1,200 times that of normal gravity. Most of these experiments were geometrically and dynamically scaled to be equivalent to U.S. Gulf Coast salt domes. The domes were modeled under static overburdens and, for the first time, under aggrading and prograding overburdens. This report focuses on the internal structure of mushroom-shaped domes, which theoretically exist in nature and are demonstrated in natural examples in the U.S. Gulf Coast, Canada, and West Germany. The experimental results enable the extremely complex internal structure of mushroom-shaped salt domes to be recognized and understood. This recognition is vital because a mushroom structure would threaten the integrity of a hypothetical repository by creating a plumbing system composed of country rocks infolded from below the diapir cap and extending to near the dome center.