Browsing by Subject "Shape Memory Alloy"
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Item Base Isolation of a Chilean Masonry House: A Comparative Study(2010-01-16) Husfeld, Rachel L.The objective of this study is to reduce the interstory drifts, floor accelerations, and shear forces experienced by masonry houses subject to seismic excitation. Ambient vibration testing was performed on a case study structure in Maip?, Chile, to identify characteristics of the system. Upon creating a multiple degree-of-freedom (MDOF) model of the structure, the effect of implementing several base isolation techniques is assessed. The isolation techniques analyzed include the use of friction pendulum systems (FPS), high-damping rubber bearings (HDRB), two hybrid systems involving HDRB and shape memory alloys (SMA), and precast-prestressed pile (PPP) isolators. The dynamic behavior of each device is numerically modeled using analytical formulations and experimental data through the means of fuzzy inference systems (FIS) and S-functions. A multiobjective genetic algorithm is utilized to optimize the parameters of the FPS and the PPP isolation systems, while a trial-and-error method is employed to optimize characteristic parameters of the other devices. Two cases are studied: one case involves using eight devices in each isolation system and optimizing the parameters of each device, resulting in different isolated periods for each system, while the other case involves using the number of devices and device parameters that result in a 1.0 sec fundamental period of vibration for each baseisolated structure. For both cases, the optimized devices are simulated in the numerical model of the case study structure, which is subjected to a suite of earthquake records. Numerical results for the devices studied indicate significant reductions in responses of the base-isolated structures in comparison with their counterparts in the fixed-base structure. Metrics monitored include base shear, structural shear, interstory drift, and floor acceleration. In particular, the PPP isolation system in the first case reduces the peak base shear, RMS floor acceleration, peak structural shear, peak interstory drift, and peak floor acceleration by at least 88, 87, 95, 95, and 94%, respectively, for all of the Chilean earthquakes considered. The PPP isolation system in the second case (yielding a 1.0 sec period) and the FPS isolation systems in both cases also significantly reduce the response of the base-isolated structure from that of the fixed-base structure.Item Characterization of Shape Memory Alloys Using Artificial Neural Networks(2014-04-28) Henrickson, James VShape memory alloys are capable of delivering advantageous solutions to a wide range of engineering-based problems. Implementation of these solutions, however, is often complicated by the hysteretic, non-linear, thermomechanical behavior of the material. Existing constitutive models are largely capable of accurately describing this unique behavior, but they require prior characterization of material parameters. Current characterization procedures necessitate extensive data collection and data processing, creating a high barrier of entry for shape memory alloy application. This thesis develops a novel approach in which a form of computational intelligence is applied to the task of shape memory alloy material parameter characterization. Specifically, this work develops a methodology in which an artificial neural network is trained to identify transformation temperatures and stress influence coefficients of shape memory alloy specimens using strain-temperature coordinates as inputs. Training data is generated through the use of an existing shape memory alloy constitutive model. Factorial and Taguchi-based methods of generating training data are implemented and compared. Results show that trained artificial neural networks are capable of identifying shape memory alloy material parameters with satisfactory accuracy. Comparison of the implemented training data generation methods indicates that the Taguchi-based approach yields an artificial neural network that outperforms that of the factorial-based approach despite requiring significantly fewer training data specimens.Item Constitutive modelling of shape memory alloys and upscaling of deformable porous media(Texas A&M University, 2005-08-29) Popov, Petar AngelovShape Memory Alloys (SMAs) are metal alloys which are capable of changing their crystallographic structure as a result of externally applied mechanical or thermal loading. This work is a systematic effort to develop a robust, thermodynamics based, 3-D constitutive model for SMAs with special features, dictated by new experimental observations. The new rate independent model accounts in a unified manner for the stress/thermally induced austenite to oriented martensite phase transformation, the thermally induced austenite to self-accommodated martensite phase transformation as well as the reorientation of self-accommodated martensite under applied stress. The model is implemented numerically in 3-D with the help of return-mapping algorithms. Numerical examples, demonstrating the capabilities of the model are also presented. Further, the stationary Fluid-Structure Interaction (FSI) problem is formulated in terms of incompressible Newtonian fluid and a deformable solid. A numerical method is presented for its solution and a numerical implementation is developed. It is used to verify an existing asymptotic solution to the FSI problem in a simple channel geometry. The SMA model is also used in conjunction with the fluid-structure solver to simulate the behavior of SMA based filtering and flow regulating devices. The work also includes a numerical study of wave propagation in SMA rods. An SMA body subjected to external dynamic loading will experience large inelastic deformations that will propagate through the body as phase transformation and/or detwinning shock waves. The wave propagation problem in a cylindrical SMA is studied numerically by an adaptive Finite Element Method. The energy dissipation capabilities of SMA rods are estimated based on the numerical simulations. Comparisons with experimental data are also performed.Item Development of a fuel-powered compact SMA (Shape Memory Alloy) actuator system(Texas A&M University, 2005-02-17) Jun, Hyoung YollThe work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.Item Experimental Characterization of Shape Memory Alloys using Digital Image Correlation and Infra-Red Thermography(2015-03-13) Cornell, StephenCharacterization of shape memory alloy materials is demonstrated using modern full-field experimental techniques. The methods presented are designed to reduce the number of experiments required for full characterization of the material. Several experiments have been explored in this work; for each type of experiment, particular attention has been given to the particular measurement methods that have been utilized. For characterization of shape memory alloys as actuators, a new experimental method has been presented as an alternative to testing multiple separate specimens or performing several experiments on the same specimen. For the actuator material experiments, temperature was measured using infra-red thermography with an accuracy of up to 2.14 ?C, and a resolution of 0.39 mm. Strain was measured using digital image correlation (DIC) with a resolution of 0.09 mm. For pseudoelastic shape memory alloy material characterization, experiments have been designed which provide data demonstrating the anisotropic behavior of the material, which are not shown by previous methods of characterization. For these experiments, the DIC measurement had a resolution of 0.08 mm. For microscopic shape memory alloy applications, particular in-situ characterization has been demonstrated which is not possible by traditional methods of characterization. DIC measurements were performed simultaneously at a micro-scale with a resolution of 0.25 ?m and at a macro-scale with a resolution of 0.022 mm. The information provided herein presents these experiments in great detail in order to demonstrate characterization methods which are currently the most reliable and efficient for analysis of shape memory alloy materials.Item Fabrication and Characterization of Nanowires(2011-10-21) Phillips, Francis RandallThe use of nanostructures has become very common throughout high-tech industries. In order to enhance the applicability of Shape Memory Alloys (SMAs) in systems such as Nano-Electromechanical Systems, the phase transformation behavior of SMA nanostructures should be explored. The primary focus of this work is on the fabrication of metallic nanowires and the characterization of the phase transformation of SMA nanowires. Various metallic nanowires are fabricated through the use of the mechanical pressure injection method. The mechanical pressure injection method is a template assisted nanowire fabrication method in which an anodized aluminum oxide (AAO) template is impregnated with liquid metal. The fabrication procedure of the AAO templates is analyzed in order to determine the effect of the various fabrication steps. Furthermore, metallic nanowires are embedded into polymeric nano bers as a means to incorporate nanowires within other nanostructures. The knowledge obtained through the analysis of the AAO template fabrication guides the fabrication of SMA nanowires of various diameters. The fabrication of SMA nanowires with di fferent diameters is accomplished through the fabrication of AAO templates of varying diameters. The phase transformation behavior of the fabricated SMA nanowires is characterized through transmission electron microscopy. By analyzing the fabricated SMA nanowires, it is found that none of the fabricated SMA nanowires exhibit a size eff ect on the phase transformation. The lack of a size e ffect on the phase transition of SMA nanowires is contrary to the results for SMA nanograins, nanocrystals, and thin films, which all exhibit a size eff ect on the phase transformation. The lack of a size eff ect is further studied through molecular dynamic simulations. These simulations show that free-standing metallic nanowires will exhibit a phase transformation when their diameters are sufficiently small. Furthermore, the application of a constraint on metallic nanowires will inhibit the phase transformation shown for unconstrained metallic nanowires. Therefore, it is concluded that free-standing SMA nanowires will exhibit a phase transformation throughout the nanoscale, but constrained SMA nanowires will reach a critical size below which the phase transformation is inhibited.