Browsing by Subject "FEM"
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Item A bidirectional MEMS thermal actuator as the building block for a programmable metamaterial(2018-10-04) Zhao, Cheng, M.S. in Engineering; Cullinan, MichaelThis thesis presents a novel bidirectional MEMS thermal actuator that is intended to be implemented as the building block for a microarchitectured material. The successful proof of concept demonstrates the potential for a new level of miniaturization for the technology that would improve existing capabilities and enable new ones. The design is built upon the bent-beam type thermal actuators with an emphasis on large travel and force output. Sensing capabilities are accomplished through piezoresistive strain gauges that provide sufficient sensitivity and resolution. An analytical model was created to calculate the performance parameters of actuator designs and was used in conjunction with optimization software to arrive at four selected designs with minimal theoretical trade-offs. Successful fabrication of the devices was achieved with standard microfabrication techniques. Preliminary testing results have demonstrated the successful operation of bidirectional actuation and confirms the validity of the conceptItem Alternative Approach on an In-Situ Analysis of the Thermal Progression During the LPBF-M Process Using Welded Thermocouples Embedded into the Substrate Plate(University of Texas at Austin, 2019) Schnell, N.; Siewert, M.; Kleszczynski, S.; Witt, G.; Ploshikhin, V.Laser powder bed fusion (LPBF-M) is a very potent technology for creating highly individualized, complex, and functional metal parts. One of the major influencing factors is the thermal progression. It significantly determines size accuracy, microstructure and process stability. Therefore, creating an enhanced understanding of thermal phenomena through measurements and simulations is crucial to increase the reliability of the technology. Current research is mainly based on temperature measurements of the upper layer, leaving major scope for the conditions at the substrate-part-interface. This area is of utmost technical importance because it serves as the main heat sink. Insufficient heat dissipation leads to accumulations of heat, deformations, and process breakdowns. This contribution presents a simple and flexible method to analyze the thermal progression close to the part inside the substrate plate. The acquired data shows very high consistency. Additionally, the results are compared to a model created using an ISEMP developed FEM-Software which shows promising results for validation studies.Item Application of commercial FEM program Abaqus to investigate delamination behavior of post-tensioned concrete curved walls(2020-08-13) Inaba, Yusuke (M.S. in civil engineering); Bayrak, Oguzhan, 1969-; Hrynyk, TrevorThe concrete delamination induced by prestressing forces is a potential problem of post-tensioned concrete containments with curved geometry. To investigate the concrete delamination mechanism, the researchers of the University of Texas at Austin completed an experimental research project in 2017. In this research project, the academic finite element method (FEM) program VecTor4, which has powerful shell-type elements for cracked reinforced concrete shells, was modified and proved to be an appropriate tool to predict the level of applied prestressing load at the delamination failure. VecTor4 has a well-defined reinforced concrete material model and capability to analyze the structures on an overall system level with low computational resources. However, its user interface has limitations, and the details of the local behavior of structures may not be captured due to its simplicity. On the other hand, commercial FEM programs generally provide a convenient graphical-based user interface and various analysis features. Still, typical commercial FEM programs are not designed to analyze the concrete structures. Some commercial FEM programs provide concrete material models; however, they tend to require significant calibration analyses to capture the behavior of reinforced concrete structures. Specifically, to capture the delamination of concrete walls with those programs, solid elements should be selected, which should increase the computational costs. However, commercial FEM programs can potentially provide the details of the local behavior of structures. Recently, an experimental test investigating the concrete delamination phenomenon was conducted. In this recent test, numerical analyses with the commercial FEM program Abaqus ware conducted as well as the analysis with VecTor4 to explore other options in commercial FEM programs. This paper will show the analysis results of both Abaqus and VecTor4 for the recent test. Additionally, the discussion on the relative merits and limitations of these programs obtained from the experience of the analyses for the recent test is presented.Item The construction and use of physics-based plasticity models and forming-limit diagrams to predict elevated temperature forming of three magnesium alloy sheet materials(2013-08) Antoniswamy, Aravindha Raja; Taleff, Eric M.Magnesium (Mg) alloy sheets possess several key properties that make them attractive as lightweight replacements for heavier ferrous and non-ferrous alloy sheets. However, Mg alloys need to be formed at elevated temperatures to overcome their limited room-temperature formabilities. For example, commercial forming is presently conducted at 450°C. Deformation behavior of the most commonly used wrought Mg alloy, AZ31B-H24, and two potentially competitive materials, AZ31B-HR and ZEK100 alloy sheets, with weaker crystallographic textures, are studied in uniaxial tension at 450°C and lower temperatures. The underlying physics of deformation including the operating deformation mechanisms, grain growth, normal and planar anisotropy, and strain hardening are used to construct material constitutive models capable of predicting forming for all three Mg alloy sheets at 450°C and 350°C. The material models constructed are implemented in finite-element-method (FEM) simulations and validated using biaxial bulge forming, an independent testing method. Forming limit diagrams are presented for the AZ31B-H24 and ZEK100 alloy sheets at temperatures from 450°C down to 250°C. The results suggest that forming processes at temperatures lower than 450°C are potentially viable for manufacturing complex Mg components.Item Modeling the low-frequency response of seagrass in a resonator tube(2022-05-04) Torres, Nicholas Antonio; Wilson, Preston S.; Lee, Kevin M; Ballard, Megan SSeagrasses are a vital part of coastal ecosystems. They serve a number of important environmental functions, but are currently declining at rapid rates. A necessary requirement to preserving these resources is an ability to monitor them. Seagrass can strongly affect acoustic propagation in seawater, and this effect can be exploited to monitor these resources. Seagrass impacts the acoustic propagation through the release of bubbles from photosynthesis as well as gas contained within the seagrass tissue itself. Previous mathematical models that treat the seagrass tissue as a fluid have not sufficiently explained acoustic propagation through seagrass. In the present work, a Finite Element Method (FEM) model was used alongside data from the literature to determine if an elastic model for seagrass captures the effects it has on acoustic propagation. The results of this model were then compared against a recently-published measurement of the shear modulus of Thalassia testudinum. Additional resonator experiments were then used to inform refinements of the FEM model. The improved FEM model resolved a number of discrepancies in the initial model. Finally, the improved model was used with resonator measurements to infer the shear modulus of the two different types of tissue present in seagrass, the epidermis and aerenchyma tissue in T. testudinum.Item Simulation of stress field condition during Waller Creek tunnel construction with a 2D finite element model(2017-08-14) Ortiz Pizzoglio, Alejandro Esteban; Gilbert, Robert B. (Robert Bruce), 1965-; Pacheco de Assis, AndreTwo-dimensional (2D) Finite Element Method (FEM) analyses are widely used as a tunnel design tool. These analyses are used to establish the initial support requirements, to estimate ground displacements and to design support systems to have adequate capacity and stiffness. Due to the complexities of ground characteristics, construction methods and the interactions between the ground and initial support lining systems, it is valuable to compare predictions from design analyses with field measurements. The objective of this thesis is to compare FEM results with field measurements for stresses in an initial support lining system for a tunnel constructed in shale using the Sequential Excavation Method (SEM), the Waller Creek Tunnel in Austin, Texas. The major conclusion is that the predictions of liner stresses from FEM are greater than what was measured in the field, particularly for the thrust in the liner. While assuming that the ground is 20 times stiffer produces predictions closer to the measurements, the predictions are still greater, particularly for the thrust. One possible explanation for the discrepancy between predications and measurements is that the stress cells did not have intimate contact with the liner.Item Superconducting Bearing Design for Outer Rotor Flywheel Using Lumped Parameter Techniques(2014) Hearn, C.; Pratap, S. B; Chen, D, Longoria, R. G.This paper describes the application of lumped parameter modeling techniques to designing high temperature superconducting bearings for outer-rotor flywheel energy storage systems. The lumped parameter models decrease computational time by 99% compared to Finite Element Analysis (FEM) without compromising fidelity needed to capture the non-linear and hysteretic force-displacement behavior between a levitated permanent magnet and bulk superconductor. The techniques formulated can be used to quickly evaluate lifting capacity and translational stiffness for a superconducting bearing design. The validity of the modeling approach has been verified by comparing results from FEM studies and experimental tests. Item Towards the predictive modeling of ductile failure(2015-12) Gross, Andrew Jeffrey; Ravi-Chandar, K.; Kovar, Desiderio; Landis, Chad; Liechti, Kenneth; Kyriakides, SteliosThe ability to predict ductile failure is considered by an experimental examination of the failure process, validation exercises to assess predictive ability, and development of a coupled experimental-numerical strategy to enhance model development. In situ loading of a polycrystalline metal inside a scanning electron microscope is performed on Al 6061-T6 that reveals matrix-dominated response for both deformation and failure. Highly localized deformation fields are found to exist within each grain as slip accumulates preferentially on a small fraction of crystallographic planes. No evidence of damage or material softening is found, implying that a strain-to-failure model is adequate for modeling fracture in this and similar material. This modeling insight is validated through blind predictive simulations performed in response to the 2012 and 2014 Sandia Fracture Challenges. Constitutive and failure models are calibrated and then embedded in highly refined finite element simulations to perform blind predictions of the failure behavior of the challenge geometries. Comparison of prediction to experiment shows that a well-calibrated model that captures the essential elastic-plastic constitutive behavior is necessary to capture confidently the response for structures with complex stress states, and is a prerequisite for a precise prediction of material failure. The validation exercises exposed the need to calibrate sophisticated plasticity models without a large experimental effort. To answer this need, a coupled experimental and numerical method is developed for characterizing the elastic-plastic constitutive properties of ductile materials using local deformation field information to enrich calibration data. The method is applied to a tensile test specimen and the material’s constitutive model, whose parameters are unknown a priori, is determined through an optimization process that compares these experimental measurements with iterative finite element simulations. The final parameters produce a simulation that tracks the local experimental displacement field to within a couple percent of error. Simultaneously, the percent error in the simulation for the load carried by the specimen throughout the test is less than one percent. The enriched calibration data is found to be sufficient to constrain model parameters describing anisotropy that could not be constrained by the global data alone.Item Validation and Comparison of Fem-Simulation Results of the Fused Deposition Modeling Process under Consideration of Different Mesh Resolutions(2022) Moritzer, E.; Hecker, F.The Fused Deposition Modeling (FDM) process is an Additive Manufacturing (AM) technology. In the FDM process, components are generated by feeding a thermoplastic polymer filament into a heated nozzle and depositing the molten material layer-by-layer in a defined way onto the building platform or an already existing component structure. The strand-by- strand deposition leads to a complex cooling situation which contributes to the non-uniform shrinkage of components in the FDM-process. Using an AM plug-in for the FEM-simulation software Abaqus, the thermal and mechanical aspects of a component can be simulated according to the temporal sequence of the manufacturing process. For this, the birth-death- method is used in the simulations. During the investigations, the simulation results regarding geometrical deviations are compared to the actual deviation of the manufactured specimens. Furthermore, the influences of the mesh resolution on the simulation results and the required time for the simulations are considered.