Browsing by Subject "FEA"

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3-Dimensional Finite Element Modeling of Selective Laser Melting Ti-6Al-4V Alloy
(University of Texas at Austin, 2014) Fu, C.H.; Guo, Y.B.
Selective laser melting (SLM) is widely used in making three-dimensional functional parts layer by layer. Temperature magnitude and history during SLM directly determine the molten pool dimensions and surface integrity. However, due to the transient nature and small size of the molten pool, the temperature gradient and the molten pool size are very challenging to measure and control. A 3-dimensional finite element simulation model has been developed to simulate multi-layer deposition of Ti-6Al-4V in SLM. A physics-based layer build-up approach coupled with a surface moving heat flux was incorporated into the modeling process. The melting pool shape and dimensions were predicted and experimentally validated. Temperature gradient and thermal history in the multi-layer build-up process was also obtained. Furthermore, the influences of process parameters and materials on the melting process were evaluated.
A bidirectional MEMS thermal actuator as the building block for a programmable metamaterial
(2018-10-04) Zhao, Cheng, M.S. in Engineering; Cullinan, Michael
This 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 concept
A method for developing the true stress-strain relationship for structural steels based on tension coupon tests
(2019-12-02) Jones, Cliff Andrew; Engelhardt, Michael D.; Williamson, Eric B., 1968-; Helwig, Todd; Clayton, Patricia; Taleff, Eric
Predicting the uniaxial stress-stress response of ductile metals like structural steel can provide valuable insight into a broad range of engineering problems. Despite a wide body of research covering more than a century, the approach and guidance related to developing the true stress-strain relationship for ductile metals—specifically structural steels—continues to change and evolve. In particular, guidance related to accurate prediction of the onset of necking and post-necking response remains a topic of ongoing research and capturing these effects remains a challenge to researchers and engineers. The research presented in this dissertation was undertaken to extend the body of knowledge in this area. Particular emphasis is placed on developing a true stress-strain relationship for structural steels that is capable of capturing the onset of necking and post-necking behavior up to fracture. In addition, as standard tension coupon load-deformation data are often the only available information from which to develop such a model, the processes and guidance presented in this dissertation require only that input information. Therefore, advanced experimental approaches and measurement techniques are not required to leverage the guidance presented herein. This path was chosen in the hopes of providing guidance that would be broadly applicable to a wide range of problems, industries, research, and practicing professionals. This dissertation proposes a method for developing a true stress-strain relationship for structural steels that can be directly used in predictive finite element analysis (FEA) models using three-dimensional (3D) solid elements. The result of this research indicate that such a model should be able to reproduce the experimental results of the tension test quite accurately, providing validation and verification of the assumed material definition. Additionally, three derivative rules are presented. These rules were distilled from existing research and provide simple guidelines for capturing necking, maintaining computational stability and uniqueness, and prohibiting post-necking cold-drawing behavior. The rules are incorporated into the recommended process for developing the true stress-strain relationship for structural steels; however, they are also presented separately so they can easily be incorporated into alternate methods for defining such a constitutive relationship. Finally, while this research has furthered the understanding of the true stress-strain relationship of structural steels, particularly in predicting necking and post-necking behavior, there is still considerable room for additional research on this topic. For example, automation, incorporating error minimizing techniques, and adding local and material-level and microstructural phenomena (e.g., void formation, growth and coalescence) each offer great potential for extending and improving the recommendations presented in this dissertation. Thus, while this effort has intentionally maintained a limited focus, it is the authors hope that it serves others as one more small step toward accurate prediction of the load-deformation behavior of structural steels and other ductile metals.
A Comparison of Modeling Methods for Predicting the Elastic-Plastic Response of Additively Manufactured Honeycomb Structures
(University of Texas at Austin, 2018) Sharma, Raghav; Le, Thao; Song, Jiaxu; Harms, Ethaniel; Sowa, Daniel; Grishin, Alex; Bhate, Dhruv
Valid and accurate models describing the mechanical behavior of additively manufactured cellular materials are crucial to enabling their implementation in critical-to-function parts. Broadly speaking, the modeling approaches commonly used in the literature fall into three categories. Each of these differs in the level of discretization at which the cellular behavior is modeled: at the level of each material point, at the level of the unit cell or at the level of a connecting member that constitutes a unit cell. Each of these three approaches relies on different characterization techniques and the way in which the resulting data is leveraged in the development of the model. In this work, we critically examine all three modeling approaches using FEA and compare their accuracy in the prediction of the elastic and plastic behavior of experimentally characterized hexagonal honeycomb structures made with Fused Deposition Modeling, and discuss the pros and cons of each method.
Design and analysis of the Hobby-Eberly Telescope Dark Energy Experiment bridge
(2010-05) Worthington, Michael Scott; Nichols, Steven P.; Beno, Joseph H.
A large structural weldment has been designed to serve as the new star tracker bridge for the Dark Energy Experiment upgrade to the Hobby-Eberly Telescope at McDonald Observatory. The modeling approach, analysis techniques and design details will be of interest to designers of large structures where stiffness is the primary design driver. The design includes detailed structural analysis using finite element models to maximize natural frequency response and limit deflections and light obscuration. Considerable fabrication challenges are overcome to allow integration of precision hardware required for positioning the corrector optics to a precision of less than 5 microns along the 4-meter travel range. This thesis provides detailed descriptions of the bridge geometry, analysis results and challenging fabrication issues.
Design and computational optimization of a flexure-based XY nano-positioning stage
(2019-07-09) Thirumalai Vasu, Sridharan; Cullinan, Michael
This thesis presents the design and computational optimization of a two-axis nano-positioning stage. The devised stage relies on double parallelogram flexure bearings with under-constraint eliminating linkages to enable motion in the primary degrees-of-freedom. The structural parameters of the underlying flexures were optimized to provide a large-range and high bandwidth with sub-micron resolution while maintaining a compact size. A finite element model was created to establish a functional relationship between the geometry of the flexure elements and the stiffness behavior. Then, a neural network was trained from the simulation results to explore the design space with a low computational expense. The neural net was integrated with a genetic algorithm to optimize the design of the flexures for compactness and dynamic performance. The optimal solutions resulted in a reduction of stage footprint by 14% and an increase in the first natural frequency by 75% relative to a baseline design, all while preserving the same 50mm range in each axis with a factor of safety of 2. This confirms the efficacy of the proposed approach in improving stage performance through an optimization of its constituent flexures.
Design and evaluation of annular quasi-zero stiffness structures for sealing applications
(2016-09-29) Kathuria, Avik; Seepersad, Carolyn; Haberman, Michael R. (Michael Richard), 1977-
This thesis presents the design, modeling and analysis of axisymmetric quasi-zero stiffness mechanism. Literature review is carried out for seals and quasi-zero stiffness structures to develop a thorough understanding. The purpose of this project is to explore the potential of adaptability of extruded quasi-zero stiffness structures for sealing applications in axisymmetric structures. For this purpose, analytical model of the hypothesized structure is developed and its important design parameters are identified. This model is based on the mathematical model of extruded structure and takes into account certain assumptions to develop important relationships. As a result, the sealing parameter of contact stress is related to the compression of the seal and the operating range of the seal is identified. In order to validate the findings of the analytical model, the developed structure is analyzed using finite element analysis. The axial symmetry of the structure is exploited to model the structure in 2D, significantly reducing the computation cost required. Material is selected on the basis of temperature and other manufacturing constraints. The seal is analyzed for stress throughout the structure and contact stress and similar curve for contact stress vs compression is extracted out from this analysis as analytical model. The results from both analytical model and finite element analysis are compared and error is computed while discussing possible sources for this error. A prototype developed using selective laser sintering is also presented. Finally, future work to refine the structure and other possible applications are discussed.
Finite Element Modeling of Metal Lattices Using Commercial FEA Platforms
(University of Texas at Austin, 2018) Arrieta, E.; Mireles, Jorge; Stewart, C.; Carrasco, C.; Wicker, R.
The introduction of geometrical features into standard solids result in cellular materials with unique performances. The deformation mechanisms originated by the introduced geometry may not be entirely captured by the current commercial FEM software; resulting in inaccuracies in predicting the performance of cellular metals. Additionally, the inconsistency of AM material properties will result in material models with uncertainty, thus, contributing to the inaccuracy of simulations. The present work shows a process for modeling the strength of EBM Ti-6Al-4V lattices structures; starting from the definition of the convenient experiments to generate the data for the development of material models at different orientation and finalizes with the assignment of these material models to the lattice FEMs. MSC Patran/Nastran is used in this work. Experimental results of the compressive strength of lattice structures are compared with those from the FEM utilizing the different material models created from the experiments.
Structural optimization for a photovoltaic vehicle
(2011-05) Ford, Bennett Alan 1984-; O'Connor, James Thomas
Photovoltaic vehicles are designed to harness solar energy and use it for self-propulsion. In order to collect sufficient energy to propel a passenger, a relatively large photovoltaic array is required. Controlling the loads imparted by the array and the body that supports it, while protecting the passenger and minimizing vehicle weight, presents a unique set of design challenges. Weight considerations and geometric constraints often lead system designers toward unconventional structural solutions. This report details analytical and experimental processes aimed at proving the concept of integrating aluminum space-frame elements with composite panels. Finite element analysis is used to simulate load conditions, and results are compared with empirical test data.
Validation of Rapid Prototyping Material for Rapid Experimental Stress Analysis
(1997) Schley, C.; Smith, G.F.
The paper will detail the validation work carried out on various Rapid Prototyping (RP) materials to determine their suitability for the application of Thermoelastic Stress Analysis. The overall objective is to drastically reduce the product design cycle, by providing "real experimental data" for correlation with Finite Element Analysis (FEA), prior to any expensive manufacturing process. In order to achieve this the homogeneity of the Rapid Prototyping material has to be established to ensure a valid transfer of results from model to actual part.