Browsing by Subject "Engineering design"

Now showing 1 - 4 of 4
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    Design optimization of heterogeneous microstructured materials
    (2014) Emami, Anahita; Tovar, Andrés; Zhu, Likun; Wasfy, Tamer; Chen, Jie
    Our ability to engineer materials is limited by our capacity to tailor the material’s microstructure morphology and predict resulting properties. The insufficient knowledge on microstructure-property relationship is due to complexity and randomness in all materials at different scales. The objective of this research is to establish a design optimization methodology for microstructured materials. The material design problem is stated as finding the optimum microstructure to maximize the desired performance satisfying material processing constrains. This problem has been solved in this thesis by means of numerical techniques through four main steps: microstructure characterization, model reconstruction, property evaluation, and optimization. Two methods of microstructure characterizations have been investigated along with the advantages and disadvantages of each method. The first microstructure characterization method is a statistical method which utilizes correlation functions to extract the microstructural information. Algorithms for calculating these correlations functions have been developed and optimized based on their computational cost using MATLAB software. The second microstructure characterization method is physical characterization which works based on evaluation of physical features in microstructured domain. These features have been measured by means of MATLAB codes. Three model reconstruction techniques are proposed based on these characterization methods and employed to generate material models for further evaluation. The first reconstructing algorithm uses statistical functions to reconstruct the statistical equivalent model through simulating annealing optimization method. The second algorithm uses cellular automaton concepts to simulate the grain growth utilizing physical descriptors, and the third one generates elliptical inclusions in a material matrix using physical characteristic of microstructure. The finite element method is used to analysis the mechanical behavior of material models. Several material samples with different microstructural characteristics have been generated to model the micro-scale design domain of AZ31 magnesium alloy and magnesium matrix composite with silicon carbide fibers. Then, surrogate models have been created based on these samples to approximate the entire design domain and demonstrate the sensitivity of the desired mechanical property to two independent microstructural features. Finally, the optimum microstructure characteristics of material samples for fracture strength maximization have been obtained.
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    Effect of geometric, material and operational parameters on the steady-state belt response for flat belt-drives
    (2015-05) Yildiz, Cagkan; Wasfy, Tamer M.; Tovar, Andres; El-Mounayri, Hazim A.
    This thesis presents a comprehensive study of the effects of material, geometric and operational parameters on flat belt-drives steady-state belt stresses, belt slip, and belt-drive efficiency. The belt stresses include: belt rubber shear, normal, axial and lateral stresses; reinforcements tension force; and tangential and normal belt-pulley contact stresses. Belt slip is measured using the driven over driver pulleys’ angular velocity ratio. Each parameter was varied over a range to understand its impact on the steady-state belt-drive response. The material parameters studied are belt axial stiffness and damping, belt bending stiffness and damping, and belt-pulley friction coefficient. The geometric parameters studied are pulley center distance, pulleys diameter ratio, and belt thickness. The operational parameters studied are the driver pulley angular velocity and the driven pulley opposing torque (load). A high-fidelity flexible multibody dynamics parametric model of a two-pulley belt-drive system was created using a commercial multibody dynamics code. In the model the belt’s rubber matrix is represented using three-dimensional brick elements and the belt’s reinforcements are represented using one dimensional beam elements at the top surface of the belt. An asperity-based Coulomb friction model is used for the friction forces between the pulley and belt. The pulleys are modeled as rigid bodies with a cylindrical contact surface. The equations of motion are integrated using an explicit solution procedure. Unlike prior models which use one-dimensional truss or beam elements for the belt, the present model uses a three-dimensional belt model which introduces the effect of the thickness of the belt rubber matrix (modeled using brick elements). This enables a more accurate prediction of the belt stresses and slip than prior models. This thesis resolves in more details the complex stick-slip friction behavior of an axially flexible belt coupled with the shear effects of a flexible rubber cushion and at the same time shows the effect of the main system parameters on this stick-slip behavior. Some of the important conclusions of the thesis include: (1) the driver pulley has two distinct contact zones - a negative traction zone and a positive traction zone - while only one traction zone is present over the driven pulley; (2) the width of the negative traction zone on the driver pulley increases with the belt-pulley coefficient of friction and decreases with the belt axial stiffness; (3) the maximum belt tension and normal contact stress occur on the driver pulley and increase with the belt thickness, belt axial stiffness, and coefficient of friction; (4) belt-drive energy efficiency increases with the belt axial stiffness, and decreases with belt thickness, belt bending damping, belt operating speed, and operating torque load. The belt-drive modeling methodology presented in this thesis which enables accurate prediction of the belt stresses and slip can in turn be used to more accurately predict the fatigue life, wear life, and energy efficiency of belt-drives.
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    Electrochemical behaviors of micro-arc oxidation coated magnesium alloy
    (2014) Liu, Jiayang; Zhang, Jing; Chen, Jie; Li, Jiliang; Na, Sungsoo
    In recent years, magnesium alloys, due to their high strength and biocompatibility, have attracted significant interest in medical applications, such as cardiovascular stents, orthopedic implants, and devices. To overcome the high corrosion rate of magnesium alloys, coatings have been developed on the alloy surface. Most coating methods, such as anodic oxidation, polymer coating and chemical conversion coating, cannot produce satisfactory coating to be used in human body environment. Recent studies demonstrate that micro-arc oxidation (MAO) technique can produce hard, dense, wear-resistant and well-adherent oxide coatings for light metals such as aluminum, magnesium, and titanium. Though there are many previous studies, the understanding of processing conditions on coating performance remains elusive. Moreover, previous tests were done in simulated body fluid. No test has been done in a cell culture medium, which is much closer to human body environment than simulated body fluid. In this study, the effect of MAO processing time (1 minute, 5 minutes, 15 minutes, and 20 minutes) on the electrochemical behaviors of the coating in both conventional simulated body fluid and a cell culture medium has been investigated. Additionally a new electrolyte (12 g/L Na2SiO3, 4 g/L NaF and 4 ml/L C3H8O3) has been used in the MAO coating process. Electrochemical behaviors were measured by performing potentiodynamic polarization and electrochemical impedance spectroscopy tests. In addition to the tests in simulated body fluid, the MAO-coated and uncoated samples were immersed in a cell culture medium to investigate the corrosion behaviors and compare the difference in these two kinds of media. The results show that in the immersion tests in conventional simulated body fluid, the 20-minute MAO coated sample has the best resistance to corrosion due to the largest coating thickness. In contrast, in the cell culture medium, all MAO coated samples demonstrate a similar high corrosion resistance behavior, independent of MAO processing time. This is probably due to the organic passive layers formed on the coating surfaces. Additionally, a preliminary finite element model has been developed to simulate the immersion test of magnesium alloy in simulated body fluid. Comparison between the predicted corrosion current density and experimental data is discussed.
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    Immersion Experiences for Biomedical Engineering Undergraduates: Comparing Strategies and Local Partnerships at Two Institutions
    (Vocational School, Diponegoro University Semarang Central Java Indonesia, 2023) Huber, Justin; Higbee, Steven; Espinosa, Christina; Bazrgari, Babak; Miller, Sharon; Biomedical Engineering, School of Engineering and Technology
    Immersion experiences for undergraduate students in biomedical engineering are key contributors to their ability to identify medical needs. Despite this, as few as 25% of surveyed programs report providing such opportunities. Since 2010 when the National Institute of Health began its R25 grant mechanism to support curricular development toward team-based design, several institutions have established programs for immersion experiences, which provide precedent for their implementation. Published results from such immersion experiences highlight successes in structure and changes in student perspectives after these experiences. As more institutions expand their biomedical engineering curriculum with new immersion-focused programs, it is important to learn from these precedents while also considering opportunities to improve. For newly funded groups that are developing and implementing programs, they may find improved success by strategic use of unique partnerships. However, these partnerships may not be immediately evident to program organizers. Our objective is to discuss two institutions that recently established programs for immersion experience. In the comparison of our two immersion programs, we found five overlapping core features that include: immersion partner collaboration, team-based immersion experiences, needs-finding emphasis, team-based engineering design experiences, and immersion assessment and evaluation. Both programs developed collaborative partnerships with nearby medical schools. Additionally, one program partnered with a community resource (i.e., Human Development Institute). Despite nuanced program differences, we found that students at both programs self-reported increased knowledge or confidence in aspects of the design process (e.g., identifying and refining user needs, concept generation). Our results also highlight student gains unique to their programs – UK students self-reported gains on disability topics and IUPUI students self-reported gains on socioeconomic awareness. In summary, immersion partner collaboration, or partnership, surfaced as a core feature for both programs, and students in both immersion programs endorsed enhanced knowledge or confidence in engineering design.