Mechanical Engineering Commons^™

Strained Hybrid Perovskite Thin Films And Their Impact On The Intrinsic Stability Of Perovskite Solar Cells, Jingjing Zhao, Yehao Deng, Haotong Wei, Xiaopeng Zheng, Zhenhua Yu, Yuchuan Shao, Jeffrey E. Shield, Jinsong Huang

Department of Mechanical and Materials Engineering: Faculty Publications

Organic-inorganic hybrid perovskite (OIHP) solar cells have achieved comparable efficiencies to those of commercial solar cells, although their instability hinders their commercialization. Although encapsulation techniques have been developed to protect OIHP solar cells from external stimuli such as moisture, oxygen, and ultraviolet light, understanding of the origin of the intrinsic instability of perovskite films is needed to improve their stability. We show that the OIHP films fabricated by existing methods are strained and that strain is caused by mismatched thermal expansion of perovskite films and substrates during the thermal annealing process. The polycrystalline films have compressive strain in the out-of-plane …

The Effect Of Number Of Corrugation On Crashworthiness Of Aluminum Corrugated Tube Under Lateral Loading, Hozhabr Mozafari, Arameh Eyvazian, Abdel Magid Hamouda

Department of Mechanical and Materials Engineering: Faculty Publications

Thin-walled tubes have been developed and are growing in use as new energy absorber structures. The objective of this study is to investigate the energy absorption and crushing characteristics of corrugated tubes with different number of corrugation in a specific length exposed to lateral loading. At the first step, experimental tests were carried out on a corrugated tube with three con'ugations (two inner and one outer) and a tube without corrugation. After that, a finite element model was developed by means of ABAQUS software in order to study the effect of corrugation number on crushing properties of thin-walled tubes. The …

Methods, Systems, And Devices For Surgical Visualization And Device Manipulation, Shane M. Farritor, Mark Rentschler, Amy Lehman, Nathan A. Wood, Adam Bock, Reed Prior

Department of Mechanical and Materials Engineering: Faculty Publications

A surgical device includes a console having a visual display and a manipulator arm, a robotic device having a camera and a connection component. The robotic device is configured to be positioned completely within a body cavity. The camera is configured to transmit visual images to the visual display. The connection component operably couples the console and the robotic device. The manipulator arm is positioned relative to the visual display so as to appear to be penetrating the visual display.

Local And Segmental Motions Of The Mobile Amorphous Fraction In Semi-Crystalline Polylactide Crystallized Under Quiescent And Flow-Induced Conditions, Xavier Monnier, Laurence Chevalier, Antonello Esposito, Lucia Fernandez-Ballester, Allisson Saiter, Eric Dargent

Department of Mechanical and Materials Engineering: Faculty Publications

The molecular dynamics of the constrained and unconstrained mobile amorphous fractions in semicrystalline polylactide (PLA) was investigated in the presence of both flow-induced crystalline structures and spherulites by fast scanning calorimetry (FSC) through cooperativity and physical aging concepts. First, the shear rate conditions leading to flow-induced crystallization were characterized by examining the relaxation of shear-induced precursors. At a temperature of 150 °C, the critical relaxation time is so long that cooling down the sheared melt to the crystallization temperature does not affect significantly the precursors. Therefore, highly oriented structures develop. The arrangement of the crystalline fraction, either in flow-induced crystalline …

Experimental Study Of Corrugated Metal-Composite Tubes Under Axial Loading, Arameh Eyvazian, Hozhabr Mozafari, Abdel Magid Hamouda

Department of Mechanical and Materials Engineering: Faculty Publications

In this study, crushing behavior of corrugated metal-composite tube was examined experimentally under axial loading condition. Six types of specimens, classified into two groups of metal and metal-composite, were tested under quasi static axial loading. The failure mechanism and failure history of the specimens were presented and discussed. The experimental result showed that corrugated metal composite tubes demonstrate perfect energy absorption characteristics in terms of uniformity of load-displacement diagram, reduction of initial peak load and controlling failure mechanism. Moreover, it was also found that adding filament wound layer of composite on the surface of metallic corrugated tube compensated weakness of …

Disturbed Cyclical Stretch Of Endothelial Cells Promotes Nuclear Expression Of The Pro-Atherogenic Transcription Factor Nf-Kb, Ryan M. Pedrigi, Konstantinos I. Papadimitriou, Avinash Kondiboyina, Sukhjinder Sidhu, James Chau, Miten B. Patel, Daniel C. Baeriswyl, Emmanuel M. Drakakis, Rob Krams

Department of Mechanical and Materials Engineering: Faculty Publications

Exposure of endothelial cells to low and multidirectional blood flow is known to promote a pro-atherogenic phenotype. The mechanics of the vessel wall is another important mechano-stimulus within the endothelial cell environment, but no study has examined whether changes in the magnitude and direction of cell stretch can be pro-atherogenic. Herein, we developed a custom cell stretching device to replicate the in vivo stretch environment of the endothelial cell and examined whether low and multidirectional stretch promote nuclear translocation of NF-kB. A fluid–structure interaction model of the device demonstrated a nearly uniform strain within the region of cell attachment and …

Built-In Bicycle Rack For Cars, Scott A. Hansberry

All Undergraduate Projects

Transporting a bicycle after riding somewhere and then needing to be pickup can be problematic. Bicycles will not fit in most vehicles without removing components. There is also the risk of damaging the inside of the vehicle. Expecting everyone to have a bike rack for their vehicle is unrealistic because the bike rack could be considered unappealing visually, take up to much space in the trunk, or limit the vehicle owner’s access to the trunk. The solution to this problem is a bike rack that mounts onto your car and then mounts your bike onto the rack. Most people don’t …

Anisotropy Evolution Due To Surface Treatment On 3d-Printed Fused Deposition Modeling (Fdm) Of Acrylonitrile Butadiene Styrene (Abs), Blake E. Lozinski

Honors Undergraduate Theses

Purpose: This paper will present insight to the methodology and results of the experimental characterization of Acrylonitrile Butadiene Styrene (ABS) using Fused Deposition Modeling (FDM). The work in this research explored the effects of print orientation, surface treatment, and ultraviolet (UV) light degradation with the utilization of Digital Image Correlation (DIC) on ABS tensile specimens.

Design/methodology: ABS specimens were printed at three build orientations (flat (0 degrees), 45 degrees, and up-right (90 degrees)). Each of these specimens were treated with three different surface treatments including a control (acrylic paint, Cyanoacrylate, and Diglycidyl Bisphenol A) followed by exposure to UV light …

Quantification Of Re-Absorption And Re-Emission Processes To Determine Photon Recycling Efficiency In Perovskite Single Crystals, Yanjun Fang, Haotong Wei, Qingfeng Dong, Jinsong Huang

Department of Mechanical and Materials Engineering: Faculty Publications

Photon recycling, that is, iterative self-absorption and re-emission by the photoactive layer itself, has been speculated to contribute to the high open-circuit voltage in several types of high efficiency solar cells. For organic–inorganic halide perovskites that have yielded highly efficient photovoltaic devices, however, it remains unclear whether the photon recycling effect is significant enough to improve solar cell efficiency. Here we quantitatively evaluate the re-absorption and re-emission processes to determine photon recycling efficiency in hybrid perovskite with its single crystals by measuring the ratio of the re-emitted photons to the initially excited photons, which is realized by modulating their polarization …

Target Lesion Calcium Arc Influence The Performance Of Stenting, Pengfei Dong, Shengmao Lin, David L. Wilson, Hiram G. Bezerra, Linxia Gu

Department of Mechanical and Materials Engineering: Faculty Publications

Percutaneous coronary intervention (PCI) is the most common revascularization procedure, in which, fibrocalcific plaques are found in 17–35% of patients undergoing PCI [1]. Numbers will rise with population aging and prolonged statin treatment. Calcifications often lead to stent under expansion and strut malapposition, with increased risk of thrombosis and in-stent restenosis [2]. Presence of calcium strongly inhibits stent performance, a well-documented metric for outcome [3]. The goal of this work is to develop the finite element models for inspecting the influence of the calcium arc extent on the stenting outcomes, such as the stress and strain distribution within the plaque, …

Growth Mechanisms Of Multiscale, Mound-Like Surface Structures On Titanium By Femtosecond Laser Processing, Edwin Peng, Ryan Bell, Craig A. Zuhlke, Meiyu Wang, Dennis R. Alexander, George Gogos, Jeffrey E. Shield

Department of Mechanical and Materials Engineering: Faculty Publications

Femtosecond laser surface processing (FLSP) can be used to functionalize many surfaces, imparting specialized properties such as increased broadband optical absorption or superhydrophobicity/- hydrophilicity. In this study, the subsurface microstructure of a series of mound-like FLSP structures formed on commercially pure titanium using five combinations of laser fluence and cumulative pulse counts was studied. Using a dual beam Scanning Electron Microscope with a Focused Ion Beam, the subsurface microstructure for each FLSP structure type was revealed by cross-sectioning. The microstructure of the mounds formed using the lowest fluence value consists of the original Ti grains. This is evidence that preferential …

Dissipative Elastic Metamaterial With A Lowfrequency Passband, Yongquan Liu, Jianlin Yi, Zheng Li, Xianyue Su, Wenlong Li, Mehrdad Negahban

Department of Mechanical and Materials Engineering: Faculty Publications

We design and experimentally demonstrate a dissipative elastic metamaterial structure that functions as a bandpass filter with a low-frequency passband. The mechanism of dissipation in this structure is well described by a mass-spring-damper model that reveals that the imaginary part of the wavenumber is non-zero, even in the passband of dissipative metamaterials. This indicates that transmittance in this range can be low. A prototype for this viscoelastic metamaterial model is fabricated by 3D printing techniques using soft and hard acrylics as constituent materials. The transmittance of the printed metamaterial is measured and shows good agreement with theoretical predictions, demonstrating its …

Narrowband Nanocomposite Photodetector, Jinsong Huang, Fawen Guo, Liang Shen

Department of Mechanical and Materials Engineering: Faculty Publications

A photodetector includes an anode that is transparent or partially transparent to light, a cathode and an active layer disposed between the anode and the cathode. The active layer includes a nanocomposite material that has a polymer blended with nanoparticles or organic electron trapping particles. The photodetector has a low dark current when not illuminated by light and has a high conductivity when illuminated by light, in which the light passes the anode and is absorbed by the active layer. The active layer has a thickness selected such that the photodetector has a narrowband spectral response.

Role Of Copper Oxide Layer On Pool Boiling Performance With Femtosecond Laser Processed Surfaces, Corey Kruse, Edwin Peng, Craig Zuhlke, Jeff Shield, Dennis Alexander, Sidy Ndao, George Gogos

Department of Mechanical and Materials Engineering: Faculty Publications

Copper pool boiling surfaces are tested for pool boiling enhancement due to femtosecond laser surface processing (FLSP). FLSP creates self-organized micro/nanostructures on metallic surfaces and creates highly wetting and wicking surfaces with permanent surface features. In this study two series of samples were created. The first series consists of three flat FLSP copper surfaces with varying microstructures and the second series is an open microchannel configuration with laser processing over the horizontal surfaces of the microchannels. These microchannels range in height from 125 microns to 380 microns. Each of these surfaces were tested for pool boiling performance. It was found …

Analytical Strip Method For Thin Cylindrical Shells, John T. Perkins

Theses and Dissertations--Civil Engineering

The Analytical Strip Method (ASM) for the analysis of thin cylindrical shells is presented in this dissertation. The system of three governing differential equations for the cylindrical shell are reduced to a single eighth order partial differential equation (PDE) in terms of a potential function. The PDE is solved as a single series form of the potential function, from which the displacement and force quantities are determined. The solution is applicable to isotropic, generally orthotropic, and laminated shells. Cylinders may have simply supported edges, clamped edges, free edges, or edges supported by isotropic beams. The cylindrical shell can be stiffened …

การจำลองแบบทางพลศาสตร์ของไหลเชิงคำนวณของของเหลวที่ไม่ละลายเข้าหากันในเครื่องปฏิกรณ์แบบจุลภาคที่ขยายขนาด, คณิน มงคล

Chulalongkorn University Theses and Dissertations (Chula ETD)

สำหรับการสกัดด้วยตัวละลายในเครื่องปฏิกรณ์ขนาดจุลภาคนั้น ของเหลวในกระบวนการจะมีคุณสมบัติที่ไม่ละลายเข้าหากันซึ่งจะทำให้เกิดรูปแบบของการไหลที่แตกต่างกันออกไป โดยการไหลแบบ slug นั้นเป็นรูปแบบการไหลที่มักจะพบได้เมื่อเป็นการไหลที่ความเร็วต่ำ ซึ่งการไหลดังกล่าวสามารถรักษารูปแบบการไหลให้คงที่ตลอดความยาวท่อโดยที่มีประสิทธิภาพในการสกัดที่สูงกว่ารูปแบบการไหลแบบอื่นๆ ซึ่งเป็นผลจากการหมุนวนภายในเนื่องจากการเคลื่อนที่ของของเหลวภายใน slug การศึกษาการสกัดด้วยตัวทำละลายด้วยวิธีการดังกล่าวได้รับการยอมรับว่ามีประสิทธิภาพที่สูงเมื่อเปรียบเทียบกับวิธีการอื่นที่มีการใช้งานอยู่ในปัจจุบัน แต่ที่ผ่านมามักเป็นการศึกษาในระดับจุลภาคซึ่งมีผลผลิตโดยรวมน้อย ในงานวิจัยนี้ได้มุ่งไปที่การศึกษาผลเนื่องจากการเพิ่มขนาดเส้นผ่านศูนย์กลางของท่อในระดับมิลลิเมตร ที่มีต่อการเปลี่ยนแปลงรูปแบบการหมุนวนภายใน และความดันตกคร่อมภายใน slug โดยทำการศึกษาด้วยการจำลองแบบทางพลศาสตร์ของไหลเชิงคำนวณแบบ 2 มิติ ของการไหลผ่านท่อที่มีพื้นที่หน้าตัดเป็นรูปสี่เหลี่ยมที่มีขนาดแตกต่างกันออกไปตั้งแต่ 1-10 มิลลิเมตร ของเหลว 2 ชนิดที่มีคุณสมบัติการไม่ละลายเข้าหากันประกอบด้วยน้ำและเคโรซีนจะถูกป้อนเข้าสู่ท่อที่อยู่ตรงข้ามกันและเกิดการผสมกันที่บริเวณข้อต่อรูปตัว T โดยเปลี่ยนแปลงค่า Weber number ในช่วง 0.002-0.02 ผลการศึกษาแสดงให้เห็นว่าการเพิ่มขึ้นของขนาดเส้นผ่านศูนย์กลางท่อทำให้เวลาการหมุนวนลดลง 1.39% และความดันตกคร่อม slug ลดลง 85.12% โดยที่มีอัตราการไหลเชิงปริมาตรเพิ่มมากขึ้น อย่างไรก็ตามพบว่ารูปแบบการไหลแบบ slug จะไม่สามารถพบได้อีกต่อไปเมื่อเป็นการไหลในท่อที่มีขนาดเส้นผ่านศูนย์กลางมากกว่า 6 มิลลิเมตร

การออกแบบและผลิตเท้าเทียมแบบไดนามิคสำหรับผู้พิการขาขาดในระดับกิจกรรมปานกลาง, ดนุพงษ์ บุตรทองคำ

Chulalongkorn University Theses and Dissertations (Chula ETD)

ในปัจจุบัน ประเทศไทยมีผู้พิการขาขาดจำนวนมากและมีแนวโน้มที่จะเพิ่มจำนวนขึ้นอย่างต่อเนื่องในทุกๆ ปี หากแบ่งตามช่วงอายุของผู้พิการจะพบว่ามีผู้พิการขาขาดในกลุ่มวัยรุ่นถึงวัยกลางคนในช่วงอายุ 15 ถึง 44 ปี ประมาณร้อยละ 39 ของผู้พิการขาขาดทั้งหมด ซึ่งมีจำนวนมากกว่าช่วงอายุอื่นๆ ผู้พิการในกลุ่มนี้จะถูกจัดอยู่ในระดับกิจกรรมปานกลางหรือ K2-K3 ซึ่งเท้าข้างที่ยังเหลืออยู่ของผู้พิการในกลุ่มนี้สามารถปลดปล่อยพลังงานในการดีดตัวไปข้างหน้าที่เพียงพอต่อการเดินด้วยความเร็วเท่ากับคนปกติ อีกทั้งยังสามารถเคลื่อนไหวได้ดีทั้งในระนาบด้านหน้าและด้านข้าง จึงสามารถเดินบนพื้นที่มีความขรุขระหรือต่างระดับได้เป็นอย่างดี แต่ทว่าผู้พิการในกลุ่มนี้ยังคงใช้เท้าเทียมที่มีบริจาคในประเทศซึ่งมีข้อเท้าแข็งเกร็ง ไม่สามารถงอและปลดปล่อยพลังงานในการดีดตัวได้เหมือนเท้าคนปกติ งานวิจัยนี้จึงมีเป้าหมายที่จะออกแบบและผลิตเท้าเทียมแบบไดนามิคสำหรับผู้พิการขาขาดในระดับกิจกรรมปานกลาง ซึ่งสามารถเก็บสะสมพลังงานในจังหวะดีดตัวได้อย่างเหมาะสม และเคลื่อนไหวได้ทั้งในระนาบด้านข้างและด้านหน้า โครงสร้างเท้าเทียมถูกออกแบบโดยใช้วิธีการไฟไนต์เอลิเมนต์เพื่อวิเคราะห์การเก็บสะสมพลังงานและการเคลื่อนไหวให้เหมาะสมกับการใช้งานของผู้พิการในระดับกิจกรรมปานกลางและวิเคราะห์ความแข็งแรงตามแนวทางมาตรสากล ISO10328 โดยจะออกแบบให้มีพลังงานที่เก็บสะสมมากกว่าเท้าเทียมในท้องตลาดเล็กน้อยเพื่อให้พลังงานที่ปลดปล่อยสูงกว่าและใกล้เคียงกับคนปกติ ใช้แนวคิดการออกแบบแบบผ่าครึ่งซีกที่ส้นเท้าและเซาะร่องที่ปลายเท้าช่วยให้เคลื่อนไหวได้ในระนาบด้านหน้า โครงสร้างหลักของเท้าเทียมทำจากวัสดุผสมคาร์บอนไฟเบอร์มีความแข็งแรงสูงและน้ำหนักเบา ซึ่งผลิตโดยใช้วิธีการอบขึ้นรูปแบบสุญญากาศที่ควบคุมความดันและอุณหภูมิ เท้าเทียมต้นแบบได้รับการทดสอบการทำงานและทดสอบการเก็บสะสมและปลดปล่อยพลังงานของเท้าเทียมด้วยวิธีการทดสอบทางกล พบว่าสามารถเก็บพลังงานปลดปลอดพลังงานได้ 0.167 และ 0.137 J/kg ตามลำดับและมีมุมงอเท้าในทิศงอลง, งอขึ้น และพลิกด้านข้างของส้นและปลายเท้าเป็นมุม 8.96 องศา,16.98 องศา, 5.72 องศา และ 7.1 องศา ตามลำดับ ซึ่งเหมาะสมกับการใช้งานของผู้พิการขาขาดในระดับกิจกรรมปานกลาง อีกทั้งยังผ่านการทดสอบความแข็งแรงตามแนวทางมาตรฐานสากล ISO 10328:2006

Organic-Inorganic Graphite And Transition Metal Dichalcogenide Based Composites For 3d Printing, Jorge Alfredo Catalan Gonzalez

Open Access Theses & Dissertations

This project was multipronged to help fuse together topics of additive manufacturing and two-dimensional (2D) layered materials, and studying the mechanical and electrical properties of the composites produced. The composites are made from the thermoplastic polymer acting as a matrix and the graphite and 2D transition metal dichalcogenides (TMDs) serving as the filler or reinforcement. Different concentrations of TMD's were added to the matrix to study the effect of composition on the mechanical and electrical properties. To shed insights into the mechanical properties, test coupons were produced as "dog bone" structures for tensile testing using the ASTM D638 type 5 …

Mechanically Activated Magnesiothermic Combustion Synthesis Of Zirconium And Hafnium Diborides, Sergio Cordova

Open Access Theses & Dissertations

Magnetohydrodynamic (MHD) generation of electric power has the potential to increase the thermal efficiency of fossil-fuel burning power plants. Electrode materials in MHD generators must possess a high melting point, high electrical and thermal conductivities, chemical stability, and resistance to thermal shock, oxidation, and plasma sparks/arcs. Ultra-high temperature ceramics based on diborides of zirconium and hafnium (ZrB2 and HfB2) are promising materials for this application. Self-propagating high-temperature synThesis (SHS) is an attractive method for their large-scale fabrication, but SHS of ZrB2 and HfB2 from elemental Zr, Hf, and B is not economically viable because of the high cost of the …

Test Methods For The Fracture And Fatigue Crack Growth Behavior Of Hot Mix Asphalts, Eduardo Garcia

Open Access Theses & Dissertations

The service life and mechanical properties of bituminous mixtures are greatly affected by distress problems such as fracture, thermal cracking, and fatigue cracking of the asphalt layers. The fracture and fatigue crack growth (FCG) behavior of bituminous mixtures are difficult to quantify due to material-, test-, and equipment-related uncertainties. The goal of this study is to introduce a systematic fracture and fatigue crack growth testing approach for hot mix asphalts (HMAs). The objective is to experimentally evaluate the fracture resistance and fracture toughness behavior of a dense-graded HMA material at different temperatures and varying thicknesses. The effect of thickness on …

Structural And Mechanical Characterization Of Nanocrystalline Tungsten And Tungsten-Based Alloy Thin Films For Extreme Environment Applications, Gustavo Martinez

Open Access Theses & Dissertations

Extreme environments associated with nuclear applications often results in degradation of the physical, mechanical and thermo-mechanical properties of the materials. Tungsten (W) exhibits unique physical and mechanical properties, which makes tungsten a good candidate for nuclear applications; however, intrinsic W exhibits low fracture toughness at all temperatures in addition to a high ductile to brittle transition. In the present work, nanocrystalline W, W-Y and W-Mo alloys were nanoengineered for nuclear applications. Nanocrystalline tungsten coatings with a thickness of ~1 µm were deposited onto Silicon (100) and Sapphire (C-plane) using RF and DC sputtering techniques under various growth conditions. Yttrium content …

Comprehensive Finite Element Modeling Of Ti-6al-4v Cellular Solids Fabricated By Electron Beam Melting, Edel Arrieta

Open Access Theses & Dissertations

Additive manufacturing permits the fabrication of cellular metals which are materials that can be highly customizable and possess multiple and extraordinary properties such as damage tolerance, metamorphic and auxetic behaviors, and high specific stiffness. This makes them the subject of interest for innovative applications. With interest in these materials for energy absorption applications, this work presents the development of nonlinear finite element models in commercial software platforms (MSC Patran/Nastran) that permit the analysis of the deformation mechanisms of these materials under compressive loads. In the development of these models, a detailed multiscale study on the different factors affecting the response …

Atomically Informed Nonlocal Semidiscrete Variational Peierls-Nabarro Model For Planar Core Dislocations, Guisen Liu, Xi Cheng, Jian Wang, Kaiguo Chen, Yao Shen

Department of Mechanical and Materials Engineering: Faculty Publications

Prediction of Peierls stress associated with dislocation glide is of fundamental concern in understanding and designing the plasticity and mechanical properties of crystalline materials. Here, we develop a nonlocal semi-discrete variational Peierls-Nabarro (SVPN) model by incorporating the nonlocal atomic interactions into the semi-discrete variational Peierls framework. The nonlocal kernel is simplified by limiting the nonlocal atomic interaction in the nearest neighbor region, and the nonlocal coefficient is directly computed from the dislocation core structure. Our model is capable of accurately predicting the displacement profile, and the Peierls stress, of planar-extended core dislocations in face-centered cubic structures. Our model could be …

Photoluminescence From Radiative Surface States And Excitons In Methylammonium Lead Bromide Perovskites, Dengyang Guo, Davide Bartesaghi, Haotong Wei, Eline M. Hutter, Jinsong Huang, Tom J. Savenije

Department of Mechanical and Materials Engineering: Faculty Publications

In view of its band gap of 2.2 eV and its stability, methylammonium lead bromide (MAPbBr₃) is a possible candidate to serve as a light absorber in a subcell of a multijunction solar cell. Using complementary temperature-dependent time-resolved microwave conductance (TRMC) and photoluminescence (TRPL) measurements, we demonstrate that the exciton yield increases with lower temperature at the expense of the charge carrier generation yield. The low-energy emission at around 580 nm in the cubic phase and the second broad emission peak at 622 nm in the orthorhombic phase originate from radiative recombination of charges trapped in defects with …

Helium Irradiation And Implantation Effects On The Structure Of Amorphous Silicon Oxycarbide, Qing Su, Shinsuke Inoue, Manabu Ishimaru, Jennifer A. Gigax, Tianyao Wang, Hepeng Ding, Michael J. Demkowicz, Lin Shao, Michael Nastasi

Department of Mechanical and Materials Engineering: Faculty Publications

Despite recent interest in amorphous ceramics for a variety of nuclear applications, many details of their structure before and after irradiation/implantation remain unknown. Here we investigated the short-range order of amorphous silicon oxycarbide (SiOC) alloys by using the atomic pair-distribution function (PDF) obtained from electron diffraction. The PDF results show that the structure of SiOC alloys are nearly unchanged after both irradiation up to 30 dpa and He implantation up to 113 at%. TEM characterization shows no sign of crystallization, He bubble or void formation, or segregation in all irradiated samples. Irradiation results in a decreased number of Si-O bonds …

Suspended Graphene-Based Gas Sensor With 1-Mw Energy Consumption, Jong-Hyun Kim, Qin Zhou, Jiyoung Chang

Department of Mechanical and Materials Engineering: Faculty Publications

This paper presents NH₃ sensing with ultra-low energy consumption for fast recovery and a graphene sheet based on a suspended microheater. Sensitivity and repeatability are important characteristics of functional gas sensors embedded in mobile devices. Moreover, low energy consumption is an essential requirement in flexible and stretchable mobile electronics due to their small dimension and fluctuating resistivity during mechanical behavior. In this paper, we introduce a graphene-based ultra-low power gas detection device with integration of a suspended silicon heater. Dramatic power reduction is enabled by a duty cycle while not sacrificing sensitivity. The new oscillation method of heating improves …

Vorticella: A Protozoan For Bio-Inspired Engineering, Sangjin Ryu, Rachel E. Pepper, Moeto Nagai, Danielle C. France

Department of Mechanical and Materials Engineering: Faculty Publications

In this review, we introduce Vorticella as a model biological micromachine for microscale engineering systems. Vorticella has two motile organelles: the oral cilia of the zooid and the contractile spasmoneme in the stalk. The oral cilia beat periodically, generating a water flow that translates food particles toward the animal at speeds in the order of 0.1–1 mm/s. The ciliary flow of Vorticella has been characterized by experimental measurement and theoretical modeling, and tested for flow control and mixing in microfluidic systems. The spasmoneme contracts in a few milliseconds, coiling the stalk and moving the zooid at 15–90 mm/s. Because the …

Low-Drag Events In Transitional Wall-Bounded Turbulence, Richard D. Whalley, Jae Sung Park, Anubhav Kushwaha, David J.C. Dennis, Michael D. Graham, Robert J. Poole

Department of Mechanical and Materials Engineering: Faculty Publications

Intermittency of low-drag pointwise wall shear stress measurements within Newtonian turbulent channel flow at transitional Reynolds numbers (friction Reynolds numbers 70 – 130) is characterized using experiments and simulations. Conditional mean velocity profiles during low-drag events closely approach that of a recently discovered nonlinear traveling wave solution; both profiles are near the so-called maximum drag reduction profile, a general feature of turbulent flow of liquids containing polymer additives (despite the fact that all results presented are for Newtonian fluids only). Similarities between temporal intermittency in small domains and spatiotemporal intermittency in large domains is thereby found.

Flowtaxis Of Osteoblast Migration Under Fluid Shear And The Effect Of Rhoa Kinase Silencing, Brandon D. Riehl, Jeong Soon Lee, Ligyeom Ha, Il Keun Kwon, Jung Yul Lim

Department of Mechanical and Materials Engineering: Faculty Publications

Despite the important role of mechanical signals in bone remodeling, relatively little is known about how fluid shear affects osteoblastic cell migration behavior. Here we demonstrated that MC3T3-E1 osteoblast migration could be activated by physiologically-relevant levels of fluid shear in a shear stress-dependent manner. Interestingly, shear-sensitive osteoblast migration behavior was prominent only during the initial period after the onset of the steady flow (for about 30 min), exhibiting shear stress-dependent migration speed, displacement, arrest coefficient, and motility coefficient. For example, cell speed at 1 min was 0.28, 0.47, 0.51, and 0.84 μm min^-1 for static, 2, 15, and 25 …

Fluid-Structure Interaction In Abdominal Aortic Aneurysm: Effect Of Modeling Techniques, Shengmao Lin, Xinwei Han, Yonghua Bi, Siyeong Ju, Linxia Gu

Department of Mechanical and Materials Engineering: Faculty Publications

In this work, the impact of modeling techniques on predicting the mechanical behaviors of abdominal aortic aneurysm (AAA) is systematically investigated. The fluid-structure interaction (FSI) model for simultaneously capturing the transient interaction between blood flow dynamics and wall mechanics was compared with its simplified techniques, that is, computational fluid dynamics (CFD) or computational solid stress (CSS) model. Results demonstrated that CFD exhibited relatively smaller vortexes and tends to overestimate the fluid wall shear stress, compared to FSI. On the contrary, the minimal differences in wall stresses and deformation were observed between FSI and CSS models. Furthermore, it was found that …