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Mechanics of Materials Commons

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2018

University of Nebraska - Lincoln

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Articles 31 - 39 of 39

Full-Text Articles in Mechanics of Materials

Frequency Dependent Deformation Reversibility During Cyclic Loading, Shuai Shao, Michael M. Khonsari, Jian Wang, Nima Shamsaei, Nan Li Jan 2018

Frequency Dependent Deformation Reversibility During Cyclic Loading, Shuai Shao, Michael M. Khonsari, Jian Wang, Nima Shamsaei, Nan Li

Department of Mechanical and Materials Engineering: Faculty Publications

High-frequency testing (HFT) is useful for accelerated fatigue testing of conventional materials that typically serve under low-frequency loading conditions, as well as for the assessment of the robustness of microelectromechanical systems which typically experience high-frequency service conditions. Using discrete dislocation dynamics, we attempt to elucidate the effect of loading frequency on the reversibility of cyclic deformation. We demonstrate that the HFT induces a higher fraction of reversible cyclic deformation because of a larger portion of elastic/anelastic deformation due to limited dislocation mobility, and a higher degree of reversibility in plastic deformation owing to the less occurrence of cross-slip.


Complementary Microscopy Techniques Applied For Characterizing The Localized Nanoscale Structure Of Poly (Vinylidene Fluoride), Wen Qian, Shuo Sun, Charles Nguyen, Wenlong Li, Stephen Ducharme, Joesph A. Turner Jan 2018

Complementary Microscopy Techniques Applied For Characterizing The Localized Nanoscale Structure Of Poly (Vinylidene Fluoride), Wen Qian, Shuo Sun, Charles Nguyen, Wenlong Li, Stephen Ducharme, Joesph A. Turner

Department of Mechanical and Materials Engineering: Faculty Publications

Poly (vinylidenefluoride) (PVDF), a well-recognized electroactive polymer, has been studied extensively over many decades. Recently, there has been increasing interest in tuning the electrical properties of PVDF from ferroelectric to piezoelectric and to pyroelectric, which can be attained via controlling the microscale structure down to the nanoscale structure [1-2]. To optimize the preparation conditions of PVDF and its copolymers, as well as to improve the performance for many applications, comprehensive analytical techniques are of great importance. In this paper, we demonstrate complementary nanoscale characterization and measurement techniques, by conducting a systematic and coordinated study involving scanning electron microscopy (SEM), high …


Flow Patterns Through Vascular Graft Models With And Without Cuffs, Chia Min Leong, Gary B. Nackman, Timothy Wei Jan 2018

Flow Patterns Through Vascular Graft Models With And Without Cuffs, Chia Min Leong, Gary B. Nackman, Timothy Wei

Department of Mechanical and Materials Engineering: Faculty Publications

The shape of a bypass graft plays an important role on its efficacy. Here, we investigated flow through two vascular graft designs±with and without cuff at the anastomosis. We conducted Digital Particle Image Velocimetry (DPIV) measurements to obtain the flow field information through these vascular grafts. Two pulsatile flow waveforms corresponding to cardiac cycles during the rest and the excitation states, with 10% and without retrograde flow out the proximal end of the native artery were examined. In the absence of retrograde flow, the straight end-to-side graft showed recirculation and stagnation regions that lasted throughout the full cardiac cycle with …


Dislocations Interaction Induced Structural Instability In Intermetallic Al2cu, Qing Zhou, Jian Wang, Amit Misra, Ping Huang, Fei Wang, Kewei Xu Jan 2018

Dislocations Interaction Induced Structural Instability In Intermetallic Al2cu, Qing Zhou, Jian Wang, Amit Misra, Ping Huang, Fei Wang, Kewei Xu

Department of Mechanical and Materials Engineering: Faculty Publications

Intermetallic precipitates are widely used to tailor mechanical properties of structural alloys but are often destabilized during plastic deformation. Using atomistic simulations, we elucidate structural instability mechanisms of intermetallic precipitates associated with dislocation motion in a model system of Al2Cu. Interaction of non-coplanar <001> dislocation dipoles during plastic deformation results in anomalous reactions—the creation of vacancies accompanied with climb and collective glide of <001> dislocation associated with the dislocation core change and atomic shuffle—accounting for structural instability in intermetallic Al2Cu. This process is profound with decreasing separation of non-coplanar dislocations and increasing temperature and is likely to be …


Mechanical Performance Of Plla Stent, Longzhen Wang, Junfei Tong, Pengfei Dong, David L. Wilson, Hiram G. Bezerra, Linxia Gu Jan 2018

Mechanical Performance Of Plla Stent, Longzhen Wang, Junfei Tong, Pengfei Dong, David L. Wilson, Hiram G. Bezerra, Linxia Gu

Department of Mechanical and Materials Engineering: Faculty Publications

Stent implantation is widely used to treat blocked lumen. Stents were meshed structure made of polymers and metal alloys, including stainless steel, cobalt chrome and nitinol [1]. Clinical studies had demonstrated that stents helped to scaffold the diseased lesion up to one year when tissue adapted to the stented environment [2]. However, the permanently implanted stents inside artery were associated with complications such as stent fracture, tissue inflammation, in-stent restenosis and thrombosis [3]. Currently, biodegradable stents are attracting more attention due to its potential long-term efficacy in treating blocked lumens. The detailed characterizations of biodegradable stents are essential for the …


Tissue Stresses In Stented Coronary Arteries With Different Geometries: Effect Of The Relation Between Stent Length And Lesion Length, Xiang Shen, Song Ji, Yong-Quan Deng, Hong-Fei Zhu, Jia-Bao Jiang, Linxia Gu Jan 2018

Tissue Stresses In Stented Coronary Arteries With Different Geometries: Effect Of The Relation Between Stent Length And Lesion Length, Xiang Shen, Song Ji, Yong-Quan Deng, Hong-Fei Zhu, Jia-Bao Jiang, Linxia Gu

Department of Mechanical and Materials Engineering: Faculty Publications

In-stent restenosis after stent deployment remains an obstruction in the long-term benefits of stenting. This study sought to investigate the influence of the relation between stent length and lesion length on the mechanics of the arterial wall with different geometries, including straight and tapered vessels. Results showed that when the length of the stent was longer than the lesion length, the maximum stress in plaque and vessel increased as the length of stent increased. When the length of the stent was shorter than the lesion length, the vessel stress induced by stent inflation was lower; both ends of the stenosis …


Scaffold Structural Microenvironmental Cues To Guide Tissue Regeneration In Bone Tissue Applications, Xuening Chen, Hongyuan Fan, Xiaowei Deng, Lina Wu, Tao Yi, Linxia Gu, Changchun Zhou, Yujiang Fan, Xingdong Zhang Jan 2018

Scaffold Structural Microenvironmental Cues To Guide Tissue Regeneration In Bone Tissue Applications, Xuening Chen, Hongyuan Fan, Xiaowei Deng, Lina Wu, Tao Yi, Linxia Gu, Changchun Zhou, Yujiang Fan, Xingdong Zhang

Department of Mechanical and Materials Engineering: Faculty Publications

In the process of bone regeneration, new bone formation is largely affected by physico-chemical cues in the surrounding microenvironment. Tissue cells reside in a complex scaffold physiological microenvironment. The scaffold should provide certain circumstance full of structural cues to enhance multipotent mesenchymal stem cell (MSC) differentiation, osteoblast growth, extracellular matrix (ECM) deposition, and subsequent new bone formation. This article reviewed advances in fabrication technology that enable the creation of biomaterials with well-defined pore structure and surface topography, which can be sensed by host tissue cells (esp., stem cells) and subsequently determine cell fates during differentiation. Three important cues, including scaffold …


Heat Transfer Across A Nanoscale Pressurized Air Gap And Its Application In Magnetic Recording, Jinglin Zheng, Yung-Kan Chen, Qin Zhou Jan 2018

Heat Transfer Across A Nanoscale Pressurized Air Gap And Its Application In Magnetic Recording, Jinglin Zheng, Yung-Kan Chen, Qin Zhou

Department of Mechanical and Materials Engineering: Faculty Publications

In this study, we investigated how a thermally actuated air bearing slider heats up a fast-spinning storage disk through a highly pressurized nanoscale air gap in a magnetic recording system. A Euleriandescription- based computational approach is developed considering heat conduction through a pressurized air film and near-field radiation across the gap. A set of field equations that govern the air bearing dynamics, slider thermo-mechanics and disk heat dissipation are solved simultaneously through an iterative approach. A temperature field on the same order as the hot slider surface itself is found to be established in the disk. The effective local heat …


Interfacial Characterization By Pull-Out Test Of Bamboo Fibers Embedded In Poly(Lactic Acid), Quentin Viel, Antonella Esposito, Jean-Marc Saiter, Carlo Santulli, Joseph A. Turner Jan 2018

Interfacial Characterization By Pull-Out Test Of Bamboo Fibers Embedded In Poly(Lactic Acid), Quentin Viel, Antonella Esposito, Jean-Marc Saiter, Carlo Santulli, Joseph A. Turner

Department of Mechanical and Materials Engineering: Faculty Publications

In this work, the apparent shear strength at the interface between a bamboo fiber and the surrounding poly(lactic acid) (PLA) matrix is quantified. A method for processing pull-out test samples within a controlled embedded length is proposed and the details of the test procedure are presented, along with a critical discussion of the results. Two series of samples are considered: untreated and mercerized bamboo fibers from the same batch, embedded in the same polyester matrix. Electron and optical microscopy are used to observe the fiber–matrix interface before and after the test, and to identify the failure mode of each sample, …