Engineering Commons^™

Characterization Of Interlayer Laser Shock Peening During Fused Filament Fabrication Of Polylactic Acid (Pla), Fabien Denise

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

The field of additive manufacturing (AM) has gained a significant amount of popularity due to the increasing need for more sustainable manufacturing techniques and the adaptive development of complex product geometries. The problem is that AM parts routinely exhibit flaws or weaknesses that affect functionality or performance. Over the years, surface treatments have been developed to compensate certain flaws or weaknesses in manufactured products. Combining surface treatments with the modularity of additive manufacturing could lead to more adaptable and creative improvements of product functions in the future. The current work evaluates the feasibility of pursuing a new research axis in …

Polyaniline/Cobalt Nanoparticle Composite Films, Rifat Mahbub

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Polymer nanocomposites have been gaining attention because of the enhanced properties of the element materials it can offer. These composites have been used in biological sector as well as quantum computing and memory devices. These are also used as different kind of sensors. Polymer composites incorporated with magnetic nanoparticles can modify the magnetic property of the nanoparticles and that has huge potential to be used in different sort of applications.

This work aims to develop a polymeric nanocomposite incorporating a conducting polymer and magnetic nanoparticles. The influence of the conducting polymer on the magnetic property of the nanoparticles was investigated. …

Growth And Characterization Of Molecular Ferroelectric Thin Films, Yifan Yuan

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Compared with inorganic ferroelectrics, organic ferroelectrics have advantages of low cost and low toxicity, are in increasing demand in capacitors, piezoelectric, and memory devices to reduce the environmental load. This work focuses on two types of organic molecular ferroelectric materials, croconic acid (CA) and 2-methylbenzimidazole (MBI). The work here introduces several origins of ferroelectricity in typical organics and their switching mechanism. We then investigated the nucleation, growth, and ferroelectric measurements of CA thin films. We explored the effect of substrate temperature and an external electric field on the nucleation and growth processes. The results can be used to improve the …

Synthesis Of Graphene And Graphene-Based Composite Membrane, Yuanjun Fan

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Vibration membrane equipped for earphone requires high performance in both mechanical properties and electronic properties. With extraordinary properties on both, graphene and graphene-based composite materials appear as a promising candidate for this application. Chemical vapor deposition (CVD) is believed to be the most convenient way to synthesize a large area (on scale of square centimeters) as well as a homogeneous thickness for the membrane. The thesis focuses on applying control variable experiment method to analyze different effects on mechanical property of the two CVD setting parameters: cooling rate, and hydrocarbon precursor. For isolating the specimens efficiently, a modified electrochemical method …

Wide Bandgap Organo‐Lead Trihalide Perovskites For Solar Cells, Miao Hu

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Methylammonium lead trihalide perovskite (MAPbX3, where MA is methylammonium, and X is a halide)-based solar cells have been extensively investigated recently, with a demonstrated and certified solar power conversion efficiency (PCE) exceeding 20%. To further boost the PCE beyond the Schockley–Queisser limit, tandem structured solar cells have been investigated based on integrating MAPbX3 and the lower bandgap solar cells. Although the best reported efficiency for this type of tandem cells is not close to the theoretically achievable value, mixed-halide perovskite MAPbBrxI3–x is still one of the most promising candidates as the wide-bandgap light absorber for the tandem application to match …

Efficiency Enhancement In Solution Processed Organic And Organic-Inorganic Hybrid Perovskite Solar Cells, Zhengguo Xiao

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Solution processed thin film photovoltaic devices are one of the most promising renewable energy sources. Organic solar cells have been intensively studied due to their advantages of light-weight, flexibility and low-cost materials and manufacturing. The organic-inorganic hybrid perovskite materials have recently shown great potential application in solar cells. The PCE increased dramatically from 3.8% in 2009 to a certified efficiency of 20.1% in 2014. In this dissertation, we focus on the efficiency enhancement for solution processed organic and organic-inorganic solar cells.

In Chapter 2, I demonstrated that the crystallinity of the ferroelectric polymer P(VDF-TrFE) at the organic active layer/ electrode …

Influence Of The Temperature On Flow-Induced Crystallization Of Isotactic Polypropylene And Propylene-Ethylene Random Copolymer, Hugo Boitout

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

When flow is applied on a semi-crystalline polymer melt, it can greatly impact how it crystallizes its final properties. Therefore, it is crucial to understand the basic mechanism of flow induced crystallization (FIC). Only then will it be possible to predict final properties from the type of resin and processing conditions. Polypropylene is one of the most widely used polymers. Its processing generally involves subjecting the melt to intense flow fields, so FIC commonly occurs.

This study investigates the influence of temperature of shear and crystallization on the FIC behavior of isotactic polypropylene (iPP). Temperature is one of the main …

Pan Nanofibers And Nanofiber Reinforced Composites, Cheng Ren

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Nanomaterials play an important role in the development of nanotechnology. They possess unique mechanical, physical, and chemical properties coupled with small size and ultrahigh surface area that can provide critical advantages for applications. Continuous nanofibers attract special interest due to their dual nano-macro nature and ability to bridge scales. Nanofibers are being considered for a broad range of applications spanning advanced filters, separation membranes, ultrasensitive sensors, micro/nano actuators, nanoprobes, tissue engineering scaffolds, protective and smart closing, and multifunctional composites. Most of these applications require certain mechanical properties and robustness. However, the literature on the mechanical behavior of nanofibers and their …

A Conductivity Testing System Coupled With A Tensile Testing Machine To Measure The Surface Properties Of Polymer Specimens, Nguyen T. Nguyen

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Polymers play an essential role in our everyday life due to their employment in a widespread range of applications. Polymers are used in industries such as space, biomedical, electronics, etc. in which their electrical and mechanical properties are major aspects which need to be investigated prior to implementation. When subjected to mechanical stimulations, polymers may exhibit changes in electrical conductivity which can vary locally within the specimens, especially in those of conducting polymers. In mechanical investigations a tensile testing machine is used to understand polymers’ strength, elasticity or other mechanical properties. In electrical analysis, using a four-point probe to examine …