Engineering Commons^™

The Study Of Corrosion On Additive-Manufactured Metals., Braydan Daniels

Electronic Theses and Dissertations

The purpose of this study was to investigate and compare the corrosion mechanisms between wrought and additive-manufactured (3D-printed) copper and stainless steel. The experimental procedure consisted of measuring the open circuit potential, electrochemical impedance spectroscopy, linear sweep voltammetry, Tafel analysis, surface topology, and scanning electron microscopy for each metal within salt water, tap water, sulfuric acid, and synthetic body fluid (excluding copper in synthetic body fluid).

Overall, printed stainless steel was more corrosion-resistant than wrought stainless steel in tap water and synthetic body fluid based on OCP, LSV, and surface topology results. Additionally, printed copper was more corrosion-resistant than wrought …

Development And Evaluation Of Modeling Approaches For Extrusion-Based Additive Manufacturing Of Thermoplastics, Christopher C. Bock

Electronic Theses and Dissertations

This work focuses on evaluating different modeling approaches and model parameters for thermoplastic AM, with the goal of informing more efficient and effective modeling approaches. First, different modeling approaches were tested and compared to experiments. From this it was found that all three of the modeling approaches provide comparable results and provide similar results to experiments. Then one of the modeling approaches was tested on large scale geometries, and it was found that the model results matched experiments closely. Then the effect of different material properties was evaluated, this was done by performing a fractional factorial design of experiments where …

In-Situ Process Monitoring For Metal Additive Manufacturing (Am) Through Acoustic Technique, Md Shahjahan Hossain

Electronic Theses and Dissertations

Additive Manufacturing (AM) is currently a widely used technology in different industries such as aerospace, medical, and consumer products. Previously it was mainly used for prototyping of the products, but now it is equally valuable for commercial product manufacturing. More profound understanding is still needed to track and identify defects during the AM process to ensure higher quality products with less material waste. Nondestructive testing becomes an essential form of testing for AM parts, where AE is one of the most used methods for in situ process monitoring. The Acoustic Emission (AE) approach has gained a reputation in nondestructive testing …

Impact Resistance Of Fiber-Reinforced Composites Using Computational Simulations, Maitham Alabbad

Electronic Theses and Dissertations

Composite materials are widely used in aerospace, automotive and wind power industries due to their high strength-to-weight and stiffness-to-weight ratios and their improved mechanical properties compared to metals. The damage resistance of composite materials due to low velocity impact depends on fiber breakage, matrix cracking and delamination between the interfaces. In this research, a numerical investigation of low velocity impact response of a multidirectional symmetric carbon-epoxy composite laminate is carried out and presented. Two different finite element models are developed for composite laminates made of non-crimp fabric to investigate their behavior under different levels of impact energy. In the first …

Optical Direct Detection Of Thermal Vibrations Of Ultralow Stiffness Micro-Nano Structures., Sri Sukanta Chowdhury

Electronic Theses and Dissertations

A direct detection optical vibrometer is constructed around an 850 nm laser and a quadrant photodetector (QPD). The limit of detection is 0.2 fW which corresponds to a minimum amplitude of 0.1 Å. The vibrometer is used to measure the thermal vibration spectra of low stiffness micromechanical structures have nanometer features. One structure measured is a cantilevered 30 μm diameter glass fiber. Vibration amplitudes as low as 1.1 Å are measured. The thermal vibration spectra show fundamental resonances at 80-250 Hz and a signal to noise ratio (SNR) of 23-55 dB. Young’s modulus of glass in the cantilevers, estimated from …

Modeling And Validations Of Control Parameters For Material Extrusion-Based Additive Manufacturing Of Thixotropic Aluminum Alloys., Lars Herhold

Electronic Theses and Dissertations

Additive Manufacturing (AM) with metals has been accomplished mainly through powder bed fusion processes. Initial experiments and simulations using Material Extrusion Additive Manufacturing (MEAM) have been performed by various researchers especially using low melting alloys. Recently Stratasys Inc. submitted a patent application for the use of their Material Extrusion technology also called Fused Deposition Modeling (FDM) where they describe the process using thixotropic semi-solid alloys. Currently this process using semi-solid, engineering type alloys such as A356 or THIXALLOY 540 aluminum have not been researched to evaluate the control parameters. This research combines the in-depth knowledge of applying thixotropic semi-solid aluminum …

Ultrasonic Nondestructive Evaluation Of Metal Additive Manufacturing., Venkata Karthik Nadimpalli

Electronic Theses and Dissertations

Metal Additive Manufacturing (AM) is increasingly being used to make functional components. One of the barriers for AM components to become mainstream is the difficulty to certify them. AM components can have widely different properties based on process parameters. Improving an AM processes requires an understanding of process-structure-property correlations, which can be gathered in-situ and post-process through nondestructive and destructive methods. In this study, two metal AM processes were studied, the first is Ultrasonic Additive Manufacturing (UAM) and the second is Laser Powder Bed Fusion (L-PBF). The typical problems with UAM components are inter-layer and inter-track defects. To improve the …

Structural And Aerodynamic Design, Procedure And Analysis Of A Small V-Shaped Vertical Axis Wind Turbine, Odari J. Whyte

Electronic Theses and Dissertations

Over the last two decades there has been a renewed interest in Vertical Axis Wind Turbines. This turbine configuration though unpopular for large-scale generation has found a niche market in the way of offshore energy harvesting. However, offshore wind has its challenges. In this thesis a detailed comprehensive study of a proposed V-shaped vertical axis turbine rotor is performed in order to examine its structural and aerodynamic characteristics. The design met and exceeded the safety parameters establish for test bed operation, showing a factor of safety of 1.87 with regard to fatigue stress response. A satisfactory fatigue stress design life …

Microstructural Analysis Of Thermoelastic Response, Nonlinear Creep, And Pervasive Cracking In Heterogeneous Materials, Alden C. Cook

Electronic Theses and Dissertations

This dissertation is concerned with the development of robust numerical solution procedures for the generalized micromechanical analysis of linear and nonlinear constitutive behavior in heterogeneous materials. Although the methods developed are applicable in many engineering, geological, and materials science fields, three main areas are explored in this work. First, a numerical methodology is presented for the thermomechanical analysis of heterogeneous materials with a special focus on real polycrystalline microstructures obtained using electron backscatter diffraction techniques. Asymptotic expansion homogenization and finite element analysis are employed for micromechanical analysis of polycrystalline materials. Effective thermoelastic properties of polycrystalline materials are determined and compared …

Freeze-Thawing Of Polyester/E-Glass As An Evaluation Of An Astm International Test Standard Proposal, Stefan Mauritz Strandlund

Electronic Theses and Dissertations

American Composites Manufacturers Association (ACMA) reported in 2009 that the four major sectors currently utilizing fiber reinforced polymers (FRP) are construction, corrosion, marine, and transportation in descending order of total FRP shipped. All of these sectors are known to be billion dollar industries and they are all involved with applications subjected to freezing and thawing. FRP encompass many characteristics that are beneficial to these sectors and also in resisting this exposure. ASTM International has yet not developed a standard to test FRP materials resistance to freeze-thaw (FT) cycling exposure. The D20.18.02 committee of the ASTM is in the process of …

The Investigation Of Nano Silica In The Cement Hydration Pro, Jonathan Samuel Belkowitz

Electronic Theses and Dissertations

With the advent of nano technology, materials have been developed that can be applied to high performance concrete mix designs. Nano silica reacts with calcium hydroxide (CH) to develop more of the strength carrying structure of cement: calcium silica hydrate (CSH). In this paper, relationships have been developed to distinguish the benefits when using different sizes of nano silica in cement paste. An extensive regime of experimental analysis was carried out to determine the effect of nano silica. Through these experiments the heat of hydration of multiple cement mix designs was measured. After that, the concentration of CH was recorded …