Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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COAR Access Rights: search.filters.coarAccessRights.open accessSubject: search.filters.subject.Additive manufacturing

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  • Master Thesis
    The Constitutive and Damage Models of Additively Manufactured Ti6al4v Alloy
    (01. Izmir Institute of Technology, 2021) Hızlı, Burak; Güden, Mustafa
    Electron Beam Melting (EBM) is one of the metal additive manufacturing methods that enable the fabrication of Ti6Al4V alloy parts with intended shapes in where this alloy is of significant interest such as aerospace and biomedical industries due to its outstanding properties. In this study, the microstructural and mechanical properties of EBM-produced Ti64 were comprehensively investigated. Microstructural analysis was conducted on as-built specimens. Microstructural analysis showed that EBM-produced Ti64 possesses α+β duplex phase with directional microstructural alterations and high porosity fraction in the part volume. Mechanical properties were investigated under tension loadings at quasi-static rates (0.001-0.1 1/s) and compression loading at quasi-static and high strain rates (0.001-2154 1/s). Thereafter, Johnson-Cook (JC) strength and damage models were individually calibrated from the experimental results of tension and compression behaviors and experimental fracture strains in order to numerically predict the material flow behavior of EBM-produced Ti64 considering the strain, strain rate, and temperature effects in the case of various loadings combined with temperature changes. EBM-produced Ti64 exhibited proximate mechanical properties in terms of tension and compression behaviors, however extremely low ductile behavior under tension loadings resulting premature failure without necking. Eventual fracture of this material occurred via tearing of the scanned layers for tension loadings and shear crack following the shear band formation propagation on 45° to loading axis for compression loadings. Calibrated JC strength and damage models for EBM-produced Ti64 were able to predict flow behavior and fracture strains within strain rate range between 0.001 and 1000 1/s. However, the JC strength model could not predict the flow behavior at excessively high strain rates (2154 1/s) due to complex deformation mechanisms including adiabatic heating.
  • Master Thesis
    Spreadability and Characterization of Metal Powders for Additive Manufacturing
    (Izmir Institute of Technology, 2020) Hasdemir, Beyza; Ahmetoğlu, Çekdar Vakıf; Yasa, Evren
    Powder Bed Fusion (PBF) is one of the Additive Manufacturing (AM) techniques, in which metal powders are used as feedstock. AM process enables the production of lightweight structures, design freedom in 3D printed parts, short cycle time, etc. AM made part properties are affected by the powder characteristics used to form the component. A part comprises hundreds of spread layers; however, a homogeneous layer is crucial for obtaining the necessary final part properties. Spreadability can be defined as a method to quantify the powder distribution through the layer. Although it has not been standardized yet, currently, it is merely controlled by following the powder flowability, a standardized characterization method for AM. This thesis investigates the spreadability of the utilized powders for AM (here only Laser-Powder Bed Fusion will be used), with the image processing algorithms in MATLAB. Besides, it also aims to examine the spreadability correlation with the other characteristics such as flow rate, apparent density, angle of repose, and thus the final 3D printed components. Samples in six different particle size distribution were characterized, and spreadability tests were performed with the L-PBF machine. The powder characterization results demonstrated that an increase in fine particle ratio by volume (below 20 µm) enhances the angle of repose (AOR). The tests demonstrated that irregularities on the spread layer could be quantified with the image processing algorithms. The 3D printed samples were found porous. The reason for porosity in the sample might base on a combination of various factors, poor spreadability, spatter formation, and other L-PBF processing parameters might be the reasons for such microstructural development.