Yazar "Skordaris, Georgios" seçeneğine göre listele

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    Cutting performance improvement of MTCVD coated cemented carbide inserts via appropriate heat treatment
    (Elsevier, 2020) Skordaris, Georgios; Bouzakis, Konstantinos Dionysios; Stergioudi, Fani; Kouparanis, Stefanos; Boumpakis, Apostolos; Bouzakis, A.
    The softening of cemented carbide at the elevated temperature of MTCVD processes results in significant reduction of their strength, and thus, high coating deformation during cutting. In this way, at interrupted cutting loads, as during turning cast iron, the cutting performance of MTCVD coated cemented carbide inserts degrades due to premature coating fatigue fracture. To overcome this problem, appropriate heat treatments of MTCVD coated inserts were conducted. The related temperatures and durations for improving the substrate properties were optimized considering obtained strength data of uncoated inserts variously heat treated and the turning performance of coated ones correspondingly heat treated. (C) 2020 CIRP. Published by Elsevier Ltd. All rights reserved.
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    Determination of strain rate depended stress and strain fields in pvd coatings on cemented carbide inserts during the repetitive impact test
    (Trans Tech Publications Ltd, 2020) Bouzakis, Antonios; Skordaris, Georgios; Bouzakis, Konstantinos-Dionysios; Gökcen, Mehmet-Gökhan; Boumpakis, Apostolos; Batuk, Ahmet-Ugur; Sisman, Süleyman
    Recently, stress, strain, strain-rate dependent curves for cemented carbide have become an established tool for evaluating the mechanical properties. In this paper, related strain-rate dependent data of a K05 insert were employed to define the developed stress and strain fields occurring in the compound coating-substrate at impact forces of various durations. In this way, the occurring maximum strains at various impact loads and times were analytically calculated. These maximum values and related fatigue endurance coating strain-rate dependent limits were consequently used to validate published coating fatigue critical impact forces associated with certain impact times. © 2020 Trans Tech Publications Ltd, Switzerland.
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    Determination of strain-rate and temperature dependent high-speed steel material data via Fe analysis of repetitive impact test imprints
    (Taylor and Francis Ltd., 2022) Bouzakis, Konstantinos-Dionysios; Bouzakis, Antonios; Skordaris, Georgios; Bouzakis, Emmanouil; Gökcen, Mehmet-Gökhan; Sisman, Süleyman; Mpoumpakis, Apostolos
    A computational and experimental method is introduced for the mathematical description of stress–strain curves for high-speed steels dependent on strain-rate and temperature. The developed method is based on an FEM-supported evaluation of imprints created on the surface of HSS (high-speed steel) specimens subjected to repetitive impacts by a cemented carbide ball indenter. The experiments were performed at various impact times and temperatures. The quasi-static HSS material properties were determined using an FEM based evaluation of nanoindentation results carried out at various temperatures on the HSS specimens. In the conducted FEM calculations, the stress, strain, and stain-rate data for the cemented carbide ball indenter were taken from a recent publication. By simulating the impact test with a finite element model, the quasi-static HSS stress–strain data were proportionally adjusted by the stress augmentation ratio (SAR) until the calculated imprint depths converged with the measured ones at various temperatures and impact times. Hence, equations were developed describing SAR depending on the strain rate and temperature. Characteristic implementation examples of these equations to describe HSS stress, strain properties dependent on strain-rate and temperature are presented. © 2021 The Author(s). Published by the Federation of European Materials Societies in partnership with Taylor & Francis Group.
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    Effect of the crystallinity of diamond coatings on cemented carbide inserts on their cutting performance in milling
    (Elsevier Science Bv, 2019) Skordaris, Georgios; Bouzakis, Konstantinos Dionysios; Kotsanis, Tilemachos; Boumpakis, Apostolos; Stergioudi, Fani; Christofilos, Dimitrios; Woda, M.
    Micro-crystalline diamond (MCD) coatings were deposited on cemented carbide inserts at different temperatures using hot filament chemical vapor deposition technique. For investigating the effect of the developed diamond crystallinity on the fatigue strength and wear behaviour of the prepared MCD coated inserts, inclined impact tests and milling investigations were conducted correspondingly. Raman spectra were recorded for capturing the crystalline phases after the film deposition and their potential changes after the impact and milling experiments induced by the mechanical and thermal loads. Thus, the explanation of the cutting performance of the employed diamond coated inserts with various crystalline phases was enabled. (C) 2019 Published by Elsevier Ltd on behalf of CIRP.
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    Stress, strain and strain-rate cemented carbide properties determined with a fem-supported evaluation of impact test imprints
    (Elsevier Sci Ltd, 2021) Bouzakis, Antonios; Skordaris, Georgios; Bouzakis, Konstantinos Dionysios; Gökçen, Mehmet Gökhan; Boumpakis, Apostolos; Batuk, Ahmet Uğur; Şişman, Süleyman
    Cemented carbide materials are key in tool manufacturing, nowadays widely used in cutting, forming and other manufacturing processes. Commonly applied methods for obtaining their strain-rate dependent material properties are insufficient due to the high hardness, mechanical strength and low deformability. In this paper, we produce relevant data for stress-strain and strain-rate curves up to strain rates of approximately 200 s(-1) with the aid of a developed FEM-supported evaluation method for remaining imprints on cemented carbide surfaces after applying impact loads at various durations and magnitudes. Regarding the impact duration, the impact loads were dynamically generated via electromagnetic or piezoelectric devices. The attained data are relevant to several applications including calculations to determine the stress and strain fields developed in cemented carbide tools imposed by impact loads at various conditions.
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    Wear and fatigue behavior of pvd and mtcvd ticn coated cemented carbide inserts in turning cast iron
    (Trans Tech Publications Ltd, 2020) Skordaris, Georgios; Bouzakis, Konstantinos-Dionysios; Stergioudi, Fani; Kouparanis, Stefanos; Boumpakis, Apostolos; Bouzakis, Antonios
    TiCN coatings of the same chemical compositions were deposited on HW/K05-K20 cemented carbide inserts via physical (PVD) and medium temperature chemical vapor deposition (MTCVD) techniques. Nano-indentations coupled with appropriate FEM simulations were used for characterizing the film and substrate mechanical properties. Furthermore, uncoated cemented carbide substrates were annealed in vacuum at temperatures and durations corresponding to the related ones during the PVD and MTCVD process for recording the effect of the deposition temperature and duration on the substrate strength properties. Perpendicular and inclined impact tests at various loads were performed for checking the coating fatigue endurance and adhesion respectively. These material data were considered in FEM supported calculations for predicting the developed stress fields in the cutting edge during turning cast iron GG30 using the PVD and MTCVD TiCN coated inserts. According to the obtained result, both coatings possess the same stress-strain properties. Hereupon, the MTCVD coatings are characterized comparably to PVD ones by improved fatigue properties and adhesion strength. Although these properties contribute to an increased tool life in finishing turning, the significant reduction of the substrate strength properties, due to the elevated temperature during the MTCVD process, results in a premature coating failure and a consequent intensive wear evolution in roughing. © 2020 Trans Tech Publications Ltd, Switzerland.