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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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    Effective application of coated tools in milling considering coating fatigue mechanisms
    (Nova Science Publishers, Inc., 2024) Bouzakis, Konstantinos-Dionysios
    The dominant wear mechanisms of coated tools in cutting vary from application to application and are different compared to those of uncoated ones. Their knowledge is crucial for explaining coating failures and appropriately adjusting, among others, the cutting conditions. In this chapter, firstly, the potential wear phenomena will be introduced developed during milling with coated cemented carbide tools. Furthermore, the tool wear evolution will be elucidated imposed by coating fatigue failures which, depending on the applied milling kinematic, might be the prevailing wear phenomena. Coating fatigue failures appear in milling due to repetitive cutting loads associated with the successive tool entries into the workpiece material. Herein, the impact duration of the relevant cutting forces and consequently developed coating strain and strain-rate combinations at endangered regions of the cutting-edge flank and rake are dominant for the coated tool life. Based on these parameters, the wear evolution of coated tools at various milling kinematics and chip geometries can be mathematically described. A related wear predictive model is introduced at the end of the present chapter. The developed model is integrated in a commercial CAM system for milling parts of complicated geometry. © 2024 Nova Science Publishers, Inc. All rights reserved.
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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.