Papers by Kyriakos Efstathiou
This paper presents the investigation of in scale production of Parthenon frieze stones by rapid ... more This paper presents the investigation of in scale production of Parthenon frieze stones by rapid prototyping methods. Various rapid prototyping methods were considered and the most economic one was selected. Additionally, the incomplete relief surfaces of the Parthenon frieze stones were fixed and solid models were created. All sixteen stones of the Parthenon west frieze were constructed in scale using additive manufacturing method (3D printing). Using special jigs, rubber molds were created and plaster was casted in order to create the in scale copies.
The Antikythera Mechanism is the most sophisticated extant ancient astronomical instrument and an... more The Antikythera Mechanism is the most sophisticated extant ancient astronomical instrument and analogue computer known and was assembled sometime between 150 and 100 BCE, almost a century after the death of Archimedes. The mechanism has a great educational potential as it appeals to inquiring minds as an astonishing artefact of science and technology. The latest research findings reveal significant cultural and social functions in its operations. This astonishing astronomical instrument has a clear interdisciplinary valueand it has that it may be used as an educational medium, to engage the general public, and especially to attract students both to/from exact sciences and to/from the humanities. The astronomical and technical knowledge embedded in the mechanism can also be used to introduce some aspects of modern science through the unknown technological achievements of Hellenic antiquity.
Wear, 2001
Thin hard physical vapour deposition (PVD) coatings attribute excellent cutting performance to ce... more Thin hard physical vapour deposition (PVD) coatings attribute excellent cutting performance to cemented carbide inserts, allowing a beneficial exploitation of modern CNC machine tools. Based on the continuous chip formation, coatings experience distinct failure mechanisms in turning. To clarify the influencing parameters on coating wear resistance release, turning experiments with TiAlN derived coatings, deposited on cemented carbide inserts have been carried out. At a variety of cutting speeds, the experimental results are explained through analytical ones obtained by means of finite elements method (FEM) calculations indicating a coating static decohesion at low cutting speeds, owing to its overstressing. On the other hand, at higher cutting speeds tribomechanical abrasive phenomena are dominant. Nevertheless, the cutting accomplishment of coated tools is impressive, in as much as even after the local initiation of coating failures the tool still exhibits adequate cutting reserves, continuing its severe service up to the end of its operational life due to abrasive flank wear. As the overall cutting length increases theoretical and experimental results show that a progressive local coating decomposition occurs while the cutting forces remain practically stable. Herewith chip formation alterations such as a gradual increase of the chip compression ratio and a consequent reduction of the tool contact stresses are induced.
Materialwissenschaft und Werkstofftechnik, 2013
ABSTRACT The knowledge of coated tool wear mechanisms in milling is central for explaining the fi... more ABSTRACT The knowledge of coated tool wear mechanisms in milling is central for explaining the film failure and selecting the appropriate cutting strategy and conditions. The described tool wear investigations in up and down milling were carried out at various cutting conditions, by coated cemented carbide inserts fixed on tool holders of different diameters. The variable stress, strain and strain rate fields developed in the tool during cutting affect the film-substrate deformation and in this way the resulting coating's loads and its fatigue failure. The effective tool life, up to a certain flank wear width was experimentally determined and correlated to the cutting edge entry impact duration (CEEID) into the workpiece material. Using a commercial CAD/CAM system, the geometry of the chip and of the contact between the cutting edge and workpiece was calculated in various milling cases and the corresponding tool wear evolution predicted. The latter converges with cutting edge entry impact duration and with the associated film fatigue critical force, affected by the coating strain rate. Die Kenntnis der Verschleißmechanismen beschichteter Werkzeuge beim Fräsen spielt bei der Erklärung des Schichtversagens sowie bei der Auswahl einer geeigneten Frässtrategie und der entsprechenden Schnittparameter eine entscheidende Rolle. Bei den durgeführten Untersuchungen wurden beschichtete Wendeschneidplatten an Fräsköpfen mit verschiedenen Durchmessern im Gleich- sowie im Gegenlauf bei variierten Schnittparametern eingesetzt. Die an der Werkzeugschneide während des Fräsvorgangs entwickelten Spannungs-, Dehnungs- und Dehnungsgeschwindigkeitsfelder beeinflussen die Verformung des beschichteten Werkzeugs und bestimmen die Belastungen an der Schicht, die ein Ermüdungsversagen auslösen können. Die Standzeit bis zu einer bestimmten Verschleißmarkenbreite wurde experimentell ermittelt und mit der Impulsdauer des Schneideneintritts (CEEID) in das Werkstück verglichen. Mit Hilfe von einem kommerziellen CAD/CAM-Programm wurden die Span- sowie die Kontaktgeometrie zwischen der Scheide und dem Werkstück berechnet und dadurch die Verschleißentwicklung bei unterschiedlichen Fräsbeispielen vorausgesagt. Dabei zeigte die Verschleißentwicklung eine gute Korrelation mit der Impulsdauer des Schneideneintritts sowie mit der entsprechenden kritischen Belastung, die von der Dehnungsgeschwindigkeit beeinflusst wird.
Journal of the European Ceramic Society, 2008
Aiming at assessing the stress distribution on the surface of a die mandrel during the extrusion ... more Aiming at assessing the stress distribution on the surface of a die mandrel during the extrusion of ceramic products, the flow of wet ground clay was simulated both in a ram extrusion device and by a FEM-based model, considering the von Mises criterion for the flow stress, the associative flow rule and the rigid-viscoplastic constitutive equation. The friction between clay and die is approached by the Tresca boundary condition, which proves a more realistic approach than the Coulomb friction law for the contact conditions between a plastically deforming material and a rigid surface. The Tresca friction factor and the material parameters of the constitutive model are determined through comparison of experimental and theoretical results. The distributions of clay sliding velocity and normal and frictional stress on the mandrel surface are then assessed through the numerical simulation model. It is found that no sticking areas appear on the mandrel surface.
Journal of Archaeological Science, 2008
This paper presents the investigation of a vaginal speculum, found during excavations in Dion, Gr... more This paper presents the investigation of a vaginal speculum, found during excavations in Dion, Greece, by means of computer tomographies. Based on this technique, the solid geometry of the structural elements of this medical instrument was reconstructed and a simulation of its operating mechanism was further conducted. Additionally important design and manufacturing data related to the vaginal speculum mechanism and its parts were obtained. The analysis provides various significant insights and further documents utilization of high level technical mechanical engineering procedures and technological sophistication in the Hellenic antiquity period.
Journal of Archaeological Method and Theory, 2011
A method for investigating the forming technique of ancient ceramic vessels is presented. The rec... more A method for investigating the forming technique of ancient ceramic vessels is presented. The recording, analysis, and comparison of the vessels' metrical properties by means of computer tomography, three-dimensional laser scanning, and solid-modeling software enables the identification of the applied manufacturing methods. A finite elements method-based simulation of the developed deformations during the vessels' manufacture offers significant insight into the applied shaping procedures. By making possible the exact recording of both the internal and external form of the vessels as well as the simulation of the forming procedure, the method represents a marked improvement to hitherto applied methods based on radiography. The method is applied on two early iron age ceramic jugs (oinochoai) found as offerings in tombs in excavations in Dion, Greece.
CIRP Annals - Manufacturing Technology, 2000
... K.-D. Bouzakis a , N. Michailidis a , N. Vidakis a , K. Eftathiou a , S. Kompogiannis a and G... more ... K.-D. Bouzakis a , N. Michailidis a , N. Vidakis a , K. Eftathiou a , S. Kompogiannis a and G. Erkens b. ... Bouzakis, K.,-D., Vidakis N., David K., 1999, The concept of an advanced impact tester supported by evaluation software in characterization of hard layered media, Int. Jour. ...
Journal of the Balkan Tribological Association
Uploads
Papers by Kyriakos Efstathiou