Πλοήγηση ανά Συγγραφέα "David, Constantine"
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Τεκμήριο Determination of the Fatigue Resistance of HVOF Thermal Spray WC-CoCr Coatings by Means of Impact Testing(2007-11) David, Constantine; Anthymidis, Konstantinos; Agrianidis, Pavlos; Tsipas, DimitriosImpact testing is an efficient experimental procedure that enables the determination of the fatigue resistance of mono- and multi-layer coatings deposited on various substrates, which was not possible with the common testing methods previously available. In this paper an advanced impact tester, able to assess the fatigue failure resistance of coatings working under cyclic loading conditions, is presented. The fatigue failure of the tested coatings was determined by means of scanning electron, optical microscopy, and EDX analysis. The test results are recorded in diagrams containing the impact load versus the number of successive impacts that the examined coatings can withstand. From the experimental results it was concluded that a hard, wear resistant HVOF thermal spray WC-CoCr coating deposited on P91 steel substrate presents a high fatigue resistance.Τεκμήριο An investigation of cutting edge failure due to chip crush in carbide dry hobbing using the finite element method(2011) Friderikos, Orestis; Maliaris, George; David, Constantine; Tsiafis, IoannisThe aim of this research is to investigate a type of failure of dry carbide hobbing that occurs when the generated chips are pinched and crushed between the hob cutting edge and the work gear tooth flank by utilizing the finite element method. This problem is of great importance because gear hobbing is extensively used in the manufacturing industry. Many machine tool manufacturers have so far developed dry hobbing techniques using carbide hobs as there is a growing acknowledgment that it is necessary to employ carbide hobbing for higher productivity and pollution free gear cutting. To meet the increasing needs of cost reduction and environmentally friendly methods, dry hobbing being employed for gear mass production has completely eliminated the need of tool cooling. However, carbide hobbing has not come into wide use due to the high cost of carbide hobs, and mainly due to the unexpected chipping of the brittle carbide material, making it difficult to control the tool service life. Dry hobbing often causes problems such as chipping of the carbide hob tooth and/or damage of the surface finishing when the generated chips are pinched and crushed between the hob cutting edge and the work gear tooth flank. A manufacturing case of helical gears is taken as a case study, and it was simulated using a coupled thermomechanical rigid viscoplastic FEM analysis. Simulations have successfully identified a chip crush between four adjacent generating positions and thus, a definite mechanism that cause chip crush is revealed. Furthermore, valuable insights during chip formation, i.e., stress, strain, strain rate, temperature gradients, etc., are also provided.