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초음파나노표면개질기술을 이용한 저널베어링 마찰 및 피로특성 연구
최갑수(Gab-Su Choi),다리스렝 스르멩닥와(Shirmendagva Darisuren),이승철(Seung-Chul Lee),김준형(Jun-Hyong Kim),아마노프 아웨즈한(Auezhan Amanov),편영식(Young-Sik Pyun) 한국트라이볼로지학회 2015 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.31 No.1
In this study, we apply an ultrasonic nanocrystal surface modification (UNSM) technique to radial journal bearings (JBs) and disks made of SUJ2 and SCM440, respectively. We investigate frictional properties of untreated and UNSM-treated specimens using a ball-on-disk tester. We construct the Stribeck curve at the boundary, under mixed and full hydrodynamic lubrication conditions for the specimens using friction data obtained from JB tests. The friction at the boundary lubrication condition and the transition period to mixed lubrication condition on the UNSM-treated specimens is reduced, which improves the service life of JBs. The major effects of this reduction in the three lubrication regimes can be explained in the terms of improved mechanical properties and the presence of micro dimples. Moreover, we estimate the friction and fatigue properties of SCM440 specimens using a ball-on-disk specimen under dry and oil-lubricated conditions. Friction test results reveal that the UNSM-treated specimens show lower friction coefficient than the untreated specimens under both dry and oil-lubricated conditions. We evaluate the fatigue properties of SCM440 specimens by calculating the Hertzian stress with respect to the failure cycles. Fatigue tests results also reveal that the UNSM-treated specimens possess a longer fatigue life than the untreated specimens. The improved properties are effective in increasing the energy efficiency of bearings.
최갑수 ( Kab Soo Choi ) 한국서양사연구회(구 서울대학교 서양사연구회) 2021 서양사연구 Vol.- No.64
There was a great deal of controversy surrounding the trial of Louis XVI, especially within National Convention at every stage of the trial (whether or not to prosecute, indictment, interrogation and pleading, and voting on guilt, sentence, ratification of the people, reprieve, etc.). In terms of 'fall of the monarchy’, the most noteworthy part is the debate over whether the king will be tried or not. This is because the ‘Constitution of 1791’ stipulated the king’s sacred inviolability, that is, the privilege of immunity. The series of debates surrounding the trial of Louis XVI give us two major implications in relation to our problem. One is the historical significance of the royal trial. In the traditional era, usurpation and assassination of kings were common events in Europe, but such expulsion of the monarch strengthened rather than undermined the historical basis and legitimacy of the monarchy. For the monarchy to formally end, an alternative political order had to be imagined, and the king’s trial was a rite of passage that must be passed for this purpose. It is not the assassination like the manner of Shakespearian tragedies which secretly kill the kings, but the king’s trial and execution carried out by the new legitimate power under the name of the popular sovereignty in broad daylight in the centre of the capital city while the crowds are gathering, that historically ended the rule of monarchs. In fact, after the execution of Louis XVI, the monarchs continued to reign, but the mystery, splendor, and awe enjoyed by the monarchy have virtually disappeared. The other is that although National Convention tried to give the royal trial a form of lawfulness in its own way, and in fact, the trial was generally conducted in the manner suggested by the ‘Girondins’, the most influential faction at the beginning of the trial, paradoxically, the argument of Saint-Just, who insisted on the immediate execution of the king without a trial, rather defined the main line of the Louis XVI trial. “On ne peut point regner innocemment.” Accepting the premises of the social contract and popular sovereignty, “Tout roi est un rebelle et un usurpateur.” Thus the events of August 10, 1792 effectively determined the fate of the monarchy. The right to revolution lay at the foundation of the legitimacy of the modern bourgeois order. (Seoul National University / kchoi7@snu.ac.kr)