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Experimental investigation of friction noise on lubricated contact
남재현,백종수,도현철,강재영 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.12
In order to remove friction noise, a lubricant is normally applied on the friction surface either after cleansing the contact surface or without any surface treatment. As the friction continues, the lubrication performance deteriorates and the friction noise can reoccur in the both cases, but the cause of friction noise may be different. This study originally investigates the mechanism of friction noise under a lubricant on either the clean or contaminated surface. During the friction noise test, the vibration and sound pressure, the changes in friction coefficient and the characteristics of the contact surfaces are measured for the two lubrication scenarios. Particularly, the surface image and chemical state on the contact area are measured by SEM/EDS analysis in sequence. The results show that friction noise under the lubrication on the clean surface is induced by the reduction of the lubricant causing the increase of friction coefficient. For the lubrication on the contaminated surface by wear debris, the lubricant is mixed and contaminated with wear debris, and then friction noise eventually occurs with the negative slope of the friction-velocity curve in the absence of the increase of friction coefficient.
Effect of anodized coating on friction noise in aluminum
남재현,강재영 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.4
This study looks at the frictional noise and vibration generated by the relative motion of steel with an uncoated Al pin and an anodized Al pin in a reciprocating system. Frictional noise occurred with both the uncoated and anodized Al pins near 2 kHz and 7.2 kHz. However, the onset of the frictional noise with the uncoated Al pin was generated relatively quickly. The sound pressure level of the two specimens was similar at the moment when the friction coefficient became similar. The results of the surface characteristics using scanning electron microscope (SEM)/energy dispersive spectroscopy (EDS) analysis shows that the uncoated Al pin sharply generated wear from the beginning of the test. And, adhesive wear occurred at the edge of the contact surface. When the friction continued, there were increases in the debris due to material transfer on the worn surface, as well as oxygen and Fe on the surface. This result suggests that the friction surface was further damaged. In contrast, the coating on the anodized Al pin protected the friction surface at the beginning of the test and delayed the damage of the surface due to friction. However, as the friction continued, the coating surface was damaged because the nickel and sulfur added in the post-processing of the coating were reduced, and the debris was increased by the material transfer. Thus, the friction coefficient gradually increased at the anodized Al pin. And, frictional noise was generated. Frictional noise at the anodized Al pin was generated by the gradual increase in the friction coefficient.
양생조건에 따른 플라이애쉬 콘크리트의 소성수축균열 특성
남재현,박종화 한국건축시공학회 2007 한국건축시공학회지 Vol.7 No.1
In this study, the property and plastic cracking pattern of concrete were compared and analyzed with the replacement ratio of fly ash 0, 5, 10, 15, 20% by cement weight. And curing conditions of concrete were given variously such as indoors(with wind speed as 0, 300, 500m/min), outdoors and chamber.The hydration temperature had a tendency to decrease as the replacement ratio of fly ash increased, and in the case of the wind speed 0m/min, it was showed that the moment that the amount of evaporation of water from surface of reference concrete was more than the volume of bleeding was 90 min since casting concrete. The time that the crack initiated had a tendency to be more quickly as the replacement ratio of fly ash increased.The number, length, width and area of crack in the indoor curing, exposed outdoor curing, enclosed outdoor curing had a tendency to decrease as the replacement ratio of fly ash increased. The crack had a tendency to decrease in sequence of exposed outdoor, enclosed outdoor curing, indoors curing.The outbreak of cracking by the change of temperature and humidity was affected by relative humidity more than temperature and the cracking had a tendency to increase as relative humidity lowered.