Papers by Author: Young Hun Chae

Abstract: Surface texturing, a sort of surface engineering, has been studied as an effective method to improve the tribological performance under lubricated contact. Those mechanisms of friction reduction, however, are not fully understood. Therefore, the sliding direction and the angle of micro-grooved crosshatch patterns for coefficient of friction were examined. The micro-grooved crosshatch pattern was fabricated by mechanical indentation method on the upper specimen and the pin-on-disc friction test was performed with lubricant of paraffin oil. The influence of angel on the friction was confirmed as friction coefficient increased proportional to the angle increase. The micro-grooved crosshatch patterns have also the potential to change the friction characteristics by sifting the lubrication regimes.

Abstract: Some surface patterns of tribological application are an attractive technology of engineered surface. Because of the friction reduction is considered to be necessary for improved efficiency of machine. This study was investigated for the effect of friction property for angles of micro-crosshatch groove surface pattern on bearing steel used pin-on-disk test. We obtain sample which can be fabricated by photolithography process. We discuss the friction property depended on an angle of crosshatch groove surface pattern. We can verify the lubrication mechanism as Stribeck curve which has a relationship between the friction coefficient and a dimensionless parameter under the lubrication condition. It was found that the friction coefficient was related to angle of crosshatch groove pattern on contact surface.

Abstract: The current study investigated the effect of micro-dimple size on reduction friction to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verified that the friction property with respect to the same pitch influences the size of dimple under lubricated sliding contact. Additionally, it was recognized from Stribeck curve that the friction property has a connection with the size of dimple. This can explain the relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has an effect on the size of surface texture on reduction friction, not only because of the density of dimple, but also because of the ratio of diameter/pitch. A ratio of approximately 0.5 is recommended under the tested friction condition. It is suggested that the ratio of d/p is an important parameter for surface texture design.

Abstract: The purpose of this study is to investigate the wear characteristics of yttria-stabilized zirconia coating as a function of effect on post-spray heat treatment. We concerned that the residual stress is due to during cooling from a high deposition temperature. We will focus on the tribological wear performance as a magnitude of residual stress. The effect of residual stress as post-spay heat treatment temperature will be discussed. The plasma-sprayed 8%Y2O3-Zirconia coating is studied to know the relationship between phase transformations and wear properties after post-spray heat treatment. Wear tests is carried out with ball on disk type on 50 N, 70 N, 90 N under room temperature. The transformation of phase and magnitude of residual stress are measured by x-ray diffraction method (XRD). Tribological characteristics and wear mechanism for post-spray heat treatment is observed by SEM.

Abstract: In contact conditions of crane sheave steel materials against a wire rope, the contact surface of the sheave generally exhibits scuff damage. In the present study, sliding wear tests using annealed-low carbon cast steel were carried out under three kinds of normal loads calculated from the actual model conditions in a pin-on-disk grease lubrication test. The sliding speed was fixed at 220mm/s. Therefore, the wear behavior and wear mechanism and the residual stress distribution of the substrate surface were examined. The results of this study indicate that the wear rate of annealedlow carbon cast steel depends on the diameter of the wires. The wear mechanism of annealed-low carbon cast steel is characterized by fatigue and abrasive wear, but the wire shows partial adhesion due to micro abrasive wear by fatigue crack propagation. The contact distribution of residual stress is independent of sliding distance. Therefore, there are constant values on the contact surface.