Papers by Author: Yong Joo Cho

Abstract: The influence of oil quantity supplied and contact bulk temperature on micro-pitting lifetime is estimated using two-roller contact machine. The failure criterion is set as 4% micro-pitting on contact surfaces, which is adopted from precedent researches. To quantify the failure rate of damaged surfaces of micro-pitting occurrence, DBR(Dark and Bright Ratio) technique was effectively implemented for observing not a sudden emergence of macro-pitting but the transition of micro-pitting growth. The change of damaged surface area was measured and calculated by the use of dark and bright ratio of test specimen pictures taken by optical microscope. The optimum oil quantity was determined to obtain the minimum oil quantity with no change in bulk temperature despite of increasing the inlet oil quantity. In conclusion, the influence of supplied oil quantity and contact bulk temperature considering film parameter on micro-pitting lifetime and the surface contact strength by the S-N curves of failure rate are quantitatively reported and expressed as empirical formulas.

Abstract: In this study, the simulation of contact fatigue based on stress analysis is conducted under Elastohydrodynamic Lubrication (EHL) state. To predict a crack initiation life accurately, it is necessary to calculate contact stress and subsurface stresses accurately. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions and the subsurface stress is obtained using rectangular patch solutions. The numerical algorithm using newton-rapson method was constructed to calculate the EHL pressure. Based on these stress values, three multiaxial high-cycle fatigue criteria are used. As a result, the effects of EHL on contact fatigue life are calculated.