Papers by Author: Jong Yup Kim

Abstract: Creep testing of Alloy 718 has been carried out at various loads in the temperature range near 650°C in constant load control mode in order to understand how to predict the creep behavior including tertiary creep. The test results have been used for evaluating the existed models, such as Theta projection and Omega method that have been widely used for predicting long term creep strain and rupture time. After determining variables and material parameters of each method with the test results, estimated creep data from each model have been compared with the each measured creep data from the creep tests. The root cause of the discrepancy between estimated and measured data has been analyzed in order to improve the existed methods. The reliability of the improved model has been evaluated in relation to creep data.

Abstract: High strength materials have been used for critical components in order to ensure the reliability of aircraft gas turbine engine. But it usually costs high to maintain their premium quality. Therefore, the optimum quality level of materials should be defined under operating condition by material property estimation technique in order to meet the requirement of reliability and economical efficiency. Most cast rotating parts of gas turbine engine have casting defects caused during the casting process. The casting defects less than certain acceptable limit can be permissible for usage. So, it is very important to understand material defect shape and distribution, and its effect on mechanical properties exactly. In this study, 17-4PH stainless steel specimens with variable internal casting defects were prepared to investigate the fatigue property characteristics. The defect fraction and condition were estimated in microstructure by statistical analysis. The correlation between estimated defect condition and fatigue property was discussed.