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This report is the result of a research program on creep-fatigue damage on engineering materials such as 316 stainless steel. The main objective of the program was to analyze, evaluate and develop a model for creep-fatigue interaction under uniaxial and biaxial stress/strain cycling at elevated temperature. The biaxial loading was torsion couples with axial loading with 30 minutes hold-time to generate the creep effect. Data was obtained from fatigue-creep tests conducted at 1150°F (620°C). Based on test data and indepth macro-micro analysis, a model which accounts for uniaxial creep damage was developed on the basis of ductility-exhaustion concept. A comparison was made between the proposed ductility-exhaustion model and the time fraction rule. The proposed model shows a better and more comprehensive prediction capability than the time fraction rule and was able to distinguish whether the failure is by creep or by low cycle fatigue. Publication of this document - WRC Bulletin No. 402 - was sponsored by the Elevated Temperature Design Committee of the Pressure Vessel Research Council