Abstract
Damage evaluation method for 316FR stainless steel based on micro crack growth behavior has been investigated to improve the life prediction method for high temperature plant. Micro-crack growth was observed in the early stage of life in the coarse grain material even at lower strain ranges. On the other hand, crack growth started in the later stage of the life at lower strain ranges in the fine grain material. The initiation life of 0.2mm length micro-crack could be evaluated by a creep-fatigue damage estimation method using the ductility exhaustion method. In this evaluation, initiation life of 0.2-mm-length micro crack in pure fatigue and creep test was used to calculate the fatigue and creep damage. Crack growth life was also able to predict by a crack growth analysis based on nonlinear fracture mechanics. The failure life of the specimen was determined by the summation of initiation and growth life and this prediction was confirmed to give a reasonable accuracy. Micro-crack initiation and growth is the main mechanism of damage in creep fatigue and lives of real components strongly depend on their allowable crack size. Therefore, the life prediction method will be rationalized by relating the life or damage evaluating in the method with micro crack length as mentioned in this study.
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