Abstract
The definition of the incubation time of creep crack growth has been discussed from the view points of scale effects of specimens. The crack length corresponding to the stage of creep deformation was found to be sensitive to the scale effects of specimens. Therefore, crack length at the early stage of creep deformation such as transient creep is different depending on specimen size. These results were assured by in situ observational and electrical potential methods. Based on these results, it was found to be reasonable to relate the definition of the incubation time of creep crack growth to the stage of creep deformation which concerns creep damage composed of micro cracks.