AN ENERGY BASED FRACTURE MECHANICS APPROACH TO DETERMINE THE EARLY CRACK GROWTH PHASE FOR NOTCHED ROUND-BARS UNDER GLOBAL STRAIN CONTROLLED CREEP-FATIGUE LOADING

摘要

Evaluating the crack initiation life of a notched component requires assessing the early crack growth phase. This is demonstrated in the first part of the paper by discussing the results of creep-fatigue tests performed on notched round-bars under global strain control. Both a potential drop measurement system and a developed load drop correlation scheme allow an experimental quantification and comparison of the early crack growth behavior for different sharp notches but same local notch root loading. In the second part, a fracture mechanic based concept is presented in order to assess this crack propagation phase for technical crack depths up to 1 mm. Based on an FEM-based procedure to evaluate the amount of crack closure a novel energy based approach is discussed in order to directly extract crack tip loading parameters for both the fatigue and creep phases. Finally, the theoretical achieved results are compared with the experimental measurements.