EVALUATION OF SCC CRACK GROWTH RATE IN BWR WATER BASED ON ELASTIC-PLASTIC FRACTURE MECHANICS PARAMETERS

摘要

This paper presents an applicability of elastic-plastic fracture mechanics parameters for evaluating a crack growth rate of stress corrosion cracking (SCC). Currently linear fracture mechanical approaches have been applied for the SCC crack growth evaluation, even though some cracks due to SCC are found in plastic deformation zones near welding where linear fracture mechanics is no longer applicable. In this paper, the authors have proposed an elastic-plastic parameter "equivalent stress intensity factor K_J" for evaluating the SCC crack growth rate based on the J-integral value, which is valid in both elastic and plastic stress fields. In order to verify the applicability of the evaluation by K_J, SCC crack growth tests were carried out in a simulated boiling water reactor (BWR) water. When the SCC crack growth rate was evaluated by the stress intensity factor K, no linear relationship between the K values and the crack growth rates was observed in the high K-value region, where a small-scale yielding condition was not met. The crack growth rates increased exponentially according to increasing the stress intensity factor to exceed the linear relationship. On the other hand, when the crack growth rate was evaluated by the elastic-plastic parameter K_J, a linear correlation between the K_J values and the crack growth rates was confirmed regardless the specimen size and the stress condition. This result suggests that by applying the elastic-plastic parameter K_J, the SCC crack growth rates in a wider range could be estimated easily with using a smaller specimen.