OS1424 軽水炉環境下でのSCCき裂進展速度の弾塑性破壊力学による評価

Abstract

Applicability of elasto-plastic parameter for evaluating stress corrosion cracking (SCC) growth rate was examined. Currently linear fracture mechanical approach has been applied for crack evaluation; even though some SCC is found in plastic deformation zone near welding areas where linear elastic fracture mechanics no longer is applicable. Authors have proposed elastic-plastic approach "equivalent stress intensity factor K_j" for evaluating SCC growth rate based on J-integral value, which is valid in both elastic and plastic stress fields. In order to verify the applicability of evaluation by K_j, SCC propagation test in compact tension specimens with varying specimen size and stress conditions were conducted in boiling water reactor environment. As a specimen, sensitized type304 stainless steel was used. When a crack growth rate (CGR) of SCC was evaluated by stress intensity factor K, linear relationship between K and CGR does not exist in the high K value, where CT specimens are out of small scale yielding condition. CGR increases exponentially according to increasing stress intensity factor K to exceed linear relationship. On the other hand when CGR was evaluated by elasto-plastic parameter K_j, linear correlation between K_j and CGR was confirmed regardless specimen size and stress condition. This suggests that by applying elasto-plastic parameter K_j for SCC behavior, CGR at high K value could be estimated easily with using a smaller specimen.