A Modified Apparent Fracture Toughness Prediction Model of RPV Steels With Warm Pre‐stress

ABSTRACT A modified apparent fracture toughness prediction model of RPV steels with warm pre‐stress was proposed. Fracture toughness tests incorporating LUCF cycles were performed on Chinese SA508‐III steel at varying warm pre‐stress levels. Test results show that the warm pre‐stress generated through LUCF cycles significantly enhances the apparent fracture toughness. However, if the warm pre‐stress level exceeds a specific threshold, the apparent fracture toughness will decrease. Finite element simulations quantified the fracture toughness at different pre‐stress levels. The analysis found that the crack tip blunting is identified as the dominant mechanism responsible for the improvement. The residual stress fields can increase plastic strain and thereby amplify the blunting effect; their contribution to toughness improvement remains secondary. A modified fracture toughness prediction model incorporating the unified constraint parameter as a correction factor was developed under warm pre‐stress conditions. The result shows that the modified model exhibits high predictive accuracy and demonstrates broad applicability to other materials.