Evaluation of Critical Fracture Stress in Low Alloy Steels by Finite Element Analysis of Small Punch Test

摘要

The critical fracture stresses (σ_(f(sp))~*) in various low alloy steels for a reactor pressure vessel(RPV) were evaluated by a small punch test (SP test) and a finite element analysis (FEA) in the cleavage temperature region(-150～-196 °C). The load-displacement curves and distances from the center to the fracture surface (D_f) of the FEA results are in good agreement with the experimental results. The maximum principal stresses (SP fracture stresses, σ_(f(sp))) were determined from the FE analysis, when the maximum load was applied to the SP test. The SP critical fracture stress, σ_(f(sp))~* in various reactor pressure vessel (RPV) steels was found to have a linear relationship with the values obtained from the precracked specimens (σ_(f(PCVN))~*). The σ_(f(sp))~* shows a lower value than σ_(f(PCVN))~* because the SP specimen had a lower triaxial stress condition. However, this result indicates that a small punch test could be a useful method to evaluate the cleavage fracture behavior of low alloy steels.