A modified Weibull stress model to predict cleavage fracture of small punch test specimens

Abstract

The small punch test (SPT) has advantages in obtaining mechanical properties of metallic materials in the International Fusion Materials Irradiation Facility. However, the significant difference in stress states between conventional specimens and SPT specimens brings challenges for SPT to estimate cleavage fracture toughness of materials. The present work proposed a modified Weibull stress model to predict the cleavage fracture of SPT specimens. In this model, the mutual effects of plastic strain and stress triaxiality on the nucleation and instability of micro defects were considered, and a concept of double threshold criteria was also proposed to redefine the fracture process zone considering the large-scale yield and low constraints of small specimens. The model successfully predicted the cumulative failure probability of cleavage fracture for notched SPT specimens at −160 ℃ and −170 ℃, demonstrating the dependence of the cleavage fracture driving force on plastic strain and stress triaxiality. This study provides a fundamental study for using SPT to predict the cleavage fracture behavior of ferritic steels.