Investigation of the tensile fracture behavior and failure criteria of domestic Zr-2.5Nb alloy under different stress triaxiality conditions

Abstract

The pressure tube (PT) is a critical component of the CANDU (CANada Deuterium Uranium) heavy water reactor, which imposes extremely high safety standards for its materials. This study investigates the tensile fracture behavior of unirradiated Zr-2.5Nb alloy, a domestically produced material for PTs, through a combination of experiments and finite element simulation. The full-range stress–strain relationship for this alloy was established using the finite-element-analysis aided testing (FAT) method. Based on the geometry of the tube, axial and transverse specimens were prepared and subjected to tensile testing. The deformation of the specimens at different stages was monitored, and the stress triaxiality was extracted through finite element simulation. The stress triaxiality distribution laws of the sheet specimens with notch in the direction of width (SNW) and the sheet specimen with a central hole (SCH) were analyzed. Additionally, the parameters of the Johnson-Cook (J-C) failure model were calibrated, and specimens with notches at different angles were designed for verification. The results showed that the Johnson-Cook failure model effectively simulates the tensile deformation and failure behavior of the domestic Zr-2.5Nb alloy. Fracture morphology was examined using scanning electron microscope (SEM), revealing the morphological characteristics of dimples, elongated dimples, and slip marks. The fracture modes of domestically produced Zr-2.5Nb alloy tensile specimens with different notches and orientations were obtained.