Novel use of three-point bend test for determining the threshold stress for hydride reorientation in Zr-2.5%Nb pressure tube material

The formation of hydrides perpendicular to the applied hoop stress is more detrimental in Zr-alloy tubular components, as it reduces fracture toughness and increases the velocity of Delayed Hydride Cracking (DHC). The formation of radial hydrides requires a minimum threshold stress (${\sigma }_{th}$)in the transverse direction of the tube. Conventionally, the threshold stress for radial hydride formation is determined using tapered gauge tensile samples—a labor-intensive process involving tube flattening, warm rolling, stress-relief heat treatment, and post-experiment sample slitting for metallographic analysis. Additionally, values obtained from conventional tapered gauge samples tend to be significantly higher than those from other methods due to the flattening process. To overcome this, a novel method is proposed for determining the threshold stress using three-point bend samples combined with Gaussian Process Regression (GPR). The threshold stress is evaluated and compared with those obtained from various other different methods, highlighting the effectiveness of the proposed approach.