EVALUATION OF FRACTURE TOUGHNESS OF Zr-2.5 Nb PRESSURE TUBE MATERIAL AS A FUNCTION OF HYDROGEN CONTENT, DEFORMATION RATE AND TEMPERATURE

摘要

In this investigation, J-R fracture characteristics of Zr-2.5Nb pressure tube material of Indian Pressurized Heavy Water Reactor (IPHWR) in cold worked and stress relieved condition have been evaluated over a range of loading rate, hydrogen content and at temperatures of 25 and 300°C. The fracture toughness tests have been carried out using 17 mm width curved compact tension specimens. Prior to testing these specimens have been gaseously hydrogen charged with hydrogen content up to 100 wppm. Both hydrogen charged and uncharged specimens have been tested at 25 and 300°C at five different pulling rates i.e. 0.02, 0.2, 2, 20 and 200 mm/min. The crack length during the fracture toughness tests has been measured using direct current potential drop technique. Various relevant fracture toughness parameters (J_Q, J_(0.15),J_(Max),J_(1.5)and dJ/da ) have been evaluated as per ASTM standard E1820. It was observed that initiation fracture toughness for as received material did not change monotonically with loading rate at 25°C. The effect of loading rate on initiation toughness was most remarkable for as-received material at 300°C as toughness increased with loading rate. However, for as received material tested at 300°C, the crack propagation toughness parameters were not significantly influenced by loading rate. The effect of hydrogen content was very significant on fracture toughness parameters as the hydrogen content increased from 5 ppm for the as-received material to 60 ppm for hydrided material. With further increase in hydrogen content the toughness parameters were unaffected. For hydrided materials both crack initiation and propagation parameters were unaffected by increase in loading rate at 25°C. At 300°C for hydride materials, while initiation toughness exhibited a decreasing trend with increasing loading rate, propagation toughness values were apparently unaffected.