Study on correlation of the fracture toughness and microshear toughness for pressure vessel steels and structural steels

摘要

In this paper, the microshear toughness, mode I and mode II fracture toughness, and their relationships were characterized for a number of pressure vessel steels and structural steels with the yield-strength-grade in the range of 300 to 1100 MPa, by a unique microshear experiment method and three-point bending as well as asymmetric four-point bending fracture mechanics tests combining FE analysis. The influences of microstructural orientation or anisotropy of materials on mode I and II fracture toughness as well as the microshear toughness were investigated. Results show that the orientation and anisotropy of materials have much less influence on mode II fracture toughness than mode I fracture toughness. For most materials tested in both L-T and T-L orientations, JIC values are larger than J{sub}(IIC) values. The ratios of J{sub}(IIC)/J{sub}(IC) in the T-L direction are always larger than that in the L-T direction. There exists a linear correlation between the normalised mode II fracture toughness J{sub}(IIC) and microshear toughness W{sub}s. However, an accurate correlation between the mode I fracture toughness and the microshear toughness has not been established. It can be seen that the mode II fracture toughness estimated by the correlation equation between the normalised J{sub}(IIC) and W{sub}s is very close to the experimental results. It is expected that the microshear test may be used to estimate the mode II fracture toughness of structures, including welded structures, in addition to its use for estimation and monitoring of conventional mechanical properties.