Fracture toughness characterisation in the ductile-to-brittle transition and upper shelf regimes using pre-cracked Charpy single-edge bend specimens

摘要

Fracture toughness data of pre-cracked Charpy single-edge bend, SE(B), specimens are compared with those of standard compact, C(T), specimens in the upper shelf and ductile-to-brittle transition regimes. Charpy sized SE(B) specimens provide ductile fracture toughness data, which are compatible with those of standard C(T) specimens. Statistical methods such as the exponential curve fitting method (ECF), the engineering lower bound toughness method (ELB), and the Master Curve method (MC) are used to provide meaningful lower bound cleavage fracture toughness estimates from the toughness scatter of the Charpy sized SE(B) specimens in the ductile-to-brittle transition regime. In this regime, according to the ELB and MC methods, SE(B) specimens provide cleavage toughness data, which tend to be non-conservative compared to those of standard C(T) specimens. However, analyses based on the exponential curve fitting method show good agreement between the fracture toughness estimates for the C(T) and Charpy size SE(B) specimens. At the lower bound toughness level (5 percent cleavage failure probability), corresponding to J = 100 N/mm, the ductile-to-brittle transition curves of SE(B) specimens are reduced by 5-8 deg C compared to those of standard C(T) specimens according to the MC-method. A constraint correction function for SE(B) specimens is presented that can be used to make cleavage toughness data of SE(B) specimens compatible with those of standard C(T) specimens.