Effect of notch shape on the fracture toughness behavior

Abstract

This study evaluates the effect of notch shape on the fracture toughness of a 500 MPa base material designed for liquefied carbon dioxide storage tanks. This study specifically focuses on assessing the crack tip opening displacement (CTOD) values for different notch shapes, including fatigue pre-cracks (R = 0.025 mm) and electrical discharge machining (EDM) notches (R = 0.07 mm and R = 0.15 mm). CTOD tests were conducted over a temperature range of −55 °C to −140 °C. The results revealed that as the notch radius increased, the degree of stress concentration decreased, leading to an increase in fracture toughness. In temperature-dependent tests, CTOD values consistently decreased as the temperature decreased, with EDM notches exhibiting a lower rate of fracture toughness reduction compared to fatigue pre-cracks, which is attributed to differences in the degree of stress concentration. Scanning electron microscopy analysis of the fracture surfaces revealed the reason for significant differences in CTOD values and fracture behaviors between fatigue pre-crack and EDM notches, particularly at −140 °C, a temperature below the ductile to brittle transition temperature. This study suggests that EDM notches, especially with radii of 0.07 mm and 0.15 mm, can effectively replace fatigue pre-cracks in CTOD evaluations, particularly at temperatures above the transition temperature, offering a more efficient method for assessing fracture toughness in cryogenic environments.