The use of SE(T) specimen fracture toughness for FFS assessment of defects in low constraint conditions

Due to the loss of constraint, shallow cracked specimens can ‘absorb’ more energy than deeply cracked specimens commonly used to define the critical value to fracture and therefore exhibit a higher fracture toughness. The increase in energy absorption allows a reduction in the inherent conservatism when assessing components in low constraint conditions. This study addresses the benefit of using shallow cracked SE(T) fracture toughness specimens in fitness for service (FFS) assessment of defects under low constraint conditions, e.g. blunt defects or shallow cracks. Tearing resistance curves (J-R curves) have been constructed by means of a virtual test framework to determine crack initiation and propagation for shallow cracked SE(T) specimens and parametric notched C(T) specimens. The effect of constraint level on J-R curves is compared. It is observed that most of the blunted C(T) specimens analysed exhibit the same or a lower toughness value than that of a shallow cracked SE(T) specimen. The results are used to show how reduced conservatism can be made in defect assessment of blunt defects or in cases in which reduced constraint conditions can be demonstrated.