The effects of pre-deformation and ageing on the ductile tearing resistance of an X65 UOE pipe material and an associated weld metal have been investigated using the SENT specimen geometry. Regarding pre-deformation of specimens with pre-existing defects it has been found that the sequence of pre-deformation applied is of importance. For specimens subjected to compressive pre-deformation virtually no effect on the resistance curve was observed. For specimens subjected to a tension-compression pre-deformation cycle it was observed an initial drop in ductile tearing resistance upon reapplication of tension loading. The magnitude of the effect depends on the magnitude of pre-deformation. For small to moderate pre-deformation the effect on the crack growth resistance curve is insignificant, but large pre-deformation can lead to a drop in tearing resistance for initial crack growth upon reloading. As the crack grows toughness matches as-received tearing resistance. It is also shown that this main effect can be captured in numerical analyses. Regarding ageing, it is in general found that this does not significantly reduce the tearing resistance. However, one exception was observed and for the weld metal, pre-deformation followed by ageing results in a significant drop in ductile tearing resistance. It is underlined that this observation cannot necessarily be generalized for all welding procedures, and this is an area which would require further studies.
The resistance to ductile tearing plays an important role in the determination of tensile strain capacity of pipes with defects (see e.g. Østby, Thaulow, and Nyhus (2007)). This fact is recognized in recent proposals for strain-based fracture assessment schemes (Østby (2007), Fairchild, Macia, Kibey, Wang, Krishnan, Bardi, Tang, and Cheng (2011)). The importance of ductile tearing resistance has lead to a drive to establish efficient procedures for obtaining relevant ductile tearing resistance based on small-scale testing.
