抄録
In recent years, construction of natural gas pipelines is expanding to severe environmental area such as seismic or permafrost region. In these regions, it can be expected that pipelines will be subjected to large deformation due to large ground movement associated with liquefaction in seismic region or frost heave in permafrost. In that case, it is focused on ductile fracture from circumferential flaw as a main failure mode. However, it has not been fully understood ductile fracture behavior under biaxial loading such as hoop stress from internal pressure and longitudinal stress.
This paper presents the influence of internal pressure on ductile fracture conducting full-scale pipe tests on machined surface notches with⁄without internal pressure. Especially, it is focused on investigation of ductile tearing from circumferential surface defect. Ductile tearing resistance curves (R-curves) obtain from pressurized and un-pressurized pipe tests show a good agreement. On the other hand, internal pressure increases the notch tip opening displacement of a circumferential surface defect at equal levels of applied longitudinal strain because a pressurized pipe is constrained in circumferential direction by internal pressure. These results indicate that high internal pressure decreases the longitudinal strain at ductile crack initiation or penetration from a circumferential surface defect.
