Ductile Crack Bifurcation and Arrest in Pressurized Pipe

This paper presents selected results on ductile crack propagation, curving and branching, and crack arrest from ten dynamic pipe rupture tests. Strain gage results adjacent to the crack path showed that a Dugdale-Barenblatt strip yield zone, of the order of eight pipe diameters in length, preceded the propagating crack tip and that the maximum principal strain direction changed from the hoop to the axial direction approximately 6 to 8 pipe diameters downstream of the crack tip. This change in principal strain direction constitutes the sufficiency condition for crack curving or branching prior to crack arrest in the absence of a crack arrester. The necessary condition for crack arrest is the sudden and sufficient increase in fracture resistance due to either increased apparent fracture toughness or a pipe opening restraint in the crack path.