No abstract

No abstract

Stress intensity factors of pressurized surface cracks at the internal surface and un-pressurized surface cracks at the external surface of an internally pressurized cylinder are estimated from stress intensity factors of a semi-elliptical crack in a finite-thickness flat plate. Curvature effects of the cylinder are determined by comparing two-dimensional finite element solutions of fixed-grip, single edge-notched plates and single edge-notched cylinders. Stress intensity factors for semi-elliptical cracks with crack aspect ratios of b/a = 0.2 and 0.98 at crack depths up to 80 percent of the cylindrical wall thickness are shown for internally pressurized cylinders with outer to inner diameter ratios, Ro/Ri, ranging from 10:9 to 5:4 for outer surface cracks and to 3:2 for inner surface cracks.

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.

The split-ring model is used to simulate full-scale pipe rupture experiments. Using experimentally measured pressures and pipe material characteristics, the model correctly predicts crack extension histories and depressurization rates. The model is also successful in predicting the occurrence of crack arrest and the arrest length.