A. F. Emery

On the Motion of an Axial Through Crack in a Pipe

Based upon photographs of running cracks, a simple split ring model is proposed to simulate axially running cracks in very ductile materials. The model is used in conjunction with a one-dimensional transient fluid flow analysis to calculate the velocity of the crack and the fluid pressure history for air, cold water, and hot water-filled pipes. The model is capable of predicting crack initiation, extension, and arrest. 15 references.

Fracture in Straight Pipes Under Large Deflection Conditions—Part I: Structural Deformations

The dynamic motion of an axially oriented through crack in a pressurized cylinder was studied numerically. Both small and large deflection theories were used, with the results suggesting that large deflections may be important for elastic, but not for plastic stress fields. Computations were also made with pressures predicted by consideration of fluid outflow through the crack and indicate that the crack shape near the tip is independent of the pressure profile.

A Procedure for Estimating the Stress Intensity Factor of a Flattened Surface Crack at a Nozzle Corner

A flattened surface crack at a nozzle corner is modeled by a segment of a semi-elliptical crack in a finite thickness plate with matching crack contour and crack pressure corresponding to the normal stresses in the uncracked nozzle corner. Lacking other solutions for comparison, a qualitative comparison was made between nondimensionalized stress intensity factors at the deepest crack penetration with those obtained experimentally for similar corner cracks in epoxy models.

Fracture in Straight Pipes Under Large Deflection Conditions—Part II: Pipe Pressures

A finite difference hydrodynamic code was developed to determine the pressures in a dumbbell pipe configuration when a through crack in the pipe wall was permitted to run along the length. Computations were made for hot water pressurized pipes for two different situations: the crack tips were cusp shaped, restricted in maximum opening, and moved at prescribed subsonic or supersonic speeds; the crack configurations were computed by iterating with the structural code (Part I). The pressurized water computations were made with special equations of state for the two-phase flow in the channel and in the crack exit plane. Significant differences in pressure profiles were obtained for the supersonic and subsonic crack speeds. The air calculations were implemented by use of the perfect gas equations of state to evaluate the differencing system, its stability and the effects of the cross-sectional area change and sonic choking. The air computations followed the exponential pattern suggested by Kanninen’s simplified model when no channel choking downstream of the crack tip occurs.

Embedded Elliptical Crack at a Corner

A procedure for estimating the stress intensity factor of an embedded elliptical crack near the corner in a region of high stress concentration such as pressurized or thermally shocked nozzle-to-cylinder junction is discussed. The procedure is then used to analyze two hypothetical embedded circular cracks near the corner of a nozzle-to-cylinder junction where stress distributions in the uncracked junction are known. Also shown are two new stress intensity magnification factors for two embedded elliptical cracks, i.e., b/a = 0.2 and 0.982, close to a free corner, i.e., a/h = b/h = 0.9.