Crack Growth in Externally Flawed, Autofrettaged Thick-Walled Cylinders and Rings

A study has been made to investigate the effect of autofrettage on crack growth in externally flawed, thick-walled cylinders and rings. With the use of singular finite elements, stress intensity factors were determined for cylinders containing a single, external crack oriented in the radial direction, subjected to either internal pressure or to a diametrical compression load normal to the crack plane. Fatigue crack growth rate experiments were conducted using several rings cut from cylinders which had been autofrettaged different amounts. The rings were fatigue cycled using the aforementioned compressive loading, which produced a properly oriented external crack. The results of these experiments show that fatigue crack growth rates can be increased by as much as an order of magnitude in cylinders which have been fully autofrettaged over those which contain no residual stresses. There is not sufficient data to model this increase in crack growth rate empirically; however, some comments are given on the effect of autofrettage residual stress on fatigue crack growth rate.