THE FATIGUE LIFE OF THICK-WALLED AUTOFRETTAGED CYLINDERS WITH CLOSED ENDS

Abstract— It is well known that the fatigue strength of a thick‐walled cylinder is enhanced by autofrettage. However, this does not appear to have been explained from fracture mechanics. The present paper shows that two uncertainties arise when this is attempted. Firstly, the distribution of residual stress resulting from the autofrettage pressure must be estimated and secondly a realistic stress intensity factors for subsequent fatigue cracking must be defined. A number of available stress intensity solutions are modified with the author's predictions to the residual stress following an elastic‐plastic autofrettage pressure in a closed cylinder of hardening material. A comparison with experiment has enabled the various approaches to be appraised. It is shown that a modified stress intensity factor of Bowie and Freese is most consistent with the propagation fatigue life observed in autofrettaged cylinders provided their solution is adapted to account for the propagation of a semi‐elliptical crack front in the presence of residual stress. Other K1 estimates appear to lead to dangerously optimistic predictions particularly within the range of fluctuating pressure where failure occurs between 105 and 106 cycles. The contribution to fatigue failure from initiation cycles is expressed as a power function of the observed life for cyclic pressures in the region of the fatigue limit. Copyright © 1991, Wiley Blackwell. All rights reserved