Experimental and analytical investigation of the effect of autofrettage on fatigue damage development in blocks containing crossbores under cyclic internal pressure

The effect of autofrettage on the fatigue life of rectangular blocks containing intersecting crossbores under cyclic internal pressure is investigated experimentally and analytically. Block specimens were autofrettaged and subsequently subjected to cyclic internal pressure until a large fatigue crack developed. For a given test pressure range, increasing the autofrettage pressure caused life to increase up to approximately a factor of three, relative to non-autofrettaged blocks. The analysis of fatigue damage development process was divided into residual stress and its maintainability, fatigue crack initiation and propagation predictions. The residual stress fields introduced by autofrettage were computed using the ANSYS;The maintainability of the residual stress was investigated with uniaxial and keyhole specimens. The residual stress in test blocks also were measured after the failure. Results of all three investigations revealed only slight to negligible residual stress relaxation for the materials and load histories studied.;The fatigue crack propagation life prediction was based on linear elastic fracture mechanics. Predicted propagation life is reasonable. Fatigue crack initiation lives for test blocks were predicted with an empirical Bergmann-Seeger parameter to account for mean stress effects. This approach predicted initiation lives conservatively within factor of 10 for all cases investigated and could be used as a design method for similar conditions.