Determination and Evaluation of Residual Stresses in Thick- Walled Cylinders Due to Autofrettage

Autofrettage is a treatment to introduce beneficial residual stresses into thick-walled cylinders to improve their performance under repeated loading by internal pressure. In the present investigation the residual stresses are measured and their effect was analysed and discussed. The experimental determination of the residual stress distribution was performed by the crack-compliance-method. The corresponding influence function for thick-walled cylinders, which is needed for the experimental stress measurement by the CC-method, was derived analytically. Besides the residual stresses this method enables one to obtain also the stress-intensity factor as a function of cut depth, which is required in the theoretical fatigue life prediction based on linear-elastic fracture mechanics. Examples of experimental data are presented. To validate the experimental results they are compared with analytical calculations. The agreement between the calculated and measured residual stresses was satisfying. Furthermore the effect of the axial dimension (plane-stress vs. plane strain), which has to be taken into account when using a thin disk for stress measurement by the CC-method, is investigated by a 3D FEM-analysis.