Relaxation of residual stresses in rotating cylinders with incisions of various shapes under creep conditions

The problem of relaxation of residual stresses under conditions of high-temperature creep in surface-hardened cylinders with incisions of semicircular, square and V-shaped profiles cantilevered on an absolutely rigid rotating disk is considered and numerically solved. A series of variable calculations has been performed for cylinders made of EI698 alloy with a radius of 3.76 mm and a length of 150 mm, hardened by shot peening: smooth, with a semicircular incision with a radius of 0.1 and 0.3 mm, a square incision with a depth of 0.1 mm, with a V-shaped incision with a depth of 0.1 mm and an opening angle of 5°, 10°, 20° and 30°. In accordance with the technology of advanced surface plastic deformation, the incisions were applied to a pre-hardened smooth sample. First, the stress-strain state in a smooth sample was determined, and then the problem of redistributing residual stresses after incision application was solved in the elastic formulation for a semicircular incision and in the elastoplastic formulation for cylinders with square and V-shaped incisions. When solving boundary value relaxation problems of residual stresses, the rotation speed and the location of the incision varied — the distance from it to the cantilevered end of the cylinder. The relaxation of residual stresses was calculated on a time base of 300 hours for a smooth cylinder for comparison with a similar solution based on the grid method and on a time base of 100 hours for cylinders with incisions. The flow theory was chosen as the law of creep. The parameters of the law are determined from experimental data on creep deformation for the EI698 alloy at a temperature of 700 °C. The stages of solving the problem correspond to the full loading cycle: “hardening at 20 °C — force load from rotation — temperature load up to 700 °C — creep for 100/300 hours — force unloading — temperature unloading up to 20 °C”. When solving all the boundary value problems, at the end of the loading cycle, a significant level of compressive residual stresses is observed on the incision surface, which is a positive fact of using plastic surface deformation technology even under conditions of high-temperature creep. The results of calculations of the kinetics of residual stresses during creep are presented in graphical and tabular forms.