An experimental study of stress redistribution in Nimonic cylinders

To predict the life of a component of an engineering system, it is essential to compute or otherwise estimate, the stresses and strains to which the material will be subjected. With this objective, many computer programmes have been written, which, it is claimed compute the stress, strain and deformation histories of components subjected to any prescribed loading sequence. A common feature of many of these programmes is the computation of creep strains, under multiaxial stress, by use of the Mises yield criterion and flow rule, coupled with either a strain-hardening or a time-hardening hypothesis. In the work described in this paper, the authors' objectives were to test the validity of these methods under conditions in which the stress distribution in the component is changing with time. The experiment was simple in concept. A thick-walled cylindrical specimen of Nimonic 80A was placed in an evacuated furnace. An electric-resistance heater was mounted concentrically inside the specimen and the walls of the furnace were water-cooled to provide a heat sink. Insulating blocks were placed at the ends of the cylinder to minimise the axial temperature gradients in the specimen. The temperature distribution in the cylinder was in the range 7000C to 8150C, which is the temperature range over which the creep behaviour of this material is well documented. (Auth.)