Turbogenerator coil retaining rings are shrunk-fitted onto the rotor
over the coils, in order to restrain them against the centrifugal force.
They are typically subjected to low cycle fatigue, with a cycle being
completed at every machine switch-on and switch-off. The subject of this
paper consists in the determination of the failure probability of a coil
retaining ring. The failure mode of the ring cracking, when it swells in
tension, due to the centrifugal force is here considered. The
reliability assessment is preceded by the study of the input variables
affecting the low-cycle fatigue load and of their stochastic
distributions. This question is tackled by the experimental
determination of the static, cyclic and fatigue curves of the involved
material and by the application of a statistical model to compute
related parameters and their standard deviations. Upon the determination
of variable distributions, the probability of failure is estimated in
the form of a cumulative distribution function by a computationally
efficient methodology, based on the Advanced Mean Value approach. The
obtained results account for the material response and the local
stressstrain states at the most loaded coil retaining ring region. The
determined probability at the end of the machine life, in the order of 10^{-12},
is compatible with reference values for structures under fatigue in the
mechanical and aeronautical fields.