  Turbo-generators shafts are manufactured through the extrusion process. This
results in the formation of weak planes along the extrusion process. It has
been observed that large longitudinal cracks often form in these shafts before
any circumferential cracks when these shafts are subjected to cyclic torsion
due to electrical line faults. The presence of these cracks could severely
compromise the shaft resonance frequencies. Dynamic response of shafts with
longitudinal and circumferential cracks is investigated. The longitudinal
cracked section of the shaft section is modeled as a shaft with reduced
torsional rigidity. The torsional rigidity is obtained as a function of the
crack depth. It was found for various shaft diameters, torsional rigidity could
be represented as a function of crack depth/ shaft radius only. The
circumferential cracked section is modeled as a torsional spring. The torsional
spring constant has been obtained using fracture mechanics. It was found the
resonance frequency of the shaft may be little affected by the presence of
longitudinal crack. The resonance frequencies of the shaft with the
circumferential crack depend on the crack length and location. The effects of
crack surface interactions for both longitudinal and circumferential cracks
were also investigated.
