Hamed Abdi - Department of Mechanical and Industrial Engineering, Northeastern University
Ashkan Vaziri - Department of Mechanical and Industrial Engineering, Northeastern University
Hamid Nayeb-Hashemi - Department of Mechanical and Industrial Engineering, Northeastern University

Turbo generator shafts are manufactured through the extrusion process. This results in theformation of weak planes during the extrusion process. Under cyclic torsion large longitudinalcracks often form in these shafts before any circumferential cracks. The presence of these crackscould severely affect the shaft resonance frequencies. Dynamic response of a shaft with longitudinaland circumferential cracks is investigated. The longitudinally cracked section of the shaft ismodeled as an uncracked shaft with same radius and reduced torsional rigidity. The torsionalrigidity correction factor is obtained as a function of the crack depth to shaft radius ratio only. Thecircumferential crack is modeled as a torsion spring and a torsion damping. The torsion spring anddamping constants are obtained using fracture mechanics. Longitudinal crack depth and length,circumferential crack depth and locationand energy loss factor are five significant parametersaffecting the shaft dynamic response; we carried out a parametric study to understand the role each parameter plays.

Longitudinal Crack, Circumferential Crack, Cyclic Torsion, Shaft Resonance Frequencies