Stiffness variation due to cracks in rotors is a well-known problem; plenty of studies to prevent/avoid catastrophic accidents and rotor bursts exist. FEM numerical results calculating natural modal frequencies for open cracked beams at different notch depths and slenderness ratios, are compared versus experimental laboratory measurements. Shaft beams under simply supported and free-free boundary conditions, focusing on solids and Timoshenko beam finite elements, are studied. Timoshenko beams employ the Mayes and Davies equivalent-length concept for crack modeling. Notched shafts provide useful upper bound frequency reductions values (breathing cracks display up to, and smaller decrements). Modal frequency splitting for each natural frequency are confirmed and validated by numerical simulation and tests. Modal frequencies splitting functions are given, obtained by simulation and experiments which reflect strong crack depth and slenderness ratio influences. Vibrational coupling energy of the frequency splitting reaches a maximum when the excitation is orthogonal to the crack orientation, conclusions are given.
