ABSTRACT
The present work deals with crack behavior, detection, analysis, determination and
diagnosis of cracked rotors. Crack detection is very important for any rotating machine.
It can save all the rotating parts like blades, impellers, fans and bearings.
Crack behavior arises up non-linear differential equations that include the most
influence of stiffness change. The nonlinear differential equations are solved by a
computer program to calculate reduction in stiffness due to crack. The theoretical
solution and calculations of stiffness reduction for rotor suspension systems was carried
out.
Programming software to predict the crack spectrum time wave form, run-up and costdown
amplitude verse rotating speed, and the difference of natural frequency due to
crack behavior unbalance amount, eccentricity and angles.
The experimental work is helpful to assure the correctness of theoretical work, so
constructing a test rig that simulates our problem has to be done. The experimental
analysis is used to predict the cracked shaft and the change in crack stiffness. Run-up
and cost down method is used for directly predicting the cracked shaft by monitoring
the shift of frequency for critical speed.
The conclusion of the results show that, crack affects the natural frequency of the shaft
and its stiffness which in turn has an effect on all vibration characteristics. The
theoretical results show sub-harmonics and harmonics of rotating shafts according to
speed, how the crack affects the natural frequency and the great effect of changing the
phase angle and how it can be used for correction the crack effects.