Rotating shafts carrying disks are broadly used in many mechanical applications like pumps, engines and turbines. It is observed that high speed and heavy duty shafts develop transverse cross-sectional cracks due to fatigue at some time during their life period. Cracks may be caused by mechanical stress raisers, such as sharp keyways, abrupt cross sectional changes, metallurgical factors, heavy shrink fits, grooves, and other stress concentration factors that promote the crack initiation.
Once a crack is initiated it propagates and the stress required for propagation is smaller than that required for crack initiation. After many cycles operating stresses may be sufficient to propagate the crack. The crack propagation takes place over a certain depth when it is sufficient to create unstable conditions and fracture take place. It is important to develop new non-destructive techniques real time based diagnosis methods to predict the behavior of a crack in order to avoid human and economical disasters.
Transverse cracks modifies the dynamic behavior of the system generating in an horizontal shaft a reduction of the rotor stiffness, which change the modal parameters and the acceleration amplitudes along the shaft. Establishing a relation between these vibration parameters and the failure characteristics of the system will leave us to characterize and predict a failure in a rotor system. In recent years, the dynamic behavior and diagnostic of cracked rotor have been gained momentum. In literature, several studies are available for cracked rotor systems, however very few authors have addressed the issue of multi-cracked rotor system.
With this relevance, it is proposed to study, the effect of crack depth on the shaft’s stiffness and natural frequencies are investigated using experimentally. Natural frequencies have been obtained through vibration analyzer system using impact hammer test under static conditions.
The experimental set up has been developed for measurement of stiffness, natural frequency, vibration amplitude e.t.c.
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