CRITICAL SPEED AND NATURAL FREQUENCY ANALYSIS OF CRACKED ROTOR SHAFT

Excessive Vibrations in machine shaft cause catastrophic failure of machine parts. Vibration in the machine part increases due to crack generation and propagation in machine shaft. Dynamic properties of rotor shaft such as natural frequency of vibration and critical speed get altered due to change in crack depth and crack location. In this paper, an experimental approach was developed to observe the effect of variation in a crack depth and location. In the present experiment single crack was generated in a rotary shaft at 4 different locations (100 mm, 200 mm, 300 mm, and 400 mm) from bearing support. Further, three different crack depths (17%, 33% and 50% of shaft diameter) was provided at each crack location. Critical speed and natural frequency of rotary shaft were obtained experimentally using Fast Fourier Transform. Critical speed varies in the range of 5% to 8.5% due to change in crack depth and crack location. Variation of natural frequency was observed 6% to 12% due to change in crack depth and crack location. Frequency vs. amplitude analysis of rotary shaft carried out using Fast Fourier Transform analyzer