Comparative study between the R-ODS and DND methods for damage detection in structures

• Comparing the robustness of the DND and the R-ODS methods for damage detection.
• Using different types of input excitations for a comprehensive comparison.
• Applying the methods to rotor- and beam-like structures.
• Using the second derivative for clear identification of crack locations.

Measured vibration responses can be processed either in their original time domain or after converting to the frequency domain for the purpose of damage detection. Recently, two new vibration-based methods have been presented separately which successfully identified the location of damage in beam-like structures. One of the methods utilises the vibration responses of cracked structures in time domain and is called deviation from normal distribution (DND). The DND method calculates the difference between actual and normal distribution of vibration responses in time domain to locate cracks. The other method is called residual operational deflection shape (R-ODS) which uses the amplitude and phase of the exciting frequency and its higher harmonics in the frequency domain as a method of crack detection. Previously, these methods were applied only to single cracked beams with sinusoidal excitation and their results were encouraging. Here, the application of the two methods has been extended to multiple cracked beams as well as rotors. Also, the effect of different types of excitations on the detection process using the two methods has been investigated through numerical and experimental examples.