Beat-Frequencies for Damage Detection

In many elasto-mechanical systems the natural frequencies and shapes of the lower-range modes are not changed very much by the onset of damage. This insensitivity is the root of many problems with methods that seek to assess the operational integrity of such systems by using low-frequency vibration measurements. In this paper it is demonstrated that the beat frequencies, which are directly measurable, can be a significantly better indicator of damage than natural frequencies. The determination of small changes in natural frequencies requires very high resolution in digitally produced frequency response functions. Methods which can assign vibration nodes may be helpful in determining the location of damage sites.