A Benchmark study of dynamic damage identification of plates

Vibration-based methods for damage detection of structures are researched extensively among the academic community. Yet only limited success in practice has been reported. A major hurdle is understood to be the discrepancy between the assumed availability of pertinent modal data and the measurability of such data from actual experiments. However, dedicated critical studies into the practicality and limitation of modal testing for structural damage detection are scarce. This paper presents a laboratory investigation, along with finite-element (FE) analysis, into the extent to which modal frequencies and mode shapes may be measured in a plate-like structure and their general sensitivities to different levels of damage. The order of measurable modes and the measurement accuracy are assessed on the basis of the actual measurement in conjunction with FE predictions. Changes in the measured modal properties are examined in light of the pattern and severity of damage. Results indicate that with a typical modal testing it is possible to obtain the first 5–6 modes for a plate structure with sufficient accuracy in the frequencies but with a gross error of around 10% in the mode shapes. Using solely a few measurable natural frequencies will be insufficient to identify the occurrence and the degree of crack-induced damage. Mode shapes can be more indicative of local damage in a plate, especially when it involves an edge crack.