Modal moment index for damage detection in beam structures

Health monitoring and damage detection in structures such as airframes are crucial to their safety and performance. Damage-induced changes in natural frequencies, damping ratios and mode shapes can be detected using experimental modal analysis (EMA), which has recently enjoyed intense research for application in structural health monitoring. A main theme of the current research has been to formulate a parameter, calculated using the measured changes in eigenparameters, which exhibits a significant “jump” at the damage location and whose value is a direct measure of the severity of the damage. A damage-sensitive parameter thus serves to localize the damage and to assess its severity, and it should likewise minimize the likelihood of false indications or of missing damage. Here, using finite element analysis of the damaged cantilevered beam, we study several existing parameters and introduce a new parameter called the Modal Moment Index (MMI). MMI is shown to jump sharply at the damage site and to have a direct relationship to the damage level.