Structural Damage Detection Based On Experimental Modal Analysis

Structures are prone to damage during their service lives, caused by factors such as corrosion, fatigue, impact and overloads. Structural damage causes deviations of geometric or material properties from nominal or baseline values. Thus, techniques for nondestructive damage detection in aerospace, civil and mechanical engineering applications are essential to ensure safety, reliability and operational life.Experimental modal analysis (EMA) has become an increasingly accepted method for determining the overall health of a structure. It uses differences of measured modal properties from baseline or nominal values to identify and assess the location and severity of damage. Damage-induced changes in natural frequencies, damping ratios and mode shapes can be detected using experimental modal analysis, which has recently enjoyed intense research for application in structural health monitoring.A main theme of the research has been to formulate a parameter, calculated using the measured changes in eigenvectors, which exhibits a significant "jump" at the damage location. This damage-sensitive parameter thus serves to localize the damage and assess its severity. It should likewise minimize the likelihood of false indications or missing damage.In this research we use experimental modal analysis of a damaged cantilevered beam to study some previously proposed pragmatic parameters which are reported by several authors to exhibit the desired jump. Two new parameters, called the correlation method and damping factor method are introduced for crack diagnosis based on the Frequency response function (FRF). These parameters likewise "jump" at the damage location. Their reliabilities are tested using the model experimental data. Results show that these two methods can detect the location and extent of damage successfully. And the former one is suitable for periodic health monitoring while the other one is fit for real time health monitoring.