Abstract

Damage detection requires non-destructive testing of structures. Vibration-based damage detection techniques identify damage based on changes in the vibration features such as natural frequencies and mode shapes. Detecting damage requires solving an inverse problem using an analysis tool that is used as a simulator to produce possible damage cases and an optimization algorithm to find the closest model to the observed vibration features. Capturing some damage cases, such as delamination, is more difficult than others in the way that delamination is revealed in higher modes of vibration. Standard Finite Element Method requires a huge computational effort to obtain natural frequencies and mode shapes. Spectral Finite Element method that benefits from frequency-dependent shape functions, is adopted in this study as the analysis tool to model the dynamic behaviour of laminated composites. A discussion is given on the observations from the output of Spectral Finite Element method and a method is suggested to calculate the complete response of the structure based on the results of Spectral Finite Element analysis. The Wittrick-Willams procedure has been implemented to identify the natural frequencies from the frequency- dependent dynamic stiffness matrix of the system. The effect of delamination on natural frequencies of vibration of delaminated composites are studied. The Genetic Algorithm has been used to develop a damage detection tool that searches for the closest model to the observed frequencies and mode shapes.