Impact Force Identification And Damage Detection Considering Uncertainty Effects

In order to meet the high demands for operation safety of structures and low cost maintenance,the technology of structural health monitoring (SHM) has been widely studied in recent years.According to the operating principle of sensors, it can be classified into two types of monitoringsystems: active and passive damage detection. The main contents of this dissertation are as follows:Firstly, a synthesis approach is presented to address the problem of uncertainty in the impactforce identification of composite stiffened panels. The effects of material uncertainty on dynamicresponses of the structure are studied by using Monte Carlo simulation. A parametric study isconducted to select the key parameters as the optimization variables in the following step of modelupdating. The technique of model updating is used to correct the modeling errors caused by materialuncertainty based on genetic algorithm (GA). Then, an improved inverse analysis technique based onthe finite element method and mode superposition method is taken for impact force identification. Inthis study, the present method is performed on a composite stiffened panel, and the effect of noise onthe performance of identification is also discussed. The results of the study show that the developedapproach is capable of identifying the impact location and reconstructing the force history accuratelyby reducing material uncertainty through the modal updating procedure.In the second part, the kernel density estimation (KDE) method is used to solve the damagedetection problem based on the spectral element method (SEM) in this paper, and the probabilitydensity functions (PDFs) of damage location can be obtained. A three-dimensional SEM includingelectromechanical coupling is developed to simulate the propagation of Lamb waves in both healthand damaged aluminum plates. The time-of-flight (TOF) of response signals in each actuator-sensorpath is calculated by a continuous wavelet transform (CWT) to measure the speeds of lamb waves.Rayleigh-Lamb equations are analyzed by a numerical calculation method and the theoretical speedsof Lamb waves in aluminum plates can be obtained, which are compared with the ones by SEM todemonstrate the accuracy of SEM. On the basis of the elliptical position technology, the KDE isintroduced as a probabilistic approach for damage detection under the effects of environmentaluncertainty. The PDFs of damage location are discussed under three levels of noise which are addedinto the response signals, and the final probability distributions are given. The results demonstrate thatthe SEM-based approach with the application of KDE is capable of identifying the damage locationsefficiently, and the maximum error is about5%.