Research On Impact Load And Damage Identification Methods For Piezoelectric Smart Structures

Based on the finite element inverse analysis and the least squares method, a method is established to identify loads on piezoelectric smart structures. The method chooses the piezoelectric responsive charge as the parameter in the object function. The initial load is determined by the unit load pre-approached method. Two examples show that the method is effective and may find its uses in load identifications of future smart structures. The system to monitor impact forces on piezoelectric smart structures is composed. The signals of impact stress wave in time domain are transformed into the analytic ones with the features of momentary sequential time using Hilbert transform. Neural networks are used to extract different characteristics out of signals for automatic identification of impact locations. Experimental results show that the method may gain better accuracy and stability and may find its uses in the health monitoring of laminated structures, such as to locate damages caused by low velocity and low energy impact loadings. Based on the modal analysis of piezoelectric laminated plates, a FEM based inverse algorithm is presented for the time history of impact loads by piezoelectric modal response. The principle of piezoelectric modal sensor is introduced and formulas of calculating modal response by using measured piezoelectric outputs are given. The highly precise direct integration scheme is used for solving modal dynamic differential equation of the structure thus a dynamic load identification method by the modal response is proposed. The method is simple, reliable and has high precision and rapid calculation convergence rate. An example of identifying impact loads demonstrates that the method is effective. The propagation characteristic of Lamb Wave in an elastic plate is analyzed theoretically. A computational model for piezoelectric dynamic impedance of laminated plate attached with PZT wafer is established. Experimental results on impact damaged pieces show that the presence of structure damages makes such characteristic information as mode frequency and value of piezoelectric impedance changed. Hereby, stress wave damage factor (SWAF) is introduced, by which the presence and extent of impact damage in structures may be evaluated. The electro-mechanical impendence method is simple, effective and can find its uses in the structural health monitoring applications. The research is partially supported by Chinese national natural Science Foundation under contract number of 50135030.