An integrated evolutionary programming and impedance-based NDE method

Nondestructive evaluation (NDE) is essential in civil and building engineering. Impedance-based method uses the electro-mechanical coupling effect of piezoceramic lead-zirconate-titanate (PZT) materials to measure the force impedance of the structure. By comparing the impedance spectra of the damaged structure with the baseline (the impedance spectra for the pristine structure), the damage in the structure can be assessed. The impedance-based method has shown some advantages over the traditional NDE methods. However, it is not able to identify the location and quantity of the damage simultaneously. This paper presents a technique to overcome this limitation. The technique first measures the variations of the electro-mechanical impedance of the structure, which is similar to the impedance-based method, so that it can inherit the advantage of convenience in operation from the impedance-based method. The damage is then identified by a system identification technique which is generally employed in the vibration-based method. Due to the numerous local optima in the search space, the traditional optimization strategies may not be able to find the correct solution. This paper selects evolutionary programming (EP) as the system identification technique for its robustness in finding the global optimum. Thus, the location and the quantity of the damage can be simultaneously identified. In order to enhance the feasibility of the integrated EP and impedance-based (inEPIB) technique, a fitness function, which can be generally applied to other methods, is proposed to discriminate the variations caused by damages from the discrepancies caused by modeling errors. Experiments are carried out on beams and plates to verify the damage detection results. The results demonstrate that both the location and extent of damage can be simultaneously identified.