Structural health monitoring of partially immersed metallic plates using nonlinear guided wave mixing

Abstract

Metallic plates are important structural components of many liquid containment structures, such as liquid storage tanks and sewer pipes. Time-dependent loads can result in fatigue and degradation of the metallic material. Nonlinear guided wave mixing has been demonstrated to be sensitive to microstructural change at the early stage of material degradation. Previous studies have been carried out using the nonlinear guided wave mixing technique on various structures in gaseous environments. However, its application to structures immersed in liquid has not been explored. This paper numerically and experimentally investigates the nonlinear guided wave mixing in an aluminum plate loaded with water on one side. Experiments are carried out with an empty metal tank and the tank filled with water, respectively. The results show that cumulative generation of harmonics at the sum frequency due to the material nonlinearity of the partially immersed plate can be achieved by mixing the fundamental leaky symmetrical Lamb (leaky S0) waves at two different frequencies. Under the same experimental conditions, the amplitudes of the guided wave signals and the values of the relative nonlinearity parameters on the partially immersed plate are different from their counterparts on the plate without water. Finally, numerical simulations are performed with the material nonlinearity of the test plate simulated by the Murnaghan constitutive model. The numerical results reveal that both the second harmonics and the combination harmonics are sensitive to the material nonlinearity of the plate loaded with water on one side.