Articles you may be interested inModal preference of cumulative second harmonic generation in Lamb waves AIP Conf.

This article describes the physical process of cumulative second-harmonic generation of Lamb-mode propagation in a solid plate. In general, cumulative second-harmonic generation of a dispersive guided wave propagation does not occur. However, the present results show that the second harmonic of Lamb-mode propagation arising from the nonlinear interaction of partial bulk waves and the restriction of the two boundaries of the solid plate does have a cumulative effect once some conditions are satisfied. Through boundary and initial conditions of excitation, the analytical expression of the cumulative second harmonic of Lamb-mode propagation has been determined. Numerical results reveal that the cumulative second-harmonic fields are symmetrical regardless of whether Lamb-mode propagation is symmetrical or antisymmetrical, and that the cumulative second-harmonic field patterns of Lamb-mode propagation are associated with the position of excitation source.

The feasibility of using the nonlinear effect of primary Lamb wave propagation for assessing accumulated fatigue damage in solid plates is theoretically analyzed. After the aluminum sheets are subjected to tension-tension fatigue loading for different numbers of loading cycles, they are subjected to ultrasonic tests near the driving frequency where Lamb waves have a strong nonlinearity. This is followed by the measurement of the amplitude-frequency curves for second harmonics of the considered Lamb waves. The experimental results show that the effect of second-harmonic generation by Lamb wave propagation is very sensitive to the accumulation of fatigue damage of solid plates.

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A nano-structured Co oxide electrode (with a Ni substrate) was successfully prepared using an entirely electrochemical process, which included the co-deposition of a Ni-Cu alloy film, selective etching of Cu from the film, and anodic deposition of Co oxide on the obtained nano-porous Ni substrate which had an average pore size of approximately 100 nm and a pore density of about 10(13) m(-2). The excellent electrochemical activity of the prepared electrode was demonstrated in terms of its pseudocapacitive performance, which was evaluated using cyclic voltammetry (CV) in 1 M KOH solution. The specific capacitance of the nano-structured Co oxide measured at a potential scan rate of 10 mV s(-1) was as high as 2200 F g(-1), which is over ten times higher than that of a flat oxide electrode (209 F g(-1)). The highly porous Co oxide also had superior kinetic performance as compared to a flat electrode. At a high CV scan rate of 50 mV s(-1), the two electrodes retained 94% and 59%, respectively, of their specific capacitances measured at 5 mV s(-1).