Nonlinear Lamb waves for the detection of material nonlinearity

This paper reports on a method that uses nonlinear Lamb waves to detect material nonlinearity. Lamb waves are well suited for the interrogation of thin metallic layers which act as waveguides, giving Lamb waves great potential in nondestructive evaluation applications. However, measuring nonlinear Lamb waves and extracting the information necessary for nondestructive evaluation is complicated by the inherent dispersive and multi-mode nature of Lamb waves. This paper presents a procedure that overcomes these difficulties and develops a reliable and robust measurement methodology. By using hybrid wedge generation and laser interferometric detection in combination with signal processing in the time-frequency domain, it is possible to make relative measurements of material nonlinearity parameters, which are an indicator of plasticity-driven damage.