Assessment of fatigue damage in solid plates through the ultrasonic Lamb wave approach

Changes (degradations) in the mechanical properties of solid plates induced by cyclic fatigue loading will influence the features of ultrasonic Lamb wave propagation, such as dispersion and attenuation. This paper has qualitatively analyzed the feasibility of using the amplitude-frequency characteristics and the stress wave factors (SWFs) of ultrasonic Lamb wave propagation to assess fatigue damage in solid plates. Liquid wedge transducers located on the surface of solid plates tested are used to generate and detect the Lamb wave signals. Based on the Ritec-SNAP ultrasonic measurement system, the experimental setup for assessing the degree of fatigue damage in solid plates using ultrasonic Lamb wave approach has been established. For several rolled aluminum sheets subjected to tension-tension cyclic loading, the experimental examinations have been performed for the relationships between the amplitude-frequency characteristics of ultrasonic Lamb wave propagation and the numbers of loading cycles (denoted by N), as well as the correlations between the Lamb wave SWFs and N. The experimental results show that the Lamb wave SWFs decrease monotonously and sensitively with the increment of cycles of fatigue loading. Based on the correlations between the Lamb wave SWFs and N, it is further verified that ultrasonic Lamb wave propagation combined with the Lamb wave SWFs can be used to effectively assess early fatigue damage in solid plates.