Abstract
This paper investigates the propagation of Rayleigh surface waves in structures with randomly distributed surface micro-cracks using numerical simulations. The results revealed a significant ultrasonic nonlinear effect caused by the surface micro-cracks, which is mainly represented by a second harmonic with even more distinct third/quadruple harmonics. Based on statistical analysis from the numerous results of random micro-crack models, it is clearly found that the acoustic nonlinear parameter increases linearly with micro-crack density, the proportion of surface cracks, the size of micro-crack zone, and the excitation frequency. This study theoretically reveals that nonlinear Rayleigh surface waves are feasible for use in quantitatively identifying the physical characteristics of surface micro-cracks in structures.
Highlights
Stress corrosion micro-cracks, on or near a material surface, can susceptibly occur in metallic structures due to fatigue loads and corrosive environments [1,2]
We focus on the mechanism of second harmonic generation and propagation of Rayleigh surface waves in metallic structures with randomly distributed surface micro-cracks
We investigate the relationship between the acoustic nonlinearity parameter and we investigate the relationship between the acoustic nonlinearity parameter and the proportion of surface micro-cracks, as well as the crack density and propagation distance in the the proportion of surface micro-cracks, as well as the crack density and propagation distance in the micro-crack zone
Summary
Stress corrosion micro-cracks, on or near a material surface, can susceptibly occur in metallic structures due to fatigue loads and corrosive environments [1,2]. It is of crucial importance to develop various non-destructive testing methods to detect and evaluate surface cracks for ensuring the integrity and safety of metallic structures. Compared with works on early material degradation, research on the detection of micro-cracks using higher harmonics of Rayleigh surface waves is still rarely reported [6]. Rjelka et al [25] have determined the relationship between material properties (third-order elastic constants) and inhomogeneous distributions of micro-cracks. They investigated the acoustic nonlinearity parameter for surface acoustic waves based on second harmonic generation. We focus on the mechanism of second harmonic generation and propagation of Rayleigh surface waves in metallic structures with randomly distributed surface micro-cracks. This work will provide a theoretical basis for detection and evaluation techniques based on nonlinear Rayleigh surface waves
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