Experimental and computational investigations on the scattering of fundamental symmetric lamb wave by edge crack at a circular hole in an isotropic plate.

Fuel vent holes in aircraft components are vulnerable to fatigue cracking and remain a significant challenge for structural integrity management. There is significant interest in using Lamb wave propagation for structural health monitoring (SHM) in such cases due to their low attenuation and rapid wide-area coverage. Unlike bulk waves, solving Lamb wave applications are more complicated and, thus, require further research, both experimentally and computationally, in order to fully exploit their potential for SHM. This paper presents experimental and computational studies of the interaction between the fundamental symmetrical mode S0 and a small through-thickness edge crack at a circular hole in an isotropic plate. The incident S0 wave is generated by a pinching force whose time dependence is a 5.5-cycle Hann-windowed toneburst of centre frequency below the cut-off for the first order Lamb wave modes (SH1). 2D Fast Fourier Transformation (2D FFT) is performed to produce the dispersion curves to identify the scattered Lamb wave mode. The scattering pattern and dependence of scattering amplitude on small crack size are reported and shown to be equivalent to a point source consisting of a particular combination of force doublets, and that the amplitude of the scattered field increases quadratically with crack length a. This study is regarded as a forward problem for a subsequent attempt to investigate the inverse problem of quantifying crack size from scattered wave measurements. Contribution of the findings to non-destructive crack detection and characterisation in SHM are also briefly discussed.