Analysis of S0/A0 guided wave mode conversion phenomenon

In this paper results of numerical and experimental analysis of guided wave mode conversion phenomenon are presented. Research presented in this paper is focused on S0/A0’ mode conversion caused by discontinuities in the form of notches and delaminations. In the numerical research Spectral Element Method is utilized for modelling of elastic wave propagation. Two kinds of structures are investigated: aluminium beam with notch and composite panel with delamination. In both cases influence of symmetrical and non-symmetrical (in respect to the thickness of structure) location of discontinuities on S0/A0’ mode conversion is investigated. Numerical results lead to the conclusion that necessary condition for mode conversion is the non-symmetric location of a discontinuity in respect to the thickness of the structure. Experimental research is based on scanning laser Doppler vibrometry and full wave-field measurements. In this approach, guided wave generation is conducted based on piezoelectric transducer while sensing process is performed for a dense mesh of points that span over an investigated area of the composite part. Only composite panel with teflon inserts with different shapes is investigated in experimental research. Moreover, only symmetric locations of teflon inserts are investigated. Mode conversion S0/A0’ was noticed clearly for the symmetrical location of teflon inserts (in respect to the panel thickness). Experimental results lead to the conclusion that in real condition always a small distortion of symmetry exists. In reality, perfect symmetry is extremely rare, so it is expected that in real-world damage scenarios mode conversion will always occur.