Guided wave mode conversion phenomenon in composite materials: numerical and experimental study

Abstract

In this paper results of numerical and experimental analysis of S0/A0 elastic wave mode conversion phenomenon at various discontinuities in glass fibre reinforced polymer (GFRP) panels are presented. Analysis of S0/A0 mode conversion effect at Teflon inserts simulating delamination and impact damage with energies 5 J, 10 J and 15 J is conducted. In the case of Teflon inserts circular inserts with the same diameters located at different depth and inserts with various shapes located at the same depth were investigated. Numerical analysis is based on the time domain spectral element method (SEM). SEM computational algorithm is adapted for parallel calculation using graphic processor units (GPUs). Numerical model takes also into account the influence of material damping. Numerical results are compared with experimental results based on full wavefield measurements using scanning laser Doppler vibrometry (SLDV). It is shown that based on the effects of S0/A0 mode conversion it is possible to detect the damage and determine its shape and size. In the research, auxiliary Non-Destructive Testing (NDT) method is also utilised. The aim of its application is to indicate the depth of discontinuity and to prove that delamination was created in the case of impact damage. The auxiliary method is based on terahertz spectroscopy (THz) where the analysis of propagation of electromagnetic waves in the terahertz band is conducted. The THz spectroscopy is a useful technique for damage assessment in the dielectric materials.