Elastic constants identification of fibre-reinforced composites by using guided wave dispersion curves and genetic algorithm for improved simulations

Abstract

There is a great potential for model-based approaches in which guided waves are utilised for damage detection, localisation and size estimation. However, to be effective, the model must accurately represent guided wave propagation behaviour, especially wave velocity dependence on the angle of propagation. Unfortunately, improperly assumed or derived through homogenisation elastic material properties can lead to larger wave velocity changes than caused by damage. In order to account for this problem, the elastic constants are estimated based on experimental measurements of Lamb waves and optimisation techniques. In the proposed approach, experimental measurements of full wavefield data of propagating Lamb waves are conducted by scanning laser Doppler vibrometer. The obtained wavefield data is processed by using the 3D Fourier transform. Slicing the data at selected frequencies yields wavenumber profiles. These profiles can be directly translated to wave propagation velocity dependence on the angle of propagation. Data can also be sliced at selected angles giving dispersion curve images. At the same time, wavenumber profiles or dispersion curves can be calculated by using a semi-analytical model for the range of material properties. A genetic algorithm is used in which the best fit between experimental data and the semi-analytical model is optimised. Experiments were conducted on a unidirectional CFRP panel and the above-mentioned procedure was applied. Identified material properties were used in the in–house code of the time domain spectral element method for simulations of the propagating waves. Finally, numerical results were compared to the experimental full wavefield data showing much better accuracy than in case of application of homogenisation techniques. Furthermore, the correctness of elastic constants determined by the proposed method was validated against the elastic constants obtained through static test standards.