Graded thermal effect on wave propagation in composite structures

The effect of the local thermo-mechanical properties of a laminated composite on waves' propagation is the topic of this paper. When compared to results obtained with either a reference temperature throughout the composite or at least a uniform one, predictive simulations emphasize some discrepancies. Yet, when monitoring structural components by means of vibrations and waves' propagation techniques, the dynamics can be significantly modified when the temperature changes. Erroneous conclusions regarding the health-state of the structure can hence be rendered if the thermal effect is not properly described in the interactions of the composite's layer. Based on the physical interactions between the composites' layers, the description of the local variations in the vibrational pattern due to thermal gradients is firstly addressed. The effect is then demonstrated on the experimental identification of the wavenumbers in a honeycomb-core composite panel. The aim of this work is to establish a reliable model that would serve as a baseline for the structural health-monitoring of composite structural components like pipes and stiffened panels. The targeted techniques are based on the propagation of waves. Depending on the relative dimension of the structure to the vibrations wavelength, some delays between wave fronts could be observed depending on the initially properties of each layer and their sensitivity to the temperature's gradient. For that purpose, the results obtained for a pipe under thermal conditions are finally presented.