On the influence of moisture absorption on Lamb wave propagation and measurements in viscoelastic CFRP using surface applied piezoelectric sensors

The understanding of the impact of environmental influence factors on propagation and damping of Lamb waves in composite materials is a topic of great interest for both design and utilization of structural health monitoring (SHM) systems. In this work, the influence of humidity absorption on the dispersive behavior of Lamb waves propagating in viscoelastic composite materials is investigated. Using a transversely isotropic material model and DMA measurements, the changes in the viscoelastic material properties due to water absorption are characterized. By means of a higher order plate theory and those mechanical properties, the dispersion curves for unconditioned and hot/wet-conditioned UD reinforced CFRP plates are then predicted. Both the changes in Lamb wave velocity and Lamb wave damping are investigated and compared with experimental values. Additionally, the changes of the sensor response, which are related to both the changes of the material properties and that of the adhesive layer, are investigated. The large impact of moisture absorption on Lamb wave excitation and propagation and its relevance for structural health monitoring (SHM) applications is shown and discussed.