Influences of environmental conditioning and damage on the dispersive propagation and damping behaviour of Lamb waves in fiber reinforced plastics

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Within the first 18 months of the initial funding phase, which have been completed at the time of preparation of this follow-up proposal, the influence of environmental and loading conditions (humidity absorption, temperature changes, static and dynamic loading), and combinations thereof, on wave propagation in fiber reinforced plastics was investigated. Additionally, methods where created to both predict changes to the propagation characteristics if the waveguides state is known and to compensate for these changes to enable the use of Lamb waves for structural health monitoring (SHM).The proposed second funding phase initially contains the work packages which were planned for the time between month 25 and 36 in the original proposal, adapted to the findings of the first phase. Primarily, this includes the conclusion of the experimental work packages and their evaluation. Additionally, the findings of the first phase are to be used to develop/extent methods that allow the evaluation of the structures health if the sensor response changes due to factors unrelated to the formation of damage. From these methods and the experimental findings, guidelines are to be developed which contain rules for the design of sensor networks for SHM under realistic conditions.It is furthermore proposed that the second funding phase contains new work packages which deal with the high sensitivity of the sensor responses to factors that show manufacturing related scatter, which were identified in the first phase. These factors include variation of the local fiber volume content (e.g. due to textile gaps), the fiber orientation and the adhesive layers properties. As it is expected that the impact of these factors is itself a function of the environmental conditions investigated in the first phase, it is also proposed to investigate the combined influence of manufacturing-related property scatter and both humidity absorption (as an example for a slowly changing influence varying over the thickness of the laminate) and temperature (as an example for a factor that can change very fast). Experiments using both simple plates and plates containing structural discontinuities are planned, with the influence of locally varying, non-damage-related changes (esp. humidity absorption) on interactions between wave and structural discontinuity (reflection, mode conversion etc.) being of special interest.Finally, the work package dealing with the creation of guidelines for the design of sensor networks will be extended to include the aforementioned influencing factors, namely manufacturing-related property scatter in combination with structural discontinuities and non-damaging environmental conditions. To achieve this, it is proposed to use both FE-based approaches to predict areas where the sensor responses complexity would be critically high and to develop/investigate methods to localize the SHM systems task, i.e. by limiting its task or the area covered by the waves.