Investigation of the effectiveness and robustness of a MEMS-based structural health monitoring system for composite laminates

Failure of layered composites can be triggered by small inner defects; such defects can be present inside the composite from the beginning, or can be incepted by external actions during the life cycle of the structure. Defects generally evolve, under repeated loadings, into a delamination or debonding between adjacent laminae, and cannot be easily detected as they are masked by the composite skin: ad hoc health monitoring systems are therefore required. To prevent any distortion of the composite microstructure, which may trigger by itself the nucleation of the aforementioned defects, sensors should not be embedded inside the composite; in addition, to avoid a mechanical interaction between the monitoring system and the structure, sensors should be as lighter as possible. To comply with these two major requirements, we have recently investigated a microelectromechanical system-based, surface-mounted health monitoring strategy for laminates. In this paper, we provide the results of an experimental campaign to show the effectiveness of this strategy, in terms of sensitivity to the length of delamination in standard specimens (independently of the loading conditions at the tip of the delamination), and its robustness, in terms of repeatability of the outcomes relevant to the monitored state. The experimental data are compared with analytical predictions based on beam bending theory, showing a good accuracy.