A LOW FREQUENCY LAMB-WAVES BASED STRUCTURAL HEALTH MONITORING OF AN AERONAUTICAL CARBON FIBRE REINFORCED POLYMER COMPOSITE

Carbon Fiber Reinforced Polymer composites have been developed since the ’60s and allow the design of resistant and innovative lightweight primary structures, replacing traditional metallic materials. However, their intensive structural use remains limited due, between also other factors, to several peculiar damage mechanisms able to quickly degrade the mechanical properties and requiring high maintenance costs due to service interruptions needed for carrying out periodical non-destructive testing inspections. One solution, more and more suggested and proposed in the literature, is then to apply a structural health monitoring approach. The present paper investigates such possibility focusing on the application of the “Design of Experiment” methodology to the performance of Lamb ultrasonic waves-based monitoring carried out using piezoelectric transducers bonded on the surface of aeronautical laminates. The choice of a Design Of Experiment approach is based on the well-known fact that the success of an ultrasonic monitoring approach is mostly based on the knowledge of the most influencing factors, but also that the today published research studies usually consider them individually. A rigorous factorial design method is then applied in order to study the influence of different operative factors. Since the worst type of damage in a composite structure is a delamination, the research is particularly focused on this kind of defect obtained both artificially, using Teflon patches, and naturally, by suitable mechanical impacts.