Smart Monitoring of a Full-scale Composite Hydrofoil Manufactured using Automated Fibre Placement under High Cycle Fatigue

Fibre reinforced composites materials offer a pathway to produce passive shape adaptive smart marine propellers, which have improved performance characteristics over traditional metallic alloys. Automated Fibre Placement (AFP) technology can provide a leap forward in Cyber-Physical automated manufacturing, which is essential for the implementation and operation of smart factories in the marine propeller industry towards Industry 4.0 readiness. In this paper, a comprehensive structural health monitoring (SHM) routine was performed on an AFP full-scale composite hydrofoil to gain confidence in its dynamic and structural performances through a number of active and passive sensors. The hydrofoil was subjected to constant amplitude flexural fatigue loading in a purpose-built test rig for 105 cycles. The hydrofoil was embedded with distributed optical fibre sensors (DOFS), traditional electrical strain gauges and linear variable displacement transducers (LVDTs). Both microelectromechanical system (MEMS) and piezoelectric (PZT) accelerometers were used to conduct experimental modal analyses (EMA) to observe changes in the modal response of the hydrofoil at regular intervals throughout the fatigue program. The hydrofoils modal response, as well as the stiffness measured using both displacements and strains, remained unchanged over the fatigue loading regime demonstrating the structural integrity of the hydrofoil. The optical fibre sensors endured the fatigue test cycles showing their robustness under fatigue loads. Furthermore, the sensing systems demonstrated the potential of being utilised as a useful maintenance tool combining their adaptability with automated manufacturing during manufacturing through integration within the hydrofoil, a structural test framework for performance measurement, data acquisition and analytics for visualization, and the prospect of decision making for maintenance requirement during any onset in structural performance.

Assessment and visualization of performance indicators of reinforced concrete beams by distributed optical fibre sensing

The implementation of structural health monitoring systems in civil engineering structures already in the construction phase could contribute to safer and more resilient infrastructure. Due to their lightweight, small size and high resistance to the environment, distributed optical fibre sensors stand out as a very promising technology for damage detection and quantification in reinforced concrete structures. In this article, the suitability of embedding robust distributed optical fibre sensors featuring a protective sheath to accurately assess the performance indicators, in terms of vertical deflection and crack width, of three reinforced concrete beams subjected to four-point bending is investigated. The results revealed that a certain strain attenuation occurs in embedded robust distributed optical fibre sensors compared to commonly used thin polyimide-coated distributed optical fibre sensors bonded to steel reinforcement bars. However, the presence of the protective sheath prevented the appearance of strain reading anomalies which has been a frequently reported issue. Performance wise, the robust distributed optical fibre sensors were able to provide a good estimate of the beam deflections with errors of between 12.3% and 6.5%. Similarly, crack widths computed based on distributed optical fibre sensor strain measurements differed by as little as ±20 µm with results from digital image correlation, provided individual cracks could be successfully detected in the strain profiles. Finally, a post-processing procedure is presented to generate intuitive contour plots that can help delivering critical information about the element’s structural condition in a clear and straightforward manner.