Load monitoring of a cantilever plate by a novel multimodal fibre optic sensing configuration

Optical fibre sensors and in particular fibre Bragg gratings (FBG) have received a lot of interest for Structural Health Monitoring in different application fields, such as aerospace, pipeline and civil engineering. FBGs are conventionally used to monitor strain and sometimes temperature. In this paper, we propose a new method for load monitoring of a cantilever plate subjected to point loading. The bending of plate is complex due to the interaction between the axial and transverse bending stiffnesses of the material. We use a novel algorithm for interrogating fibre Bragg grating sensors based on both hybrid interferometry and FBG spectral sensing. The method is demonstrated in this paper using a single-mode optical fibre containing four FBG sensors to estimate both the point loading position and the loading magnitude at an arbitrary location on a 1 m$$^{2}$$ 2 cantilever plate. The algorithm first utilizes point strain information through spectral sensing as well as strain from interferometric sensing over a long path. The gratings are interrogated using Wavelength Division Multiplexing (WDM). We calibrated the system using an experimental model. This model was then verified by using single point static loading tests and comparing the calculated sensing position with the actual position. The method achieved a good estimation of loading position achieving a measurement error of about 9% in a 2D plane. The analysis discusses the possible sources of inaccuracies. This study forms the basis of our future work involving morphing smart-wing sections for the purpose of load monitoring. Article highlights A new optical sensing configuration is demonstrated for load and structural health monitoring of cantilever structures. The algorithm successfully estimates the position of an arbitrary load on a cantilever plate, with an error of 9%. This methodology will be extended to monitor more complex structures, in- cluding morphing aircraft wing sections.