Crack Propagation Quantification In Fibre-Reinforced Polymer Composites Through Distributed Optical Fibre Sensing

The progression of predictive models for crack propagation in fibre-reinforced polymer composites requires the quantification of crack development induced by both static and cyclic loading. The challenge of precisely measuring crack propagation becomes more intensified when cracks are not externally visible, such as in the case of delamination crack progression in thick composites. Traditional techniques, like 3D digital image correlation (3D DIC), can be employed to detect relative changes in strain distribution at the surface. However, these methods may prove insufficient, particularly for composite components with thicknesses ranging from 10mm to 100mm. Distributed optical fibre sensing emerges as a solution, enabling precise spatial measurement of strain along the fibre's length with a remarkable resolution of 0.65mm. Embedding fibres strategically in the composite during production allows measurements in close proximity to the crack surface. Placing fibres in the direction of crack growth facilitates the observation of changes in strain distribution, markedly enhancing the precision in quantifying the delaminated area compared to conventional surface monitoring methods. This investigation offers a comprehensive overview of the design, implementation, and experimental application in simple joint geometries. It places specific emphasis on large steel-glass fibre polymer composite bonded joints, commonly referred to as wrapped composite joints. The technique is initially applied to a straightforward wrapped splice joint with 1D crack propagation. The experimental results robustly affirm the effectiveness of the proposed monitoring system and postprocessing methods subjected to both static and cyclic loading conditions. The system and methods effectively quantify the propagation of debonding cracks. In summary, these findings underscore the achievability of accurately quantifying delamination crack propagation by embedding distributed optical fibres in thick composites. This study contributes valuable insights for the development of predictive models and strongly reinforces the practical significance of employing distributed optical fibre sensing in crack monitoring.