Crack monitoring in cement mortar under impact loading using distributed optical fiber sensing

Distributed fiber-optic sensing techniques based on Rayleigh scattering are widely used to monitor strain field evolution caused by crack initiation and propagation in structures. However, a universal specimen design for crack identification and monitoring under dynamic loading remains lacking. This study investigates the feasibility of using the optical frequency domain reflectometry (OFDR) technique for crack monitoring in cement mortar samples subjected to drop-hammer three-point bending tests. Experiments were conducted on samples embedded with distributed optical fiber sensors of varying diameters. The strain distribution was accurately captured using 2 mm and 2.5 mm optical fibers, allowing for crack detection at peak strain values and precise localization. The discrepancy between the actual crack position and the peak strain location was within 2 mm, while the error between the calculated and measured crack opening displacement (COD) remained within ±10 %. These findings confirm that OFDR enables accurate identification of crack location and width under impact loading. Moreover, the technique can predict crack initiation and propagation trends, demonstrating its potential for dynamic structural health monitoring.