Abstract <p>We investigated the application of distributed fiber-optic sensors (DFOS) based on Rayleigh scattering for high-resolution strain measurements in heterogeneous materials under four-point bending tests. Experiments on potassium salt compare full-length and two-point bonding strategies, showing that bonding configuration significantly affects the measured strain variability and interpretation of material behavior. The strain profile over the height of the specimen during the four-point bending test was registered using DFOS and used to estimate the position of the neutral axis. The results highlight both capabilities and limitations of DFOS in geomechanical applications.</p>