Predicting damage evolution via resonant frequencies in three-point bending tests: Experiments and LDEM simulations

In the present study, the crack propagation process in pre-notched concrete beams subjected to three-point bending was monitored by tracking variations in resonant frequencies. The tests were conducted under displacement-controlled conditions until final failure, using an incremental loading procedure. At each load step, the beam was subjected to impulse excitation, and the response was recorded by sensors positioned along the beam. A signal-processing methodology based on the Fast Fourier Transform (FFT) was then applied to extract the resonant frequencies from the recorded data. To complement the experimental analysis, a numerical investigation was performed. A version of the Lattice Discrete Element Method (LDEM) was implemented to simulate damage progression. The damage state obtained from the LDEM simulation was subsequently imported into a Finite Element Method (FEM) solver to perform modal analysis, providing additional dynamic characteristics such as mode shapes and resonant frequencies for direct comparison with the experimental results. The changes in resonant frequencies and mode shapes obtained from both the numerical and experimental analyses were compared. The results demonstrate that these dynamic characteristics are effective for monitoring damage evolution in the structure and predicting final failure. Emphasis is placed on the role of numerical simulation in supporting the interpretation of the experimental damage process.