Correlation between crack propagation history and AE characteristics: Combined characterization from AE and DGS

Acoustic emission (AE) signals contain important information about material failure. However, the results usually need to be supplemented with other technologies. The characteristics of direct observation of optical technology can provide direct evidence for verifying AE results. In this study, the mode I fracture behavior of polymethyl methacrylate under wedge loading was investigated. A synchronous acousto-optical system was developed, combining AE, high-speed imaging, and digital gradient sensing (DGS). The system captured the fracture process and corresponding AE signals. AE source localization was achieved via a velocity-independent simplex method. The DGS method determined the crack-tip position and stress intensity factor (SIF). A comparison of acousto-optic data shows that the AE signal originates near the crack tip. The dominant AE frequency (15.7 kHz) matched the longer rupture duration (∼80 μs). The secondary frequency (38.6 kHz) corresponded to the shorter rupture duration (∼30 μs). Finite element simulations confirmed the inverse relation between AE frequency and rupture duration. Further, the SIF history and radiated energy were calculated. Results showed that the higher the energy release rate at the fracture time, the greater the radiation energy. This shows the strong coupling between fracture mechanics and AE features. The results provide a basis for applying acousto-optical methods to opaque materials and structural health monitoring.