Steel Fibre Reinforced Concrete (SFRC) has been a commonly used fibrous composite since the 1960s. The failure mechanism of SFRC is yet to be fully understood. Indeed, there is a lack of research on the cracking process of SFRC members under bending action. Acoustic Emission (AE) technique is one of the popular non-destructive testing (NDT) methods. In this study, AE technique was used to experimentally investigate the fracture process of SFRC beam under bending. To achieve the objective, signal based analysis was performed to locate the source of the major cracks. Specific tasks and findings include the following.

a) A new onset time identification methodology was developed based on power transmitted by the wave, and the algorithm was found to be more reliable and accurate than...[ Read more ]

Steel Fibre Reinforced Concrete (SFRC) has been a commonly used fibrous composite since the 1960s. The failure mechanism of SFRC is yet to be fully understood. Indeed, there is a lack of research on the cracking process of SFRC members under bending action. Acoustic Emission (AE) technique is one of the popular non-destructive testing (NDT) methods. In this study, AE technique was used to experimentally investigate the fracture process of SFRC beam under bending. To achieve the objective, signal based analysis was performed to locate the source of the major cracks. Specific tasks and findings include the following.

a) A new onset time identification methodology was developed based on power transmitted by the wave, and the algorithm was found to be more reliable and accurate than previous methods particularly in low SNR values.

b) A new 3D fingerprinting technique was developed to separate and extract the onset time for intersected wave during the high burst rate period of the test. The results were validated with signals from the ball drop test as well as simulated signals.

c) A framework for source localization in heterogeneous (damaged) concrete was developed. The proposed framework first pre-select and replace the arrival time with high residual by calculated arrival time after the first cycle. With the new arrival time, the source location was optimized by updating the spatial coordinate in an iterative process. Results of each iteration are used to update the velocity field in the next iteration. The framework was validated with results from 2D Monte Carlo Simulation.

Using a) b) and c), crack source was localized and the fracture process was studied. The result indicates that the source identified is in good agreement with surface cracks visually observed during the test. The fracture process was validated using parametric AE analysis. It was found that the major crack starts to propagate after two-third of the maximum stress was reached and most of the damage occurs after maximum load. From the parametric study, the cracking type is predicted as tension crack or shear crack. The prediction of cracking types is a good match with the actual cracks. The AE results also reflect increased ductility in SFRC material with higher fiber volume fraction.

In addition, an AE tomography technique using bias was developed, and a series of simulation was performed to validate the accuracy and reproducibility of identifying the damaged region. An interesting finding is that damage may be identifiable with a smaller number of impacts that do not cover the whole region of interest, but accuracy depends on the number of wave crossing the damaged area.