[4C3] Monitoring the development of surface-breaking cracks using permanently installed low-cost ultrasonic arrays in fatigue tests
J An, X Sun, S Bhat, N Larrosa, A Velichko, B Drinkwater and J Zhang
University of Bristol, UK
Monitoring crack development is crucial for ensuring safety, assessing structural health, optimising maintenance strategies and advancing scientific knowledge in the field of structural engineering. It enables proactive maintenance, cost-effective asset management and the development of innovative solutions for a safer and more sustainable built environment. In this paper, the application of using permanently installed low-cost ultrasonic arrays for monitoring the development of surface-breaking cracks is explored. In the experimental measurements, a 5 MHz ultrasonic array with 18 elements is permanently attached to the top surface of a single edge notch bend specimen, which is fabricated according to ASTM standard E647-15. A clip gauge is installed around an initial electrical discharge machining (EDM) cut mouth to measure crack mouth opening distance (CMOD). Additionally, a digital camera is focused on the tip of the EDM cut to measure surface displacement and strain through the correlation method. During the four-point bending fatigue tests, experimental datasets are recorded from the ultrasonic arrays, clip gauge and digital camera. The authors focus on the development of low-cost array designs, fabrication, installation and post-processing techniques for analysing ultrasonic array data to measure parameters related to crack development, including crack length, CMOD and crack tip opening distance (CTOD). The post-processing techniques developed for analysing the ultrasonic array data are validated by comparing the measurement results with the data obtained from the clip gauge and the digital camera. These reference measurements serve as a benchmark to assess the accuracy and reliability of the post-processing techniques in determining parameters such as crack length, CMOD and CTOD. It is demonstrated that the low-cost ultrasonic arrays exhibit reasonable and reliable performance in detecting and monitoring cracks. The developed post-processing techniques prove effective in accurately measuring important parameters such as crack length, CMOD and CTOD. These findings validate the feasibility and applicability of using low-cost ultrasonic arrays and the associated post-processing techniques for crack monitoring and characterisation. The results provide confidence in the practical use of these methods for assessing the structural integrity and crack development in various applications.
