Using the local wavenumber method
Carbon fiber/epoxy composite materials have been increasingly used in numerous fields owing to their excellent properties. Unfortunately, these composite structures are highly susceptible to damage during long-term service. As a remedy, non-destructive testing techniques have been proposed for accurate evaluation and safety monitoring of composite structures. An example is the non-destructive ultrasonic testing methods that are capable of inspecting inaccessible locations and offer online structural health monitoring when coupled with advanced sensing technology. In recent years, research on the damage localization and characterization of composite structures based on ultrasonic guided wave testing techniques have gained momentum with several delamination monitoring methods being proposed.
Recently, a team of researchers at Jiangsu University: Dr. Guoqi Zhao, Dr. Ben Wang, Professor Wenfeng Hao, and Professor Ying Luo in collaboration with Dr. Haosen Chen from Beijing Institute of Technology presented a finite element analysis and experimental investigation for detecting and localizing delamination damages in fiber-reinforced composite structures. Specifically, they utilized the wave number method of propagating guided waves to localize and characterize mode I delamination in carbon fiber/epoxy composite laminates. Their work is currently published in the journal, Composite Structures.
In their approach, the authors commenced their research by creating two-dimensional finite element models of composite laminates with delamination. Finite element simulations were carried out to investigate the wave propagation in the created composite laminates at different center frequencies. Moreover, the guided waves were excited at each grid point using non-contact scanning laser doppler vibrometer and actuated by piezoelectric senor. Furthermore, the delamination location was evaluated base on the local wavenumber method. Finally, the feasibility of the developed approach was assessed in two way: first by conducting mode I interlaminar fracture tests using double cantilever beam specimen and secondly by carrying out experimental case studies to verify its applicability.
The authors observed unique mechanisms and variations in guided wave interaction with delamination. For instance, the wave propagation velocity was transformed at the delamination, whereas the wave attenuation and dispersion were directly proportional to the center frequency, that is, it increased with an increase in the center frequency. Nonetheless, the presented local wavenumber method for guided waves was capable of accurately locating and characterizing the delamination damages in composite laminates. The resolution of the damage location could be improved by increasing the center frequency of the excitation signal. It was worth noting that the presented method could be directly applied to the non-destructive testing of composite structures, and its performance could be improved by incorporating efficient analysis methods and advanced hardware facilities.
In a nutshell, the study presented a waveguided method for effective detection and monitoring of delamination damages in composite structures. Based on the results, the presented method proved feasible for cost-effective and efficient location and characterization of delamination damages in composite laminates. In a statement to Advances in Engineering, the authors said their study would enable the development of advanced methods for non-destructive testing of engineering structures.
Zhao, G., Wang, B., Hao, W., Luo, Y., & Chen, H. (2020). Localization and characterization of delamination in laminates using the local wavenumber method. Composite Structures, 238, 111972.