Health monitoring of timber beams retrofitted with carbon fiber composites via the acoustic emission technique

This paper proposes a methodology for monitoring of timber beams retrofitted with CFRP (Carbon Fiber Reinforced Polymer) via the acoustic emission technique (AE). The work proposes the use of multi-resonant sensors linearly distributed along the element. The spectral energy of the located AE events is proposed to separate the signals into two groups, depending on the predominant frequency band, between two resonant bands of the used sensor. To avoid the influence of the attenuation, the spectral energy is corrected by the attenuation curves empirically determined. By means of bending tests on beams with two retrofitting layouts, it is demonstrated how the signals grouped into the high-frequency group are located at the areas where the final CFRP-wood delamination took place or where the final failure of the element is concentrated. This result is very promising for health monitoring of retrofitted timber elements in real scenarios.