Fig. 6: Signal distribution (amplitude and peak frequency) during the flexural deformation of natural, densified, and TiO2-densified bamboo.

a Natural bamboo. b Densified bamboo. c TiO2-densified bamboo. The gray dashed line in (a–c) divides the amplitude of AE signals into three parts: 30–70, 70–90, and 90–110 dB, respectively. d Proportion of different AE signals representing different fracture mechanisms in the three bamboo materials prior to the point of maximum flexural stress (Red dashed line in a–c).