Fig. 5: Representative damage modes and real-time acoustic emission (AE) peak frequency signals in natural, densified, and TiO₂-densified bamboo.

a Schematic diagram of AE set-up. b AE signal characteristics. c AE signals of tensile fracture of single bamboo fiber with the identified Type I and Type III signals in red and green highlight. d AE signals of natural bamboo flexural process with the identified Type II signals in yellow highlight. e AE signals of densified bamboo flexural process with the identified Type IV signals in purple. f AE signals of TiO₂ densified bamboo flexural process with classification of four types of signals. g Classification of AE signals. To clarify the signal classification, all types of signals are only highlighted in (f).