Three-dimensional structural characterization and mechanical properties of bamboo parenchyma tissue

Bamboo is predominantly composed of parenchyma and fibers, with parenchyma constituting approximately 52% of the bamboo culm wall. The bamboo fibers function as the primary load-bearing elements, its structure and performance have been studied in detail. However, investigations concerning the structure and mechanical properties of parenchyma tissue remain limited. Consequently, this study focuses on the comprehensive characterization of the three-dimensional (3D) structure of bamboo parenchyma. Additionally, the study encompasses the evaluation of tensile and compressive properties of parenchyma tissue, along with an analysis and discourse on failure mechanisms. Parenchyma cells can be categorized into two types: long cells, accounting for approximately 89.37%, and short cells. The measured tensile strength and elastic modulus of the parenchyma tissue are 48.81 MPa and 706.48 MPa, respectively. The propagation of cracks leading to tensile failure predominantly occurs along the middle lamella, accompanied by partial penetration through cell walls. Concerning parenchyma tissue compression, three discernible stages can be identified: the elastic stage, plateau stage, and densification stage. The axial load-bearing capacity of parenchyma tissue exceeds that of the tangential and radial orientations. Axial compressive strength and elastic modulus of the parenchyma are measured at 18.82 MPa and 5.24 GPa, respectively. Compression failure modes in parenchyma tissue encompass compression bending and cell fracture, shear failure of the middle lamella, and detachment and debonding of the cell wall. The comprehensive structural and mechanical parameters derived from this investigation provide valuable insights for the development of numerical models and understanding the various mechanical properties of bamboo.