Cracking stress origin in round bamboo at tissue and cellular scales: computer-assisted vascular bundle identification

Bamboo is prone to cracking during harvesting, storage, and service due to moisture-induced stress, which limits its practical application. Ascertaining the causes of bamboo cracking is critical for addressing bamboo cracking defects. In this study, a computer-assisted vascular bundle recognition programme was proposed to investigate the cracking stress of bamboo. The results show that the average shrinkage rate of vascular bundle tissue is 11% higher than that of parenchyma tissue, and the imbalance in shrinkage proportions between the two tissues leads to cracking stress exerted by vascular bundle tissue on the surrounding parenchyma tissue. The radial gradient in vascular bundle tissue results in a progressive decrease in cracking stress from the outer to the inner surface of the bamboo. Furthermore, the greater hygroscopicity of parenchyma cells leads to larger variations in moisture content as environmental humidity changes, thereby promoting the development of cracking stress at the cellular level. Bamboo fibres, by contrast, possess low porosity and high cell wall density, conferring superior resistance to crack initiation and propagation.