Intelligent analysis technology of bamboo structure. Part I: The variability of vascular bundles and fiber sheath area

The vascular bundle is the most important structural unit of bamboo that determines the growth of bamboo and the properties of bamboo-based materials. A systematic understanding of the characteristics of vascular bundle is the key to clarify the structure-property relationship of bamboo. In this paper, the YOLO (You Only Look Once) algorithm was applied to the field of bamboo structure and a detection model was proposed to solve the key technical problems regarding automatic detection, positioning, counting, and automatic measurement of relevant parameters of vascular bundles. The precision of the detection model was up to 99.59 %, and able to achieve the work in minutes that cannot be done manually. Furthermore, we studied the variation of inter-plant and the variation of axial direction of Moso bamboo [Phyllostachys edulis (Carr)H. de Lebaie]. The results indicated that the total number of vascular bundles of Moso bamboo from 12 different areas was 7196 ± 698, the distribution density of vascular bundles was 2.49 ± 0.58 per mm2, the fiber volume fraction was 23.68 ± 1.89 %. The apparent differences of vascular bundles in different areas result from the growing environment. There were approximately 8000 vascular bundles in the base of Moso bamboo while the number decreased to around 300 at the top, and the decreased vascular bundles were mainly semi-open type and open type. The total area of fiber sheath decreased linearly from base to top of internodes, while the fiber volume fraction was 20–30 % constantly.