Structural analysis on cutting notch of tea stalk by X-ray micro-computed tomography

Abstract

Quantitative analysis on cutting notch of tea stalk is one method to better understand shear resistance and mechanical properties of the stalk, which could improve cutting performance and efficiency for tea harvesting. Optimal design of the cutter might be achieved through structural analysis of cutting notch by X-ray micro-computed tomography (micro-CT). The third inter-node of the stalks were sampled and scanned by micro-CT after they were cut at different cutting depths (0.7, 1.5, 2.3 mm) and cutting edge angles of cutter (30°, 35°, 40°). The structural change of the cutting notch and cutting force was observed. Grey-scale histogram analysis and bimodal segmentation method were used to extract the information about cutting notch from 2D slice images. A 3D model of the stalk was established with reconstruction and volume rendering. Besides, maximum cross-sectional area ratio of cutting notch (MCSARCN) and volume ratio of cutting notch (VRCN) were calculated. The results show that MCSARCN and VRCN had a closely relationship with the cutting force, cutting depth and cutting edge angle according to 3D tomographic images and 2D slice images. Both MCSARCN and VRCN increased with cutting depth, despite of cutting edge angle. For cutting edge angle of 30°, 35° and 40° at different cutting depths, MCSARCN increased from 4.89% to 9.47%, from 8.51% to 22.83% and from 4.30% to 16.87%, respectively. Meanwhile, VRCN increased from 1.59% to 2.13%, from 2.98% to 5.76% and from 3.04% to 5.01%, respectively. When cutting depth was 1.5 mm, cutting force increased but VRCN present a decreased trend with cutting edge angle. X-ray micro-CT could be used to analyze the structure on cutting notch of tea stalks which is helpful in optimizing the structural parameters of the cutter.