Experimental Study on Basic Physical Parameters and Mechanical Properties of Codonopsis pilosula Seedlings

This research investigates the physical and mechanical properties of Codonopsis pilosula seedlings to provide fundamental mechanical data to address issues like high damage rates and low efficiency in mechanized transplanting. After precise physical parameter measurements, we classified the seedlings into four types: l-type, Y-type, V-type, and W-type. The l-type was the most common, accounting for a large proportion (80.95%) of the total, with a median length of approximately 270 mm, a median diameter of around 5.0 mm, and an average individual weight of about 2.83 g. Freshly harvested seedlings had an average moisture content and density within the typical range for this species. Using the Box–Behnken design method, we determined that the primary and secondary factors affecting tensile force (FN) and tensile strength (σ) were sample diameter (D), sample length (L), and loading speed (V). Sample diameter had a significant impact: FN increased rapidly as the diameter grew, while tensile strength (σ) decreased. The tensile strength of different regions of the seedling (i.e., head, middle, and tail) showed distinct characteristics, with relatively small deviations between theoretical and experimental values. For the whole seedling, errors in tensile force (FN) and strength (σ) between measured and theoretical values were below 5%. The average Young’s modulus, Poisson’s ratio, and shear modulus were also calculated. These mechanical property indices thus provide crucial references for future related research.