Bending Deformation and Inclination Angle Variation of Pepper Leaves at Different Growth Stages Under Droplet Impact

Investigating the dynamic response of pepper leaves at different growth stages under droplet impact is of great significance for optimizing spray deposition processes. In this study, high-speed imaging combined with mechanical modeling was employed to systematically analyze the inclination angle variation and bending deformation behavior of pepper leaves at the seedling, flowering, and fruiting stages under droplet impact. The temporal evolution of petiole inclination angle and leaf blade inclination angle under different impact velocities and impact positions was investigated, and the energy transfer mechanism of bending energy during droplet impact was quantitatively analyzed. The results showed that pepper leaves exhibited a typical damped oscillation response after droplet impact. As the droplet impact velocity increased, the degree of leaf deformation increased significantly and the vibration duration was prolonged markedly. When the impact velocity increased from 0.89 to 1.53 m s−1, the maximum vertical displacement (Δhmax) near the leaf tip increased from 0.8 to 1.9 mm at the seedling stage, from 0.6 to 3.1 mm at the flowering stage, and from 1.2 to 4.5 mm at the fruiting stage. Along the leaf length direction, both the maximum inclination angle variation and vertical displacement gradually increased from the near-petiole region toward the near-tip region because of reduced local stiffness and weaker structural constraints. In contrast, the maximum inclination angle variation generally decreased with increasing growth stage, mainly due to the increase in leaf mass and enhanced structural support. Based on the bending energy model, the conversion of droplet kinetic energy into leaf structural deformation energy was further analyzed. The results demonstrated that the bending energy of leaves increased significantly with increasing droplet impact velocity. When the droplet kinetic energy increased from 3.4 μJ to 8.0 μJ, the maximum bending energy increased from 0.063 μJ to 0.21 μJ. Among different regions, the near-tip area exhibited the highest bending energy response because of its higher flexibility and lower bending stiffness. These findings provide new insights into the interaction mechanism between droplets and flexible leaves and offer a theoretical basis for improving spray deposition efficiency and optimizing spraying strategies for pepper plants at different growth stages.