Theoretical model and parameter optimization of embryo eggshell perforation under impact

Prior to in-ovo vaccination, the eggshell must be perforated at the air cell region; however, inappropriate perforation parameters can easily cause hole-shape deformation, crack propagation, and shell membrane damage, thereby affecting hatching safety. To obtain low-damage perforation parameters, this study independently designed an impact perforation experimental device for embryo eggs, established a Pogorelov-Griffith bending-fracture coupled model, and optimized punch diameter D, impact velocity V, and impact force F by combining single-factor experiments, three-factor three-level orthogonal experiments, and GA-BP neural network optimization. The mechanical damage score S, constructed from the hole-shape deviation index DI and crack length CL, was used as the primary evaluation indicator, and the effects of the optimized parameters on hatch-of-viable, late embryonic mortality, visible contamination rate, methylene blue penetration, and shell membrane damage were further evaluated through simulated in-ovo manipulation experiments. The results showed that the effects of D, V, and F on S followed the order of "D > V > F". An increase in punch diameter significantly aggravated hole-shape deformation and crack propagation; impact velocity exhibited an optimal window within the range of 2.2-2.3 m/s; and results of impact force tended to stabilize near 1.5-1.6 N. The GA-BP model showed good predictive ability for S, with an overall R² of 0.91 and an RMSE of 0.02. Based on the combined results of mechanical optimization and biological validation, the recommended parameters were D = 2.0 mm, V = 2.25 m/s, and F = 1.6 N. This parameter group had the lowest S, milder dye penetration and shell membrane damage, a lower visible contamination rate, and the highest hatch-of-viable among the perforation-treated groups. This study indicates that S can serve as a mechanical evaluation indicator for screening low-damage perforation parameters, and the recommended parameter window can provide experimental evidence for optimizing eggshell perforation in in-ovo vaccination.