Fracture type and excitation and detachment forces of Chinese walnuts under dynamic conditions in vibration harvesting

Abstract

Vibration harvesting is a highly effective method for the large-scale mechanised harvesting of walnuts. However, theoretical analysis and study of the detachment force and fracture type under dynamic conditions is lacking in the current research on walnut detachment during vibration harvesting. Here, a theoretical model of walnut motion under applied vibration is established to obtain the relationship between the excitation force and the response frequency and amplitude. A stress analysis of the Chinese walnut fruit is then carried out to determine the fracture type. Dynameter and field harvesting experiments were conducted to verify the theoretical analysis and make further explorations. The results demonstrate the correctness of the formula for calculating the excitation force and verify that the fracture type of walnuts under vibration harvesting is bending fracture. The proposed fracture zone index β is found to be between 0.235 and 0.385. Moreover, using a novel video extraction method, the walnut fruit detachment force was determined to range from approximately 6.2 to 8.4 N. These results provide a reference for choosing vibration parameters and calculating the excitation force.