Виявлення закономірностей руйнування шкаралупи волоського горіха при комбінованому навантаженні в системі із зворотно-поворотним жорном

This study explores the process of shell fracture in a locally cultivated walnut variety in a reciprocating millstone setup that implements combined compression, shear, and torsion loading. The task addressed is to enable cracking across the entire shell surface while maintaining kernel integrity, which determines the yield of marketable produce. In the first stage, shell fracture forces were experimentally determined under localized loading from a natural cleft and a whole shell, followed by statistical processing using a two-parameter Weibull distribution. It was found that fracture from the cleft side occurs at lower loads than from the whole shell side, confirming the anisotropy of the shell's mechanical properties. In the second stage, the effect of roughness pitches of 10, 13, and 16 mm on the fracture force was studied. Experiments have shown that at a 10 mm pitch, fracture occurs with the lowest force; increasing the pitch to 13 and 16 mm increases the fracture force due to a decrease in local stress concentration. A comparison of the two experimental stages revealed that the geometry of the working surfaces determines the conditions for fracture without changing the general pattern: when loading from a natural cleft, lower forces are required. For a fracture probability of at least 0.95 for any nut orientation, a load of approximately 350 N is required. Additionally, the strength characteristics of the kernel were determined using an ST-2 structure analyzer; the average fracture force under direct loading is approximately 1200 grams (≈ 120 N). The results provide a mechanically sound basis for selecting the parameters of the working parts of a nut cracking machine and a safe range of operating loads