Characterization of walnut shell crushing under multi-point loading based on numerical simulation

Nuts are widely consumed nutrient-dense foods requiring efficient shelling for quality preservation. Walnuts represent an ideal model for nut-cracking studies due to their characteristic shell structure and mechanical properties. understanding walnut shell fracture mechanisms requires investigation of internal mechanical properties; however, traditional experimental methods often fail to accurately capture stress evolution under real loading conditions. Therefore, this study adopts a finite-discrete element method (FDEM) combined with cohesive elements to construct a numerical model of the walnut shell, aiming to analyze the stress transfer mechanism on the surface of the walnut shell. This study introduces a non-uniform distribution coefficient to describe the stress distribution characteristics on the surface of the walnut shell under multi-point loading conditions and delves into the impact of loading positions and the number of loading points on the crushing characteristics of the walnut shell, thereby revealing the cracking mechanism of the walnut shell under multi-point loading. The research results show that the internal stress distribution within the walnut shell exhibits significant non-uniformity under different loading conditions. Especially under four-point loading with a non-uniform distribution coefficient of 0.92, the number of stress concentration points on the surface of the walnut shell is significantly higher than other loading methods. These results demonstrate that walnut shell failure primarily stems from tensile stress amplification at weak zones (e.g., suture lines), not shear. The validated model achieves 98.1 % accuracy against device tests, showing that optimized four-point loading maximizes fragmentation.