Abstract: In order to clarify the influence of impact load on damage and fracture characteristics of walnut during primary processing, in this paper, based on the continuum damage theory, the existence of damage was first proved by uniaxial compression test. Then, the damage and fracture models of walnut were established by single impact and repeated impact loading tests using the drop hammer impact test bench. Finally, the influence of walnut size between 30mm and 44mm on model characteristic parameters was discussed. The results showed that the damage accumulation coefficient was the minimum value 3.89 when the walnut size was 35mm, when the walnut size was 30mm, the threshold energy required for cracking was 4.74J/kg. The walnut fracture was caused by the damage of walnut. The energy threshold is the judgment standard for walnut crack generation, and the damage accumulation coefficient quantifies the damage resistance ability of walnut. The threshold energy is linearly with the increase in the walnut size. The relationship between the walnut size and damage accumulation coefficient conforms to polynomial function. The results are helpful to control walnut fracture during primary processing.

Key words: walnut, size effect, physical characteristics, damage fracture, agricutural product processing

摘要： 为明晰核桃在初加工过程中冲击载荷对其损伤断裂特性的影响，基于连续介质损伤理论，首先通过单轴压缩试验证明损伤的存在，然后使用落锤冲击试验台开展单次冲击和反复冲击加载试验，分别建立核桃损伤和断裂模型，最后探讨核桃尺寸在30~44mm区间时对模型特征参数的影响。结果表明：核桃尺寸为35mm时，损伤累积系数为最小值3.89；核桃尺寸为30mm时，产生裂纹需要阈值能量为4.74J/kg。核桃损伤是其发生断裂的成因。能量阈值是核桃裂纹产生的判定标准，损伤累积系数量化核桃抵抗损伤的能力，核桃尺寸与能量阈值和损伤累积系数分别满足线性关系和多项式关系。研究结果有助于在初加工过程中对核桃损伤断裂进行调控。

关键词: 核桃, 尺寸效应, 物理特性, 损伤断裂, 农产品加工