冲击载荷下谷物籽粒裂碎机理及数值模型构建方法

The impact load is the main cause of grain cracking in harvesting, processing and other links. However, the mechanism for the crack or the breaking of grain, especially crack initiation,propagation model,impact energy threshold and fracture model of grain are not clear. In this project, the impact test platform will be completed, which using electromagnetic induction principle to accelerate impact body. And some guiding theories will be used, including agricultural material science, Hertz contact mechanics, fracture mechanics and so on, which focus on the broken process of grain under impact. Meanwhile, the single grain impact test will be completed by the combination of the scanning electron microscope, the Micro-CT image analysis, the high-speed photography and the discrete element numerical simulation. In future, the origin and propagation mechanism of grain cracks under impact will be elucidated from macroscopic and microscopic perspectives. And the functional relationship between fragmentation threshold,grain properties and impact conditions will be established. Meanwhile, the impact data under different impact conditions, the similarity criterion, Weibull statistics and powder engineering principle will be used to build the numerical model of breaking probability and breaking degree of grain. And the comprehensive value of impact resistance of grain will be refined through above numerical model. In summary, the grain fragmentation theory and the fragmentation model under impact will be eventually established in this project. Overall, the research results provide a theoretical basis for the design and optimization of the key working parts of the equipment such as grain harvesting and processing, and enrich the basic theories and methods of the research on the characteristics of agricultural granular materials.

收获加工等环节中冲击载荷是导致谷粒裂碎的主因，然而谷粒裂纹及破碎的机制，特别是谷粒裂纹扩展模式、冲击能阈值和破碎模型尚不清楚。本项目以电磁加速冲击试验为研究切入点，融合高速摄像、Micro-CT图像分析、电镜扫描观测和离散元数值模拟等测量技术，以农业物料学、赫兹接触和断裂力学等理论为指导，分析单谷粒冲击裂碎过程，从宏观和微观角度阐明谷粒在冲击载荷下的裂纹源起、形成和扩展机制，获取冲击能与谷粒属性和冲击条件间函数关系。采用不同冲击条件下谷粒裂碎数据，同时结合相似准则、威布尔统计和粉体工程原理构建谷粒冲击破碎概率和破碎程度数值模型，提炼谷粒抗冲击破碎综合值，建立冲击载荷下谷粒裂碎理论及数值模型表征方法。研究结果对谷物收获加工等装备关键工作部件设计及工艺优化提供理论依据，丰富农业散粒体物料特性研究的基础理论与方法。

从“田间到餐桌”流通环节中，谷物易受机械冲击载荷而破碎。项目以谷物冲击破碎行为为切入点，自主搭建、升级和改造基于电磁加速原理的冲击试验台；通过试验探究冲击速度、尺寸和含水率等属性参数对谷物破碎的影响，分析谷物破碎模式，结合破碎概率模型获取能量阈值和临界冲击速度；采用离散元法和有限元法模拟冲击体与谷物的冲击过程，探究谷物受到冲击载荷后的破碎响应；通过压缩试验探究谷物性参数对其力学性能的影响，对比分析谷物承受冲击载荷和静态载荷的破碎行为差异和联系。基于上述研究内容，项目总结了如下开创性研究成果：（1）建立谷物冲击破碎的试验和模拟方法，探究谷物在冲击动载荷和准静态载荷下的破碎过程及裂纹演化规律，明晰谷物破碎机理。（2）建立谷物破碎概率模型，为农业物料的破碎条件确定提供指导。研究结果对谷物收获加工等装备设计优化提供理论依据，丰富农业物料特性研究的基础理论。