土壤高速流变凿削耦合行为下摆式犁体长切削寿命调控机理及实现新方法

Horizontally Reversible Plough (HRP) is an important kind of High-speed mouldboard ploughs, and plowshank and plowtip of HRP take the greatest responsibility for tillage. It is demonstrated in field conditions that the service life of HRP is strongly associated with plough failures on the plowshank and plowtip zones. This is basically due to high-speed soil rheology and hence a challenging issue in agricultural engineering. Our previous experimental evidences have validated that the peak cutting temeperatures during HRP tillage appear at the locations close to plowshank and plowtip,i.e the severest plow-failure zones.This may be sufficiently related to soil coupling actions and furrow failure. In this regard, we presume that the foregoing cutting temperature decrease may delay the plow-failure and hence offer HRP life extension, which, however, has not been investigated so far. Therefore this study concentrates on the issue. To achieve this, we shall try embedding heat pipes into the plowshank and plowship zones to decrease the highest temperatures.The main objectives of this study are to investigate soil rheology, flow behaviours and soil-tool interaction to determine the crucial factors on furrow failure, explore the relationship between the peak cutting temperature and the severest wear land at the plowshank and plowship zones, clarify how the heat pipes control the furrows at plowshank and plowtip, and obtain the optimum operation parameters as well as the best configurations and shapes of HRP. The obtained research results will give the great significances for both high-speed plow life extensions and safe foodstuff-supplying in China.

摆式犁体是高速铧式犁重要的耕作部件，铧尖/胫刃是摆式犁体最关键的作业部位。铧尖/胫刃区由于土壤高速流变凿削耦合作用诱发的耕犁损伤，已严重影响犁体的切削寿命，是业内一挑战性课题。我们前期研究发现，铧尖/胫刃区作业温度最高，影响土壤流变对犁体的凿削行为，与犁体的耕犁损伤程度密切相关；推测“降低铧尖/胫刃区作业温度，可减小土壤流变对损伤区的凿削耦合作用，能延长犁体切削寿命“，但这在以往的基础研究中并未受到足够重视。本项目将致力于这方面一系列问题的研究，率先提出在损伤区植入热管，借助相变传热降低其作业温度；主要内容包括：土壤高速流变凿削条件下，影响犁体切削寿命耕犁损伤的程度和机理；犁体损伤区耕犁损伤程度与其最高作业温度的关联性；热管对损伤区最高作业温度的调控机制；植有热管的犁体最佳组合工作参数和最优犁体结构。从理论-实践角度阐明机理，验证预测，研究结果对提高我国高速铧式犁的耕作寿命具有实际意义。

本项目以摆式犁体为研究对象，从摆式犁体作业温度与其使用性能、耕作寿命相互依赖关系角度，首次将热管相变传热理论全面引入到，减小高速梭式耕作条件下犁体耕犁损伤程度的思想中，并以此为核心展开研究。主要进展与成果归结为以下四个方面：1）依据土壤物化特性，建立了土壤力学模型；采用流体动力学（CFD）数值计算和扫描电子显微镜（SEM）相结合的方法，研究了复杂外场、不同性状土壤和工况条件下，土壤粘塑性流态行为与犁体面细观力学作用过程，揭示了摆式犁体犁铧铧尖区、犁胸胫刃区耕犁损伤的力学机制。2）依据经典 Jaeger 移动热源理论思想，采用瞬态线性热源解析方法，揭示了铧尖/胫刃区─土壤热量分配机理；基于土壤切削机制，引入金属切削理论思想，搭建了土壤-犁体热密度实验测试研究平台，并依据反求热传系数法，首次测得了不同类型土壤-犁体的热量分配系数；并进一步采用热流固耦合计算的方法，研究了不同性状土壤和工况条件下，铧尖/胫刃区温度场分布及变化状况，阐明了铧尖/胫刃区局部作业高温与其耕犁损伤程度的关联性。3）搭建了热管特征参数试验测试平台，确定了热管等价导热系数，等价比热以及等价密度等特性运行参数；建立了犁体热分析模型，采用有限元方法，研究复杂外场、不同工况土壤条件下，植有热管的铧尖/胫刃区温度场分布及变化，揭示了热管对铧尖/胫刃区局部作业高温的调控机制。4）构建了摆式犁三维实体几何模型，采用了牛顿拉夫森迭代算法程序、有限元分析模型以及扫描电子显微镜(SEM)实验测试等相结合的方法，确定了植入犁体热管的蒸发段与热源的最佳距离、热管最优截面形状及结构参数，获得了新型摆式犁体结构；并以此制造出新型犁体，进行田间试验，证实“降低胫刃/铧尖区作业温度，减小土壤流变对损伤区的扰动凿削作用”是延长犁体切削寿命的新方法。