树枝直刃剪切数学模型与试验

【目的】基于材料力学和弹性地基梁理论对直刃刀片剪切树枝过程进行理论建模,并根据该模型计算出直刃刀片剪切树枝所受的剪切力。【方法】以石硖品种龙眼树枝为试验材料,利用万能材料试验机和摩擦试验台等仪器测定龙眼树枝的相关力学特性参数和滑动摩擦因数,测量并用模型计算树枝不同含水率(w)、直径和不同刀片刃角下动刀片剪切龙眼树枝的峰值剪切力,剪切试验所用刀具的刃角分别为10°、20°和30°。【结果】当树枝直径为20.4 mm、相对含水率为76%、刀片刃角为20°时,刀片剪切力理论计算曲线与试验曲线趋势一致,峰值剪切力的误差约为2.3%;当树枝直径为15.3 mm,刀片刃角为20°,且树枝含水率大于纤维饱和点(30%)时,刀片峰值剪切力随含水率升高而增大,计算值在试验值的误差范围内;当树枝直径为24.6 mm、含水率为76%,且刀片刃角从10°增大到30°时,峰值剪切力显著增大,计算值处于试验值的误差范围内。【结论】该理论模型可用于预测剪切力并分析不同力学参数对峰值剪切力的影响,为修剪机具剪切机构的设计和优化提供参考。

Development and verification of a mathematical model of straight blade cutting longan branches

Objective]To model the process of straight blade cutting longan branches based on material mechanics and elastic foundation beam theory, and to calculate the shearing force of branches from the straight blade cutting using the model. Method]Shixia longan branches were used as test materials. The mechanical parameters of the branches and the coefficient of friction between the branch and blade were measured using a universal material test machine and a custom friction tester. The peak shearing forces were measured by the universal material testing machine and also calculated by the developed model un-der conditions of different branch moisture contents ( M) , branch diameters ( d) and blade bevel angles (θ) . The blade used in the cutting tests had a bevel angle of 10 ° , 20 ° or 30 ° .Result]When M=76%, d=20. 4 mm and θ=20 ° , the calculated curve showed the same trend as the curve derived from the ex-perimental results, and the error of the peak shearing force was around 2. 3%. When d=15. 3 mm,θ=20° and M >30% which was the fiber saturation point, the peak shearing force increased with the incre-ment of M and calculated values were within the error ranges of the experimental data. When M=76%, d=24. 6 mm and θ increased from 10 ° to 30 ° , the peak shearing force increased significantly and the calculated values were also within the error ranges of the experimental data.Conclusion]The model can be used to estimate the shearing force and investigate the effects of different mechanical parameters on the peak shearing force. The results will provide theoretical reference for the design and optimization of prun-ing machines.