## 3 Results and Discussion
### Results of Shearing Tests and Analysis  
Figure 8 presents the changes of maximum shearing energy consumed and maximum force used in stalk cutting at 15 different cutting points with three differed angles. From the aspect of shearing force, the values of 0\({}^{\circ}\) increased from \(8.5\pm 5.9\) N to \(19.0\pm 3.5\) N, from \(23.0\pm 3.1\) N to \(27.0\pm 6.8\) N in In1 and In3, and the values decreased to \(14.3\pm 2.4\) N from \(17.3\pm 3.5\) N and increased to \(20.7\pm 1.7\) N in In2. The same variation pattern could be observed in the cuts of 15\({}^{\circ}\) and 30\({}^{\circ}\), that is the maximum shearing forces steadily increased as cutting position moving from the top down in In1 and In3, and slightly dropped before rose again in In2. The reason for this trend is that In1 and In3 are both tapered with a narrow top and a wide bottom and In2 is a long cylinder with a hollow inside [17]. As shown in Table 2, it was found that that the cutting angle did not significantly influence the maximum shearing force at any cutting point (\(p<0.05\)). This indicated that in the cutterbar configuration level angle would not affect its maximum shearing force.  
From total shearing energy, it was clear that in each internode the energy consumption increased as cutting point moving towards the bottom of the crop, while the growing speed was faster in In1 and In3 than in In2. For example, the shearing energy of 0\({}^{\circ}\) increased from \(12.6\pm 2.8\) mJ to \(40.0\pm 25.2\) mJ, from \(42.0\pm 22.6\) mJ to \(58.8\pm 3.7\) mJ and from \(62.2\pm 13.0\) mJ to \(85.0\pm 19.3\) mJ in In1, In2 and In3, respectively. Again, this was related to the structure of each internode. Moreover, the significance analysis in Table 2 showed that different cutting angle had obvious influence on the total shearing energy in In2 and In3, but not in In1 (\(p<0.05\)). Also, the shearing energy was greater with larger shearing angle. The reason for this was that stalk cross sectional area of In2 and In3 grew faster than of In1 with increased level angle. As the rice plant is largely deformed when cut by upper cutterbar, it is evident that different shearing angle can have a direct impact on energy consumption. Thus, in the configuration of the cutterbar, it is necessary to adjust level angle according to rice plant deformation. Specifically, the angle can be determined by Equation (5) and Figure 3. For example, for a cutterbar locating at the height in between [\(Y_{i}\), \(Y_{i+1}\)], the corresponding angle should be [\(\theta_{i+1}\), \(\theta_{i}\)].  
Figure 8: Shearing properties variation on whole stalk.  
The shearing speed selected in this experiment was 20 mm\(\cdot\)min\({}^{-1}\) (about 0.33 mm\(\cdot\)s\({}^{-1}\)), much smaller than the actual speed used in rice harvesters (about 1500-2000 mm\(\cdot\)s\({}^{-1}\)) [19]. Two reasons for the speed selection were: (1) more accurate and detailed data can be obtained through a quasi-static shearing process; and (2) though some of the shearing properties may change under different shearing speed, their variation patterns are similar and can still provide baseline information to increase cutterbar working efficiency. However, shearing tests under actual shearing speed are still necessary to be studied to gain a full understanding of the shearing process and to provide more information for harvester cutterbar configuration.