Breaking paths of rice stalks during threshing

During rice threshing, stems are easily broken and usually mixed with the grains, making it difficult for further automatic processing. Thus, in order to improve the efficiency of grain cleaning during harvesting, it is beneficial to reduce the breakages of rice stems. The threshold values of rice stalks in both the transverse and longitudinal directions under tension, compression and bending forces were studied. Based on the real time threshing loads that occur during threshing, the breaking paths of the rice stalks were determined by applying combined loading tests and fracture mechanisms proposed. When subjected to single load, rice stalk is a hard material to break. Tension fracture is the major failure mechanism of the rice internodes that are wrapped with leaf sheath. Combinations of bending & tension or compression & tension can easily break a complete rice stalk or even a cluster of rice straws. Therefore, breaking paths of rice stalks during threshing include the rice stem internodes (with leaf sheath) are easily fractured under the coupling of three-point bending and tension; the stem cores are broken under compression and tension, but the stem nodes are brittle and susceptible to initial damage caused by bending or compression. These findings can help facilitate design of the combine harvesters by assisting with the design of mechanisms that can reduce rice stem breakages during threshing and improve grain stalk separation.