## 1 Introduction  
The stubble after the harvesting of main crop rice can grow again and give a second production which is called ratoon crop rice. The economic advantages of rice ratooning are the low production cost, short duration and better quality, while the primary barrier to its further popularization is the low yield [1]. Though studies have reported the agronomical techniques to improve ratoon crop yield, such as variety screening, fertilizer management [2], stubble height control [3], harvest time selection [4], etc., its yield is still highly limited by the harvesting of main crop rice [5]. Currently, the main crop rice is harvested by low-efficient and expensive manpower, or by conventional harvesters with a high stubble rolling rate (40-50%) used in single or double cropping rice [6]. A double-cutterbar harvester with a wide header is an alternative method to address this issue. When aiming to develop an efficient double-cutterbar structure for main crop rice harvesting, rice plant deformation and shearing properties should be tested and analyzed to provide the baseline for the structure configuration. There are two requirements of main crop rice harvesting to obtain a better ratoon season yield [7]: (1) control the height of stubble (around 300-400 mm) left in the field according to the agronomic requirements, which are mainly decided by rice species and harvest time; (2) reduce the stubble rolling rate (the ratio of the width of two caterpillars to harvest width) as the nodal buds on the stubble can hardly generate rice tillers once damaged by the caterpillar. Based on the requirements mentioned above, several main crop rice harvesters have been designed and tested. For example, [PERSON] et al. (2016) designed a main crop rice head spike harvester using a transplanter chassis with narrow wheels. This one-cutterbar harvester only harvests panicles with partial stalks and has a stubble rolling rate of 25.15%, but the spikes harvested must be processed additionally and the machine's working efficiency was only 0.24 h\(\cdot\)h\({}^{-1}\)[8]. [PERSON] et al. (2017) proposed a wide header (2.55 m) harvester to reduce the stubble rolling rate during main crop rice harvesting. Though this machine reduced the rolling rate to 27.5%, its working efficiency, only 0.13 h\(\cdot\)h\({}^{-1}\), could not meet the practical demand [9]. It is obvious that though widening the harvest width could directly decrease the stubble rolling rate, it also brings in more input material in a specific time, which causes the inevitable size enlargement or working speed slowdown of harvesters. A special double-cutterbar structure shown in Figure 1 is a potential method to address the aforementioned issue. The structure comprises an upper cutterbar and a lower cutterbar. The upper cutterbar installed on the header frame can lower the straw-grain ratio by reducing the stalk length on the panicle. The function of the lower one is to cut the remain plant again to have the stubble height as required. Taking the respective advantages of the double-cutterbar structure and the wide header, it is feasible to design an efficient main crop rice harvester with low stubble rolling rate. To implement the functions of the two cutterbars, it is necessary to configurate the cutterbars according to the rice plant deformation during harvesting. In the past, plenty of studies were carried out on the measurement of stalk crop deformation calculation properties. [PERSON] et al. (2004) calculated the bending stress and the modulus of elasticity of sunflower stalks using the bending forces measured by a cantilever test in the field [10]. [PERSON] et al. (2009) measured the bending stress and modulus of elasticity of wheat stem and found these parameters increased as the moisture content decreased and decreased as the cutting height of stem increased [11]. [PERSON] and [PERSON] (1998) studied the bending properties of sorghum stalks under quasi-static deformation at different growing stage using a universal testing machine [12].