关键词: 紫云英, 力学性能, 脱粒, 碰撞, 损伤

Abstract:  Astragalus sinicus (Chinese milkvetch) is one of the main rotation crops in rice field in the south of China, and also an important forage or green manure crop. During the fallwinter season and land fallow period, planting green manure could increase content of soil organic matter. This improves soil fertility and renews soil production. It plays a vital role not only in the sustainable development of agriculture, crop industry and grain quantitative safety, but also the sustainable development of environment, food qualitative safety and human health. In recent years, with the rapid growth of Astragalus sinicus planting area in China, Astragalus sinicus harvesting mechanization technology and equipment requirement have increased rapidly. The research on Astragalus sinicus mechanized harvesting technology appeared relatively late in China. Naturally, the refitted Astragalus sinicus harvesters from rice combine harvesters were used. The refitted Astragalus sinicus harvesters have inadequate stable performance due to the lack of special harvesters. Limited design of the key components also lacked supporting essential theory. The previous researches on mechanical properties and collision mechanism of grain seeds have mostly focused on big crop seeds, but Astragalus sinicus seeds have been rarely studied. In this research, from Contactimpact view, the surface compression mechanical properties of Astragalus sinicus seeds were measured, and the analysis on collision mechanism was explored during fullfeeding Astragalus sinicus threshing. The study found that the central deformation increased linearly with the increase of the pressure load. The central deformation changed a little slower under low pressure load. The distribution function of the maximum stress and the central deformation were derived during Astragalus sinicus threshing process. In the early stages of collision, the maximum stress of Astragalus sinicus seeds increased sharply when the central deformation increased. On the contrary the maximum stress changed gradually in the late stages. The relatively velocity function between the Astragalus sinicus seed and the threshing spiketooth was established. The critical approaching speed between them was obtained when damage occurred to Astragalus sinicus seeds during threshing. Through the theoretical analysis and calculation, the critical approaching speed was 27.31 m/s when damage occurred to Astragalus sinicus seeds during threshing. This means that the critical threshing speed was faster than 32 m/s when the broken rate of Astragalus sinicus seeds increased significantly. In this experiment, a typical Astragalus sinicus in Hefei District, Anhui Province, China, Yijiangli was selected as the experimental object. The average moisture content of Astragalus sinicus seeds was around 9.45% at harvesting stage. The data of Astragalus sinicus seeds in the test field were as follows: the average elastic modulus at length direction was 441.75 MPa, and the average ultimate strength was 189.24 MPa. The research also obtained the variation curve of the threshing rate and the broken rate with the threshing speed. According to experimental verification, the threshing speed was controlled less than 25 m/s in practical application, the indexes of Astragalus sinicus threshing could reach excellent performance. The threshing rate was more than 99.5%, and the broken rate was less than 0.33% when the threshing speed was 25 m/s. The research provided a theoretical foundation for further exploring the damage mechanism in Astragalus sinicus harvesting, and it also provided technological support for the design and optimization of Astragalus sinicus threshing.

Key words:  Astragalus sinicus, mechanical properties, threshing, impact, damage