In order to analysis relationship between mechanical properties and microstructure of tangled forage stems, then to provide guidance for breeding fine varieties and designing new herbage haverster, four kinds of stems at fruiting stage of perennial forage legumes (Medicago sativa lower cellulose, Erect crownvetch strain and Medicago sativa Gannong No. 3, Creeping type crownvetch) were chosen to perform the tensile and shear tests by the electronic testing machine CMT2502. The microstructure of forage stems was observed, and the SEM images of transverse and longitudinal section of forage stem were got by scanning electron microscopy. The results show that forage stem is a typical kind of porous, no-continuous, no-homogeneous and anisotropic composite material. Forage stems have enough strength and good flexibility, and its strength depends on the thickness of thick-walled cells and the numbers of vascular bundles, as well as the connection form and strength of cells in stems. The average Young's modulus of forage stems in the 4 species are 1 427.3、 673.0、 1 377.5、 441.7 Mpa, respectively; The average maximum shearing stress with the slippery angle of 30° are 96.24、 60.9、 124.1、 84.4 N, respectively. The new species of Medicago sativa lower cellulose and Erect crownvetch strain were easier for mechanical harvesting because of high strength, low flexibility and less shearing force.%为分析缠结牧草茎秆力学性能与显微结构的相互关系,进而指导牧草品种优育和设计开发新机具、新工艺提供理论依据,该文以2种新育品系低纤维苜蓿、直立型小冠花和对照品种甘农三号苜蓿、匍匐型小冠花结荚期底部茎秆为研究对象,在500 N微机控制电子万能试验机上测试了茎秆的拉伸和剪切应力—应变规律；试验观察了茎秆的微观组织结构,得到了茎秆扫描电镜下的解剖构造图像.研究表明:牧草茎秆是一种典型的多相、筛状、不连续、不均匀和各向异性的复合材料;同一品系不同品种牧草茎秆生物力学特性不同,其强度和刚度主要取决于各自机械组织的厚度、维管束的数量以及各组织及其细胞之间的连接形式和连接强度.4种牧草结荚期拉伸试验测得平均弹性模量分别是1427.3、673.0、1377.5、441.7 Mpa; 30°滑切试验测得平均最大剪切力分别是96.24、60.9、124.1、84.4 N,2种新品系牧草结荚期茎秆均比对照品种刚度大,柔韧性小,需剪切力小,更易机械化收获.
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