穴盘水稻秧苗茎秆蠕变与应力松弛特性的试验研究  

Experimental study on characteristics of creep and stress relaxation for rice seedling stem raised in cell tray

作　　者：马瑞峻[1,2] 萧金庆 郑普峰 张亚丽 陈瑜 邱志[1,2] Ma Ruijun;Xiao Jinqing;Zheng Pufeng;Zhang Yali;Chen Yu;Qiu Zhi(College of Engineering,South China Agricultural University,Guangzhou 510642,China;Engineering Research Center of Guangdong for Rice Transplanting Technology and Equipment,Guangzhou 510642,China)

机构地区：[1]华南农业大学工程学院,广州510642 [2]广东省水稻移栽机械装备工程技术研究中心,广州510642

出　　处：《农业工程学报》2018年第13期43-53,共11页Transactions of the Chinese Society of Agricultural Engineering

基　　金：国家自然科学基金项目(31471418);广东省公益研究与能力建设项目(2014A020208105;2014A020208018)

摘　　要：为深入了解穴盘水稻秧苗茎秆拉伸过程中的力学特性,该文利用微控电子万能试验机对穴盘水稻秧苗茎秆常规拉伸、蠕变与应力松弛特性进行测试与分析。试验表明:常规拉伸一般有2次断裂,1次断裂前,应力-应变为线性关系,没有明显的屈服过程,且平均断裂应力大小随加载速率的增加而呈线性增加;拉伸蠕变和应力松弛过程分别利用伯格斯四元件模型和麦克斯韦五元件模型进行描述。通过对曲线进行拟合,得到相关的模型参数,基于选用的流变模型和本构方程,结合秧苗茎秆的生物体特点,分别对蠕变速率、蠕变柔量和应力松弛速率、应力松弛时间进行分析,结果表明:蠕变和应力松弛过程都是弹性动力与黏滞阻力之间彼此牵制的过程;蠕变过程产生与蠕变时间和初始应力呈正相关的塑性应变,应力松弛过程导致茎秆大分子链发生变化,均对秧苗茎秆造成一定损伤;秧苗茎秆内部含有柔嫩与粗壮2种组织结构。研究结果可为秧苗机械拔取的损伤评估和相关仿真分析提供参考。In order to understand the mechanical property of rice seedlings stem raised in cell tray in the stretching process, the general tensile, creep and stress relaxation property of rice seedlings stem were tested with JK-100 KE micro-control electronic universal testing machine（UTM） and analyzed. The test variety of rice was Huahang No.31, planting in plastic cell tray in the field in Qilin North of South China Agricultural University. After growing for 25 days in the field, the seedlings had 3 to 5 leaves, and the seedlings with straight stalks and good growth were selected for the experiment. In experiment process, two ends of seedling stem samples were fixed in upper and lower clamps of the UTM respectively, and the original distance between 2 clamps was 20 mm. The frequency of data acquisition was 1/s. In the general tensile test, the loading rates were 2, 4, 6, 8, 10 and 12 mm/min, respectively, and 20 repetitions were carried out under each loading rate. In the creep test, the loading speed was 0.1 N/s. When the stress reached about 1.5 MPa, the stress began to be maintained, the test was ended after being maintained for 1 200 s, and the tensile creep curve of the seedling stem was obtained. The creep test was repeated 20 times. In the stress relaxation test, the loading speed was 0.6 mm/min. When the strain reached about 2.5%, the strain began to be maintained. The test was ended after being maintained for 1 200 s, and the tensile stress relaxation curve of the seedling stem was obtained. The stress relaxation test was repeated 20 times. The results of general tensile test showed that the seedling stalks usually ruptured 2 times due to the structural features of the covering leaf sheath. And before the first rupture, the stress-strain curve was linear. The fracture strain was 5.2%-9.6%, the fracture stress was 3.1-7.3 MPa, and the modulus of elasticity was 0.46-0.93 MPa. And the average fracture stress increased linearly with the increase of loading rate. In this study, the tension creep and stress relaxa

关 键 词：蠕变 黏弹性 流变 水稻秧苗 应力松弛 常规拉伸 本构方程 

分 类 号：O341[理学—固体力学] S511[理学—力学]