| 籽棉压缩与应力松弛力学特性及模型构建 |
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| 引用本文： | 孔凡婷,吴腾,陈长林,孙勇飞,谢庆,石磊.籽棉压缩与应力松弛力学特性及模型构建[J].农业工程学报,2021,37(7):53-60. |
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| 作者姓名： | 孔凡婷 吴腾 陈长林 孙勇飞 谢庆 石磊 |
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| 作者单位： | 农业农村部南京农业机械化研究所，南京 210014 |
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| 基金项目： | 江苏省农业科技自主创新资金项目（CX(18)3046）；中央级公益性科学研究院所基本科研业务费专项（S202014）；中央级公益性科学研究院所重点任务-粮棉油收获（15创新-2002） |
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| 摘 要： | 为深入研究籽棉压缩及应力松弛过程的力学特性并构建其本构模型,该研究以籽棉为研究对象开展试验,分别利用改进西原模型和五元件广义Maxwell模型对压缩和应力松弛的应力应变曲线进行描述。通过定义的本构模型对不同含水率及喂入量的籽棉力学特性试验数据结果进行参数辨识,得到相关模型参数,并探究不同因素对压缩及松弛过程应力的影响规律。研究结果表明:曲线拟合法求解籽棉压缩及应力松弛过程本构模型参数的决定系数均大于0.9,改进西原模型、五元件广义Maxwell模型可以较好地描述籽棉压缩力学特性和应力松弛特性。对籽棉压缩及应力松弛力学特性解析显示,模型参数表现出明显的应力规律:通过Duncan均值比较结果可知:籽棉压缩本构模型参数中不同含水率组间弹性模量差异均显著(P0.05),不同喂入量组间串联虎克体弹性模量差异显著(P0.05),压缩应力值与含水率、喂入量呈正相关关系;籽棉应力松弛模型参数中不同含水率及喂入量组间弹性模量及粘性模量差异均显著(P0.05),弹性模量、粘性模量与含水率及喂入量均呈正相关关系。籽棉压缩与应力松弛力学特性的研究可为籽棉压缩过程机理研究、模拟仿真提供理论依据,缩短机具研发过程。
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| 关 键 词： | 压缩 应力松弛 本构模型 试验研究 籽棉 |
| 收稿时间： | 2021/1/4 0:00:00 |
| 修稿时间： | 2021/3/19 0:00:00 |
Mechanical properties and construction of constitutive model for compression and stress relaxation of seed cotton |
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| Kong Fanting,Wu Teng,Chen Changlin,Sun Yongfei,Xie Qing,Shi Lei.Mechanical properties and construction of constitutive model for compression and stress relaxation of seed cotton[J].Transactions of the Chinese Society of Agricultural Engineering,2021,37(7):53-60. |
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| Authors: | Kong Fanting Wu Teng Chen Changlin Sun Yongfei Xie Qing Shi Lei |
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| Institution: | Nanjing Institute of Agricultural Mechanization, Ministry of Agriculture and Rural Affairs, Nanjing 210014, China |
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| Abstract: | Cotton is one of the most important cash crops and textile materials in the world. The cotton production of China is also ranked at the top of the world, in terms of planting area and total yield. Specifically, the growing area of cotton is annually more than 3 million hectares. Packing storage and transportation of seed cotton have become two main determinants of production capacity in the cotton industry. However, the traditional storage and transportation of seed cotton cannot meet the high demand for the machine-picked cotton area in recent years. The packing facilities inevitably need to fit into the specific producing conditions in China, such as local topography, climate, and vegetation. Mechanical properties of seed cotton are thus fundamental, including compression and stress relaxation, to the optimal design of equipment for harvesting, stacking, and packing. Most previous researches were focused mainly on the mechanical properties of corn, wheat, and herbage straw in agricultural materials. Few studies were reported on the mechanical properties of seed cotton, particularly on compression and stress relaxation. Taking the seed cotton as the research object in this study, a systematic test of mechanical properties was performed on the compression and stress relaxation of seed cotton. An improved Nishihara model and a generalized Maxwell 5-element mechanical model were selected to represent the stress-strain curves of compression and stress relaxation. Various level factors were utilized to verify the constitutive models for the compression and stress relaxation of seed cotton. Relevant model parameters were obtained to determine the influence rules with different factors. The results showed that the determination coefficients of parameters in the constitutive model were beyond 0.9 using the curve-fitting in the compression and stress relaxation of seed cotton. An obvious regularity of coefficients indicated that two models were better suitable for the compression and stress relaxation of seed cotton. There was also a significant influence of water content and feeding quantity on the mechanical properties of seed cotton. Furthermore, the compression stress was positively correlated to the water content and feeding quantity. In addition, the viscosity coefficient and elastic modulus increased significantly at a higher level of water content, due mainly to the porosity of cotton fiber. The cell wall of fiber became stronger and tougher, because the hydrophilic groups on the cellulose macromolecule absorbed water from the external environment. The curl of cotton fiber also made the fiber shrink longitudinally and elastic elongation during the compression under the larger amount of feeding quantity, where there was a significant increase in the overall longitudinal deformability of seed cotton and the elastic modulus. The viscosity coefficient and packing height both rose up significantly, while the pressure transmission path was longer for the naturally stacked seed cotton in the same compression chamber, as the feeding quantity was larger. The main reason was that the bending deformation, contact and extrusion were induced to generate the greater local stress between the fiber bodies during the compressing process of seed cotton. Moreover, the water content was positively correlated to the elastic modulus and viscosity coefficient of seed cotton. This positive correlation was possible because the natural twist of cotton made the fibers entangled, linked, and adhered, difficult to disperse during the stress relaxation of seed cotton. Correspondingly, the elastic modulus and viscosity coefficient increased significantly, as the feeding quantity increased. This improvement was due mainly to a non-uniform attenuation rate of pressure during the stress relaxation of seed cotton. There were much more contact points of fiber curl subjected to the greater feeding amount of seed cotton. The elastic modulus increased, while the relaxation pressure was transferred from the bottom to the top of seed cotton. The adhesion force between fibers and the viscosity coefficient rapidly rose with the motion resistance increased. This finding can provide an insightful theoretical basis to simulate the compression of seed cotton in most machine-picked cotton areas. |
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| Keywords: | compression stress relaxation constitutive model experimental study seed cotton |
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