| 谷子籽粒压缩力学性质及损伤裂纹形成机理 |
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| 引用本文： | 孙静鑫,杨作梅,郭玉明,崔清亮,武新慧,张燕青.谷子籽粒压缩力学性质及损伤裂纹形成机理[J].农业工程学报,2017,33(18):306-314. |
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| 作者姓名： | 孙静鑫 杨作梅 郭玉明 崔清亮 武新慧 张燕青 |
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| 作者单位： | 山西农业大学工学院,太谷,030801 |
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| 基金项目： | 国家重点研发计划课题（2016YFD0701801）；山西农业大学科技创新基金项目（201212）；山西农业大学博士科研启动基金项目（412576） |
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| 摘 要： | 在谷子联合收获机及谷子加工机械装备设计研制中需要掌握谷子籽粒的基本物性参数和力学性质,以及受压致谷子谷壳与米粒损伤及裂纹形成过程,从而确定和优化工作参数.为此该文测定了不同含水率下(25.1％,20.9％,17.5％,15.2％)4种优质谷子品种(晋谷21,张杂10号,吨谷,长谷)籽粒的基本物性参数,包括千粒质量、三轴尺寸等,并研究了不同含水率、品种和压缩方位(长度、宽度和高度方向的压缩方位)对谷子籽粒的压缩力学性质的影响,对试验数据进行了多响应完全随机区组分析.结果表明:同一品种谷子籽粒的长、宽、高、千粒质量、算数平均径、几何平均径均随含水率的降低而减小,不同品种间的物性参数差异显著(P＜0.001);影响屈服载荷、变形量、破坏能以及表观弹性模量的主要因子依次是压缩方位、含水率、品种.对于同一种谷子,籽粒的长度、宽度和高度方位压缩时的屈服载荷和表观弹性模量都随着含水率的升高而减小,压缩变形量和破坏能随着含水率的降低呈先减小后增大的趋势.长度、宽度和高度方位压缩时,损伤裂纹的形成过程及发生机理、扩展形态和部位均不同,分别是:从籽粒的尖冠处沿着胚和胚乳连接处扩展,形成几乎贯穿籽粒长度方向的裂纹:从上下两接触点处由应力集中形成的贯穿籽粒宽度方向的裂纹;从腹面的种脐处沿胚乳抗压性最弱的部位延伸且贯穿籽粒一半的裂纹.研究结果为谷子播种,联合收获机及相关加工机械的设计、参数优化提供依据.
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| 关 键 词： | 含水率 力学特性 弹性模量 谷子籽粒 品种 压缩方位 |
| 收稿时间： | 2017/7/1 0:00:00 |
| 修稿时间： | 2017/9/11 0:00:00 |
Compression mechanical properties and crack formation law of millet grain |
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| Sun Jingxin,Yang Zuomei,Guo Yuming,Cui Qingliang,Wu Xinhui and Zhang Yanqing.Compression mechanical properties and crack formation law of millet grain[J].Transactions of the Chinese Society of Agricultural Engineering,2017,33(18):306-314. |
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| Authors: | Sun Jingxin Yang Zuomei Guo Yuming Cui Qingliang Wu Xinhui and Zhang Yanqing |
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| Institution: | College of Engineering, Shanxi Agricultural University, Taigu 030801, China,College of Engineering, Shanxi Agricultural University, Taigu 030801, China,College of Engineering, Shanxi Agricultural University, Taigu 030801, China,College of Engineering, Shanxi Agricultural University, Taigu 030801, China,College of Engineering, Shanxi Agricultural University, Taigu 030801, China and College of Engineering, Shanxi Agricultural University, Taigu 030801, China |
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| Abstract: | Millet contains protein,vitamin B1 and other mineral elements needed for human health,which has functions of enhancing blood circulation,brain tonic,and sleep quality.In recent years,the market demand for millet is rising.However,the mechanization level of millet harvesting is low.Manual harvesting is very common,which requires high labor intensity,has low efficiency and results in insufficient supply of millet.In this paper,we systematically investigated effects of moisture content and varieties of millet on its physical parameters,effects of millet varieties and compression azimuth on the compression mechanical properties (including yield load,deformation,failure energy and apparent elastic modulus) of millet,and effects of compression azimuth on crack formation of millet.The study results are expected to provide the basis for the design and optimization of millet harvester and related processing machinery.In this paper,the 1000-grain weight was measured by an electronic balance,the triaxial sizes by a vernier caliper,and the moisture content by fast grain moisture analyzer for four millet varieties:Zhangza-10,Dungu,Jingu-21,Changgu.The sphericity of the millet,the arithmetic mean diameter and the geometric diameter were calculated using the triaxial sizes.The compression tests were carried out along X,Y,Z axis using a texture analyzer and the data were analyzed by SAS statistics software.The yield load,deformation,and failure energy were obtained from the force-distance curve measured by a texture analyzer.At the same time,the apparent elastic modulus was calculated according to the Hertz formula.The experimental results were summarized as follows in six categories.1) For the physical parameters of the millet,with a moisture content between 15.2％ and 25.1％,the length,width,height,1 000-grain weight,average diameter and geometric mean diameter of millet grain decreased as the moisture content decreased.The millet length,width and thickness range from 2.028 to 2.112 mm,1.818 to 1.931 mm,1.413 to 1.513 mm,respectively.The sphericity of millet was more than 84％;the arithmetic mean diameter varied from 1.750 mm to 1.852 mm;and the geometric mean diameter 1.732 mm to 1.834 mm.Therefore,the shape of millet can be regarded as ellipsoid.There were significant differences (P＜0.001) in the triaxial sizes,1000-grain weight,sphericity,arithmetic mean diameter and geometric mean diameter among different varieties.When the moisture content of millet was about 25％,the 1000-grain weight of Jingu-21 was 3.473 g,which was the heaviest millet,while Zhangza-10 was 3.264 g,which was the lightest millet.The moisture content has a negligible effect on the sphericity.The effect of varieties on sphericity was significant (P＜0.001).2) For factors on the compression mechanical properties,the influence of moisture content,compression azimuth,and variety on the compression mechanical properties were significant (P＜0.01).The significant factors affecting the compression mechanical properties were compression azimuth,moisture content,and variety in a sequence from the most significant to the least significant.3) For the effects of the moisture content,for the same kind of millet,the yield load and apparent elastic modulus decreased as the moisture content increased during compression in X,Y,Z axis.The yield load decreased slowly when moisture content ranged from 20.9％ to 25.1％.The deformation and failure energy first decreased and then increased as the moisture content increased.For the same azimuth compression,the better the quality of the millet,the more compact the internal structure,and the smaller the deformation.4) For crack formation of the millet:on the X axial,a crack started from the crest of the grain along the junction of embryo and endosperm,and then extended throughout the X axis.On the Y axis,a crack started from the connection point of grain and probe and the connection point of grain and base throughout the Y axis because of stress concentration.On the Z axis,a crack started from the junction of embryo and endosperm on the back to the ventral hilum along the weakest part of endosperm resistance extending throughout half of the grain.5) For the effects of compression azimuth,the yield load increased in turn on the X,Y,and Z axis and the deformation and failure energy decreased on the X,Z,and Y axis in turn.The apparent elastic modulus of the millet increased in turn on the X,,Y,and Z axis.This result indicated that millet was not uniform and it was an anisotropic body.6) For the effects of millet varieties,with the same moisture content,the compression mechanical properties of Jingu-21,Dungu,Changgu and Zhangza-10 varied from large to small.This indicated that Jingu-21 had a relatively good compression resistance and quality. |
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| Keywords: | moisture content mechanical properties elastic modulus millet grain varieties compression azimuth |
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