【作者】 郭文斌；

【导师】 王春光；

【作者基本信息】 内蒙古农业大学 ， 农业机械化工程， 2009， 博士

【摘要】 马铃薯属于固体粘弹性生物物料,其生物力学特性和淀粉含量都与物料本身组织结构有关。淀粉主要充填在马铃薯内部组织细胞中,以细胞淀粉的形式存在,受到外力作用时,载荷通过细胞中的水分及淀粉物质颗粒作用在细胞壁上,从而对马铃薯的生物力学特性产生影响。本文针对内蒙古呼和浩特地区产紫花白和底希芮品种马铃薯进行了压缩和应力松弛试验研究,并对马铃薯压缩和应力松弛特性参数与淀粉含量的相关性进行了分析,通过学科间的交叉研究,寻求用力学特性参数检测马铃薯淀粉含量的方法;在对马铃薯压缩和应力松弛特性的研究中还引入了虚拟样机技术,基于虚拟样机技术建立了马铃薯压缩和应力松弛过程的虚拟样机模型,并对其压缩及应力松弛过程进行了仿真。本研究主要内容如下:(1)在不同加载速率下,采用平顶圆柱压头和平板压头对马铃薯整茎和圆柱试样进行了压缩试验。获得了马铃薯整茎和圆柱试样的压缩曲线,由二次抛物线模型回归得到了弹性模量、刚度等压缩特性参数,从曲线可以看出马铃薯压缩过程中无明显生物屈服点;对两个品种马铃薯不同压缩速率下整茎、圆柱试样的压缩特性进行了对比,得出不同速率下整茎试样压缩特性参数差异并不显著,压缩初始阶段曲线基本重合,因此实际检测及储运中,在弹性范围内外载荷施加的速率对马铃薯完整块茎挤压影响较小。研究对整茎及圆柱试样压缩特性分析的同时,探讨了造成整茎和圆柱试样压缩特性差异的原因,圆柱试样由于压缩过程中水分流失,物料密度增加,其压缩过程中弹性模量随应变的增加而增加;而整茎压缩时,物料组织发生粘性流动,整茎的刚度值随变形量的增加而减小。圆柱压头对马铃薯整茎压缩时,物料破裂前达到的应变较小,可看作粘弹性变形过程,其应力应变关系可用Maxwell模型进行描述。本研究基于粘弹性理论分析了平顶圆柱压头对马铃薯整茎压缩时的粘弹性变形过程,获得了整茎压缩的本构方程,由试验数据进行回归确定了马铃薯块茎物料受压时表现出来的弹性模量和粘性系数,为进一步研究马铃薯整茎的力学特性奠定了基础。(2)在不同常变形量下,利用平顶圆柱压头和平板压头分别对马铃薯整茎和圆柱试样进行了应力松弛试验研究。建立了马铃薯应力松弛过程的流变学模型,确定了物料松弛过程中的弹性模量、粘性系数和松弛时间,并分析了常变形量不同对两个品种马铃薯整茎及圆柱试样松弛参数的影响,得出整茎物料受长时间挤压时的变形量不同,其松弛后残留的弹性也明显不同。根据所得试验数据,对整茎和圆柱试样应力松弛特性进行了分析,探讨了造成整茎和圆柱试样松弛特性差异的原因,松弛过程中圆柱试样呼吸作用较强、水分散失较多,应力松弛时间较长;而整茎应力松弛过程中应变较小,松弛时间较短。(3)利用碘比色法测定了马铃薯试样的淀粉含量,对准静态压缩速率下紫花白和底希芮品种马铃薯圆柱试样和整茎试样的压缩、应力松弛特性参数与试样的淀粉含量进行了相关性分析。获得了与淀粉含量相关性显著的力学特性参数。其中对于两个品种圆柱试样,压缩和应力松弛过程中的弹性模量与试样的淀粉含量、含水率均显著相关;对于两个品种整茎试样,压缩过程中的破裂点刚度、破坏能、粘性系数与整茎淀粉含量相关性比较显著。针对与两个品种马铃薯淀粉含量相关性显著的压缩、应力松弛特性参数,经多元回归分析,建立了力学特性参数与马铃薯淀粉含量的回归方程,经检验回归方程有意义。(4)引入了虚拟样机技术,根据试验研究和理论分析所得的结果,在ADAMS仿真环境下建立了马铃薯整茎压缩和应力松弛过程的仿真模型。将马铃薯压缩及应力松弛过程的仿真曲线与试验曲线进行了对比,验证了模型的正确性,同时分析了模型各元件应力应变随时间变化的规律,并在仿真环境下模拟了不同加载速率、不同仿真时间对马铃薯压缩及松弛曲线的影响。更多还原

【Abstract】 Potato is a kind of agricultural viscoelastic material, both biological mechanics characteristics and starch content of potatoes are related to its biological tissues. The starch mainly exists in the cells of potato biological tissues. when the material suffers the exogenic action, the force loads on the cell wall by the water and starch granule, so the starch content probably has an obvious effect on the biological mechanics characteristics of potatoes. The compression and stress relaxation tests were accomplished for Zi Huabai and Desiree potatoes in our study. The correlation between mechanical properties and starch content of potatoes were acquired, and the method would be found to predict the starch content of potatoes by mechanical tests. In the study, the compression and stress relaxation models were established by the virtual prototyping technology. The compression and stress relaxation processes of the potato were simulated with ADAMS technology.(1) The compression tests were completed in different loading rates for cylindrical samples and tubers of the potato. The compression curves were measured and compression characteristic parameters were determined by regression analysis, and no obvious biological yield point appeared on the curve. When the tuber was compressed in different loading rates, the initial stage of compression curve was approximatively superposed. There was insignificant difference for parameters which were acquired in different loading rates. Meanwhlie, the difference of compression characteristics between samples and tubers was discovered in the test results. When the sample was compressed by flat indenter, the water in cell tissue ran off, and the density, elastic modulus of the sample increased as the strain grew. When the tuber was compressed by cylindrical probe, the tissue of potato appeared viscous flow, and the stiffness of the tuber decreased as the deformation increased.When the tuber was compressed to the rupture point by cylindrical probe, the tuber had showed a minor strain, and the viscoelastic deformation process can be described by the Maxwell model. The viscoelastic deformation process were analysed, and the constitutive equation of the tuber compression was obtained. The elastic modulus and viscosity coefficient in the model were determined.(2) The stress relaxation tests were completed under two constant deformations with cylindrical samples and tubers of the potato. The stress relaxation model was established and the parameters in the model were determined. The study results showed that the residual elastic behavior was quite different under two constant deformations for tubers. According to the test results, the difference of stress relaxation characteristics between samples and tubers was discovered. During the relaxation process, the sample had a heavy respiration and water loss, and its relaxation time was longer than that of the tuber.(3) In order to get the correlation between the starch content of potato and its mechanical rheological characteristics, the starch content of samples and tubers were measured in the study by using IODINE-STARCH colorimetric method. The mechanical property parameters which correlate closely with the starch content were determined. For cylindrical samples of two potato cultivars, the elastic modulus which was obtained in compression and relaxation tests correlates closely with the starch content and water ratio. For tubers of two cultivars, the stiffness, energy at rupture point, and viscosity coefficient correlate closely with the starch content. The regression equations were established for starch content and mechanical parameters.(4) Virtual prototyping technology was introduced to the study. According to the results of compression and relaxation tests, the virtual prototype models of compression and relaxation were established for potato tubers with ADAMS technology. By comparing the simulation curve with the experiment curve, the validity of models were verified. When models were running, the stress and strain of elements in models were detected, and the rules were analysed. At the same time, the compression in different loading rates and the stress relaxation in different time spans were simulated, and the simulation results showed the effects of loading rates and time spans for potato’s compression and stress relaxation.更多还原