稻秸高密度压缩过程中应力松弛的试验研究

摘要

为揭示农作物秸秆高密度压缩成型后应力松弛的规律及明确秸秆高密度压缩成型工艺的有关参数，以稻秸秆为试验对象，采用闭式压缩的方式，选取三元件广义 Maxwell 模型（ zener 模型）和四元件广义 Maxwell 模型两个流变模型（下面简称三元件模型和四元件模型），利用控制变量的研究方法和 MatLab 软件中 cftool 工具进行拟合。结果表明：四元件模型的拟合效果要优于三元件模型，粘弹性参数的变化范围：E1＝2．071～6．687MPa、η1＝1．046～3．060MPa· s、E2＝0．237～0．811MPa、η2＝12．780～48．090MPa· s，试验结果都存在 E1＞η1，E2﹤η2；在应力松弛过程的0．7s 以内松弛速率最快，松弛过程持续90s 左右应力趋于平稳，残余应力较小。该试验可为秸秆高密度压缩成型工艺的优化设计提供理论参考。%In order to improve the compression conditions and parameters , and verify the relationship of stress-relaxa-tion, straw was compressed and two rheological models were analyzed in the present study , which was useful for the de-sign of the compression molding equipment .The analytical method that control variables and cftool tools in MATLAB were used to discussed fitting curve .The different compression force , length of straw , and feed quantity were discussed the mechanical behavior related to stress relaxation of rice straw in closed compression tube .The results showed that: the four components which contain two Maxwell model parallel is better than a Maxwell components in parallel a spring ele -ment model to describe the rice straw stress relaxation process .The rheological model of rice straw in the test conditions and the relevant rheological parameters of the model were obtained .The change of characteristic parameters rangeas fol-lowed: E1=2.071~6.687MPa,η1=1.046~3.060MPa· s,E2=0.237~0.811MPa,η2=12.780~48.090MPa· s.All the results showed the similar result that E 1>η1 and E2 ﹤η2.This means the rheological of rice straw is not same as to the rheological of solid or fluid .Usually , the stress relaxation time was used to characterize the stress relaxa-tion, which depends on the initial stress and the stress relaxation time ratio .It was found that an optimum feed quantity which has the fastest stress relaxation ,which is the same result as the previous researchers .The stress relaxation was fas-test at the condition of 1.85g.The range of the first stress relaxation time is 0.40~0.67s and the second is 39.19~89.56s at the different compression force .The curves tend to become smooth at the end of 90 s .which has a small re-main stress .The fastest relaxation rate occurs at 0 .7 s at the stress relaxation process under the conditions of remaining any two experimental factors unchanged .