共查询到16条相似文献，搜索用时 203 毫秒
1.
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。 相似文献
2.
品种及含水率对谷子籽粒力学性质的影响 总被引：1，自引：1，他引：0
谷子籽粒群是具有黏弹性性质的生物材料,谷子加工储藏和机械收获等作业环节需考虑其黏弹性,该文研究了不同品种、不同含水率对谷子籽粒群黏弹性力学指标的影响。该试验以不同品种、不同含水率为试验因素,以谷子籽粒群的瞬时弹性模量、迟滞弹性模量、松弛时间和黏度系数为试验指标进行蠕变试验,并对试验结果进行方差分析。结果表明:谷子籽粒群的蠕变特性可由四元件Burgers模型描述,不同含水率、不同品种谷子籽粒群的蠕变参数各异。品种对谷子籽粒群的迟滞弹性模量影响显著,晋谷21号谷子籽粒群的迟滞弹性模量均值为0.609 3 MPa,显著高于张杂10号的0.522 2 MPa。含水率对谷子籽粒群的瞬时弹性模量、迟滞弹性模量和黏度系数影响均显著,均呈随含水率升高而降低的趋势,含水率为12.10%的谷子籽粒群的瞬时弹性模量0.752 6 MPa显著高于含水率为16.05%的0.613 6 MPa和20.00%的0.569 7 MPa,含水率为12.10%、16.05%、20.00%的谷子籽粒群的迟滞弹性模量分别为0.706 4、0.583 5、0.407 5 MPa,含水率为12.10%的谷子籽粒群的黏度系数1 234.7 MPa·s显著高于20.00%的796.8 MPa·s,含水率对谷子籽粒群的松弛时间影响不显著。该文通过试验研究了不同品种和不同含水率的谷子籽粒群的蠕变特性,为谷子低损收获、加工储藏及参数优化提供了理论支持。 相似文献
3.
为更加精确地解析农业松散物料压缩时表现出的应力松弛行为及松弛后的成型效果,简化应力松弛模型并获得更加直观的应力松弛特征参数,该研究将Riemann-Liouville分数阶微积分理论引入农业松散物料流变学特性研究中,以农业生产后残留的玉米秸秆与马铃薯废渣为研究对象,推导建立了用于描述秸秆-薯渣混合物料应力松弛特征的分数阶模型,并以松弛比与松弛时间比率为试验指标,完成了混合物料在不同压缩密度下的应力松弛试验,利用所建立分数阶模型对应力松弛试验曲线进行了拟合回归分析,并与广义Maxwell模型的拟合结果进行了对比与参数相关分析。结果表明:1)分数阶模型可准确描述秸秆与薯渣混合物料的应力松弛过程,其对松弛曲线的拟合精度高于五元件广义Maxwell模型,决定系数R~2介于0.996 4～0.999 5之间。2)分数阶模型仅有两个模型参数,分数阶阶数β与粘弹性系数K,其中β与应力松弛后残留弹性的占比、松弛比均极显著负相关,可直接用于表征物料松弛后的永久变形程度,预测其成型效果;K与弹性模量及粘性系数、松弛时间比率均极显著正相关,可用于表征混合物料的粘弹性特征及其应力松弛快慢程度。该研究成果推动了分数阶微积分理论在农业松散物料流变学特性研究领域的应用,通过分数阶模型建立了秸秆-薯渣混合物料的应力松弛特性与成型效果的联系,可为进一步改进农业松散物料成型方法、获取最佳成型条件提供依据。 相似文献
4.
完整稻秆卷压过程应力松弛试验 总被引：1，自引：7，他引：1
为深入研究完整稻秆在卷捆压缩过程中的流变特性,该文利用自制的钢辊式圆捆机卷压试验台进行了完整稻秆卷压过程应力松弛试验研究。选择稻秆含水率、草捆干物质质量、卷捆钢辊转速、稻秆喂入速度为试验因素,并以应力松弛时间和平衡弹性模量作为应力松弛特性评价指标,进行4因素5水平正交旋转组合试验。结果表明:完整稻秆卷压过程应力松弛模型可用1个Maxwell单元和1个弹簧并联组成的三元件方程表示;各因素对应力松弛时间贡献率排序依次为稻秆含水率、草捆干物质质量、稻秆喂入速度、卷捆钢辊转速;对平衡弹性模量贡献率排序依次为草捆干物质质量、稻秆含水率、稻秆喂入速度、卷捆钢辊转速;当稻秆含水率为65%、草捆干物质质量为17 kg、卷捆钢辊转速为257 r/min、稻秆喂入速度为1.6 kg/s时,应力松弛时间和平衡弹性模量可分别达最佳值17.08 s和4.01 k Pa。试验结果可为圆型打捆机对完整稻秆的卷压工艺优化及其压缩机理分析提供必要的理论与技术支持。 相似文献
5.
收割期芦竹底部茎秆机械物理特性参数的试验研究 总被引：14，自引：10，他引：14
试验研究芦竹底部茎秆的机械物理特性，以获得其最大破坏应力、弹性模量等机械物理特性参数，并分析芦竹切割过程中应力、应变分布状态，能为芦竹切割刀具和切割方式的设计提供理论依据和基础技术参数，对低能耗、高效率的芦竹切割器的设计具有重要的指导意义。该文利用微机控制电子万能材料试验机对收割期的芦竹底部的茎秆进行了顺纹拉伸、压缩、弯曲试验，获得试验条件下顺纹拉伸、压缩、弯曲的应力－应变曲线，并进行了分析。试验测得芦竹底部茎秆顺纹拉伸最大抗拉强度平均值为123 MPa，弹性模量值为1260 MPa；顺纹压缩最大抗压强度平均值为52 MPa，弹性模量值为595 MPa；顺纹弯曲最大抗弯强度平均值为125 MPa，弹性模量值为1715 MPa。结果表明，芦竹破坏应力参数接近毛竹，远大于玉米、小麦等茎秆的破坏应力参数，芦竹的机械化收割不宜采用传统的切割器。 相似文献
6.
基于流变特性的不同品种苹果果皮质地评价 总被引：3，自引：3，他引：0
为探究苹果果皮表面碎裂损伤的原因和评价不同品种果皮的质地。采用电子万能试验机对丹霞、红富士和新红星苹果果皮进行拉伸松弛和蠕变特性试验,得到了果皮松弛的初始应力、残余应力、应变保持和蠕变的初始应变、应力保持、蠕变量;建立了苹果果皮松弛和蠕变的数学模型,对松弛和蠕变特性参数进行了相关性和主成分分析。结果表明:松弛和蠕变试验结果揭示出不同品种果皮的流变特性和内部组织结构存在差异。不同品种果皮的初始应力较大时,松弛平衡后的残余应力较大;初始应变较大时,蠕变量较小。新红星果皮的弹性因子贡献率较高,而红富士果皮的黏性因子贡献率较高,反映出红富士果皮表面中较新红星和丹霞果皮表面容易碎裂损伤,在采收、运输等过程中红富士的果皮较新红星和丹霞的果皮易受机械损伤。研究结果可为苹果品种的优育及其质地评价体系的建立和完善提供参考。 相似文献
7.
为探究不同果蔬化学组分与细胞结构之间的差异及其对质地特性的影响,本研究对6种不同果蔬原料的化学成分、细胞微观结构、力学特性及质地特性进行分析。结果表明,苹果与梨的果糖含量较高,苹果的细胞结构较大;桃中蔗糖、水溶性果胶（WSP）与总酸的含量较高,细胞较小且排列密集,与其他果蔬差异较大;马铃薯与山药之间的差异主要体现在细胞结构方面。统计分析结果表明,纤维素（CEL）含量与应力-松弛特性参数均呈极显著正相关（P<0.01）;蔗糖、WSP含量与质地剖面分析（TPA）特性参数均呈极显著负相关（P<0.01）;颗粒密度、孔隙度与部分应力-松弛特性参数和质地特性呈极显著正相关（P<0.01）;细胞壁厚度、微观结构参数与部分质地特性呈显著正相关（P<0.05）。研究发现,影响新鲜果蔬质地特性的3个核心指标为黏滞系数（η）、体积密度、螯合性果胶（CSP）含量。本研究可为果蔬原料保鲜与加工利用提供一定的理论依据。 相似文献
8.
原料组分及应力松弛与方便米线品质的关系 总被引：5，自引：1，他引：4
以福昌、九峰、兴业、一枝秀等4种大米为原料制作方便米线,研究了米线品质特征与原料米化学成分、淀粉凝胶应力松弛特性的相关性,并结合应力松弛参数探讨了原料成分对米线品质的影响。结果表明,方便米线最大剪切应力为10.34~18.39 g/mm2,平均剪切应力为4.72~6.56 g/mm2,拉伸强度为7.77~15.72 g/mm2,拉伸形变为53.14~80.84 %,干物质吸水率为98.80~153.26 %,煮沸损失为12.09~24.39 %;原料大米粗蛋白含量越高,粗脂肪含量越低,平均剪切应力越大,挤压凝胶第一要素模型的胡克体弹性模量E1越小,其硬度越高,弹性和黏性越低;直链淀粉含量越高,支链淀粉含量越低,拉伸强度越高,松弛时间 τ1 越高,松弛时间 τ2 越低;松弛时间 τ 是方便米线品质控制中不可忽视的重要因素;建立的方便米线品质因素与原料大米成分间的交互效应方程具有较高的拟合度,此方程对于方便米线加工原料的选择具有指导意义。 相似文献
9.
紫花苜蓿圆捆机卷压过程的应力松弛特性与模型建立 总被引：1，自引：1，他引：0
牧草属于粘弹性物料,研究其应力松弛特性对降低圆捆机功耗、提高草捆质量具有重要意义。该文通过搭建圆捆机试验平台,结合各钢辊对草捆径向作用力分析,进行了紫花苜蓿应力松弛试验。采用无线电阻应变仪与ANSYS模拟相结合的方法,获取了卷压过程中捆室上半部分钢辊对草捆的径向作用力。在对应力松弛试验曲线和模型原理分析的基础上,确定了牧草应力松弛行为可采用2个Maxwell元件和1个弹簧元件并联组成的广义麦克斯韦尔模型模拟。利用残数法求得模型中应力松弛时间和平衡应力流变参数,分别为76.92、23.25 s和3.65 k Pa。该研究可为进一步探索喂入量、压缩频率、含水率与物料流变特性等参数间的关系,为节能圆捆机的设计提供理论依据及技术支持。 相似文献
10.
木薯力学特性测试 总被引：5，自引：4，他引：1
木薯力学特性参数的研究,对木薯收获机械的设计、动力学仿真、数学模型建立具有重要意义。采用物理试验方法,利用中国科学院长春科新试验仪器研究所生产的WDW3100微机控制电子万能实验机,测定了华南205木薯块根、茎秆物理力学特性参数,且对数据进行了数理统计分析,结果表明,木薯块根可视为一各向同性材料,其平均轴向拉伸强度、轴向压缩强度、径向压缩强度、轴向剪切强度、径向剪切强度、抗弯强度、轴向弹性模量、径向弹性模量分别为：0.34、0.74、0.76、0.22、0.37、2.66、7.23、7.22 MPa;木薯茎秆为一各向异性材料,其平均轴向拉伸强度、轴向压缩强度、径向压缩强度、轴向剪切强度、径向剪切强度、抗弯强度、轴向弹性模量、径向弹性模量分别为：10.23、6.26、1.43、1.86、2.53、10.80、5.24、35.36 MPa。 相似文献
11.
The effect of mixing time (6 and 20 min) and starch content were studied on doughs prepared with three wheat flours differing in high molecular weight subunit composition. Rheological measurements were performed in dynamic oscillation: frequency and strain sweeps, stress relaxation, and in large deformation viscosity measurements. The flours were diluted with starch to cover flour protein contents of 10–15%. Water was added to keep the starch‐water ratio constant when doughs were prepared with different protein contents. By increasing the starch content of the doughs, the rheological properties approached those of a starch‐water mixture prepared with the same starch‐water ratio as in the dough. The effect of the starch granules was reinforced by prolonged mixing. This may explain the higher values of the storage modulus and relaxation times observed after 20 min of mixing. Qualities related to gluten properties, appeared more clearly in large deformation viscosity measurements. 相似文献
12.
Characterization of the rheological properties of wheat flour dough during mixing and baking without modifying its structure or mechanical properties is not easy. In this work, the effect of dough setting pre‐orientation and strain orientation during characterization are assessed for differently structured wheat flour doughs (various water contents and addition of glucose oxydase). Rheological properties were measured in dynamic shear as rotational (CSL2100 fitted with a cone‐plate geometry) or radial (CP20 fitted with a plate‐plate geometry) small deformation mode and in lubricated squeezing flow and relaxation called large deformation mode. In comparison with radial shearing, rotational shearing induces a much larger preorientation of the network and thus a strain‐hardening phenomenon that affects the rheological measurements (storage modulus is overestimated) but relaxes, at least partially, during a rest period. Consequently, a longer period of time has to be allotted (allowing stress relaxation) before starting measurements. Plate‐plate geometry induces less preorientation and allows measurement a few minutes after setting. However, it has less discrimination of the differently structured dough than the cone‐plate geometry used in rotational mode. Results which partially agree with those of the CP20 are obtained using the lubricated squeezing flow followed by stress relaxation. 相似文献
13.
Dynamic viscoelastic properties at 25 degrees C of gluten and glutenin gels were obtained from Canadian common wheats of different strengths. The relaxation spectra showed a maximum intensity at a characteristic relaxation time (tau). The relaxation modulus associated with this maximum was taken as the strength of the glutenin or gluten gel transient network (G(tau)). The ratio of G(tau) for glutenin and gluten gels from the same cultivar ranged from 5.6 for an extra strong cultivar to 51.1 for a soft wheat. This gives indirect evidence that the gliadin fraction weakens the glutenin gel network more in weaker cultivars. In addition, the fact that both glutenin and gluten gels showed extensive stress relaxation coupled with the fact that addition of l-cysteine to a gluten gel eliminated the network structure at 25 degrees C and resulted in a power law stress relaxation spectrum suggests that the transient network in gluten is a reversible network. This power law relaxation pattern was not seen here for an entangled polymer melt (poly(dimethylsiloxane)). It was also found here that the viscosity of the gluten gel (G(tau) x tau) trended best with the tensile stress build-up in a uniaxial tensile test of gluten gels. Together, these results indicate that both network strength and relaxation times should be considered in characterizing the linear viscoelastic properties of hydrated cereal proteins. 相似文献
14.
15.
J. D. C. Figueroa C. I. Manuel Z. J. Hernndez‐Estrada B. Ramírez‐Wong 《Cereal Chemistry》2012,89(4):211-216
The stress relaxation behaviors of soft and bread‐type wheat kernels were studied using the generalized Maxwell model. The data showed two phases, a fast phase at short times of about 1.52–16.88 sec (τ1 and τ2) and a slow phase with longer times of about 81.28–793.81 sec (τ3 and τ4). The shorter decay of σ1 can be explained by very weak forces that affect mainly the rheological properties. The slow decay (σ4) located at longer relaxation times resulted from strong forces. The first derivative obtained from the stress relaxation curve of intact wheat kernels was quite similar in shape to the dough farinograms. The stress relaxation parameters showed differences in springs, relaxation times, and viscosities of bread wheat compared with soft‐type wheat kernels. The stresses σ1 and σ4 were correlated with wheat kernel, flour, rheological, and breadmaking properties; so especially were the elasticity of the spring (σ0) and viscosity of the fourth Maxwell element (η4), which were significantly correlated with all the quality properties, whereas σ2, σ3, η1, and η2 did not show correlation at all, except that η2 was correlated with falling number and volume of CO2. 相似文献
16.
Foods are frequently subjected to dynamic loading during harvesting, handling, transportation, and processing. Accurate prediction of dynamic responses of foods under these loading conditions requires better understanding of their dynamic visco-elastic properties. In this article, dynamic equilibrium was determined according to sinusoidal stress–strain. When a visco-elastic specimen is subjected to a sinusoidal varying stress, the resulting strain will be a sinusoidal response of the same frequency as the stress, out of phase by a lag angle. Experiments were conducted to measure the complex modulus of intact Daguanshan peaches and Luyu pears, the phase angle by which the strain lags the stress, and their relationship with initial pre-loading and vibration input power over a range of frequencies. Both the complex modulus and the phase angle increased as the frequency increased from 20 to 200 Hz. Initial pre-loading had a significant effect on the complex modulus, but not on the phase angle. Vibration input power had no significant effect on the complex modulus and phase angle. The phase angle depends not only on internal friction but also on the inertia of intact fruit. 相似文献