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91.
92.
Brian Joseph Edwards Mohammad Hadi Nafar Sefiddashti Bamin Khomami 《Entropy (Basel, Switzerland)》2022,24(2)
The challenge of calculating nonequilibrium entropy in polymeric liquids undergoing flow was addressed from the perspective of extending equilibrium thermodynamics to include internal variables that quantify the internal microstructure of chain-like macromolecules and then applying these principles to nonequilibrium conditions under the presumption of an evolution of quasie equilibrium states in which the requisite internal variables relax on different time scales. The nonequilibrium entropy can be determined at various levels of coarse-graining of the polymer chains by statistical expressions involving nonequilibrium distribution functions that depend on the type of flow and the flow strength. Using nonequilibrium molecular dynamics simulations of a linear, monodisperse, entangled C1000H2002 polyethylene melt, nonequilibrium entropy was calculated directly from the nonequilibrium distribution functions, as well as from their second moments, and also using the radial distribution function at various levels of coarse-graining of the constituent macromolecular chains. Surprisingly, all these different methods of calculating the nonequilibrium entropy provide consistent values under both planar Couette and planar elongational flows. Combining the nonequilibrium entropy with the internal energy allows determination of the Helmholtz free energy, which is used as a generating function of flow dynamics in nonequilibrium thermodynamic theory. 相似文献
93.
94.
采用静态拉伸方法在连续升温条件下动态地测量了大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5(Vit1)的黏度随温度的变化关系.在应变速率与温度的关系曲线中,观测到了与玻璃转变和晶化过程相联系的多个应变速率峰.在玻璃转变温度Tg以上,大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5的过冷液体呈现Newton流体特征,其黏度与温度的关系符合Vogel Fulcher-Tammann (VFT)关系式,拟合得到脆度D*=36,VFT温度T0=319K,脆度参数m=30,这说明Zr41T
关键词:
大块金属玻璃
应变速率
剪切黏度
自由体积 相似文献
95.
变分原理分析开裂简支箱梁剪力滞效应 总被引:1,自引:1,他引:0
变分原理通常应用于箱形截面梁剪力滞效应弹性分析,本文基于换算截面法,运用变分原理推导了预应力混凝土简支箱梁均布荷载作用、钢筋混凝土简支箱梁集中荷载作用的剪力滞系数计算公式,考虑了混凝土开裂对箱梁剪力滞效应的影响,并与试验结果和规范方法进行了对比分析。变分原理分析开裂混凝土箱梁剪力滞效应方法力学概念明确,是其弹性分析适用范围的拓展,亦可推广应用到混凝土连续箱梁开裂后的剪力滞效应分析,具有广阔的应用前景。 相似文献
96.
磁流变弹性体若干物理量的数值分析 总被引:1,自引:0,他引:1
应用有限元方法,考虑了颗粒的磁化饱和过程与非线性磁化过程,计算得到了磁流变弹性体中的磁场分布,进而研究了在不同磁场大小、不同颗粒体积比浓度下磁流变弹性体在成链方向的相对磁导率,计算结果和实验结果取得了一致。利用Maxwell应力张量,计算了磁场引起的磁流变弹性体的附加剪切模量。分析了颗粒体积比浓度、外加磁场对磁流变弹性体的磁致剪切模量的影响。研究了颗粒为旋转椭球形状时,颗粒的放置方式与其长短轴之比对磁流变弹性体的磁致剪切模量的影响。计算结果表明,磁流变弹性体的相对磁导率随颗粒体积比浓度的增大而增大,随磁场强度的增大而减小,颗粒的形状和放置方式对磁流变效应有很大的影响。 相似文献
97.
本文采用磁流体力学模型,数值研究了平板位形下双撕裂模线性增长率关于等离子体电阻η和黏滞v的定标关系.结果表明,对于有理面间距较大的情况,线性增长率关于电阻和黏滞的指数定标率随着黏滞的增加逐渐由γ∝ η3/5v0的定标变化到γ∝η5/6v-1/6的定标;而对于有理面间距较小的情况,其指数定标率随着黏性的增加从γ∝η 1/3 v0的定标逐渐变化到γ∝η2/3v-1/3的定标.本文还给出了初始阶段对称的双撕裂模的非线性演化,发现在非线性阶段对称的双撕裂模将转化为反对称的双撕裂模,并解释了相应的物理机理. 相似文献
98.
The paper presents the results of density and viscosity measurements in liquid derivatives of benzene and pyridine, well purified, degassed or aerated, depending on temperature, in the whole liquidity range. Gaseous admixtures were found to affect the viscosity of liquids. From one to three Arrhenius regions were observed, depending on the structure and orientational freedom of the molecules. the results are discussed on the background of 1H NMR relaxation time studies with regard to the effect of dipole interactions on the structure of close packing. 相似文献
99.
《Wave Motion》2017
An analytical model is developed to investigate the sound transmission loss from orthogonally rib-stiffened double laminated composite plates structure under a plane sound wave excitation, in which first order shear deformation theory is presented for laminated composite plates. By using the space harmonic approach and virtual work principle, the sound transmission loss is described analytically. The validity and feasibility of the model are verified by comparing the present theoretical predictions with numerical results published previously. The influences of structure geometrical parameters on sound transmission loss are subsequently presented. Through numerical results, it can be concluded that the proposed analytical model is accurate and simple in solving the vibroacoustic behavior of an orthogonally rib-stiffened double laminated composite plates. 相似文献
100.
Elise Mourier René Fulchiron Françoise Méchin 《Journal of Polymer Science.Polymer Physics》2010,48(2):190-201
Thermoplastic segmented polyurethanes (TPUs) are an important class of thermoplastic elastomers with a two‐phase microstructure arising from the thermodynamic incompatibility between hard (HSs) and soft segments. This microphase separation observed on cooling from a homogeneous state is often combined with the solidification of either or both types of segments. In this study, the structuring mechanism of two TPUs with HSs based on 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol was investigated from rheological measurements. Hence, in addition to the structuring temperature influence, the effect of an applied preshear flow in the melt polymer was analyzed, in particular. The results clearly show an enhancement of the solidification kinetics by the preshear. Indeed, the measured structuring time can be reduced by more than 1 decade. Rheo‐optical microscopy observations coupled with a shearing hot stage corroborated these results and showed the modification of the microstructure by the shear. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 190–201, 2010 相似文献