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991.
992.
E. Mitsoulis S. G. Hatzikiriakos K. Christodoulou Dimitris Vlassopoulos 《Rheologica Acta》1998,37(5):438-448
The excess pressure losses due to end effects in the capillary flow of two linear low-density polyethylene resins (LLDPE)
were studied. These losses were first determined experimentally by using two methods: 1) by extrapolating experimental data
of pressure drop versus length-to-radius ratios (L/R) to zero capillary length and 2) by means of using orifice dies (L/R≅0). Both methods resulted in practically the same end corrections. Numerical simulation was also used to model this important
aspect of experimental rheology. The constitutive equations used in the simulations are a multimode K-BKZ equation, a multimode
Phan-Thien/Tanner, and finally a purely viscous Carreau equation. It was found that the numerical predictions agreed qualitatively
but underestimated the experimental data for the various geometries used to determine the end effects. Furthermore, it is
demonstrated that the entrance pressure loss is also insensitive to extensional rheology, while it depends more strongly on
the shear rheology. This finding raises doubts as to the usefulness of end pressure (known also as Bagley correction) as a
method of determining the extensional viscosity of polymer melts at high rates.
Received: 18 December 1997 Accepted: 21 May 1998 相似文献
993.
994.
I.IntroductionThereareimportantapplicationsfortheor}:ofplanea'iscoelasticit}'Inthefieldsofgeology,miningandconstructingetc.,butformostproblemsofviscoelastici[}'.theirsolutionsareobtainedfromthecorrespondingelasticsolutionsb}'"leansofthecorrespondenceprinc… 相似文献
995.
用Eshelby理论研究复合材料线粘弹性本构关系 总被引:2,自引:0,他引:2
本文用Eshelby微力学理论分析,得到短纤维增强材料(SFRC)和基体材料两者的粘弹性本构方程之间存在简单的正比关系。发现体积含量为f的短纤维无序取向SFRC一维力学行为,等效于体积含量为F的短纤维单轴取向SFRC在取向轴上的力学行为。 相似文献
996.
高应变率下的矿岩特性研究 总被引:6,自引:1,他引:6
本文采用霍普金森杆(S.H.P.B.)装置对三种磁铁矿和一种化岗岩在应变率为102~103S-1范围内的力学特性进行了研究。文中给出了矿岩在不同应变率下的动态破坏强度,动态弹性模量、动态应力-应变曲线和分析结论。 相似文献
997.
Lorenzo Codecasa Ruben Specogna Francesco Trevisan 《Journal of computational physics》2010,229(19):7401-7410
By exploiting the geometric structure behind Maxwell’s equations, the so called discrete geometric approach allows to translate the physical laws of electromagnetism into discrete relations, involving circulations and fluxes associated with the geometric elements of a pair of interlocked grids: the primal grid and the dual grid. 相似文献
998.
Davide S. A. De Focatiis John Embery C. Paul Buckley 《Journal of polymer science. Part A, Polymer chemistry》2010,48(13):1449-1463
An experimental study was made of the effects of prior molecular orientation on large tensile deformations of polystyrene in the glassy state. A new hybrid glass-melt constitutive model is proposed for describing and understanding the results, achieved by parallel coupling of the ROLIEPOLY molecularly-based melt model with a model previously proposed for polymer glasses. Monodisperse and polydisperse grades of polystyrene are considered. Comparisons between experimental results and simulations illustrate that the model captures characteristic features of both the melt and glassy states. Polystyrene was stretched in the melt state and quenched to below Tg, and then tensile tested parallel to the orientation direction near the glass transition. The degree of strain-hardening was observed to increase with increasing prior stretch of molecules within their entanglement tubes, as predicted by the constitutive model. This was explored for varying temperature of stretching, degree of stretching, and dwell time before quenching. The model in its current form, however, lacks awareness of processes of subentanglement chain orientation. Therefore, it under-predicts the orientation-direction strain hardening and yield stress increase, when stretching occurs at the lowest temperatures and shortest times, where it is dominated by subentanglement orientation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1449–1463, 2010 相似文献
999.
A constitutive model for evaluating the compressive behavior of Poly(methyl‐methacrylate) (PMMA) open‐cell foams is herein proposed. Specifically, the study investigates the viscoelastic and viscoplastic behaviors of the PMMA open‐cell foams. The constitutive equation is expressed in terms of the following polymer and foam properties: elastic modulus, relative density, as well as the relaxation and densification constants. PMMA open‐cell foams are manufactured using a gas foaming/particulate leaching method and uniaxial compression tests are performed. The mechanical properties and compressive stress‐strain responses obtained from the experiments are compared with those predicted by the proposed constitutive model. The results suggest that the constitutive model is an apt one for assessing and evaluating the compressive behaviors of PMMA open‐cell foams. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 436–443, 2007 相似文献
1000.
L. A. Golotina L. L. Kozhevnikova T. B. Koshkina 《Mechanics of Composite Materials》2007,43(2):127-132
A structural model is suggested for elastomers filled with particles of two fractions — with diameters exceeding 10 μm and submicronic ones. In each fraction, the particle diameter varies randomly, but between the fractions, the average particle
diameter differs by several orders of magnitude. It is assumed that the small particles, together with the matrix, behave
as a homogeneous medium relative to the large ones. By using this model, the mechanical behavior of composites based on elastomers
filled with different volume contents of solid particles is investigated.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 2, pp. 191–200, March–April, 2007. 相似文献