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981.
On the application of the additive decomposition of generalized strain measures in large strain plasticity 总被引:2,自引:0,他引:2
In the present paper two thermodynamically consistent large strain plasticity models are examined and compared in finite simple shear. The first model (A) is based on the multiplicative decomposition of the deformation gradient, while the second one (B) on the additive decomposition of generalized strain measures. Both models are applied to a rigid-plastic material described by the von Mises-type yield criterion. Since both models include neither hardening nor softening law, a constant shear stress response even for large amounts of shear is expected. Indeed, the model A exhibits the true constant shear stress behavior independent of the elastic material law. In contrast, the model B leads to a spurious shear stress increase or drop such that its applicability under finite shear deformations may be questioned. 相似文献
982.
动脉狭窄内低密度脂蛋白传输的数值研究:LDL的浓度极化现象 总被引:6,自引:0,他引:6
用计算机数值模拟的方法 ,对低密度脂蛋白 ( LDL)在动脉狭窄血管段内的质量传输进行了研究。计算结果表明 ,由于血管壁渗流的存在 ,LDL这样的脂质大分子会聚积在血管的内壁表面 ,发生一种工程上称为浓度极化的现象。LDL浓度在动脉狭窄口后的流动分离点出现峰值。该浓度峰值随雷诺数和动脉狭窄度的增加而呈逐渐下降的趋势。作者认为 ,该区域 LDL浓度的局部升高是引发动脉粥样硬化局部性和动脉狭窄产生的一个非常重要的原因。 相似文献
983.
在连续介质力学基础上建立了一个广义双剪粘弹塑性海冰动力学本构模型。该模型在海冰屈服前采用Kelvin-Vogit粘弹性模型,考虑中间主应力和静水压力对海冰屈服的影响选用广义双剪应力屈服准则作为海冰屈服判据,屈服后采用相关联的正则流动法则。采用该本构模型对渤海海冰动力过程进行了48小时数值模拟,讨论了辽东湾海冰的厚度、密集度、冰速和主应力的分布规律,其中海冰厚度分布与卫星遥感资料符合良好,从而有效地验证了该广义双剪粘弹塑性本构模型在海冰动力学中的可靠性。 相似文献
984.
985.
H. Watanabe Kunihiro Osaki Mutsuo Matsumoto Dobrin P. Bossev Cathy E. McNamee Masaru Nakahara Ming-Long Yao 《Rheologica Acta》1998,37(5):470-485
Nonlinear rheological features were investigated for an aqueous solution of tetraethylammonium perfluorooctyl sulfonate (C8F17SO3
–N+(C2H5)4; abbreviated as FOSTEA). In the solution (c=0.045 mol/l; 28.3 g/l), spherical micelles of FOSTEA were connected with each other to form threads of pearl-necklace shape.
These threads were further organized into a transient network to exhibit linear relaxation characteristic of living polymers,
single-mode terminal relaxation widely separated from faster relaxation processes. Nonlinear relaxation experiments against
large step-strains γ(≤8) revealed that the terminal relaxation mode had a γ-insensitive relaxation time but its relaxation
intensity exhibited significant damping (much stronger than that for entangled polymers). In contrast, the relaxation time
and intensity for the fast relaxation modes first increased and then decreased with increasing γ. Under shear flow, the FOSTEA
threads exhibited strong thinning of the viscosity. These nonlinear features of the FOSTEA threads were compared with those
of other threadlike micelles, analyzed on the basis of an empirically introduced constitutive equation, and discussed in relation
to strain/low-induced scission of the living threads.
Received: 20 February 1998 Accepted: 30 July 1998 相似文献
986.
K. Kirschke 《Rheologica Acta》1982,21(4-5):508-510
Generally solutions of high polymers show a shear-rate dependent flow behaviour and so the properties of these fluids have to be measured under conditions of shear corresponding to the practical service. Capillary viscometry is suitable for achieving high rates of shear but relaxation phenomena can effect the results, which is proved experimentally. The flow behaviour of a lubricant blended with a high polymer additive is measured and a graphical representation of the dependence of flow behaviour on temperature and rate of shear is recommended. 相似文献
987.
通过扭转试验对高聚物注浆材料剪切性能进行试验研究,并在扫描电子显微镜(scanning electron microscope, SEM) 下观测了试件断面处胞体形状破坏特征,在此基础上通过有限元数值模拟,对其剪切变形力学响应特征及剪应力分布规律进行了研究。结果表明:密度对高聚物材料的剪切强度及剪切模量影响显著,且随着高聚物材料密度的增加,其剪切强度和剪切模量被显著提升;高聚物材料胞体分布遵循能量最低原理,密度越大,胞体表面积越小,表面能越小,体系越稳定;面心立方体堆砌模型可以较好模拟材料剪切变形行为,且密度越大,拟合效果越好。 相似文献
988.
复合材料层合扁球壳的非线性强迫振动 总被引:4,自引:0,他引:4
研究了考虑横向剪切的对称层合圆柱正交异性扁球壳的非线性强迫振动问题,得到了共振周期解和非共振周期解.最后,还分析了横向剪切对幅频特性曲线的影响 相似文献
989.
Matti Keentok Marcus P. Newberry Peter Gras Frank Bekes Roger I. Tanner 《Rheologica Acta》2002,41(1-2):173-179
A selection of four commercial flours has been subjected to extensive rheological measurements as part of a comprehensive
program of wheat improvement. The results have been used to determine which of the many types of rheological measurements
provide significant discrimination between various types of modern baker's flours (including biscuit flours) and to procure
data suitable for use in mathematical models describing the dough rheology. The rheological measurements undertaken include
oscillatory shear at low amplitude, steady shear at a low shear rate, stress relaxation and extensional viscosity testing.
Although oscillatory shear data show minor differences between these flours, the other tests show significant variations and
these provide very good discrimination between the different flour types in comparison with conventional dough testing (e.g.
by the extensograph). The current dough rheological measurements provide further insight into molecular structure. In the
future, mathematical (constitutive) models are expected to provide a means of predicting processing and baking behaviour of
bread dough.
Received: 27 June 2001 Accepted: 28 August 2001 相似文献
990.
Hiroshi?SuzukiEmail author Gerald?G.?Fuller Tomoe?Nakayama Hiromoto?Usui 《Rheologica Acta》2004,43(3):232-239
Development characteristics of dilute cationic surfactant solution flow have been studied through the measurements of the time characteristics of surfactant solution by birefringence experiments and of the streamwise mean velocity profiles of surfactant solution duct flow by a laser Doppler velocimetry system. For both experiments, the concentration of cationic surfactant (oleylbishydroxymethylethylammonium chloride: Ethoquad O/12) was kept constant at 1000 ppm and the molar ratio of the counter ion of sodium salicylate to the surfactants was at 1.5. From the birefringence experiments, dilute surfactant solution shows very long retardation time corresponding to micellar shear induced structure formation. This causes very slow flow development of surfactant solution in a duct. Even at the end of the test section with the distance of 112 times of hydraulic diameter form the inlet, the flow is not fully developed but still has the developing boundary layer characteristics on the duct wall. From the time characteristics and the boundary layer development, it is concluded that the entry length of 1000 to 2000 times hydraulic diameter is required for fully developed surfactant solution flow.List of abbreviations and symbols A1, A2 Coefficients for time constant fitting [-] - B Breadth of the test duct [m] - C1, C2 Coefficients for time constant fitting [-] - D Pipe diameter [m] - DH Hydraulic diameter [m] - g Impulse response function [Pa] - H Width of the test duct [m] - n Index of Bird-Carreau model [-] - Re Reynolds number (=UmDH/) - ReD Pipe Reynolds number (=UmD/) - Rex Streamwise distance Reynolds number (=U0x/) - T Absolute temperature [K] - t Time [s] - ta Retardation time [s] - tb Build-up time [s] - tx Relaxation time [s] - tx1, tx2 Relaxation time for double time constant fitting [s] - t Time constant in Bird-Carreau model [s] - U Time mean velocity [m/s] - Um Bulk mean velocity [m/s] - Umax Maximum velocity in a pipe [m/s] - U0 Main flow velocity [m/s] - u Friction velocity [m/s] - x, y Coordinates [m] -
Shear rate [s–1] -
Mean shear rate [s–1] - n Birefringence [-] - 99% boundary layer thickness [m] - Solution viscosity [Pa·s] - P, S Surfactant and solvent viscosity [Pa·s] - 0,
Zero and infinite viscosity of Bird-Carreau model [Pa·s] - Characteristic time in Maxwell model [s] - Water kinematic viscosity [m2/s] - Density [kg/m3] - Solution shear stress [Pa] - P, S Surfactant and solvent shear stress [Pa] - Time in convolution [s] 相似文献