Modelling flow enhancement in nanochannels: Viscosity and slippage

With a large number of experimental and modelling papers reporting higher than expected liquid flow rates in both hydrophobic and hydrophilic nanochannels published in the last few years, there is a need to develop a coherent theoretical framework to explain these phenomena. In this work we will introduce a complete modelling and present a comparison between experimental data and predicted flows, showing good agreement.     

滑移线教学中粗糙平冲头压入半无限体的非Prandtl解探讨

针对经典教材滑移线理论教学中光滑平冲头和粗糙平冲头压入半无限体计算结果相同问题,构建了粗糙平冲头压入半无限体的非Prandtl滑移线场。与Prandtl场解相比,摩擦的存在使单位接触压力和应力状态影响系数增加了11%,与光滑平冲头压入半无限体计算结果相比,x方向的应力增加约82%,计算结果更能准确反映摩擦使变形力增加的塑性理论,有助于学生理解滑移线法以及滑移线理论的研究和应用。

     

Effects of slip condition on MHD stagnation-point flow over a power-law stretching sheet

The steady two-dimensional magnetohydrodynamic stagnation flow towards a nonlinear stretching surface is studied. The no-slip condition on the solid boundary is replaced with a partial slip condition. A scaling group transformation is used to get the invariants. Using the invariants, a third-order ordinary differential equation corresponding to the momentum is obtained. An analytical solution is obtained in a series form using a homotopy analysis method. Reliability and efficiency of series solutions are shown by the good agreement with numerical results presented in the literature. The effects of the slip parameter, the magnetic field parameter, the velocity ratio parameter, the suction velocity parameter, and the power law exponent on the flow are investigated. The results show that the velocity and shear stress profiles are greatly influenced by these parameters.     

Static analysis of composite beams with weak shear connection

The objective of the present paper is to analyse the static behaviour of elastic two-layer beams with interlayer slip. The Euler–Bernoulli hypothesis is assumed to hold for each layer separately, and a linear constitutive equation between the horizontal slip and the interlaminar shear force is considered. The applied loads act in the plane of symmetry of the composite beam, and the material and geometrical properties do not depend on the axial coordinate. Closed-form solutions for displacements and interlayer slips are developed. A second order differential equation is derived for the interlayer slip whose solution is used to determine the deflections and slopes. Examples illustrate the application of the method presented.     

元代都城琉璃瓦釉层的EDXRF和SEM-EDS分析

元代的琉璃瓦制作技术承自宋辽,对明清产生重要影响,是中国琉璃瓦制作技术发展的过渡时期。元上都与元中都所使用的琉璃瓦,代表了元代早期和中期琉璃瓦制作技术的最高水平。为探索元代不同时期琉璃瓦的制作技术和工艺特点,结合考古资料与相关文献,以X射线荧光光谱法（EDXRF）为基础,结合扫描电镜与能谱仪（SEM-EDS）,对元上都遗址、元中都遗址出土琉璃瓦样品釉层组成进行了测定。分析结果显示,元上都与元中都釉层包括釉与化妆土,化妆土厚度在122~260 μm之间。元上都孔雀蓝釉琉璃瓦釉料属于PbO-K₂O-SiO₂体系,和元大都孔雀蓝釉组成相似,原料组成为石英、硝、铅末、铜末;蓝釉琉璃瓦化妆土结构致密,CaO与SiO₂含量大于20%,原料可能是钙长石与黏土,应是釉料的一部分。元上都绿釉与元中都绿釉黄釉琉璃瓦釉同为PbO-SiO₂体系,基本原料组成都为石英,铅末,着色剂分别为铜与铁。元上都绿釉配方与北宋时期的接近,釉料配方也符合《营造法式》记载,但逐渐减少铅的比例为获得更浅的釉色,在元中期逐渐稳定;元中都黄釉琉璃瓦釉料铅硅比与元大都相近,配方在元中期探索中逐渐固定,沿用至明代早期,是提升明中期釉料的基础;两处遗址绿釉琉璃瓦与元中都黄釉琉璃瓦化妆土与胎釉结合紧密,Ca含量很高,厚度较薄,很可能是石灰浆[Ca(OH)₂],工匠在施加化妆土时既节约成本又能提高产品质量。三种釉色分别属于PbO-K₂O-SiO₂与PbO-SiO₂两种体系,组成原料差异明显,都用于建筑装饰,极大丰富了琉璃釉色,化妆土的应用在琉璃技术中也是一项创新。能量色散X射线荧光光谱具有分析快速、状态稳定的特点,已在琉璃瓦测试研究中得到普及,而元上都元中都琉璃瓦釉层的研究结果,补充了元代琉璃瓦的研究资料,并对探索中国琉璃瓦工艺发展历程提供一定科学依据。     

Micromechanics of semicrystalline polymers: Yield kinetics and long-term failure

The process of plastic deformation in semicrystalline polymers is complicated due to the operation of a variety of mechanisms at different levels and is strongly dependent on their underlying microstructure. The objective of this work is to establish a quantitative relation between the microstructure and the mechanical performance of semicrystalline polymers, as characterized by elasto-viscoplastic deformation. To do that, a micromechanically based constitutive model is used. The model describes the material as an aggregate of two-phase layered composite inclusions, consisting of crystalline lamellae and amorphous layers. The starting point for adding quantitative abilities to the model, in particular for the yield kinetics, is formed by experimental observations on both the yield kinetics and the time-to-failure of polyethylene at different temperatures, which reveal the contribution of two relaxation processes. To predict the thermo-rheologically complex short-term and long-term failure behavior, the crystallographic slip kinetics and the amorphous yield kinetics are re-evaluated, and the Eyring flow rule is modified by adding a temperature shift function. To enable the prediction of both tension and compression, a non-Schmid effect is added to the constitutive relation of each slip system. The creep behavior of polyethylene is then simulated directly using the multiscale, micromechanical model, predicting the time-to-failure, controlled by plastic deformation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

油漆、油墨中Pb、Cd、Cr(Ⅲ)、Cr(Ⅵ)含量测定

建立了1种检测油漆、油墨中Pb、Cd、Cr(Ⅲ)、Cr(Ⅵ)含量的方法.用电感耦合等离子体发射光谱法(ICPAES)测定其中的铅、镉、总铬含量,方法的精密度小于6%,加标回收率为96.2%~100.2%.用二苯碳酰二肼分光光度法测定Cr(Ⅵ),其方法的加标回收率为80.0%~90.0%.X射线光电子能谱法(XPS)分析油墨中铬的形态主要为三价.实验结果表明:油墨中Pb含量低于0.20 mg/kg,Cd含量低于0.04 mg/kg,Cr(Ⅵ)含量低于2.00 mg/kg;油漆中Cd含量低于6.00 mg/kg,均符合ASTM F963-2011美国玩具产品标准要求.8种油漆样品中,有6种铅含量超过90 mg/kg,有1种油漆Cr(Ⅵ)含量高达1.33×104mg/kg,不符合ASTM F963-2011标准.Pb、Cd、Cr(Ⅵ)检出限分别为0.04、0.2、2.0 mg/kg.     

以不同铕配合物为探针分子的温敏漆制备及性能

以氧化铕（Eu₂O₃）、甲基丙烯酸（MAA）、水杨酸（HSal）、肉桂酸（HCA）和菲咯啉（Phen）为原料制备了Eu（MAA）₃Phen、Eu（Sal）₃Phen和Eu（CA）₃Phen探针分子,并将不同探针分子分别加到甲基丙烯酸甲酯（MMA）中,在过氧化苯甲酰（BPO）引发下聚合,制得一系列温敏漆样品。采用红外光谱仪、荧光光谱仪和扫描电子显微镜对探针分子的结构、发光性能、形貌和温敏漆的温度猝灭性能进行了表征,研究了不同配体对探针分子发光性能和温敏漆温度猝灭性能的影响。结果表明,探针分子Eu（MAA）₃Phen的荧光强度明显高于Eu（Sal）₃Phen和Eu（CA）₃Phen,相应的3种温敏漆Eu（MAA）₃Phen/PMMA、Eu（CA）₃Phen/PMMA和Eu（Sal）₃Phen/PMMA均有良好的温度猝灭特性,但是对比发现在55~65℃范围内Eu（MAA）₃Phen/PMMA和Eu（CA）₃Phen/PMMA温敏漆的灵敏度较高,而在35~45℃范围内Eu（Sal）₃Phen/PMMA温敏漆的灵敏度较高,可见不同的温敏漆适用于不同的温度范围。     

On the wall slip phenomenon of elastomers in oscillatory shear measurements using parallel-plate rotational rheometry: II. Influence of experimental conditions

The use of parallel-plate rotational rheometry to characterize ex situ pre-prepared samples of rubber-like polymers is motivated by, for example, the investigation of magneto-rheological elastomers. When exceeding a critical excitation amplitude in oscillatory shear experiments, these elastomeric samples are prone to slip at the sample-plate contact interface. This phenomenon, known as wall slip, starts to occur at the sample's outer rim and leads to an imperfect force transfer onto the sample. This results in a systematic error of measured rheological material quantities.A thorough investigation is presented to reveal how this phenomenon is affected by selected experimental conditions, namely the static axial preload and measuring frequency. For this purpose disc-shaped samples composed of an unfilled silicone rubber are prepared by casting and examined by means of a controlled stress rotational rheometer equipped with a serrated rotor configuration.The oscillatory strain sweep experiments suggest that wall slip, exclusively present at the serrated rotor surface, is significantly influenced by the static preload. In contrast, only a slight frequency dependence is observed within the examined experimental conditions.Further insights into the wall slip mechanism were attained by two novel methodologies. It is shown that it is possible to produce a master curve for the various applied preloads. This demonstrates that the physical mechanism behind wall slip is independent of the axial force. Furthermore, we derive an empirical model for the criterion governing the onset of wall slip. This links the critical stress at which wall slip is initiated to the static friction condition and geometrical aspects of the rotor configuration. From this it is anticipated that the conditions for reliable experiments involving ex situ pre-prepared samples composed of low damping elastomers can, in the future, be estimated a priori.