Study on the blackening phenomenon of leaded glass during microgroove molding using nickel phosphorous mold

Precision glass molding (PGM) is a recently developed method to fabricate glass microgroove components. Lead glass is commonly used as an optical material due to its high refractive index and low transition temperature. A nickel-phosphorous (Ni–P) plated mold is traditionally employed in the PGM process for microstructures optics. However, leaded glass is subject to color change and can blacken during the PGM process, reducing the light transmittance of microgrooves. In this paper, an equation for the redox reaction between Ni and Pb is proposed, which is based on the diffusion of inner Ni atoms to the surface of the mold and the standard electrode potential of the Pb ions in leaded glass. A viscoelastic constitutive model of the glass is established to simulate the compression stress distribution during molding. Finally, the effects of molding pressure, molding temperature, and mold material on glass blackening are studied. The results show that the blackening of leaded glass is caused by Pb enriching the surface. The rise in molding stress and temperature increases the deformation of Ni–P plating, which promotes the diffusion of Ni atoms. By adding a titanium incorporated diamond-like carbon (Ti-DLC) coating, the deformation of the Ni–P plating during molding is suppressed, and the diffusion of Ni atoms can be prevented. In this way, the blackening of leaded glass can be prevented.     

主动约束层阻尼板结构动力学建模研究

将有限元法和GHM法相结合，给出了建立主动约束层阻尼（ACLD）板结构动力学模型的新方法。建模时，考虑到粘弹材料（VEM）的纵向位移影响，采用GHM方法描述VEM的本构关系，解决了VEM的力学特性随温度和频率变化的难点，避免因VEM的复杂本构关系而产生的微分积分方程。算例表明本文给出的建模方法是准确的，ACLD结构能够有效控制结构振动。     

聚苯硫醚／聚砜共混物的动态黏弹行为及相容性研究

研究了聚苯硫醚／聚砜熔融共混物的的加工流变行为以及共混物在不同温度下的动态黏弹响应；并对其相容性作出判断。结果表明，聚苯硫醚的加入显著改善了共混物的流动性，使其可在较低温度下成型；熔融态共混体系的相容性较差，固态条件下的相分离程度及损耗因子峰值大小依赖于组成变化。     

Viscoelastic, Thermal and Mechanical Properties of Dicyclopentadiene Bisphenol Diyanate Ester / Epoxy Co-polymers

Summary Dicyanate ester containing dicyclopentadiene cycles and epoxy co-polymers were prepared by copolymerization between epoxy and dicyclopentadiene bisphenol cyanate esters (DCPDCE). Viscoelastic properties of the co-polymers were characterized by the technique of dynamic mechanical analysis (DMA), which indicated that the introduction of E51 in the co-polymers would effectively improve the toughness of DCPDCE, while the thermal dimensional stability would be weakened. Results from thermogravimetric analysis (TGA) are in good accordance with the T_g values from DMA curves. Mechanical testing of the cured co-polymers shows that E51 can improve the mechanical properties of the co-polymers while its usage is controlled among 5% to 15%.     

BLOOD VISCOELASTICITY FOR CONDITIONS OF PHYSIOLOGICAL FLOW IN SMALL ARTERIES

The viscoelasticity of blood is quantified by studying the oscillatory flow of suspensions of RBC in plasma in 218 μm and 400 μm glass capillary tubes. The flow conditions are chosen to reflect normal physiological flow in small arterial vessels. Data are obtained for suspension hematocrits between 35 and 80 percent, and at physiological temperature (37°C) The results indicate that the elastic component of the viscoelasticity of blood is effectively negligible for the conditions of this study; the measured pressure gradient-flowrate relationship is dominated by the viscous component of blood viscoelasticity.     

On the use of a spectrum-based model for linear viscoelastic materials

A new spectrum-based model for describing the behavior of time-dependent materials is presented. In this paper, unlike most prior modeling techniques, the time-dependent response of viscoelastic materials is not expressed through the use of series. Instead, certain criteria have been imposed to select a spectrum function that has the potential of describing a wide range of material behavior. Another consequence of choosing the spectrum function of the type used in this paper is to have a few closed form analytic solutions in the theory of linear viscoelasticity. The Laplace transform technique is used to obtain the necessary formulae for viscoelastic Lame' functions, relaxation and bulk moduli, creep bulk and shear compliance, as well as Poisson's ratio. By using the Elastic–Viscoelastic Correspondence Principle (EVCP), material constants appearing in the proposed model are obtained by comparing the experimental data with the solution of the integral equation for a simple tensile test. The resulting viscoelastic functions describe the material properties which can then be used to express the behavior of a material in other loading configurations. The model's potential is demonstrated and its limitations are discussed.     

Study on residual stress in viscoelastic thin film using curvature measurement method

Using LSM (laser scanning method), the radius of curvature due to thermal deformation in polyimide film coated on Si substrate is measured. Since the polyimide film shows viscoelastic behavior, i.e., the modulus and deformation of the film vary with time and temperature, we estimate the relaxation modulus and the residual stresses of the polyimide film by measuring the radius of curvature and subsequently by performing viscoelastic analysis. The residual stresses relax by an amount of 10% at 100°C and 20% at 150°C for two hours.     

矿井提升机钢丝绳的粘弹性研究

以纤维芯钢丝绳为对象，研究其粘弹性力学性能。首先，从理论上推导钢丝绳单向拉伸时的拉力一位移关系，确定钢丝绳变形的时间相依性；然后，在应力松弛试验的基础上，建立钢丝绳的粘弹性力学模型，试验结果和分析表明，该模型能较好地描述钢丝绳在单轴拉伸过程中的应力松弛现象。纤维芯钢丝绳广泛用于矿井提升机中，在考虑钢丝绳的粘弹性性能后，提升机的卷筒所受的周向压力会随时间变化，卷筒的屈曲失效分析应该考虑这种效应。     

Dynamic response of a double-deck circular tunnel embedded in a full-space

A three-dimensional dynamic model for calculating the ground-borne vibrations generated by harmonic loads applied on the interior floor of a double-deck circular tunnel is developed. The response of the system is obtained coupling the interior floor subsystem and the tunnel-soil subsystem in the wavenumber-frequency domain. The interior floor is modeled as a thin plate of infinite length in the train circulation direction and the tunnel-soil system is described using the Pipe in Pipe model. Some numerical instabilities of the resulting expressions are overcome by using analytic approximations. The results show that the dynamic behavior of the interior floor clearly influences the magnitude of the coupling loads acting on the tunnel structure. The soil response to a harmonic load acting on the double-deck tunnel is compared to the one obtained for the case of a simple tunnel finding significant differences between them for the whole range of frequencies studied. The proposed model extends the prediction of train-induced vibrations using computationally efficient models to this type of tunnel structure.     

Viscoelastic responses of flow driven by a permeable disk investigated by ultrasound velocity profiling

Ultrasound velocity profiling was applied to viscoelastic flow induced around a moving permeable disk. There were two objectives to this measurement. The first was to find technical advantages and restrictions when applying ultrasonic Doppler velocimetry to a viscoelastic liquid. This issue has not been clarified even though ultrasonic pulses may interact with an elastic medium in the monitoring of the Doppler shift frequency. The second objective was to determine the fluid physics of a viscoelastic liquid around a permeable object, which will help in designing mixing process for materials subject to strong rheological resistance. In this paper, we report a representative response of a viscoelastic liquid in terms of its spatiotemporal velocity distribution. The response highlighted is cyclic lateral waves that form behind the disk, which were hardly detectable by particle image velocimetry. We discuss multiple reasons for this phenomenon considering not only fluid properties but also the measurement principle of ultrasound velocity profiling as applied to viscoelastic liquid.