3-D Finite-Element Numerical Simulation of Centrifugal Induction Electrosalg Casting Solidification Process

A 3-D finite-element numerical simulation model of temperature field for CIESC casting solidification process was developed with the aid of ANSYS software and a series ofcorresponding experiments were made. The results showed that the good agreement was obtained between the numerical simulation and the experiments. Based on the numerical simulation results, the characteristics of tem- perature distribution in the castings during CIESC solidification process were analyzed and summarized. According to the G/R1/2 method and numerical simulation results, there is no any shrinkage defect in the CIESE casting and structure of casting is fine and compact.     

混凝土徐变系数与徐变度的对比分析

基于现有的试验资料,高层及大跨度民用建筑的徐变分析只能参照桥梁结构中的徐变系数方法或水工结构中的徐变度方法进行.从徐变系数的定义出发,利用积分中值定理和叠加原理,推导并修正了加载龄期与起算龄期不同时徐变收缩应变增量的表达式,对比了应用徐变系数分析徐变的有限元法和应用徐变度分析徐变的初应变法在效率和精度上的差别,并建议应从概念设计的角度出发,采用徐变度的初应变法来估算徐变对高层及大跨度民用建筑的影响.     

水胶比及矿物掺和料对净浆塑性收缩影响

采用自行设计测定塑性收缩的方法,对不同胶凝材料净浆在不同水胶比情况下的塑性收缩变化规律及矿物掺和料对塑性收缩的影响进行了研究。试验结果表明,净浆塑性收缩与水胶比有关;水胶比为0.28~0.35时,塑性收缩随水胶比的增加而减小,而在0.35~0.45范围内随水胶比的增加而增加;矿物掺和料的品种及掺量对净浆的塑性收缩也有很大的影响。     

Effect of nanoclay on shrinkage control of low profile unsaturated polyester (UP) resin cured at room temperature

The addition of a small amount of nanoclay (1-3 wt%) can provide excellent volume shrinkage control of unsaturated polyester (UP)/styrene (St)/poly(vinyl acetate) (PVAc) systems cured at room temperature. PVAc serves as the low profile additive (LPA). In this study, both temperature-induced phase separation of the uncured resin mixture and transmission electron microscopy (TEM) of the cured sample revealed that nanoclay resided in the LPA-rich phase, leading to a higher reaction rate and earlier onset of micro-cracking in the LPA-rich phase or at the interface of the LPA-rich and UP-rich phases. Consequently, an earlier volume expansion during curing was observed in reactive dilatometry, resulting in better shrinkage control. On-line measurement of the composite thickness change during vacuum-infusion liquid composite molding [e.g. the Seemann Composite Resin Infusion Molding Process (SCRIMP)] further proved excellent volume shrinkage control of nanoclay filled systems, leading to a smoother composite surface.     

Modeling for prediction of restrained shrinkage effect in concrete repair

A general model of autogenous shrinkage caused by chemical reaction (chemical shrinkage) is developed by means of Arrhenius' law and a degree of chemical reaction. Models of tensile creep and relaxation modulus are built based on a viscoelastic, three-element model. Tests of free shrinkage and tensile creep were carried out to determine some coefficients in the models. Two-dimensional FEM analysis based on the models and other constitutions can predict the development of tensile strength and cracking. Three groups of patch-repaired beams were designed for analysis and testing. The prediction from the analysis shows agreement with the test results. The cracking mechanism after repair is discussed.     

中国不饱和树脂工业进展

综述了近几年中国不饱和树脂(UPR)及其下游产品的技术进展,其中包括:低收缩性UPR、阻燃乙烯基树脂、胶衣树脂、树脂制造工艺的改进、UPR工业废水处理,生物基UPR及复合材料,功能化UPR的研究应用。     

2011-2012年世界不饱和聚酯树脂工业进展

介绍了2011-2012年国外不饱和聚酯原料市场动态,国外企业运营情况。综述了不饱和聚酯树脂领域的研究及应用进展,涉及不饱和聚酯树脂及其复合材料的电性能、收缩性能、力学性能、生物复合材料、表面处理、阻燃性能及环保等。     

Multi-methacrylated star-shaped,photocurable poly(methyl methacrylate) macromonomers via quasiliving ATRP with suppressed curing shrinkage

Novel, star-shaped multifunctional poly(methyl methacrylate) (PMMA) macromonomers with well-defined average number of pendant methacrylate groups were synthesized by copolymerizing MMA with 2-hydroxyethyl methacrylate (HEMA) via quasiliving ATRP with a tetrafunctional initiator in methanol at 10 °C, followed by methacrylation of the hydroxyl groups of the HEMA units. The resulting tailor-made poly(methyl methacrylate-co-2-methacryloylethyl methacrylate), P(MMA-co-MEMA), multifunctional macromonomers were used as cross-linking agents in photocuring of MMA, a solvent for its own polymer, and thus chemically homogeneous PMMA networks were formed in which the tetrafunctional initiator moiety provides inherent, additional branching points in the resulting cross-linked materials. This approach, even in the presence of relatively low amounts of macromonomers of ∼35–45%, provides sol-free products and up to ∼40% less polymerization shrinkage than that by curing of MMA with a conventional low molecular weight bifunctional methacrylate. These new, unique star-shaped PMMA macromonomers are potential cross-linkers in a variety of solvent-free applications where low curing shrinkage and high conversions are critical requirements, such as in several engineering materials, coatings, dental fillings and restorations, bone cements etc.     

Evaporation rate effect on starting point of shrinkage stress development during drying process in solvent cast polymer film

To reveal the effect of drying conditions on shrinkage stress existing between a film and a substrate, a polystyrene/toluene solution was coated on a glass substrate, and the volume fraction of toluene at the time when the stress starts to grow (?_S) was measured at various drying temperatures and evaporation rates. ?_S decreased with increase of drying temperature at a constant evaporation rate, while ?_S increased with increase of evaporation rate at a constant drying temperature. From these results, it was suggested that the dominant factors affecting the starting point of stress were both the chain mobility and the measurement time‐scale. Considering the two factors, the tendency of ?_S with the drying conditions is quite similar to that of the solvent content at glass transition point, and this fact indicates a strong correlation between the starting point of stress and the glass transition of coated solution. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

基于粉煤灰掺量的砂浆塑性收缩开裂本构关系的研究

研究了粉煤灰掺量对于砂浆塑性收缩性能和塑性粘度的影响。试验表明,随着粉煤灰掺量的增加,砂浆抗裂指数增大,开裂所需时间增加,塑性粘度降低;建立了粉煤灰掺量与砂浆抗裂指数、开裂时间的本构关系,及掺加粉煤灰后砂浆塑性粘度与抗裂指数的本构关系。