一种新型磁流变复合胶及其可控流变特性

以羰基铁粉为磁性颗粒、甲基硅油和明胶/琼脂胶溶胶溶液的复合物为基体及各种添加剂制备了多组类液态磁流变复合胶样品。利用流变仪分别在旋转剪切模式和振荡剪切模式下对样品进行流变特性试验研究。结果表明,基体胶质物的含量对其流变特性影响较大。基体胶质物含量越高,剪切屈服强度越大且最大为92.1k Pa;胶质物含量对磁流变复合胶的线性粘弹性范围几乎没有影响;胶质物含量越高,磁流变复合胶的剪切储能模量越大,且绝对模量最大变化可达2.526MPa;添加纳米Si O2能提高磁流变复合胶的剪切屈服应力且能拓宽磁流变复合胶在磁场下的可调范围。     

A Prediction Method of the Behavior of Adhesively Bonded Structures under Cyclic Shear Loading Based on a Characterization of the Viscous Aspects of the Adhesive in an Assembly

The capabilities of structural bonding are more and more used. Estimating the abilities of an adhesive to endure repetitive loadings and to keep stable its mechanical properties along service life is an essential point to analyze in order to conduct fatigue assessments. The aim of this study is to develop a predictive tool for describing the fatigue behavior of an adhesive in an assembly under cyclic loadings. The approach developed analyzes the influence of viscosity on the mechanical behavior of an adhesive in an assembly based on monotonic and creep test results. Thanks to the evaluation of viscous phenomena, it is possible to predict the cyclic response of the adhesive. The experimental approach uses a unique bonded joint designed to limit the stress concentrations and with a maximum stress state in the center of the adhesive. In this paper, following the strategy developed under monotonic loading, experimental results under cyclic loading are presented for different types of loading using several load ratios and amplitudes. These results underline that the evolution of viscous deformations depends on the loading type. Under shear loading and for a ductile structural adhesive, the experimental results are well described using a viscoelastic–viscoplastic constitutive model with nonlinear viscous parameters. This model makes it possible to analyze the influence of different parameters on the mechanical response of bonded joints under cyclic shear loadings.     

Mechanische Eigenschaften zyklisch be‐ und entfeuchteter Zeolithgranulate

The production of zeolite granules varies in the amounts of binder content and different drying/activation temperatures. Here, the influence of moisture content and cyclic moisture loading and unloading on the mechanical properties like the strength of three different types of zeolite granules has been studied by uniaxial compression tests. The force‐displacement curves and scanning electron microscopy pictures of the granule and fracture surfaces show that with increasing number of moistening‐drying cycles, a continuous decrease in the strength of granules take place due to non‐regenerative damage of the structure.     

Dynamic rheological behavior of reactively compatibilized polypropylene/polyamide 6 blending melts

The dynamic rheological behavior is measured by small amplitude oscillatory shear on rotational rheometer for polypropylene/polyamide 6 (PP/PA6) blends compatibilized by a polypropylene grafted maleic anhydride (PP‐g‐MAH). Scanning electron microscope (SEM) results show that the PP/PP‐g‐MAH/PA6 (=100/6/40wt) is sea‐island structure, the PP/PP‐g‐MAH/PA6 (=100/6/60wt) blend is semi‐cocontinuous. Coarse PA6 zones can be observed when the weight ratio is 100/6/80. At low frequency the complex viscosity, dynamic modulus of the PP/PP‐g‐MAH/PA6 (PP/PP‐g‐MAH = 100/6wt) blends first increase then drop with the increase of PA6 weight content in the range of 0–100, the maximum value arrives at the weight content of 60. The Cole–Cole plots as well as the weighted relaxation spectra of the blends have a main arc and a tail when the weight ratio of PP/PP‐g‐MAH/PA6 is in the range of 100/6/20–100/6/60, but have different shapes when the weight ratio increases to 100/6/80 and 100/6/100. The possible reason is the weight ratio of 100/6/80 and 100/6/100 is close to the phase inversion point. In fitting the storage modulus data at low frequency, Palierne's model with two parameters interfacial tension and interfacial shear modulus is better than Bousmina's model. Palierne's model with only one parameter of interfacial tension can not fit the data well. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42091.     

Microstructure and properties of carbon fiber sized with pickering emulsion based on graphene oxide sheets and its composite with epoxy resin

The Graphene oxide (GO) sheets were used for preparing the epoxy resin Pickering emulsion. The particle size and the zeta potential of the Pickering emulsion were measured to evaluate its stability. The stable emulsion could be served as the film former of sizing agent for carbon fiber (CF). The effect of the Pickering emulsion stabilized by GO sheets on the properties of CF and the interfacial adhesion property of CF reinforced composite were investigated. Scanning electron microscopy (SEM) images showed that there existed a layer of sizing agent film with GO sheets evenly on the CF surface. Abrasion resistance and stiffness values of CF were tested and the results indicated that the sized CF conformed to the requirement of CF handleability. The interlaminar shear strength (ILSS) test indicated that the interfacial adhesion of the composite could be greatly improved. The fracture surfaces of CF composites were examined by SEM after ILSS tests. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42285.     

Plugging behavior of gellan in porous saline media

In this article, the hydrodynamic behavior of dilute aqueous solutions of a natural polysaccharide—gellan in the porous media under the modeled oilfield conditions is described. The hydrodynamic properties of gellan and poly(acrylamide) solutions in saline porous media are compared. The influence of inorganic salts NaCl, KCl, CaCl₂, MgCl₂, and BaСl₂ on sol–gel and gel–sol transitions of dilute gellan solutions was evaluated. The mechanism of sol–gel transition in the presence of individual alkaline and alkaline‐earth metal salts is described on the basis of literature data. The viscometric measurements revealed that the effectiveness of salts to enhance gelation of gellan changes in the following order: BaСl₂ > CaCl₂ ≈ MgCl₂ > KCl > NaCl. The sol–gel and gel–sol phase transitions of gellan solution were also observed upon addition of oil field water containing 73 g L^?1 of alkaline and alkaline earth metal ions. During the injection of gellan solutions into the porous media saturated by saline water an oscillation of the injection pressure was observed. Such behavior of gellan is explained by either the sol‐to‐gel and the gel‐to‐sol transitions of the polymer taking place in saline water or the step‐by‐step plugging of high permeable channels until all high permeable channels of sand packs are plugged due to gellan invasion. The application of brine‐initiated gelation of gellan for water shutoff operations (WSO) in field conditions was demonstrated. Higher technological effectiveness of gellan injection in comparison with existing gelation systems was shown. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41256.     

Self‐nucleation–induced nonisothermal crystallization of nylon 6 from the melt

The effect of thermal treatment over a wide range of temperature (130–280°C) on the crystallization behavior of nylon 6 was studied by using DSC, FTIR, and polarized light microscope equipped with a hot stage. The crystallization and the subsequent melting behavior of the nylon 6 samples treated at different temperatures (T_s) were classified into four types. When T_s was higher than 236°C or lower than 213°C, the crystallization behavior of nylon 6 was insensitive to the variation of T_s. When T_s was in the range of 213–235°C, the crystallization behavior was sensitive to the change of T_s. The polarized light microscopic experiments have demonstrated that a large amount of tiny ordered nylon 6 segments/cluster persisted when nylon 6 film are heated to 231°C. Consequently, the fastest crystallization speed was observed. As T_s was between 214 and 223°C, both the T_m and the ΔH_m were higher than those of the nylon 6 samples treated at other temperature. The polarized light microscopic investigations have also demonstrated that molten nylon 6 crystallizes by using the un‐molten nylon 6 crystals as nucleation center at 220°C. Crystallization at higher temperature produces nylon 6 with thicker crystalline lamella. The above results are helpful for rational design of thermal treatment procedure to obtain nylon 6 with different crystalline features. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42413.     

Enforcement avoidance behavior near automated speed enforcement areas in Korean expressways

Automated speed enforcement system (ASES) has been deployed as a safety countermeasure on Korean roadways to reduce speeding-related traffic crashes; information on ASES locations is mandated to be open to the public. However, because drivers are alerted about enforcement via on-board navigation systems and roadside signs, they can avoid enforcement by momentarily reducing their speeds near ASES locations. This enforcement avoidance behavior (EAB) can induce sudden changes in speed near the enforcement locations and thereby increase risk of crash occurrence.     

In-depth analysis of drivers’ merging behavior and rear-end crash risks in work zone merging areas

This study investigates the drivers’ merging behavior and the rear-end crash risk in work zone merging areas during the entire merging implementation period from the time of starting a merging maneuver to that of completing the maneuver. With the merging traffic data from a work zone site in Singapore, a mixed probit model is developed to describe the merging behavior, and two surrogate safety measures including the time to collision (TTC) and deceleration rate to avoid the crash (DRAC) are adopted to compute the rear-end crash risk between the merging vehicle and its neighboring vehicles. Results show that the merging vehicle has a bigger probability of completing a merging maneuver quickly under one of the following situations: (i) the merging vehicle moves relatively fast; (ii) the merging lead vehicle is a heavy vehicle; and (iii) there is a sizable gap in the adjacent through lane. Results indicate that the rear-end crash risk does not monotonically increase as the merging vehicle speed increases. The merging vehicle's rear-end crash risk is also affected by the vehicle type. There is a biggest increment of rear-end crash risk if the merging lead vehicle belongs to a heavy vehicle. Although the reduced remaining distance to work zone could urge the merging vehicle to complete a merging maneuver quickly, it might lead to an increased rear-end crash risk. Interestingly, it is found that the rear-end crash risk could be generally increased over the elapsed time after the merging maneuver being triggered.     

炭黑增强橡胶复合材料的大变形细观力学模型

为考察炭黑对橡胶复合材料超弹性力学行为的影响,首先,利用不同填充体积分数的炭黑增强橡胶复合材料的准静态力学试验数据,对现有的基于均质化方法的"变形放大"细观力学模型的大变形表征能力进行了评估。其次,在此基础上提出了新的"第一不变量放大"关系,并获得了较为合理的预测结果。最后,利用随机序列吸附算法建立了较接近材料真实细观结构的球形颗粒填充数值模型,进行了大变形情况下的三维数值模拟;为考察颗粒聚集效应的影响,还设置了颗粒均匀随机分布和团聚随机分布两种形式。计算结果与试验数据的对照表明:提出的三维细观数值模型已经能在一定程度上预测填充橡胶的大变形宏观力学行为,且颗粒团聚随机分布模型的预测能力更好一些。试验结果验证了该模型的合理性,所建模型为进一步的相关研究提供了参考。