Cure monitoring of CFRP composites by dynamic mechanical analyser

The cure characteristics of carbon/MTM44-1 epoxy composite prepreg and neat MTM44-1 epoxy resin are monitored using a dynamic mechanical analyser (DMA). This study also assesses whether the simple containment device recommended by the DMA manufacturer for powder and gel is suitable for prepregs. The device is a disposable 0.1-mm thick stainless steel pocket. The cure behaviour of the packaged materials is compared with that of the unpackaged prepreg. All the samples are cured following the manufacturer's 180°C-isothermal schedule with heating rates of 2 °C/min and 5 °C/min. The tests highlight that: (i) the cure of composite prepregs and resin can be monitored using a DMA; (ii) the stainless steel pocket does not influence the cure of the prepreg and resin; and (iii) the softening and melting of the uncured resin, the resin low viscosity state and the subsequent gelation-vitrification-solidification of the resin are detected with this method.     

Coupled Orientation and Stretching of Chains in Mesoscale Models of Polydisperse Linear Polymers in Startup of Steady Shear Flow Simulations

Polydisperse linear polymers are studied in startup of steady shear flow simulations using dissipative particle dynamics. The results show that with an increase in polydispersity the stress overshoot declines while the steady‐state stress increases. Various physical characteristics of the systems are studied including frequency of nonbonded interactions, gyration radius data, flow alignment angles, and average bond lengths. The patterns in the data suggest higher forces are necessary to orient and stretch long chain fractions in the flow direction. Relaxation modulus data prove the broad range of relaxation mechanisms in polydisperse systems. Linear viscoelasticity theory is used to quantify the relaxation spectrum. The results indicate an increase in the longest relaxation time in systems with higher polydispersity. The steady‐state shear viscosity results show higher viscosities with an increase in polydispersity at all shear‐rates. The good agreement of the characteristic behaviors of modeled polydisperse polymers with experiments is encouraging for future work.

     

基于糖和苯硼酸动态共价键的高效蛋白质表面修饰方法

糖和蛋白质的相互作用参与了很多重要的生命过程.研究糖和蛋白质的相互作用有多种手段,石英晶体微天平(QCM)是其中重要的一种.研究中常需要将蛋白质通过共价键连接在天平芯片的表面.但是,用于检测糖分子的蛋白质多为植物凝集素,它们的分子量大,表面可修饰位点少,通过共价键修饰在芯片表面的效率偏低.本文提出一种基于糖和苯硼酸之间动态共价键的新修饰方法,能够大幅度提高蛋白质在芯片表面的修饰效率.     

硫化天然橡胶的本征自修复与固相回收加工

通过小分子模拟试验和应力松弛,发现甲基丙烯酸铜(MA-Cu)比氯化铜(CuCl_2)更适合用作硫化天然橡胶中二硫键交换反应催化剂,并且硫化天然橡胶中的二硫键交换反应需要在高于120°C的温度下才能高效进行,这保障了相关制品在较低温工作时的结构与性能稳定.进一步的实验结果表明,硫化天然橡胶在MA-Cu辅助作用下获得了多次自修复与固相回收加工性能,损伤自修复后的硫化天然橡胶与固相回收加工的再生硫化天然橡胶,其拉伸强度均可恢复到原始材料强度的80%左右.     

Dynamic Aggregation Operators Based on Intuitionistic Fuzzy Tools and Einstein Operations

The idea of combine aggregation and intuitionistic fuzzy information plays essential role in multi criteria decision making (MCDM) process. However, this new branch has attracted researchers that study in different fields recently. In this paper, we study MCDM problems with intuitionistic fuzzy environment. Firstly, we introduce some operations related with Einstein t-norm and t-conorm such as, Einstein sum, product and exponentiation. After that, we define dynamic intuitionistic fuzzy Einstein averaging (DIFWA${}^{?}$) operator and dynamic intuitionistic fuzzy Einstein geometric averaging (DIFWG${}^{?}$) operator. Their notable property is that collect and aggregate values in different period based on Einstein operations in intuitionistic fuzzy set (IFS)s. In addition, we compare the defined operators with the existing intuitionistic fuzzy dynamic operators and get the corresponding relations. We establish two methods using with DIFWA${}^{?}$ and DIFWG${}^{?}$ to solve MCDM problems with intuitionistic fuzzy tools. Finally, an illustrated example is presented to show the applicability of the introduced methods.     

正交复合材料面层夹层板非线性理论及应用

针对复合材料面层夹层板的构造和变形特点，考虑横向剪应力在面层和芯层粘结处的连续条件，应用Ｈａｍｉｌｔｏｎ原理建立了基于五个未知函数的正交铺设复合材料面层夹层板的非线性精化理论。对静力学问题，控制方程化简为由四个基本未知函数表述。文中还分析了简支正交铺设复合材料面层夹层板的非线性弯曲，给出了载荷—挠度特征关系和板中应力的分布状况。数值计算表明，夹层板面层和芯层粘结处的层间剪应力在工程设计中是十分重要的。     

Shear dependence of viscosity for perfluoropolyether fluids

The shear dependence of the bulk viscosities of two structurally different types of perfluoropolyether fluids was determined by two different techniques. The first involved direct measurement in a high shear Couette viscometer, the second utilized the time-temperature superposition principle to establish master curves from viscosity determinations at low shear rates and temperature; the results are comparable. Both fluids begin to show non-Newtonian behavior at shear rates above 10,000 s^–1.     

Measurement of energy release rate and energy flux of rapidly bifurcating crack in Homalite 100 and Araldite B by high-speed holographic microscopy

High-speed holographic microscopy is applied to take three successive photographs of fast propagating cracks in Homalite 100 or in Araldite B at the moment of bifurcation. Crack speed at bifurcation is about 540 m/s on Homalite 100, and about 450 m/s on Araldite B. From the photographs, crack speeds immediately before and after bifurcation are obtained, and it is found that discontinuous change of crack speed does not exist at the moment of bifurcation in the case of Homalite 100, but exists in the case of Araldite B. From the photographs, crack opening displacement (COD) is also measured along the cracks as a function of distance r from the crack tips. The measurement results show that the CODs are proportional to √r before bifurcation. After bifurcation, the CODs of mother cracks are proportional to √r, though the CODs of branch cracks are not always proportional to √r. The energy release rate is obtained from the measured CODs, and it is found that energy release rate is continuous at bifurcation point in both cases of Homalite 100 and Araldite B. Energy flux that shows the energy flow toward a crack tip is also obtained.