同步辐射SAXS原位在线检测纤维微结构系统的研究

研制开发了一套适用于同步辐射大科学装置上的原位在线检测装置,运用远程计算机控制,以同步辐射SAXS为手段,可实现纤维内部微缺陷的原位在线检测。原位在线检测可以表征高性能纤维在制备过程中缺陷和结构变化与工艺之间的关系,这是制备高性能纤维的关键所在。通过设备调试与实验,该系统可实现原位在线检测碳纤维、芳纶和超高分子量聚乙烯3大高性能纤维在不同温度、不同张力以及不同气氛下微缺陷与结构演化过程。     

Tailoring structures and properties of mesophase pitch-based carbon fibers based on isotropic/mesophase incompatible blends

Blends composed of isotropic and mesophase pitches in various proportions were used as precursors for carbon fibers. The effects of composition on the morphology of blends, precursor spinnability, transversal texture, and mechanical properties of the final carbon fiber were studied. The blends are binary incompatible phase-separation systems. When the content of isotropic pitch is ≤30 %, it is distributed uniformly in the mesophase matrix as spheres; whereas, complete phase inversion occurs when the content is ≥35 %. Blends containing isotropic pitch in dispersion phase show good spinnability and small-diameter fibers can be continuously drawn. The transversal texture of carbon fibers is transformed from a radial type with a crack along the fiber axis to an intermediate morphology between radial and random type by blending 20–30 % isotropic pitch. The tensile strength of carbon fibers with 20–30 % IPc is 2.5 times as high as the AR-based CF without the reduction of Young’s modulus.     

铝基复合材料半固态压缩变形组织演化同步辐射原位CT研究

利用原位快速同步辐射计算机断层扫描技术,研究纳米颗粒增强Al-10%(质量分数)Cu复合材料的半固态压缩过程,并利用三维图像定量化分析其半固态压缩变形过程中微观组织结构,特别是微孔的演变过程。结果表明:纳米颗粒增强铝基复合材料在半固态压缩过程中的微孔演变可分为3个主要阶段,即微孔闭合阶段,微孔潜伏阶段和微孔的迅速长大阶段。通过对不同变形阶段微孔分布的定量化数据分析和组织观察,进一步分析纳米陶瓷颗粒增强铝基复材的半固态压缩变形机制。借助同步辐射原位成像技术开展铝基复材受载下的四维(三维+时间)研究,可为探究铝基复合材料的半固态变形行为提供参考。     

Changes in microfibril angle in cyclically deformed dry coir fibers studied by in-situ synchrotron X-ray diffraction

Dry coir fibers are characterized by wide-angle X-ray scattering coupled with tensile tests. The fibers exhibit elastic and plastic behavior with the yield point at a strain of about 2%. In-situ experiments document that the cyclic loading and unloading beyond the yield point does not reduce the stiffness of the fibres, since they recover their initial stiffness by every increase of the strain. The diffraction data show that the microfibril angle (MFA) of cellulose fibrils in the coir fibre cells is inversely proportional to the magnitude of the applied strain. In average, the relatively high MFA of about 45° in the unstrained state decreases linearly upon straining until the fibers break at about 35% strain. When the strain is released during the tensile experiment the MFA tends to recover its original magnitude. No significant differences in the dependence of MFA on strain are detected in elastic and plastic regions, respectively. The results demonstrate that the tissue with helical architecture does not have to be saturated with water in order to exhibit the effect of the recovery of the mechanical function when cyclically loaded. This indicates differences in the architecture of the coir cell wall in comparison with that of compression wood with high MFA whereby similar phenomena were observed in the wet state.     

TB6合金热压缩变形行为研究

本文主要研究了热变形过程中变形温度、应变速率对TB6合金组织性能的影响。研究表明流动应力随应变速率的升高而增大,随变形温度的升高而减小。而变形温度对流动应力的影响程度与应变速率的大小有关。     

Fabrication of a planar polymeric deformation Bragg sensor component by excimer laser radiation

Polymethylmethacrylate is irradiated by a UV-laser in order to modify its optical properties photochemically. Thus, by a lithographic method, the refractive index can be locally increased in a controllable way permitting the manufacturing of integrated-optical waveguiding and dispersive structures at the surface of a planar polymer chip. By this method, a polymeric Bragg sensor in integrated-optical form was fabricated by the UV-light of an excimer laser. The surface topography and the functional properties of the planar polymeric deformation Bragg sensor have been examined. Experiments concerning the evanescent field of the sensor have also been carried out in order to clarify the Bragg reflection mechanism.     

In situ mechanical characterization during deformation of PVC polymeric foams using ultrasonics and digital image correlation

Cellular solids such as polymeric foams are finding increasing applications including its use as a core material for sandwich structures. In this study, a novel method is used to measure both the longitudinal and shear wave speeds of a material simultaneously while applying a compressive load in four different densities of polymeric foams made from the same base polymer, polyvinyl chloride (PVC). The study showed that there was a significant difference in evolution of the wave speeds and hence in the apparent modulus during deformation of the lower density foams in comparison to the higher density foams. The non-contact full-field method of digital image correlation (DIC) is used to gain insights into the failure modes during deformation. The lower density foams undergo heterogeneous deformation and failed due to buckling of cell walls. In contrast, the higher density foams undergo nominally homogeneous deformation due to plastic collapse. The failure mode transition is shown to be governed by the relative density of the foams and the mechanical properties of the polymer.     

Tensile-force-induced delamination of polymeric coatings in tightly jacketed double-coated optical fibers

To maintain the mechanical strength, the glass fiber of optical fibers is coated by polymeric materials during the fabrication process. However, when the external tensile-force-induced shear stress at the interface of the glass fiber and primary coating is larger than its adhesive stress, the polymeric coatings will be delaminated from the glass fiber and optical fiber will lose its mechanical strength. In this article, the tensile-force-induced delamination of polymeric coatings in tightly jacketed double-coated optical fibers is investigated. To minimize the coating's delamination, the tensile-force-induced shear stress at the interface of the glass fiber and primary coating should be reduced. The method to minimize such a shear stress is to select suitable polymeric coatings as follows. The Poisson's ratio of the primary coating and the Young's moduli of the secondary coating and jacket should be increased, but the Young's modulus of the primary coating and thickness of the secondary coating should be decreased. On the other hand, the thickness of the primary coating has an optimal value. The selection of the adhesive shear stress between the glass fiber and primary coating in the minimization of the coating's delamination is also discussed.     

Formation and decay of a smectic mesophase during orientation of a PET/PEN copolymer

An analysis has been made of time resolved wide angle X-ray scattering during the deformation of a 50%poly(ethylene terephthalate)/50%poly(ethylene 2,6naphthalate) copolymer at 120°C at a draw rate of the order of 10 s^–1. During the initial fast deformation a meridional reflection associated with a smectic mesophase is observed to form. After the initial deformation, the mesophase reflection decays at a rate of about 1 s^–1. During the decay, the lateral halfwidth of the meridional reflection increases indicating attrition of the smectic mesophase regions from the lateral interfaces. The sample deforms in a non-uniform manner. After the applied deformation ceases, the sample continues to thin down in the region of the X-ray beam. This is attributed to the lack of crystallisation during the 5 s timescale of observation. Analysis of the azimuthal profile of the strong inter-chain diffuse diffraction at 2.8 nm^–1 shows that the mesophase is associated with extended chains with a characteristic high alignment of segments along the deformation. During the period of decay of the mesophase it is proposed that the chain segments can be effectively divided into just two components: oriented mesophase and isotropic amorphous regions. The analysis indicates that the proportion of the mesophase varies from 80 to 40% during the observed decay period.     

Microstructural development in a low carbon Ti-microalloyed steel during deformation within the ferrite region

Microstructural evolution of ferrite in a low carbon Ti-microalloyed steel, during deformation within the ferrite region, was investigated by using torsion testing. Warm deformation characteristics of ferrite were studied by analyzing of its flow curves, optical microstructures and electron back-scattered diffraction maps. The results show that an unstable sub-boundaries network forms and then these transform into high angle boundaries, with further straining. It was found that the occurrence of continuous dynamic recrystallization is responsible for the development of very fine ferrite grains with high angle boundaries.     

SAXS/WAXS/DSC study of temperature evolution in nanopolymer electrolyte

Soft matter polymer electrolytes as nanostructured materials are very attractive components for batteries and for opto-electronic devices as a new generation of dye-sensitized solar cells. (PEO)₈ZnCl₂ polymer electrolytes were prepared from PEO and ZnCl₂. The nanocomposites (PEO)₈ZnCl₂/TiO₂ themselves contained TiO₂ nanograins. In this work, the influence of TiO₂ nanograins or the morphology and ionic conductivity of the nanocomposite was systematically studied by small-angle X-ray scattering (SAXS) simultaneously recorded with wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) at the synchrotron ELETTRA. Shown by previous impedance spectroscopy measurements (IS), the room temperature conductivity of nanocomposite polymer electrolyte increased more than two times above 65 °C, relative to pure composites of PEO and salts. The SAXS/DSC measurements yielded insight into the temperature-dependent changes of the grains of the electrolyte as well as into the effects of heating and cooling rates. The crystal structure and temperatures of melting and crystallization of the nanosize grains was revealed by the simultaneous WAXS measurements.     

Tensile dilatometric studies of deformation in polymeric materials and their composites

The theory for volume changes in deformation for polymeric materials is presented, together with a brief literature review of the general area of tensile dilatometry. The theory has been used to enable the prediction of the volumetric response of a material to a deformation, which allows for the detection of the onset of cavitation (volume increasing)-type mechanisms in materials displaying such responses. A series of experiments has been performed using an instrumented tensile dilatometry technique on PMMA and on talc-filled reinforced polypropylene at 23 and 60 °C. The engineering constants, tensile modulus and lateral contraction ratio were measured and found to be viscoelastic. The determination of strain in three mutually perpendicular directions during the instrumented tensile test resulted in the measurement and prediction of the volumetric strain response with applied load. A significant cavitation-type mechanism was recorded in the case of the talc-filled reinforced polypropylene, whereas PMMA showed a deviatoric type mechanism. The volume strain has been found to be directly related to the bulk modulus for these materials. Finally, a new method of presenting volumetric strain versus applied stress data is shown and its relevance explained.     

微米炭纤维吸附水溶液中镉离子的性能

采用煤基炭棒阳极,在氦气/乙炔气氛下直流电弧放电制备了直径0.4μm～0.6μm、长度数十微米的炭纤维。以该微米炭纤维(MCFs)为吸附剂,研究水中镉离子在其上的吸附性能。考察了MCFs的表面性质、时间、溶液pH值及镉离子初始浓度对吸附的影响。实验表明,浓硝酸氧化处理可明显增加MCFs表面含氧官能团数量,吸附能力显著增加;吸附动力学数据符合准二级速率方程。pH值对吸附影响较大。酸性条件下,吸附等温线可用Langmuir方程和Freundlich方程拟合;沉淀发生条件下,可用表面沉淀模型拟合。MCFs的单位质量和单位比表面积的吸附量都很大,当pH=5.50和平衡浓度为2 mg.L-1时其吸附量分别为5.7 mg.g-1和0.058 mg.m-2。结果表明,MCFs在环境保护中显示出潜在应用前景。     

The effect of processing parameters on the mechanical properties of auxetic polymeric fibers

Auxetic polymeric fibers have been produced using a melt-spinning technique. The effect of the processing parameters on the fibers has been examined. It was found that the auxetic effect occurs over a very tight temperature window with screw speed, take-off speed and die geometry affecting homogeneity and auxeticity. This is an important finding as it provides a method of producing more homogeneous auxetic fibers with tailored values of Poisson’s ratio.     

SAXS法研究掺杂SiO2干凝胶的孔结构特性

利用溶胶-凝胶酸碱二步催化法和常压干燥法制备了掺有不同含量添加物的SiO2干凝胶.通过小角X射线散射实验,计算得到了各掺杂SiO2干凝胶的比表面积、胶体颗粒和孔隙的平均切割长度,并分析了添加物对SiO2干凝胶孔结构的影响.结果表明,加入TiO2粉末和短切纤维,能够获得高比表面积的SiO2干凝胶;而加入SiO2纳米颗粒及短切纤维降低SiO2干凝胶的比表面积,平均粒径变大;短纤维的加入可在一定程度上限制干凝胶的收缩.