氮化硅新相P6和P6＇的理论研究：一种研究陶瓷材料的新工具

在原子尺度上构建模型,采用密度泛函理论结合准谐波近似研究了氮化硅新相（P6和P6＇相）的点阵常数、弹性常数和弹性模量. 并使用β-Si3N4作基准材料来测试计算结果的准确性. 研究发现β-Si3N4的晶胞常数和弹性常数与实验值吻合相当好. 研究了P6和P6＇相在30～55 GPa的各向异性因子、脆性和力学稳定性,结果表明两相属于金属性和脆性材料,且晶体的脆性和各向异性都随着压强的升高而增大. β相在40 GPa和300 K时会转变成P6＇相. 当压强继续升高到53．2GPa时,P6＇相又转化成δ相．同时研究了氮化硅的热容、体积和体模量等性质随温度的变化规律．     

用于电响应红外反射窗的液晶聚合物薄膜特性研究

提出了一种红外反射器件,通过载体液晶在电场下的转向控制胆甾型液晶聚合物粒子在器件中的排布方向,实现红外反射与透射之间切换.其中,胆甾型液晶聚合物粒子是实现红外反射关键.介绍了胆甾型液晶聚合物薄膜的制备方法,并采用超声波破碎的方法制备液晶粒子.研究了液晶混合物中不同比例的交联剂液晶1对液晶聚合物薄膜脆性和反射波段的影响,发现当液晶1占100%时,液晶聚合物薄膜的脆性最大,且其清亮点最高,并且薄膜的反射波段随着液晶1比例的增加而向短波方向偏移.同时,研究了薄膜厚度对液晶聚合物粒子的影响,发现液晶薄膜厚度越小,制备的液晶聚合物粒子越小且越均匀,其制成的器件电驱动性更好.该研究有利于帮助电响应红外反射窗的性能优化.     

Ageing and rejuvenation in glassy amorphous polymers

Physical ageing of amorphous polymers well below their glass transition temperature leads to changes in almost all physical properties. Of particular interest is the increase in yield stress and post-yield strain softening that accompanies ageing of these materials. Moreover, at larger strain polymers seem to rejuvenate, i.e. aged and non-aged samples have identical stress-strain responses. Also, plastically deforming an aged sample seems to rejuvenate the polymer. In this work we use molecular dynamic simulations with a detailed force field suitable for macromolecular ensembles to simulate and understand the effects of ageing on the mechanical response of these materials. We show that within the timescales of these simulations it is possible to simulate both ageing and rejuvenation. The short range potentials play an important role in ageing and rejuvenation. A typical yield drop exhibited by glassy polymers is a manifestation of a sudden relaxation in the short range structure of an aged polymer. Moreover, the aged polymers are known to be brittle. We show that this is intimately related to its typical stress-strain response which allows it to carry arbitrarily large mean stresses ahead of a notch.     

弹性波速径向变化在非常规储层可压性评价中的应用

非常规储层的开发均需要进行压裂,所以对非常规储层可压性的评价就变得很重要。岩石的脆性是影响储层可压性的重要因素,是优选压裂层位的重要指标。该文在单极子波形正演模拟及波速径向变化计算的基础上,针对非常规储层,应用弹性波速径向变化来评价储层脆性,并分析这种方法在非常规储层可压性评价中的应用效果。通过实例分析可看出,对于相邻两套致密砂岩储层,脆性好的井段压裂后产能也较高,证实了此方法对可压性的分析结果;对于煤储层,煤层段弹性波速降低明显,反映煤层可压性较好,这与煤层段的压裂效果也是相符的。所以,对于非常规储层,基于弹性波速径向变化评价脆性的方法能够很好地反映非常规储层可压性的强弱。     

Two kinds of composite films: Graphene oxide/carbon nanotube film and graphene oxide/activated carbon film via a self-assemble preparation process

Two kinds of free-standing composite films, including graphene oxide and activated carbon film as well as graphene oxide and carbon nanotube film, were fabricated through a simple suspension mixing and then natural deposition process. The films were characterized by various measurement techniques in detail. The results show that the composite films without any treatment almost still remain the original properties of the corresponding precursors, and exhibit loose structure, which can be easily broken in water; whereas after treated at 200 °C in air, the films become relatively more dense, and even if immersed into concentrated strong alkali or acid for five days, they still keep the film-morphologies, but regretfully, they show obvious brittleness and slight hydrophilicity. As soon as the treated films are performed in high concentrated strong alkali for about one day, their brittleness and wettability can be improved and became good flexibility and complete hydrophilicity.     

Ab-initio study of electronic and elastic properties of B2-type ductile YM (M=Cu, Zn and Ag) intermetallics

A theoretical study of structural, electronic, elastic, thermal and mechanical properties of nonmagnetic intermetallics YM (M=Cu, Zn and Ag), which crystallize in CsCl-type structure, is performed using first principles density functional theory based on full potential linearized augmented plane wave (FP-LAPW) method. The calculations are carried out within the generalized gradient approximation (GGA) for the exchange correlation potential. The calculated ground state properties such as lattice constants, bulk modulus and elastic constants agree well with the experiment. From energy dispersion curves, it is found that these compounds are metallic in nature. The ductility of these intermetallics is determined by calculating the bulk to shear ratio B/G_H. The calculated results indicate that YAg is the most ductile amongst the present YM compounds. The results obtained are compared with the available experimental and theoretical results. The mechanical and thermal properties are predicted from the calculated values of elastic constants.     

Theoretical Study on the High-Temperature P6 and P6' Phases of Si3N4: A Tool to Aid in Ceramics Development

Atomistic modeling based on the density functional theory combined with the quasi-harmonic approximation is used to investigate the lattice parameters and elastic moduli of the P6 and P6' phases of Si3N4. β-Si3N4 is set as a benchmark system since accurate experiments are available. The calculated lattice constants and elastic constants of β-Si3N4 are in good agreement with the experimental data. The crystal anisotropy, mechanical stability, and brittle behavior of P6- and P6'-Si3N4 are also discussed in the pressure range of 30-55 GPa. The results show that these two polymorphs are metallic compounds. The brittleness and elastic anisotropy increase with applied pressure increasing. Besides, the phase boundariesof the β→P6'→δ transitions are also analysed. The β phase is predicted to undergo a phase transition to the P6' phase at 40.0 GPa and 300 K. Upon further compression, the P6'→δ transition can be observed at 53.2 GPa. The thermal and pressure effects on the heat capacity, cell volume and bulk modulus are also determined. Some interesting features are found at high temperatures.     

氮化硅新相P6和P6'的理论研究：一种研究陶瓷材料的新工具

在原子尺度上构建模型,采用密度泛函理论结合准谐波近似研究了氮化硅新相(P6和P6'相)的点阵常数、弹性常数和弹性模量. 并使用β-Si₃N₄作基准材料来测试计算结果的准确性. 研究发现β-Si3N4的晶胞常数和弹性常数与实验值吻合相当好. 研究了P6和P6'相在30～55 GPa的各向异性因子、脆性和力学稳定性,结果表明两相属于金属性和脆性材料,且晶体的脆性和各向异性都随着压强的升高而增大. β相在40 GPa和300 K时会转变成P6'相. 当压强继续升高到5     

环状对苯二甲酸丁二酯低聚物CBT的研究进展

环状对苯二甲酸丁二酯低聚物CBT作为目前唯一工业化的芳香基环状低聚物,以其超低熔体黏度、边聚合边结晶特性、开环聚合无反应热、无小分子副产物释放等优点受到工业界和学术界的共同关注,尤其是在连续纤维增强复合材料领域得到了广泛应用。本文从CBT的制备方法与聚合机理入手,系统梳理了CBT聚合过程的流变行为、聚合与结晶的关系、结晶形貌、复合材料的制备及应用、基体树脂的脆性机理、纯树脂及复合材料体系增韧方法、边聚合边结晶过程等方面的研究进展,并就存在的问题进行了展望,对CBT及其它芳香基环状低聚酯研究及应用具有指导意义。