机械系统拓扑结构的通用表达模型设计

提出了一种适用于机械系统的通用拓扑模型——环基树拓扑结构模型 ,研究了环基树的性质及自动生成算法 ,介绍了运动和力的拓扑表等概念 ,给出了两个基于环基树结构的通用自由度计算公式。研究结果为机械系统的计算机表达、管理、维护和加工提供了统一机制 。

Mechanical properties of short carbon/glass fiber reinforced high mechanical performance epoxy resins

To research the relationship between epoxy and fiber inherent property and mechanical properties of composite,we prepared a series of composites using three kinds of high mechanical performance epoxy resins as matrices and reinforced by the same volume fraction(5%)of short carbon and glass fiber.Their mechanical properties were investigated from the perspective of chemical structure and volume shrinkage ratio of epoxy.We analyzed their tensile strength and modulus based on the mixing rule and Halpin-Tsai eq...

Jatropha curcas L. oil extracted by switchable solvent N, N-dimethylcyclohexylamine for biodiesel production

Biodiesel, which is a renewable and environmentally friendly fuel, has been studied widely to help remedy increasing environmental problems. One of the key processes of biodiesel production is oil extraction from oilseed materials. Switchable solvents can reversibly change from molecular to ionic solvents under atmospheric CO_2,and can be used for oil extraction. N, N-dimethylcyclohexylamine(DMCHA), a switchable solvent, was used to extract oil from Jatropha curcas L. oil seeds to produce biodiesel. The appropriate extraction conditions were:1:2 ratio of seed mass to DMCHA volume, 0.3–1 mm particle size, 200 r·min-1agitation speed, 60 min extraction time, and 30 °C extraction temperature. The extraction ratio was about 83%. This solvent extracted the oil more efficiently than hexane, and is much less volatile. By bubbling CO_2 under 1 atm and 25 °C for 5 h, the oil was separated, and DMCHA was recovered after releasing CO_2 by bubbling N_2 under 1 atm and 60 °C for 2 h. The residual solvent content in oil was about 1.7%. Selectivity of DMCHA was evaluated by detecting the protein and sugar content in oil. Using the oil with residual solvent to conduct transesterification process, the oil conversion ratio was approximately 99.5%.

The Versatile Method to Control the Orientation of BN Particles in Thermoset Matrix

A new thermally conductive thermoset composite has been developed. A hybrid organic-inorganic material composed of an epoxy resin crosslinked with a flexible diamine hardener, and a BN, was prepared by incorporating epoxy structure units covalently into a BN via the sol-gel approach. The precursor was obtained by the reaction of DGEBA （diglycidyl ether of bisphenol A） with TEOS （tetraethyl orthosilicate）. The precursor was then hydrolyzed and co-condensated with tetraethyl orthosilicate which is covalently bond with the hydroxyl groups on the BN surface at room temperature to yield epoxy-BN hybrid sol-gel material. FTIR spectroscopy confirmed the formation of organic and inorganic network. The thermal conductivity as measured by thermal conductive analyzer showed an increase up to 0.4048 W/m.K, for a mixture containing 0.4 wt% of BN fillers in the epoxy matrix. Moreover, the optimum conditions for surface modification of BN particle were also investigated.

Characteristics of Cyanate Ester and Fluorenyl Epoxy-Based Polymer-Ceramic Composites

In the field of highly integrated printed circuit board （PCB）, the heat resistant substrate with low water absorption is very important material. To get the resin composition for the high functional substrate material with low moisture absorption and high glass transition temperature （Tg） simultaneously, a fluorenyl ＂Cardo＂ epoxy was incorporated into novolac cyanate ester resin. As an optimum curing agent for the fiuorenyl epoxy, methyl nadic anhydride （MNA） was selected. Silica powders as fillers were added into the resin composition. The partial replacement of the cyanate ester resin with the fluorenyl epoxy could reduce the moisture absorption with keeping high glass transition temperature over 300 ℃. The laminate, which was fabricated from prepregs made with 40 wt% silica-filled resin composition and glass fabric, showed high Tg of 317 ℃ and low moisture absorption of 0.57%.

Synthesis and Characterization of Modified Epoxy Resins by Silicic Acid Tetraethyl Ester and Nano-SiO_2

A kind of modified epoxy resins was obtained by condensation of epoxy resin with silicic acid tetraethyl ester（TEOS） and nano-SiO2. The reactions were performed with hydrochloric acid as a catalyst at 63 ℃. The structure, thermal stability and morphological characteristics of the modified epoxy resins were studied through infrared spectra（FT-IR） analysis, thermogravimetric（TG） analysis and scanning electron microscopy respectively. It has been found from the IR and TG study that modified epoxy resins have greater thermal stability than epoxy resins, and its thermal stability has been improved by the formation of inter-crosslinked network structure. The modified epoxy resins exhibit heterogeneous morphology and heterogeneity increases with more TEOS feeding, which in turn confirms the formation of inter-crosslinked network structure in modified epoxy resins.

Light Weight Insulating Material Prepared from Rice Husk

Pakistan is at 12th number in the rank of rice production countries. Along with the production of 4,500 thousand metric tons of rice enormous quantity of rice husk is left as waste. Light weight thermal insulating material was prepared from rice husk. Epoxy resin was used as a binder and was mixed with rice husk to give it strength, the sample was compressed at 7000 psi to produce cylindrical shape block. The thermal conductivity of the sample A, B, C and D of thickness 1, 2, 3 and 4 cm respectively was measured 0.0241, 0.0240, 0.239 and 0.0219 watts/m-k, which was lower than the common mortar by 51.74%, therefore it could be used in buildings and roof as an insulating material. This would be a suitable alternative which would not only save energy but also solve the environmental disposal problems as well. The results are very promising and we hope insulation material prepared would be useable in hot climate regions like Pakistan in buildings to prevent heat transfer.

Synthesis and Property Studies of Transparent Resins Containing Rare Earth Complex Eu(Ⅲ) (TTA)_2(MA)_2 Phen·H_2O

A new rare earth complex Eu（III） （TTA）2（MA）2Phen · H2O was synthesized and characterized by element analysis, FTIR, UV, thermal analysis, and fluorescence spectra. The strong fluorescence and high thermal stability of Eu（III） （TTA）2（MA）2Phen · H2O were used to modify resin. The copolymer containing europium was prepared by copolymerization of Eu（III） and styrene/α- methylacrylic acid, and characterized by FTIR and fluorescence spectra. The fluorescence spectra showed that the copolymer was a sort of materials with good fluorescence property, and the higher fluorescence intensity came from the higher europium content.

Enhanced flexural performance of epoxy polymer concrete with short natural fibers

Epoxy polymer concrete(EPC) has found various applications in civil engineering. To enhance the flexural performance of EPC,two kinds of short natural fibers with high specific strength(sisal fibers and ramie fibers) have been incorporated into EPC. The results of mechanical tests show that a small loading of natural fibers(0.36 vol%) can significantly increase the flexural strength of EPC by 25.3%(ramie fibers) or 10.4%(sisal fibers). This enhancement is achieved without any sacrifice of compressive strength of EPC. The reinforcing effects of short natural fibers on the flexural properties and compressive properties of EPC decrease with further increase in fiber content, due to the insufficient wetting of fibers by epoxy resin which results in poor interfacial bonding. The reinforcing mechanisms of short natural fibers are explored according to the observation of fracture surfaces and micromechanical modelling. It is found that the parallel model based on the rule of mixture can be a good approximation to describe the improvement in flexural strength of the short natural fiber reinforced EPC at low fiber volume fractions.

A novel cerrobend block in the radiation therapy

This study was carried out to look for the substitute products of lead cerrobend block and determine whether the products can give more radiation dose to the tumor in the skin and superficial tumors in radiotherapy treatment. Five kinds of PbO/ Er203/Epoxy（E-51） samples used as the cerrobend block in the electron beam radiotherapy treatment were prepared success- fully by a solidified forming approach. The central axis depth dose and off-axis dose profiles in the water phantom were calcu- lated using BEAMnrc/DOSEXYZnrc user codes. The results revealed that there were more energy deposition events induced by low energy electron beams in the surface of the water phantom. These electron beams were attributed to Compton scattering and photoemission between photons and erbium, plumbum elements. The maximum dose （Dm） and the depth at the maximum dose （Rm） were linearly dependent on the mass fraction of erbium and plumbum element in the sample. The max dose and its depth varied depending on the combined actions of new electrons and transmission electrons.