钛合金表面激光熔覆TiB2-TiC/Ni复合涂层的真空摩擦磨损性能

采用激光熔覆技术在TC4钛合金表面制备以反应合成TiB2和TiC颗粒为增强相的Ni基复合涂层,利用УТИТВ-100型销-盘摩擦磨损试验机研究了激光熔覆层在真空(10-5Pa)中的干滑动摩擦磨损性能,利用光学显微镜和扫描电子显微镜观察了摩擦偶件的磨损表面形貌,讨论了激光熔覆层的磨损机制。结果表明,激光熔覆层的摩擦系数在0.25～0.5之间,明显低于TC4合金的摩擦系数(0.45～0.8),磨损体积约为TC4合金的40%。随法向载荷和滑动速度的增加,激光熔覆层的磨损体积增加,激光熔覆层的磨损机制主要为粘着磨损和粘附转移物引起的磨粒磨损。     

Effects of braiding angle on modal experimental analysis of three-dimensional and five-directional braided composites

In this paper, the experimental modal analysis of three dimensional (3D) and five (5)-directional braided composite cantilever beams with different braiding angle was conducted systematically with a simple testing system. Preforms were made by four-step 1 × 1 square integral braiding method. The first three order modes of composite specimens were derived, which are different with braiding angles. The experimental result and mechanism were discussed. Experimental observations and analytical predictions show that the natural frequency of specimens decreased and the damping ratio of specimens increased when the braiding angle increased. Furthermore, specimens with smaller braiding angle will be valuable for the better anti-exiting property, and have an opposite effect on dissipation of vibration energy. The comparison between the specimens with different braiding angles reveals that braiding angle is a crucial factor for the vibration performance design of 3D and 5-directional braided composites.     

基于模糊贝叶斯网的危害性分析方法

针对传统的故障模式、影响与危害性分析(FMECA)方法不足的问题,提出了一个基于模糊贝叶斯网的危害性分析方法。该方法将模糊理论与贝叶斯网推理技术结合起来,用三角模糊数来描述专家的模糊评分值;通过模糊集合映射,将其转化为评级的模糊子集;以置信结构的模糊规则,表示故障模式的属性与危害度之间的关系;利用贝叶斯网络推理算法综合置信结构的模糊规则,通过贝叶斯网推理得到模糊子集形式的危害度,再经过去模糊计算,得到故障危害等级的清晰值,从而确定故障模式的危害程度。实验结果表明,所提方法能够提高传统分析方法的准确性和应用范围。     

The effect of graphene presence in flame retarded epoxy resin matrix on the mechanical and flammability properties of glass fiber-reinforced composites

The effect of adding graphene in epoxy containing either an additive (MP) or reactive-type (DOPO) flame retardant on the thermal, mechanical and flammability properties of glass fiber-reinforced epoxy composites was investigated using thermal analysis; flexural, impact, tensile tests; cone calorimetry and UL-94 techniques. The addition of MP or DOPO to epoxy had a thermal destabilization effect below 400 °C, but led to higher char yield at higher temperatures. The inclusion of 10 wt% flame retardants slightly decreased the mechanical behavior, which was attributed to the poor interfacial interactions in case of MP or the decreased cross-linking density in case of DOPO flame retarded resin. The additional graphene presence increased flexural and impact properties, but slightly decreased tensile performance. Adding graphene further decreased the PHRR, THR and burning rate due to its good barrier effect. The improved fire retardancy was mainly attributed to the reduced release of the combustible gas products.     

多质量目标的曲轴NTR弯曲镦锻成形工艺优化

研究提高曲轴NTR弯曲镦锻外形质量的工艺参数优化方法。以中速船用6G32曲轴为例,借助数值模拟方法预测曲轴成形结果,设定曲轴外形质量评价准则。应用正交实验方法设计实验方案,模拟多种工艺条件下曲轴弯曲镦锻成形。根据实验结果,以降低曲轴成形塌角缺陷、减少飞边量、降低设备载荷为目标,采用响应面分析方法,建立评价指标与各工艺参数的函数表达式,优化始锻温度、NTR设备肘杆终锻角、模具运动方式、模具运行速度等曲轴NTR弯曲镦锻工艺参数。     

Development of carbon nanotubes reinforced hydroxyapatite composite coatings on titanium by electrodeposition method

Carbon nanotubes (CNTs) are outstanding reinforcement material for imparting strength and toughness to brittle hydroxyapatite (HAP). This work reports the electrodeposition of CNTs reinforced HAP on titanium substrate at −1.4 V vs. SCE during 30 min with the functionalised CNTs concentration ranging from 0 to 2 wt.%. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX), high resolution transmission electron microscopy (HRTEM), mechanical and biological studies were used to characterise the coatings. Also, the corrosion resistance of the coatings was evaluated by electrochemical techniques in simulated body fluid (SBF) solution.     

Air cooling for a large-scale motor

This article experimentally and numerically investigates the thermal performance of a large-scale motor with a capacity of 2350 kW. The large-scale motor consists of a centrifugal fan, two axial fans, a shaft, a stator, a rotor and a heat exchanger with 637 cooling tubes. The test rigs are set up to measure the performance of the fans and the temperature distributions of the motor. The models of the fan and motor have been implemented in a Fluent software package to predict the flow and temperature fields inside the motor. The calculated results show good agreement with the measured data. In order to improve the motor thermal performance, several methods have been adopted, which are aiming to enhance the fan performance by changing the geometry, to redesign a new heat exchanger with guide vanes, and to optimize the distance between the axial fans. The modified design can decrease the temperature rise by 6 °C in both the stator and rotor.     

Oxidative dehydrogenation of ethylene glycol into glyoxal over phosphorus-doped ferric molybdate catalyst

Test data for the catalytic oxidation of ethylene glycol (EG) into glyoxal obtained with a laboratory continuous flow tubular reactor are reported. A ferric molybdate catalyst modified with triammonium phosphate was used. Reaction parameters (temperature, contact time) affect the product distribution. The yield of glyoxal for the Fe-Mo-P catalyst was 43.3% at 88.9% conversion, whereas the corresponding values for the Fe-Mo (unmodified catalyst) were 20.5 and 97.2%. The addition of phosphorus formed a new Fe₂M₀P₁₂ phase which restrains the reaction pathway towards carbon oxides.     

Simultaneous polarographic chemometric determination of lead,copper, vanadium,cadmium and nickel

Chemometric approaches, such as classical least squares (CLS), principal component regression (PCR), partial least squares (PLS) and iterative target transformation factor analysis (ITTFA), were applied to the simultaneous determination of mixtures of lead, copper, vanadium, cadmium and nickel by differential pulse polarography (DPP). The conventional and first-derivative polarograms of the mixtures were used to perform the optimization of the calibration procedure by chemometric models. The proposed method was applied satisfactorily to the determination of a set of synthetic mixtures of metal in Britton–Robinson buffer (pH 2.87) and potassium thiocyanate and acceptable results were obtained. The results obtained by the application of the different chemometric approaches are discussed and compared. It was found that factor analysis methods generally give better results than CLS and no significant advantages were found with the application of derivative technique, except for ITTFA in this polarographic work.