Mg-5Y-3Sm-0.8Ca-0.5Sb合金的高温蠕变行为

采用蠕变实验和理论计算,研究了时效态Mg-5Y-3Sm-0. 8Ca-0. 5Sb合金在250～300℃和50～70 Pa条件下的蠕变行为。结果表明,该合金具有良好的抗高温蠕变性能,其在300℃和70 MPa下的稳态蠕变速率为3. 28×10-8s-1。在50～70 MPa的应力下,当温度由250℃升到300℃时,应力指数由2. 30变为3. 22;在250～300℃的温度下,当应力由50 MPa升到70 MPa时,蠕变激活能由65. 4 kJ/mol变为81. 0 kJ/mol。     

Effect of nonlinear thermal radiation on 3D magneto slip flow of Eyring-Powell nanofluid flow over a slendering sheet with binary chemical reaction and Arrhenius activation energy

An analysis is performed to study the combined effects of nonlinear thermal radiation, Arrhenius activation energy, chemical reaction and heat generation/absorption on the steady three-dimensional magnetohydrodynamic flow of Eyring-Powell nanofluid flow over a slendering stretchable sheet with velocity, thermal and solutal slips. The prevailing partial differential equations are transmuted into coupled non-linear ordinary differential equations via with the suitable similarity transformations. The resultant non-linear coupled differential equations are solved numerically by using the R-K 4^th order method along with shooting scheme. The results are calculated to measure the influence of sundry parameters on velocity, temperature, concentration, shear stress, temperature gradient and concentration gradient are presented graphically and in tabular form. It is noticed that the temperature is more impactable for higher values of radiative heat transport. The local Sherwood number decays exponentially for all the values of the chemical reaction parameter. We compared the present results for the limiting cases with previously published results, which has shown reliability and efficiency.     

CO2注入井封隔器早期密封失效机制研究

为了揭示CO_2注入井中性能优良的氢化丁腈橡胶封隔器早期密封失效的机制,根据失效井的特征分析以及CO_2的相态特点,提出实现恒定泄压速度的室内实验方法,并对不同CO_2泄压速度下橡胶表面进行形貌观测和力学性能测试分析。结果表明:随着泄压速度的增加,橡胶表面出现了小气泡、大气泡甚至气泡破裂等龟裂现象,橡胶的密封性能均明显变差;注气井突然泄压时,橡胶内部的气体在短时间内无法渗出,其在内外压差作用下会膨胀形成气泡甚至爆裂,这是造成CO_2注入井封隔器早期密封失效的主要原因。为了防止封隔器的早期密封失效,推荐现场井口泄压速度控制在5 MPa/h以内。     

Research on slag-resistance of ZrN-SiAlON-SiC-C composite refractory in different atmospheres

The ZrN-SiAlON composite powder was synthesized using low-grade zircon and bauxite by carbothermal reduction nitridation at first and then ZrN-SiAlON-SiC-C composite refractory were fabricated with the ZrN-SiAlON powder, SiC particles, and a small amount of Si powder as raw materials and sucrose as the binder. The slag resistance of these composites in O₂, N₂ and Ar atmosphere was investigated by X-ray diffraction, scanning electron microscopy, and energy dispersion spectra. The results show that the pores in the inside of ZrN-SiAlON-SiC-C composite refractory were enlarged in oxygen atmosphere due to oxidation, which leads to the decrease in slag resistance. In argon atmosphere, blast furnace slag destroyed the sintered body of zircon, corundum, and cristobalite with the formation of CaZrO₃, then infiltrated into and filled the pores inside the refractory to form a dense layer, which hindered the further erosion of the blast furnace slag. In the reducing atmosphere, the interfacial energy of the gas-liquid phases became larger due to the reactions between blast furnace slag liquid and the gas, resulting in a larger wetting angle which prevented the erosion.     

The isothermal reduction kinetics of chromium-bearing vanadium–titanium magnetite sinter

The reduction of chromium-bearing vanadium–titanium magnetite sinter (CVTMS) by CO was investigated at 1123–1223?K. The reduction degree increased with increasing temperature. The isothermal reduction kinetics of CVTMS was analysed, according to Sharp analysis and ln–ln analysis, the kinetic mechanism of reduction process for all samples in different basicity can be represented as f(α)?=?1.61(1?α)[?ln(1?α)]^1–1/1.61. The reaction activation energy of all samples (R?=?1.9, 2.1, 2.3, obtained according to the components of the materials burdening used in sintering process) at different reaction degrees were calculated by the model-free method. And the pre-exponential factors of reaction also were calculated by the mathematical method. The rate controlling step for the reduction process under the present reduction condition was chemical reaction.     

脱硫胶粉在乳化改性沥青中的应用

考察了不同规格胶粉及不同脱硫程度的脱硫胶粉对橡胶改性乳化沥青性能的影响,结果表明,采用100目胶粉即可制备出橡胶改性乳化沥青,但乳化沥青的性能较差;采用活化度为50%左右的100目脱硫胶粉制备乳化沥青时,脱硫胶粉的用量相比于胶粉可大幅提高;在通过外掺100目50%左右活化度的脱硫胶粉(质量分数15%,以沥青计,下同)和质量分数2%的苯乙烯-丁二烯-苯乙烯嵌段共聚物改性的乳化沥青中添加质量分数1%的丁苯胶乳,所制备橡胶改性乳化沥青无筛上剩余物,5 d储存稳定性为2.9%,蒸发残留物的25℃针入度、软化点和5℃延度分别为55 (0.1 mm)、64.5℃和22.5 cm,能够满足乳化改性沥青的技术指标要求。     

在轨维修后端模块接口机构的研究

在轨维修可以大大的延长空间科学仪器的使用寿命,节省大量的经济成本。为了实现空间望远镜后端模块的在轨操作和更换,设计了一套与之对应的接口机构,能够解决在轨快速定位与安装。根据321运动学定位准则,详细介绍了该接口机构的内部组成和工作原理;然后把该接口机构与后端模块进行组件级有限元仿真,仿真结果表明一阶模态远高于整机基频可以有效地避免发射时候的共振;设计了一套平面内的工装来模拟后端模块,利用等效质量法对整个机构进行重力卸载;搭建实验平台,利用激光跟踪仪来测量整个后端模块的重复定位安装精度,实验数据表明,X,Y,Z 3个方向的重复平移定位误差分别为±5.58μm,±3.24μm及±3.63μm,优于总体指标±10μm;热实验结果表明整个机构可以完全释放由于温度变化产生的形变,具有很高的热稳定性;使入射光线和靶面的相对位置持续稳定,保证了较高的成像质量。为其他空间在轨维护装置提供强有力的参考价值。     

Ultrafine porous boron nitride nanofiber-toughened WC composites

Porous fibers are widely used in catalysis chemistry and hydrogen storage but are rarely used in structural ceramics. In this study, spark plasma sintering was used to prepare an ultrafine porous boron nitride nanofiber-toughened WC composite for the first time. The obtained WC-0.05 wt% ultrafine porous boron nitride nanofiber composites exhibited better properties (ie, a 2.3% increase in hardness and a 19.6% increase in fracture toughness) compared to those of the pure WC specimen. The fiber porosity improved the second phase-WC matrix microstructural combination. The described approach is a novel preparation method for the WC composites. Furthermore, a new toughening mechanism, which is based on “pinning and stretching”, was determined. These findings suggest that porous boron nitride fibers can be considered to be second phases for toughening the WC composites.     

单自由度八杆仿生机构构型与尺度同步设计方法

单自由度八杆仿生机构杆长参数较多，是仿生机器人领域研究的难点之一。为提高设计效率，提出一种构型与尺度同步设计方法。在选定的运动链和机架的基础上，以不等式形式分步给出运动可行性及外形约束条件，使得上一步的杆长可作为下一步求解的已知值。通过该过程，在得到八杆仿生机构构型的同时，快速得到所有杆长的初步可行域。循环上述过程，逐步缩小约束条件的范围，可使得八杆机构的杆长快速接近目标值。在此基础上，分类讨论了连杆搭接顺序、约束条件及基本运动链的差异对求解难度及构型结果的影响。利用所提出的单自由度八杆仿生机构的设计方法，在对初始条件进行合理选取的前提下，可在初步得到构型的同时将杆长限定在较小范围内，实现了构型与尺度的同步设计。该方法还可应用于其他单自由度机构的设计当中，具有较好的借鉴意义。