Deformation bands in fully pearlitic steel during wire drawing

The deformation of fully pearlitic steels during wire drawing has been investigated for both longitudinal section and transverse section by back-scattered electron imaging(BSEI),electron back-scattered diffraction(EBSD),and transmission electron microscope(TEM).The results show that a large number of deformation bands(DBs)composed of a mixture of kink-like bands and shear-like bands were observed both in the longitudinal section and the traverse section of the drawn wires.The formation of such bands involves two aspects:heterogeneous deformation in the scale of pearlite colonies and instability of ferrite-cementite interfaces due to stress concentration during wire drawing.The development of such bands in fully pearlitic steels dominates the formation of metallographic texture,reduces the pearlite interlamellar spacing and promotes the development of<110>fiber crystalline texture of ferrite matrix during wire drawing.     

The random walking method for the steady linear convectiondiffusion equation with axisymmetric disc boundary

In this article,the random walking method is used to solve the steady linear convection-diffusion equation(CDE)with disc boundary condition.The integral solution corresponding to the random walking method is deduced and the relationship between the diffusion coefficient of CDE and the intensity of the random diffusion motion is obtained.The random number generator for arbitrary axisymmetric disc boundary is deduced through the polynomial fitting and inverse transform sampling method.The proposed method is tested through two numerical cases.The results show that the random walking method can solve the steady linear CDE effectively.The influence of the parameters on the results is also studied.It is found that the error of the solution can be decreased by increasing the particle releasing rate and the total walking time.     

Stability switches and Bogdanov-Takens bifurcation in an inertial two-neuron coupling system with multiple delays

In this paper,we investigate an inertial two-neural coupling system with multiple delays.We analyze the number of equilibrium points and demonstrate the corresponding pitchfork bifurcation.Results show that the system has a unique equilibrium as well as three equilibria for different values of coupling weights.The local asymptotic stability of the equilibrium point is studied using the corresponding characteristic equation.We find that multiple delays can induce the system to exhibit stable switching between the resting state and periodic motion.Stability regions with delay-dependence are exhibited in the parameter plane of the time delays employing the Hopf bifurcation curves.To obtain the global perspective of the system dynamics,stability and periodic activity involving multiple equilibria are investigated by analyzing the intersection points of the pitchfork and Hopf bifurcation curves,called the Bogdanov-Takens(BT)bifurcation.The homoclinic bifurcation and the fold bifurcation of limit cycle are obtained using the BT theoretical results of the third-order normal form.Finally,numerical simulations are provided to support the theoretical analyses.     

上海地区冬季住宅室内外颗粒物浓度的相关性

对上海市某住宅建筑室内外PM10、PM2.5、PM1的浓度进行了测量,研究了最小通风量（外门窗关闭）条件下3种天气时颗粒浓度随时间变化的规律以及相关性,分析了颗粒物浓度与环境温湿度参数之间的关系.研究结果显示,测试期间,室内外空气中细颗粒（PM 2.5）占可吸入颗粒（PM 10）浓度比例分别达65％和87％以上;无明显室内源时,I/O比值小于1且随粒径减小而减小;室内外颗粒浓度相关性与粒径大小有关系,PM1、PM2.5的浓度相关性大于PM10.研究还表明,颗粒物浓度的关联性与天气状况有关系,多云、雨天和阴天时浓度关联性有显著差别;颗粒物的浓度受到室内外温湿度的影响,且受天气状况影响而呈现复杂性.     

发泡丁腈橡胶-金属密封板的制备

针对发泡橡胶-金属密封板的泡孔不均匀而导致的密封板密封性较差的问题,采用丁腈橡胶为涂覆层,不锈钢板为基体制备发泡丁腈橡胶-金属密封板,分别研究时间、温度、发泡剂用量和环氧树脂用量四个单因素对涂覆橡胶发泡率的影响,采用正交实验优化出最佳工艺条件为:发泡剂用量10%、环氧树脂用量30%、硫化温度140 ℃和硫化时间20 min.200 ℃热稳定性实验结果表明,密封板不起皮、失重为0.08 g; 偏光显微镜研究密封板的微观形貌表明,泡孔平均直径为68.35 μm,发泡均匀,有助于密封性能的提高.     

壁湍流猝发事件检测与提取方法研究

在重力式低速水洞中完成了湍流边界层流场测量,并分别利用自相关方法和小波分析方法,对对数律区中一测点处的速度信号进行了分析。结果表明,自相关方法对于平均猝发周期的检测精度较高;小波分析方法可用于猝发事件的提取,但对平均猝发周期的检测精度较低。为此,进一步提出了一种同时基于自相关方法和小波分析方法的壁湍流猝发事件快速检测与提取方法,并总结了该方法的具体实施步骤。与原方法相比,该方法既能够精确检测湍流平均猝发周期,又能够提高猝发事件的提取精度。     

自然环境中混凝土内湿度响应规律

基于饱和水汽压方程探讨了湿度采用相对湿度和水汽密度表达形式间的关联,并通过理论推导和现场实测法研究了自然环境中空气湿度变化和混凝土内不同深度处湿度响应规律,从而建立了自然环境湿度作用谱和混凝土内湿度响应谱模型.试验结果表明:所构筑的自然环境湿度作用谱和混凝土内湿度响应谱模型可用于描述环境湿度变化与混凝土内湿度响应规律.自然环境相对湿度曲线随时间发生周期性波动,而混凝土内湿度随距表层深度的增加而增大且一定深度处相对湿度短时间内基本恒定.与采用相对湿度表达形式相比,采用水汽密度表达形式可更好地定量表征不同环境条件下的环境湿度变化规律.     

Synthesis of Cu nano-particle in toluene used for conductive ink with a binder of polyurethane

Copper nanoparticles with a size of about 150 nm were prepared in toluene using oleic acid as protecting agent. The nanoparticles were used to prepare conductive Cu ink with a polyurethane binder. Oleic acid was used to prevent the nanoparticles from oxidization and agglomeration. The prepared Cu nanoparticles were characterized by X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The resistivity of the copper film on glass substrate that was prepared using Cu nanoparticle ink reached about 1.5× 10-4 2. cm-1 after it was annealed to 120 ~C. Both the nanoparticle ink and the films were characterized by XRD, fourier transform infrared （FT-IR）, and the thermogravimetry-differential scanning calorimetry instrument （TG- DSC）.     

基于支持向量机回归的飞行载荷参数识别研究

飞行载荷参数识别是单机寿命监控中的重要技术,主要通过建立飞行参数与飞行载荷之间的转换关系,实现间接获取关键部位的载荷谱。针对飞行参数与飞行载荷之间非线性识别问题,结合飞机典型的机动动作,提出了一种改进的支持向量机回归(SVM-R)飞行载荷识别模型。该模型首先采用主成分分析缩减SVM-R模型输入,再利用交叉验证和遗传算法优化SVM-R模型设置参数,最后根据优化参数训练得到飞行载荷的SVM-R识别模型。通过在半滚机动动作下,飞行参数识别某一部位弯矩的实例分析,验证了优化改进的SVM-R模型对飞行载荷识别的最大残差可控制在实测载荷的20%以内,平均残差控制在实测载荷的3%以内,且优于未经优化的SVM-R模型。     

Analytical model of elastic modulus and coefficient of thermal expansion for 2.5D C/SiC composite

To make better use of 2.5D C/SiC composites in industry, it is necessary to understand the mechanical properties. A finite element model of 2.5D composites is established, by considering the fiber undulation and the porosity in 2.5D C/SiC composites. The fiber direction of warp is defined by cosine function to simulate the undulation of warp, and based on uniform strain assumption, analytical model of the elastic modulus and coefficient of thermal expansion (CTE) for 2.5D C/SiC composites were established by using dualscale model. The result is found to correlate reasonably well with the predicted results and experimental results. The parametric study also demonstrates the effects of the fiber volume fraction, distance of warp yarn, and porosity in micro-scale on the mechanical properties and the coefficients of thermal expansion.