动态载荷激励下的床身结构动力学响应

考虑到数控加工系统的振动及噪声问题,建立了数控机床床身的参数化有限元模型,在模态分析基础上计算固有频率与振动幅值。以简谐力作为动态激振载荷,在350-800Hz频率段进行扫频计算,获得了位移—频率和应力—频率曲线,确定了各阶共振频率点的响应幅值,谐振响应结果表明第2阶模态频率对床身的危害性较大。采用Full方法(完全法)对床身进行瞬态动力学分析,计算出了时域下的位移和加速度响应曲线,分析了机床启动阶段冲击载荷对床身的激励影响。在参数化建模基础上实现了床身结构动力学优化,使其动力学性能得到有效改进,有利于数控机床的高速化发展。     

太阳辐照度绝对辐射计的光电不等效性修正

针对绝对辐射计光电不等效性来源复杂、实验测量难度大的特点,提出了修正太阳辐照度绝对辐射计(SIAR)光电不等效性的有限元单元法。结合SIAR的测量方法,对真空中辐射计的腔温响应进行了实验测试。基于有限元单元法,建立了与实验腔温度响应相对误差仅为0.14%的有限元模型,对接收腔的温度响应进行了实验测试。测试结果显示:入射光功率为73.8mW时,接收腔与热沉之间的温度差异约为0.85K,响应的时间常数为29.8s。运用建立的有限元模型对SIAR的光电不等效性进行了评估和修正。结果表明:太阳辐照度绝对辐射计的光电不等效性来源主要为不同加热途径和不同加热区域引起的偏差,SIAR的光电不等效性因子N为0.999 621±0.000 004。该修正模型完善了仪器的修正体系,提高了测量精度,为绝对辐射计的发展提供了可靠的数据来源。     

Correlating phase and microstructure development versus dielectric properties in La and Er co-doped Bi4Ti3O12 ferroelectric ceramics

Bi_3.25La_0.75−xEr_xTi₃O₁₂ and Bi_3.25La_0.75Ti_3−xEr_xO_12−δ ceramics were prepared and studied in this work in terms of dopant-induced phase and microstructure development as well as dielectric response. The results show that introduction of Er³⁺ tends to reduce the materials’ sintering temperature and average grain size. Moreover, it was noted that in these systems the substitution site of this dopant is controlled by valence state and ionic radii mismatch effects. In particular, even when a nominal substitution of Ti⁴⁺ is conceived, here it is found that Er³⁺ also incorporates at the (Bi,La)³⁺ sites. These and other interesting concluding remarks from this work, including Er³⁺ tolerance, were possible only after comparing, especially, the X-ray diffraction results and the intrinsic ferroelectric characteristics extracted from the dielectric measurements.     

光电化学响应分析Ni201在中性溶液中形成表面钝化膜的半导体性质

应用光电化学响应法和:Mott-Schottky曲线法,研究了Ni201在500℃空气中生成的氧化膜和在pH值为8.4的中性缓冲溶液中阳极氧化生成钝化膜的半导体性质,分析了Ni201表面钝化膜的结构和组成.Mott-Schottky曲线表明,Ni20l在该中性溶液中生成钝化膜的平带电位约为0.40 V,其在500℃空气中生成的氧化膜的平带电位约为0.15 V,前者的载流子浓度约是后者的34倍.在中性缓冲溶液中生成钝化膜的光电流谱表明,Ni201的结构由内层NiO和外层Ni（OH）₂构成,其带隙宽度分别为2.8和1.6 eV.其中,具有晶体结构的内层NiO的带隙宽度与Ni201在500℃空气中生成的氧化膜的带隙宽度2.4 eV相似.通过光电化学法和Mott-Schottky曲线建立Ni201表面钝化膜的电子能带结构模型,解释了其内层NiO和外层Ni（OH）₂同是p型半导体组成的钝化膜的半导体性质.     

超精密滚珠丝杠进给系统的谐响应分析

超精密滚珠丝杠进给系统除了在工作台轴向存在外界激励,电机在启动和刹车时产生的冲击以及电机轴输出端的振荡特性都可能导致整个进给系统产生振荡,而利用目前的滚珠丝杠进给系统有限元模型不能准确地分析出电机轴输出端的转矩动载荷对进给系统产生的谐响应。针对此问题,提出一种新的进给系统有限元模型,保证了其谐响应分析的准确性。     

有裂纹的功能梯度材料板平面问题的随机动态响应(英文)

研究有裂纹的功能梯度材料板平面问题的随机动态断裂,建立平面问题的随机模型。功能梯度材料的物理力学性能沿厚度方向的非均匀随机变化为沿厚度方向的随机场。作用在裂纹面上的动荷载为时间的平稳随机过程,裂纹与功能梯度材料面平行。通过分层法,将随机场的问题转化为多个随机变量的问题进行求解。利用积分变换方法和奇异积分方程技术,得到动态响应的解析形式和裂纹起始扩展的概率计算公式,分析了各参数(裂纹长度、随机场参数和裂纹位置)对动态应力强度因子的影响。结果表明:随着裂纹长度、随机场参数β以及裂纹位置比率 h2/h 的增大,应力强度因子的数学期望和标准方差均相应增大。     

用快速成形技术制造玻璃模具电火花加工电极

本文叙述了用快速成形技术制造玻璃模具电火花加工电极.对客户提供的玻璃器皿样品尺寸进行三坐标测量,并将样品的尺寸放大1 mm以补偿样品生产时的收缩.利用快速成形技术对样品进行三雏造型,并制得样品的树脂原型.利用熔模铸造技术和树脂原型来制作模具电火花加工的电极.用这种工艺可以快速得到铜电极,实现玻璃模具的快速加工.     

快速砂型铸造用模具材料的新进展

快速砂型铸造用模具材料,是实现快速砂型铸造的重要因素.分析和比较了当前快速砂型铸造用模具材料的现状,并指出研究适合快速砂型铸造用模具材料和进行表面处理为今后的发展方向.     

Liquid film effect on dynamics of optical oxygen probe. Comparison with polarographic oxygen probes. Diffusion coefficients measuring technique

The dynamic behaviour of the optical oxygen probe at the presence of the liquid film is well described by unsteady one-directional oxygen diffusion into the probe membrane through liquid film. It is shown that the asymmetry caused by hyperbolic form of the Stern-Volmer relation between the probe signal and oxygen concentration is strongly suppressed in the presence of liquid film for the optical probes used in this work. In such case, the response calculated with respect to the mean oxygen concentration in the membrane describes well the optical oxygen probe dynamics.Liquid film effects on the signal of the optical and the polarographic oxygen probes are compared. Special attention is paid to find properties of membranes minimizing the liquid film effect on the rate of its response. From this point of view, the most suitable material for the optical probe membrane is one with high diffusivity but low solubility. Thus, silicone (used by optical probe manufacturers in these days) is the least suitable material. When both probes are covered with the same membrane, the response of polarographic probe is faster and less influenced by the liquid film compared with optical one. From this point of view, the polarographic probe is more suitable for monitoring of fast changing oxygen concentration in bulk liquid as it occurs, e.g. measurement of k_La in gas-liquid dispersions, usually with the need to know the L_L parameter characterizing the liquid film diffusion resistance. In addition, only the polarographic probe allows determination of a local value of the parameter L_L (under the given hydrodynamic conditions where the probe is situated) which is not possible with an optical probe. The optical probe is more suitable for measurements under steady-state conditions and for slower oxygen changes, even under the conditions, when the liquid film resistance is high in comparison with the membrane resistance as it occurs for diffusivity measurements in liquids. A modified method for evaluation of the oxygen diffusion coefficient in liquids from the dynamic probe response is presented.     

Photoanodic response of iron oxide electrode in aqueous solution and its application to Pb removal under visible light irradiation

The iron oxide electrode was prepared from thermal oxidation of iron at 600 °C for 3 h in air atmosphere. This electrode with the structure of Fe₃O₄ and α-Fe₂O₃ showed the response of photoanodic current to the light with wavelength shorter than 600 nm. The band gap energy of this electrode was 1.99 eV. The onset potential of distinct steady photocurrent and also the flatband potential were 0.80 and 0.09 V vs. Ag/AgCl, respectively, in 0.1 M HNO₃ aqueous solution. The cell consisting of the iron oxide photoanode in HNO₃-Pb(NO₃)₂ and the graphite cathode in H₂SO₄-Ce(SO₄)₂ caused the PbO₂ deposit on the surface of the former electrode due to visible light irradiation without application of voltage. By holding the potential of this electrode at more positive value than 0.90 V, the photoanodic removal rate of Pb²⁺ in HNO₃-Pb(NO₃)₂ solution was higher than that observed when Ce⁴⁺ was used as electron acceptor.