不同固体表面下激光多普勒测速的数值模拟

激光多普勒测速仪(LDV)的测量精度和应用受到光电探测器、环境状况、频谱加宽和信号处理等因素影响。本文根据条纹模型和散射机理建立了固体LDV的数学模型,并通过数值模拟详细分析了固体表面特性和测量精度之间的关系,实验结果和数值模拟结果符合得很好。LDV能够精确地测量出固体表面运动速度,但要求被测固体的表面粗糙度在一定范围内,而且这个范围由条纹间距和有效探测体宽度决定。     

Influence of casting surfaces on fatigue strength of ductile cast iron

Quantitatively evaluating the fatigue strength of ductile iron (DI) with casting surfaces involves several complicated factors such as surface roughness, transition of microstructures from surface to interior, several types of defects and residual stresses. Tension–compression fatigue tests have been performed using DI having casting surfaces composed of a ferritic structure, a ferrite‐pearlitic structure and a pearlitic structure. Residual stresses were relieved by annealing in order to separately evaluate each factor. The parameter model was applied for quantitative evaluation of fatigue strength. Surface roughness was considered to be mechanically equivalent to a defect, and the effective defect size due to the interaction between the surface roughness and a defect was defined. The present study proposes a method of evaluating the maximum defect size using statistics of extremes and the lower bound of the scatter of fatigue strength, for practical design.     

丝网印版的分辨率特性研究

分析了丝网目数、丝径等几何参数及网版的厚度、粗糙度对丝网印刷精度的影响;对网版制作过程中的丝网选择,网版涂布曝光等注意事项做了研究,为获得高质量的网版提供了理论依据。对实际生产具有重要指导意义。     

去离子水中电火花毛化技术工艺试验研究

在煤油和去离子水中,针对9Cr2Mo轧辊钢进行了电火花毛化加工试验。通过对数据的对比分析,研究了在不同工作液条件下,脉宽和峰值电流的变化对加工件表面粗糙度和单位面积上凹坑数的影响规律。结果表明,去离子水更适用于电火花毛化加工。     

球墨铸铁件软氮化后加工形成的石墨坑对表面质量的影响

介绍了粗糙度的定义,指出球墨铸铁件在软氮化后进行珩磨加工时形成的石墨坑对表面质量的影响,并提出相应的表面质量控制方法。     

喷丸强化对合金化奥贝球铁疲劳性能的影响

喷丸处理是改进金属工件疲劳性能最常规的表面处理方法。文中研究了喷丸处理对合金化奥贝球铁(AD)I疲劳性能的影响。等温淬火包括875℃保温90 min奥氏体化处理,然后在320℃、365℃和400℃进行等温处理。用直径0.4～0.6 mm的丸喷丸后的试样做旋转弯曲疲劳试验。对试样进行XRD和SEM分析,测定显微硬度和粗糙度,研究试样的疲劳性能。结果表明,在320℃、365℃和400℃等温处理的试样喷丸后疲劳强度分别增加了27.3%、33.3%和48.4%。     

氮化铝陶瓷基片的集群磁流变效应研磨加工

采用集群磁流变效应研磨加工方法对氮化铝(AlN)陶瓷基片进行研磨加工,系统地分析了主要工艺参数的影响和最终经过精密研磨后的加工表面形貌特征。结果表明,集群磁流变效应研磨加工方法可以实现对氮化铝(AlN)陶瓷基片的高效率高精度研磨加工,原始表面Ra1.730μm经过粗研10 min和精研30 min后可以达到0.029μm,下降两个数量级。在粗研阶段,选用二氧化硅磨料#4000、磨料体积分数12%、研磨盘转速150 r/min、研磨压力3.5 kPa,可以获得较高的材料去除率和较光滑的加工表面。     

Double-template fabrication of three-dimensional porous nickel electrodes for hydrogen evolution reaction

Three-dimensional (3D) porous nickel structures were fabricated via a double-template electrochemical deposition process. The construction of the foam structures was achieved by means of a hydrogen bubble dynamic template, prepared from Cu electrodeposition at high current densities. Subsequently, a Ni layer was electrodeposited on the Cu 3D template. During the nickel coating, the typical finger-like microstructure of the Cu foam becomes denser and changes to a cauliflower microstructure. The hydrogen evolution reaction (HER) on these macroporous Ni electrodes was evaluated in 30 wt.% KOH solution by means of polarization curves and electrochemical impedance spectroscopy (EIS). Results demonstrate greater apparent activity of the developed electrodes towards HER in comparison with commercial smooth Ni electrode. The 3D porous Ni electrocatalyst obtained from Cu templates synthesized at the lowest current density and the highest electrodeposition time yielded the best electrochemical activity for HER.     

Adhesion resistance surfaces against clay resulting from biomimetic adaptation

To improve the dewetting characteristic and reducing the clay adhesion of molds, a series of “morphological” and “functional” biomimetic roughness units was fabricated on 45^# steel mold surfaces by laser and machining methods. The anti-adhesion and wettability behaviors of samples with different roughness units were investigated. The results indicated that the adhesion forces of samples with different roughness units were lower than that of the smooth one and decreased with increasing the area ratio of roughness units. Contact angle measurements of water on biomimetic roughness surfaces showed that the apparent contact angle increased from 76.9° to 97.5° with the increase of area ratio of biomimetic units. The anti-adhesion mechanism of biomimetic mold was the dual roughness structure of biomimetic units that could decrease the wettability of mold surfaces and reduce the adhesion of clay.