多金属3D打印的SLM设备工艺参数库试验研究

针对特定的金属3D打印机,加工不同金属均需反复实验,因此建立成形工艺参数数据库十分必要。以某国产金属打印设备为研究对象,以加工Al Si10Mg合金的工艺方法为例,采用正交试验方法和微观组织分析法验证其选择最佳工艺参数组合的正确性,最终通过多种金属的加工得到该设备的激光功率、扫描间距、扫描速度对打印不同金属的致密度、抗拉强度以及断后伸长率的影响的规律。结果显示选择激光功率时要充分考虑金属的熔点、易氧化、反光率等特性,扫描间距对成形不同金属的力学性能影响敏感度最大,为建立更多金属成形工艺数据库提供了参考。     

Assessment of chemical and microbiological parameters of indoor swimming pool atmosphere using multiple comparisons

The aim of this study was to evaluate the air quality of an indoor swimming pool, analyzing diurnal and seasonal variations in microbiological counts and chemical parameters. The results indicated that yeast and bacteria counts, as well as carbon dioxide (CO₂), nitrogen oxides (NO_x) and O₃ concentrations, showed significant diurnal difference. On the other hand, temperature, relative humidity (R.H.), yeast counts and concentrations of CO₂, particles, O₃, toluene, and benzene showed seasonal differences. In addition, the relationship between indoor and outdoor air and the degree of correlation between the different parameters have been calculated, suggesting that CO₂, fine particles and NO_x would have indoor origin due to the human activity and secondary reactions favored by the chemical and environmental conditions of the swimming pool; while O₃, benzene and toluene, would come from outside, mainly. The overall results indicated that indoor air quality (IAQ) in the swimming pool building was deficient by the high levels of CO₂ and microorganisms, low temperatures, and high R.H., because frequently the limits established by the legislation were exceeded. This fact could be due to the poor ventilation and the inadequate operation of heating, ventilation, and air‐conditioning systems.     

载荷影响下的机电阻抗协整结构损伤识别方法

高频机电阻抗(electromechanical impedance, 简称EMI)方法利用粘贴在结构表面的压电传感器(piezoelectric transducer, 简称PZT)进行主动激励，通过连续监测和分析PZT机电导纳信号的变化评估结构的健康状态；然而EMI方法容易受到环境工况变化的影响，导致结构损伤的误报。针对此问题，采用时间序列协整方法处理及消除结构工作载荷对阻抗谱特征信号的影响。该方法是基于结构动荷载作用下PZT阻抗谱导纳信号的非平稳特征，将动荷载影响下的阻抗谱非平稳时间序列经线性组合变换成平稳时间序列，根据得到的协整余量序列有效判断结构的健康状态。为验证该方法的有效性，开展了动应力影响下铝梁结构的螺栓松动损伤识别实验。结果表明，协整消除了动态应力对EMI方法的影响，当铝梁内存在持续变化的应力时，仍可以准确识别螺栓松动。机电阻抗协整方法能够消除结构健康监测中荷载作用的影响，及时准确地进行结构损伤识别。     

面向流屑角突变建模的切削状态参数经验公式的获得及应用

从提高流屑角突变模型的预测精度出发,建立了切削状态参数与3个切削控制参数之间关系的新经验公式。提出了一种通过迭代法准确设定有限元仿真软件刀-屑摩擦因数的方法,并通过直角切削Al6061-T6工件的有限元仿真试验,获得了一组不同切削控制参数组合条件下的切削状态参数数据。根据该数据拟合出剪切角φ、刀-屑摩擦角β、剪切应力τs关于刀具前角γ0、进给量f和切削速度v的经验公式,并通过一组直角切削试验,验证了所得经验公式的有效性。将新建经验公式应用于流屑角突变建模过程后,所得模型关于突变临界切削宽度的平均预测误差减小了27.2%。     

定向长钻孔整体水力压裂增透技术在赵固二矿的应用

针对赵固二矿煤层透气性低、钻孔有效影响半径小，实施定向长钻孔代替底板岩巷进行区域瓦斯治理期间钻孔工程量大、瓦斯抽采效果不理想的问题。结合煤层赋存特征及钻孔施工情况，采用定向长钻孔整体水力压裂增透技术，理论分析了合理坐封位置、压裂参数，完成200 m煤巷条带一次整体压裂，最大泵注压力24.3 MPa、累计注水量1 613 m³。并基于煤层全水分变化，考察确定了单个钻孔压裂影响范围达到巷道两帮30 m，有效改善了煤体储层特性，提高了煤层瓦斯抽采效率。在实现定向钻孔对预抽煤巷条带可靠控制的同时，最大程度降低了钻孔工程量、缩短了瓦斯治理周期，为实现矿区“以孔代巷”及高效安全开采提供了技术支撑。     

Effect of Sr doped the YFeO3 rare earth ortho-ferrite on structure,magnetic properties,and microwave absorption performance

Given the remarkable performances of rare earth multiferroic ortho-ferrites with magnetic optical and dielectric properties, the Y_1-xSr_xFeO₃ (x = 0, 0.05, 0.1, 0.15) perovskite structure microwave absorbing ferrite materials was successfully synthesized by Sr²⁺ ions A-site doping based on sol-gel technology in this paper. The XRD of all samples was refined with FullProf software, which confirmed the formation of the orthogonal perovskite structure (SG: Pnma). The SEM and TEM results display the average particles size of the samples is distributed between 110 and 160 nm. The increase of Sr doping concentration leads to the increase of particles size, which may be related to the growth of preferred orientation and incomplete substitution. The XPS analysis shows that Fe³⁺ was accompanied by the presence of Fe²⁺ with the doping of Sr²⁺ ions and oxygen vacancies increased significantly. The samples change from weak ferromagnetic state to paramagnetic state with the increase of Sr content. The minimum reflection loss (RL) of the Y_0.95Sr_0.05FeO₃ samples at 12.2 GHz reached −30.87 dB with thickness of 2.2 mm, where its effective absorption bandwidth (EAB, RL ≤ −10 dB) reached 2.4 GHz (11.3–13.7 GHz). Moreover, the EAB of the Y_0.85Sr_0.15FeO₃ samples reached 2.64 GHz, and the corresponding range is 9.0–11.6 GHz (X-band).     

A recurrent neural network using historical data to predict time series indoor PM2.5 concentrations for residential buildings

Due to the severe outdoor PM2.5 pollution in China, many people have installed air-cleaning systems in homes. To make the systems run automatically and intelligently, we developed a recurrent neural network (RNN) that uses historical data to predict the future indoor PM2.5 concentration. The RNN architecture includes an autoencoder and a recurrent part. We used data measured in an apartment over the course of an entire year to train and test the RNN. The data include indoor/outdoor PM2.5 concentration, environmental parameters and time of day. By comparing three different input strategies, we found that a strategy employing historical PM2.5 and time of day as inputs performed best. With this strategy, the model can be applied to predict the relatively stable trend of indoor PM2.5 concentration in advance. When the input length is 2 h and the prediction horizon is 30 min, the median prediction error is 8.3 µg/m³ for the whole test set. For times with indoor PM2.5 concentrations between (20,50] µg/m³ and (50,100] µg/m³, the median prediction error is 8.3 and 9.2 µg/m³, respectively. The low prediction error between the ground-truth and predicted values shows that the RNN can predict indoor PM2.5 concentrations with satisfactory performance.     

Quantitative study of the kinetics of hydrogen evolution reaction on aluminum surface and the influence of chloride ion

The behaviors and kinetics of hydrogen evolution reaction (HER) on pure aluminum with passive film in the presence and absence of chloride ion are quantitatively investigated by using the tip generation/substrate collection mode of scanning electrochemical microscopy (SECM) with dual Al/Pt ultramicroelectrode (UME) as tip electrode and Pt UME as substrate electrode. The standard rate constants k⁰ and transfer coefficients α_H of HER in ClO₄⁻- and Cl⁻-containing solution are 6.9 × 10⁻⁷ cm/s and 0.22, 7.1 × 10⁻⁶ cm/s and 0.19, respectively. Results show that the kinetic of HER is slow and the destruction of Cl⁻ on passive film can significantly promote the HER on Al surface. Moreover, these α_H far less than commonly used 0.5 in corrosion research, can explain the great difference between theoretical Tafel slopes and experimental results. Besides, the existence of current plateau in Al electrode explains the large difference in corrosion potential during parallel testing.     

ZL109铝合金车削表面完整性实验研究

设计了三因素四水平正交车削实验,综合运用极差分析、方差分析等方法,研究了切削参数对硅铝合金ZL109车削表面完整性的影响规律,得到了切削参数对于表面粗糙度、残余应力和显微硬度的影响程度和趋势,分析了ZL109车削表面完整性的形成机理,以期为切削参数优选提供实验和理论基础。研究结果表明,进给量f对表面粗糙度具有显著影响,切削速度v和进给量f增加会导致表面残余拉应力增大,显微硬度受切削参数的影响较小。