水泵转子径向圆跳动检测数据修正

针对应用千分表和电涡流传感器进行水泵转子径向圆跳动检测时,检测结果出现正弦变化规律的现象,分析了安装偏心误差对检测结果的影响原理,建立了相应的数学模型.运用最小二乘拟合法计算出变化曲线的幅值及初相位,从而消除偏心误差实现误差分离.结果表明,当将所提方法应用在水泵转子径向圆跳动检测的工程实践中时,可以有效消除安装偏心引起的误差,从而提高检测精确度.拟合平方和误差约为0. 000 9,所提方法可以广泛应用于轴类工件的检测实践.     

Metallic glass–steel composite with improved compressive plasticity

A Zr_52.5Cu₁₈Ni_14.5Al₁₀Ti₅ bulk metallic glass toughened with a commercially available spring-shaped steel wire has been produced by centrifugal casting. The addition of the steel spring significantly affects shear band nucleation and propagation through the blockage, deflection and multiplication of shear bands at the glass–spring interface. As a result of the more homogeneous distribution of the plastic strain, the room temperature plasticity increases from 0.9% for the monolitic glass to about 4% for the glass–spring composite. Given the low volume fraction of the spring used in the composite (4.2 vol.%), these results demonstrate the extreme effectiveness of the steel spring for improving the plasticity of the metallic glass.     

Creep resistance of as-cast Mg-5Al-5Ca-2Sn alloy

In the present study, creep properties of as-cast Mg-5Al-5Ca-2Sn(AXT552) alloy were investigated by means of a GWT304 creep testing machine at temperatures of 175 °C and 200 °C in the stress range of 35-90 MPa. Results show that creep rates increase with applied stress at an identical temperature. Creep strain at 100 hours is 0.0518% and 0.083% at creep conditions of 175°C/75 MPa and 200°C/60 MPa, respectively, which is comparable to MRI230 D and much lower than most of AX series alloys. By the observation and analysis for samples before and after creep tests using a Shimadzu XRD-7000 type X-ray diffractometer(XRD) and a Hitachi S-3400 N type scanning electron microscope(SEM), it was found that Al_2Ca(C15) phase precipitated out of C36 phase or matrix. The cavity formation and connection at the interface of soft matrix and hard intermetallics caused the propagation of cracking along the eutectic phase during creep process and dislocation accommodated grain/phase boundary sliding is expected to be the dominant creep mechanism.     

Glass formation in Fe-Cr-Zr-B-Mo alloys by tuning Nb addition

Fe-based bulk metallic glasses (BMGs) with high boron content have potential application as a coating material used in the framework for storing spent nuclear fuels to support their safe long-term disposal. The high glass forming ability (GFA) and large supercooled liquid region are therefore required for such Fe-based BMGs in either the glassy powder fabrication or the subsequent coating spraying. In order to meet these requirements, the influence of Nb content on the GFA of Fe₅₇Cr₁₀Zr₈B₁₈Mo_7−xNb_x (x=1–5, at.%) alloys was investigated, as Nb has positive roles in GFA and thermal stability of BMGs. The results indicate that a fully amorphous phase in the as-cast samples with 3 mm in diameter is obtained for both the Fe₅₇Cr₁₀Zr₈B₁₈Mo₅Nb₂ and Fe₅₇Cr₁₀Zr₈B₁₈Mo₄Nb₃ alloys. The corresponding supercooled liquid regions of the two BMGs are 78 K and 71 K, respectively. The mechanism for improving their GFA was analyzed based on the principle of metal solidification, the parameters for glass formation and thermal properties of the alloys. The compression strength and Vicker’s hardness of the two BMGs are 1,950 MPa and 1,310 HV, 2,062 MPa and 1,180 HV, respectively. The developed BMGs with high B content, good GFA, and very high hardness can be used as coating materials to the framework for spent nuclear fuels.

     

基于LAPW算法磁记忆信号相变特性的研究

当应力达到临界屈服点时,铁磁性金属构件将产生塑性形变,造成重大的安全隐患。金属磁记忆检测技术可以快速、有效地检测出应力集中区域,但是,目前尚无有效的方法对临界屈服点处的磁记忆信号特征进行定量化分析。采用基于密度泛函理论的线性缀加平面波法(LAPW),建立了磁力学耦合模型,分析了临界屈服点的磁记忆信号特征,计算了弹性形变和塑性形变范围内,体系的差分电荷密度、原子磁矩、晶格结构随应力的变化关系。研究结果表明:随着应力的增加,固体中原子之间的结合力逐渐减弱,晶格结构的稳定性变差;当应力达到临界屈服点时,固体发生相变,磁记忆信号产生突变,磁记忆效应减弱。理论计算结果与实验结果具有很好的一致性。     

时变转速运行状态下鼠笼电机转子断条故障诊断

电机电流信号特征分析(MCSA)是诊断鼠笼电机早期转子断条故障的常用方法。当电机在时变转速状态下运行时,转速和滑差连续变化,定子电流表现为非平稳信号,MCSA不再有效。本文提出一种鼠笼电机时变转速运行状态下的早期转子断条故障诊断新方法。该方法的核心是对定子电流Park矢量模平方信号作离散小波变换,然后根据转子断条故障特征频率2sf在转速连续变化期间的波形演变图谱以及小波能量变化判断故障发生与否。在3k W电机实验台上对所提出的方法进行实验验证,实验结果证实了所提方法的有效性。     

基于SH导波的防腐层能量密度检测机理研究

涂敷防腐层是确保油气管道完整性非常重要的手段,但因环境或外力等因素使防腐层产生剥离、孔洞等缺陷。本文针对埋地管道外涂防腐层轴向剥离、孔洞缺陷,利用粘弹性动力学理论建立能量平衡单元体F的双层结构波动模型,对单元体F的频散特性、能量密度和导波衰减进行理论分析和数值计算,并设计SH-EMAT换能器进行了防腐层剥离缺陷实验研究。研究表明:防腐层剥离程度可引起单元体F中各模态频散特性变化,防腐层剥离厚度越大,SH导波模态对应相速度、群速度越大,且差异显著。在一定频率范围内,其相速度与防腐层剥离缺陷尺寸成正比。导波能量衰减依赖于能量密度因子QE且独立于导波模态,能量密度趋向于防腐层等效粘弹性介质的剪切速度倒数;单元体F中能量密度因子QE的特征参数可为管道防腐层剥离、孔洞缺陷内检测的量化研究提供理论依据。     

高强钢CO2激光-MAG复合焊接性能

为了研究CO₂激光-熔化极活性气体保护焊（MAG）复合焊接性能,采用CO₂激光和CO₂激光-MAG复合焊接590MPa级高强度钢,对其焊接接头的显微组织和力学性能进行了研究.结果表明,激光-MAG复合焊接的焊缝金属中,MAG电弧作用区主要为珠光体和贝氏体,激光作用区主要为马氏体;激光-MAG复合焊接的焊缝金属中Mo和Mn合金元素的分布具有不均匀性;激光和激光-MAG复合焊接的试件焊接接头拉伸性能完全满足要求,焊缝强度高于基体强度;激光-电弧复合焊缝金属在-60℃～+15℃试验温度范围内的冲击韧性比激光焊缝金属高;激光-MAG复合焊接焊缝金属硬度在250～400 HV之间,高于基体金属的硬度.     

酚醛泡沫的燃烧行为及阻燃研究进展

酚醛泡沫因兼具优异的保温性能和阻燃性能在工程领域得到广泛应用,但其经高温燃烧后质量残留率很低,炭层疏松、强度低,离开火焰后还易出现阴燃现象。目前有关酚醛泡沫燃烧行为的研究大多集中在如何进一步提高酚醛泡沫塑料的阻燃等级或在改善其脆性的同时不降低固有的阻燃性能,还未见关于酚醛泡沫燃烧全过程行为的综述报道。文章介绍了酚醛泡沫在明火燃烧和阴燃状态的燃烧行为,分析了影响酚醛泡沫燃烧行为的因素,并总结了现有酚醛泡沫阻燃研究的进展。目前酚醛泡沫的燃烧行为及阻燃研究主要集中在泡沫的明火燃烧,对酚醛泡沫阴燃问题的研究重视不足,缺乏针对酚醛泡沫燃烧全过程的行为和机理探究。因此,提出应加大对酚醛泡沫阴燃行为的研究投入,注重对酚醛泡沫燃烧全过程的机理探索与阻燃方案研究,设计并研发出解决酚醛泡沫燃烧全过程问题的有效途径。     

Highly electrocatalytic activity Ruddlesden−Popper type electrode materials for solid oxide fuel cells

To promote the viability of commercial solid oxide fuel cell (SOFC), developing novel oxygen electrodes with high electrochemical activity is essential. Herein, a series Ruddlesden-Popper oxides, Sr_3?xLa_xFe₂O_7?δ (SLFx), are successfully synthesized and evaluated as potential cathode materials for SOFC. The oxygen desorption behavior, electrochemical activity and oxygen reduction reaction (ORR) kinetics of the SLFx cathodes are systematically discussed. The Sr_2.9La_0.1Fe₂O_7?δ (SLF10) cathode exhibits highest oxygen vacancy concentration and excellent electrocatalytic performance, as evidenced by a low polarization resistance of 0.14 Ω cm² and high maximum power density of 0.77 W cm^?2 at 700 °C. From electrochemical impedance spectra and distribution of relaxation times analysis, the oxygen adsorption/desorption process is the rate-limiting step toward ORR at the cathode interface. Furthermore, SLF10 shows considerable polarization overpotentials in both SOFC and solid oxide electrolysis cell (SOEC) modes, indicating that SLF10 is a promising bifunctional electrode for electrocatalytic oxygen reaction.