磁流变阻尼器非线性动力学行为的实验研究

磁流变阻尼器具有阻尼力大范围高度可控且耗能功率小的优点,在结构的半主动控制中有广泛的应用。磁流变流体及其元器件的动力学行为因其磁流变现象而存在滞回效应,对这种滞回效应的研究是其相关应用的基础。对磁流变阻尼器在多种激励电流与加载频率下的滞回动力学行为进行了实验研究,并进行了数学建模与参数识别。结果表明:磁流变阻尼器的阻尼力大小由激励电流控制,其非线性滞回特性具有频率依赖性;实验数据与模型仿真值的比较显示,模型可以准确模拟磁流变阻尼器滞回阻尼特性。     

The FKBP5 Gene Affects Alcohol Drinking in Knockout Mice and Is Implicated in Alcohol Drinking in Humans

FKBP5 encodes FK506-binding protein 5, a glucocorticoid receptor (GR)-binding protein implicated in various psychiatric disorders and alcohol withdrawal severity. The purpose of this study is to characterize alcohol preference and related phenotypes in Fkbp5 knockout (KO) mice and to examine the role of FKBP5 in human alcohol consumption. The following experiments were performed to characterize Fkpb5 KO mice. (1) Fkbp5 KO and wild-type (WT) EtOH consumption was tested using a two-bottle choice paradigm; (2) The EtOH elimination rate was measured after intraperitoneal (IP) injection of 2.0 g/kg EtOH; (3) Blood alcohol concentration (BAC) was measured after 3 h limited access of alcohol; (4) Brain region expression of Fkbp5 was identified using LacZ staining; (5) Baseline corticosterone (CORT) was assessed. Additionally, two SNPs, rs1360780 (C/T) and rs3800373 (T/G), were selected to study the association of FKBP5 with alcohol consumption in humans. Participants were college students (n = 1162) from 21–26 years of age with Chinese, Korean or Caucasian ethnicity. The results, compared to WT mice, for KO mice exhibited an increase in alcohol consumption that was not due to differences in taste sensitivity or alcohol metabolism. Higher BAC was found in KO mice after 3 h of EtOH access. Fkbp5 was highly expressed in brain regions involved in the regulation of the stress response, such as the hippocampus, amygdala, dorsal raphe and locus coeruleus. Both genotypes exhibited similar basal levels of plasma corticosterone (CORT). Finally, single nucleotide polymorphisms (SNPs) in FKBP5 were found to be associated with alcohol drinking in humans. These results suggest that the association between FKBP5 and alcohol consumption is conserved in both mice and humans.     

氢氟酸-硝酸体系中Ti-6Al-4V的腐蚀加工溶解特征

利用E-t曲线、动电位极化曲线研究了氢氟酸-硝酸体系中溶液主体成分、温度对Ti-6Al-4V腐蚀加工溶解行为和特征的影响,通过测试阳极与阴极反应动力学揭示钛合金腐蚀加工动力学规律。研究结果表明,在该溶液体系中钛合金的腐蚀加工是侵蚀-溶解-钝化循环往复的过程,硝酸的钝化作用与氢氟酸的溶解作用同时存在,当钝化膜的生成速度和钛基体的溶解速度达到动态平衡时,腐蚀速度处于相对稳定的状态。腐蚀加工初期阶段氢氟酸浓度会影响钛合金表面氧化膜的破坏,浓度较低时,氧化膜较难破坏,自腐蚀电位正移;浓度较高时,氧化膜容易被腐蚀溶解,自腐蚀电位负移。氢氟酸浓度和温度增加,反应活化能减少,腐蚀溶解加剧。氢氟酸浓度较低时,温度对加工速度的影响占主导地位;浓度增加到80 m L/L,温度的影响减弱,氢氟酸起主要作用。硝酸的钝化作用在减少总体腐蚀速度的同时可有效改善微观表面的凹凸不平,使微观表面趋于平整。     

高功率激光照射致材料气化与熔池行为

激光深熔焊接小孔内前沿孔壁上的动态行为与焊接小孔的动态波动关系密切。为了进一步探明激光照射在前沿孔壁上产生的物理现象,设计激光倾斜照射在板材上的试验以模拟激光照射在倾斜的小孔内前沿孔壁上的状态。拍摄观察激光照射作用下材料的熔化与气化行为,深入分析熔池流动状态与蒸气特征在不同的激光照射角度与不同的照射能量密度时的变化规律。结果显示,激光照射作用下材料熔化形成的熔池表面易产生波动涟漪,且涟漪产生的频率与移动速度随照射激光功率密度的增加而增加。由于涟漪的存在使得涟漪处局部激光照射倾角发生改变,材料对激光的吸收率大幅提高,局部可产生更多蒸气,在气化反冲作用力下,涟漪可被剥离形成飞溅熔滴。     

近β钛合金中两相组织不协调变形行为的晶体塑性有限元研究

本文基于晶体塑性模型,研究了近β钛合金中(α β) 两相组织的不协调变形行为。首先,双晶体模型的计算结果表明(α β) 两相组织中的塑性变形是不协调的,而且α相的变形行为与晶体取向和加载方向密切相关。另外,通过耦合三维Voronoi几何模型,探讨了近β钛合金中球状初生α相对宏观力学响应的影响。利用该CPFE-VT数值模型,研究发现α相与β相的不协调变形导致了合金强度随α相体积分数的增加而成线性降低。此外,β基体中α相的分布对合金应力-应变响应也有较大的影响。本文针对具有两相组织的近β钛合金建立的晶体塑性有限元模型为钛合金组织控制技术的发展以及性能预测提供了重要的技术途径。     

等离子蒸发制备的纳晶镍的压缩变形机理

与传统粗晶金属材料相比,纳晶金属具有特殊的变形机理。为了探索纳晶金属的变形机理,本文以等离子蒸发结合热压烧结制备的块体纳晶镍为研究对象,进行了准静态压缩力学性能测试,并且利用XRD和TEM技术对试样压缩前和压缩后的微结构演化进行了研究。结果表明：块体纳晶镍表现出较高的压缩强度和较好的韧性,且强度和韧性均具有率相关性。同时,纳晶镍压缩变形后晶粒尺寸较压缩前减小,但其微应变增加。结合纳晶镍的力学行为和压缩过程中微结构的演化,本文预测晶界位错运动和晶界滑移的联合机制是块体纳晶镍压缩过程中塑性变形的主要机理。     

Corrosion behavior of Ti-35Nb-7Zr-5Ta alloy prepared by spark plasma sintering in Hank’s artificial body fluid北大核心CSCD

Biomedical Ti-35Nb-7Zr-5Ta(Ti-Osteum) alloys was prepared by spark plasma sintering (SPS). Corrosion behavior and mechanism of the alloys was investigated in Hank’s solution by means of open-circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Both commercially pure titanium (TA1) and Ti-6Al-4V (TC4) alloy were also investigated to make a comparison. The results showed that, in comparison with TA1 and TC4 alloy, the Ti-Osteum alloy prepared by SPS exhibited a good corrosion resistance with lower corrosion current, lower passive current density and higher polarization resistance, but more or less the similar corrosion potential. As a result, the corrosion resistance of the three materials may be ranked as follows: Ti-Osteum＞TC4＞TA1. The excellent corrosion resistance of Ti-Osteum alloy prepared by SPS in simulated artificial body fluid may be attributed to its higher sintered density, β-type single phase microstructure, and a stable passive film mainly consisted of titanium oxide, nio bium oxide, zirconium oxide, and tantalum oxide on its surface. © 2016, Corrosion Science and Protection Technology. All rights reserved.     

Method for evaluating the reliability of compressor impeller of turbocharger for vehicle application in plateau area

As turbocharging diesel engines for vehicle application are applied in plateau area, the environmental adaptability of engines has drawn more attention. For the environmental adaptability problem of turbocharging diesel engines for vehicle application, the present studies almost focus on the optimization of performance match between turbocharger and engine, and the reliability problem of turbocharger is almost ignored. The reliability problem of compressor impeller of turbocharger for vehicle application when diesel engines operate in plateau area is studied. Firstly, the rule that the rotational speed of turbocharger changes with the altitude height is presented, and the potential failure modes of compressor impeller are analyzed. Then, the failure behavior models of compressor impeller are built, and the reliability models of compressor impeller operating in plateau area are developed. Finally, the rule that the reliability of compressor impeller changes with the altitude height is studied, the measurements for improving the reliability of the compressor impellers of turbocharger operating in plateau area are given. The results indicate that when the operating speed of diesel engine is certain, the rotational speed of turbocharger increases with the increase of altitude height, and the failure risk of compressor impeller with the failure modes of hub fatigue and blade resonance increases. The reliability of compressor impeller decreases with the increase of altitude height, and it also decreases as the increase of number of the mission profile cycle of engine. The method proposed can not only be used to evaluating the reliability of compressor impeller when diesel engines operate in plateau area but also be applied to direct the structural optimization of compressor impeller.     

弹簧结构参数对赋能型金属C形环力学行为及密封性能的影响

为研究核电站上赋能型金属C形环的内置弹簧圈的结构参数对密封性能的影响,建立C形环三维弹塑性有限元分析模型,通过实验验证该理论模型的可靠性,并分析弹簧结构参数(包括簧圈节距、簧丝线径和弹簧中径等)对C形环力学行为和密封性能的影响。结果表明:对于百万千瓦级核反应堆压力容器用金属C形密封,其簧圈节距、簧丝线径和弹簧中径分别控制在1.9~2.0 mm、1.7~1.8 mm和8.3~10.7 mm范围内时可保证C形环具有较好的密封性能;气密性实验验证上述结果的正确性,同时C形环压缩变形后密封面较平整,表层无裂纹、局部脱落或起皮等不良现象,满足工程使用要求。     

基于键合图的RV减速器动力学仿真

为研究RV减速器系统的弹性特性、齿轮间啮合刚度和阻尼对系统动态特性的影响,需要对系统进行建模和仿真分析。简述了RV减速器的结构、传动特点并对功率流进行分析,基于键合图理论建立RV减速器的动态仿真模型,推导出系统的状态方程,用Matlab进行系统动力学仿真分析,得到输出转速及加速度曲线,较好地反映了系统的动态特性。为RV减速器的设计、改进提供一定的理论依据。仿真结果表明:键合图模型是一种相当优越的数学模型,键合图理论与方法为RV减速器动力学特性的研究提供了一种新方法与途径。