采用电磁缓速制动器的汽车滑移率计算模型

针对目前车辆的可靠性和安全性存在的问题,建立了采用电磁缓速制动器的汽车在制动过程中滑移率的计算模型,分析了电磁缓速制动器在辅助制动过程中对汽车滑移率的影响,研究了制动临界情况下滑移率与地面附着系数之间的相互关系,为电磁缓速制动器的设计及其与车辆间的匹配,以及车辆制动过程中滑移率的最佳控制打下了基础.     

Microstructure and thermal physical parameters of Ni60-Cr3C2 composite coating by laser cladding

To satisfy performance and long life requirements for hot forging die, Ni60-Cr₃C₂ composite coatings were prepared on the high-speed steel W₆Mo₅Cr₄V₂ using laser cladding technology. Laser clad coatings with different ratios of Ni60:Cr₃C₂ were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX) and microhardness tester, respectively. Specific heat capacity and thermal conductivity were measured by Laser Thermal Constant Meter. Thermal expansion coefficient and elastic modulus were measured by Dynamic Mechanical Thermal Analyzer and Electro-Hydraulic Servocontrolled Testing System, respectively. The results indicated that Ni60+50wt% Cr₃C₂ composite coating had dense and homogeneous structure, as well as a metallurgical bonding with the substrate. With the increase of Cr₃C₂ content, volume of chromium-containing compounds in the composite coating increased, microhardness increased and microstructure refined. The thermal physical parameters results showed that Ni60+ 50wt% Cr₃C₂ composite coating was overall worse than W₆Mo₅Cr₄V₂, but had a higher hot yield strength to alleviate hot fatigue and surface hot wear of hot forging die during hot forging and thus improve the service life of hot forging die.     

Investigation on the morphology of martensite in carbon steels

The effect of carbon content on the morphology of martensite in carbon steels has been studied in depth. It is found that not all the packet martensites obtained in carbon steels quenched from elevated temperature are lath martensite. The packet martensite obtained thus should be divided into two categories: packet thin plate martensite (i. e. lath martensite) and packet plate martensite. The former is only found in low carbon steels, the latter mainly in medium and high carbon steels. The morphology of martensite in steels with different carbon contents has been researched in detail using optical microscopy, SEM and TEM. A new criterion is proposed for identifying the category of martensite. Based on this new criterion, it is found that as-quenched steels withC _c⩽0.2% contains lath martensite; that with 0.2%<C _c<0.4% contains a mixture of lath and plate martensite. The structure of as-quenched steels withC _c⩾0.4% is completely of plate martensite. The curve of the relative volume percentage of martensite without internal twins versus carbon content has been redetermined. Finally, the misinterpretation of experimental results by previous investigators is analysed. Project supported by the Science and Technalogy Committee of Hunan Province Synopsis of the first author He Yuehui, professor, born in Sept., 1963, received Ph D degree in 1994, majoring in metallurgy of non-ferrous, powder metallurgy, heat treatment of metals, metal product, and intermetallic compounds, has published more than 100 scientific articles.     

PBL剪力连接件的疲劳试验与分析

为了研究PBL (Perfobond Leiste)这种新型剪力连接件的抗疲劳性能,基于深圳南山大桥剪力连接件的尺寸和要求,设计并制作了6个PBL剪力连接件的推出试件进行疲劳试验.试验在MTS815机器上进行,采用常幅正弦波荷载,加载频率为3 Hz,试验应力比为0.1.通过对试件进行常幅荷载的循环加载,观察试件中钢与混凝土块的相对滑移、连接件的破坏模式、疲劳寿命以及应变的特征等.试验结果表明：主要开裂方向为连接件底部斜向下呈45°,裂缝的宽度同裂缝与竖向的夹角成反比;疲劳荷载作用时,PBL连接件的抗疲劳性能良好,孔径越大试件的疲劳寿命越长;试验从一定程度上说明腹板越厚和疲劳荷载幅值越小,滑移量的增长速度越慢,同时孔径越大和疲劳幅值越小,滑移量的增长速度也越慢.     

Phase transition and elastic properties of NbN under hydrostatic pressure

First-principles pseudopotential calculations are performed to investigate the phase transition and elastic properties of niobium nitrides(NbN). The lattice parameters ao and c0/a0, elastic constants C ij, bulk modulus B0, and the pressure derivative of bulk modulus B0 ′ are calculated. The results are in good agreement with numerous experimental and theoretical data. The enthalpy calculations predict that NbN undergoes phase transition from NaCl-type to NiAs-type structure at 13.4 GPa with a volume collapse of about 4.0% and from AsNi-type to CW-type structure at 26.5 GPa with a volume collapse of about 7.0%. Among the four types of structures, CW-type is the most stable structure. The elastic properties are analyzed on the basis of the calculated elastic constants. Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail. The longitudinal and shear-wave velocities, V P, V S and V m increase with increasing pressure, respectively. The Debye temperature Θ D increases monotonically with increasing pressure except for NiAs-type structure. Both the longitudinal velocity and the shear-wave velocity increase with pressure for wave vector along all the propagation directions, except for V TA([100]) and V TA[001]([110]) with NaCl structure and V TA[010]([100]) with the other three types of structures.     

Design of small-area and high-efficiency DC-DC converter for 1 T SRAM

The direct current-direct current (DC-DC) converter is designed for 1 T static random access memory (SRAM) used in display driver integrated circuits (ICs), which consists of positive word-line voltage (V _PWL), negative word-line voltage (V _NWL) and half-V _DD voltage (V _HDD) generator. To generate a process voltage temperature (PVT)-insensitive V _PWL and V _NWL, a set of circuits were proposed to generate reference voltages using bandgap reference current generators for respective voltage level detectors. Also, a V _PWL regulator and a V _NWL charge pump were proposed for a small-area and low-power design. The proposed V _PWL regulator can provide a large driving current with a small area since it regulates an input voltage (VCI) from 2.5 to 3.3 V. The V _NWL charge pump can be implemented as a high-efficiency circuit with a small area and low power since it can transfer pumped charges to V _NWL node entirely. The DC-DC converter for 1 T SRAM were designed with 0.11 μm mixed signal process and operated well with satisfactory measurement results.     

Influence of drying methods on fractal geometric characteristics of mesoporous silica aerogels

Chemical modification/ambient drying method and freeze drying method were introduced to research the synthesis of mesoporous silica aerogels. By analyzing N2 gas adsorption/desorption isotherms, the fractal geometric characteristics of gels were focused. The overall surface fractal dimensions were determined by analyzing N2 gas adsorption branch and a Frenkel-Halsey-Hill (FHH) equation was empolyed to determine surface fractal dimension Df . It is found that, during ambient drying process, VTMCS/VWetgel ratio plays a crucial role in the changes of geometric feature, the key point is 50%, when the ratio is lower, and surface roughness increases with the ratio, when it exceeds 50%, the surface is almost unaffected by the modification. While freeze drying always tends to get larger Df , freeze drying process could cause a rough surface of the gels. Compared with traditional porosity and specific surface area analyses, fractal geometry may be expected to be favorable for mesoporous structural analyses of materials.     

Selective leaching of vanadium from V-Ti magnetite concentrates by pellet calcification roasting-H_2SO_4 leaching process

A novel method of pellet calcification roasting-H_2 SO_4 leaching was proposed to efficiently separate and extract vanadium(V) from vanadium-titanium(V-Ti) magnetite concentrates.The leaching rate of V is as high as 88.98%,while the leaching rate of impurity iron is only 1.79%.Moreover,the leached pellets can be used as raw materials for blast furnace ironmaking after secondary roasting.X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy with energy dispersive X-ray spectrometry(SEMEDS) analyses showed that V~(3+) was oxidized to V~(5+) after roasting at 1200℃,and V~(5+) was then leached by H_2 SO_4.X-ray diffraction(XRD) analyses and single factor experiment revealed a minimal amount of dissolved Fe_2 O_3 during H_2 SO_4 leaching.Therefore,a high separation degree of V and iron(Fe) from V-Ti magnetite concentrate was achieved through H_2 SO_4 leaching.Compared with the traditional roastingleaching process,this process can achieve a high selectivity of V and Fe,and has excellent prospects for industrial production.     

High harmonic exploring on different materials in dynamic atomic force microscopy

In atomic force microscopy(AFM), high-frequency components consisted in dynamic tip-sample interaction have been recently demonstrated as a promising technique for exploring more extensive material properties. Here we present an exploratory study of high harmonic atomic force microscopy by force-spectroscopy and high harmonic imaging. Since these components are very weak compared to the fundamental response, we firstly designed a high harmonic cantilever by tuning the second order flexural resonance frequency to an integer 6 times of its fundamental mode(i.e. ω_2=6ω_1). Moreover, it is verified that high harmonic can discern extra features than topographies on different samples with amplitude/frequency modulation(AM/FM) dynamic AFM mode. In AM mode, the first resonance amplitude and 6 th harmonic amplitude were discussed. The 6 th harmonic is more sensitive than the first order response. In FM mode, it is noted that the decaying rate of the 6 th harmonic frequency is approximately 6 multiples to the slope of the fundamental frequency shift when the tip approaches to the surface of sample. This non-destructive method was also adopted to investigate the local interlayer coupling and intercalation in the two-dimensional graphene films tentatively.     

Low temperature synthesis of amorphous La<Subscript>0.7</Subscript>Zn<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> films grown on p<Superscript>+</Superscript>-Si substrates and its resistive switching properties

Amorphous La_0.7Zn_0.3MnO₃ (LZMO) films were deposited on p⁺-Si substrates by sol-gel method at low temperature of 450 °C. The Ag/LZMO/p⁺-Si device exhibits invertible bipolar resistive switching and the R _HRS/R _LRS was about 10⁴-10⁶ at room temperature which can be kept over 10³ switching cycles. Better endurance characteristics were observed in the Ag/LZMO/p⁺-Si device, the V _Set and the V _Reset almost remained after 10³ endurance switching cycles. According to electrical analyses, the conductor mechanism was in low resistor state (LRS) governed by the filament conductor and in the high state (HRS) dominated by the traps-controlled space-charge-limited current (SCLC) conductor.     

面向飞机结构健康监测的花萼状涡流传感器优化设计

针对飞机金属螺栓连接结构中螺栓孔孔边裂纹损伤定量监测需求, 在Goldfine等研究基础之上, 提出了一种花萼状涡流阵列传感器, 并通过构建的半解析正向等效模型进行传感器结构参数优化设计;实施2A12-T4铝合金拉伸疲劳在线监测实验验证优化后花萼状涡流阵列传感器的裂纹定量监测能力.模型仿真结果表明, 在不同感应线圈间距下激励线圈和感应线圈的宽度存在最优值.程序载荷谱作用下2A12-T4铝合金试件疲劳裂纹监测试验结果表明:经频率点优选和结构优化设计后, 将花萼状涡流传感器各通道幅值比变化曲线中的拐点作为特征点, 传感器通道1能对累积损伤进行监测, 通道2、3、4能对疲劳裂纹扩展长度进行定量监测, 监测精度达到1 mm;所提出的花萼状涡流传感器能实现对疲劳试件从累积损伤到疲劳裂纹扩展整个寿命周期的监测;可望将花萼状涡流传感器应用于实际飞机金属螺栓连接结构的结构健康监测之中.     

疲劳荷载作用下植筋锚固粘结的滑移性能

为研究疲劳荷载对植筋拉拔承载力、粘结应力的影响,设计植筋直径为16~25 mm、锚固深度为10d~25d（d为植筋直径）的10组拉拔试件进行疲劳试验,试件经200万次荷载上限为0.45P_u的疲劳加载后均未破坏,施加静载至破坏。加载过程中测量植筋的应变、滑移和荷载。结果表明：疲劳荷载削弱了承载能力,试件经疲劳荷载作用后极限承载力下降,粘结应力的减小随循环加载次数增加呈对数发展趋势。分析了粘结应力与试件破坏形态的关系。对于拔出破坏的试件,达到一定植筋深度后,胶筋界面的粘结应力是控制试件破坏与否的主要因素。增加植筋直径和锚固深度,粘结应力峰值逐渐降低,沿锚固长度的应力分布曲线趋于平缓,提高了植筋整体受力性能。     

高温多轴变幅疲劳损伤累积

为进行高温多轴变幅疲劳寿命预测,以应力幅作为损伤变量,采用经典的Chaboche模型进行多轴疲劳损伤计算.多轴加载下等效应力的确定是根据单轴加载下的本构关系,利用多轴等效应变求出等效应力.修正Chaboche疲劳累积损伤模型中应力指数表达式的形式,根据Chaboche损伤累积模型,求解变幅加载下的疲劳损伤.推导出多级加载的Chaboche疲劳损伤累积公式,将其用于变幅加载块的疲劳损伤估算.寿命预测结果与试验结果接近,误差基本在2倍因子之内,说明了寿命估算方法的可行性.     

Effect of polycarboxylate-type superplasticizer on the paste fluidity based on the water film thickness of flocs

The excess water film theory and the properties of flocs are integrated to examine the effect of the polycarboxylate-type superplasticizer on the paste fluidity.The theory states that excess water can surround the flocs rather than the particles and that the cell consists of a floc and a superficial water film.Experiments on limestone powder pastes were conducted to verify the theory.The superplasticizer dosage(sp%)and the water–powder ratio by volume(Vw/Vp)were systematically varied.A sedimentation balance method was used to measure the size distribution of the flocs in the limestone powder pastes.The water film thickness(WFT)of flocs was then calculated and shown to determine the paste fluidity.Based on this WFT of flocs,the effect of the sp on the paste fluidity was determined and then compared with the effect of water.     

Simulation of the precipitation process of Ni75AixV25-x alloys incorporated in the microelasticity field

The microelasticity field was incorporated into the microscopic phase-field equation for the ternary alloy systems, the morphology evolution and coarsening behavior of the Ni75AixV25-x alloy were simulated. The γ phase precipitates initially for Ni75Al7aV17.9 and Ni75Al5.5V19.5 alloys and the two phases transform from the equiaxed or strip-like to the quadrate as the growth and coarsening processes. For the anisotropic elasticity interaction of the system, the orientation of γ is along the 〈001〉 directions and the θ phase is along the short axis direction of [10]. Analysis of the structure and the pair-correlation functions indicate that the average precipitate length scale of the particles increases at the late-stage coarsening, and the dynamical scaling behavior is obeyed.     

Nonlinear dynamics theory on the steady state interface pattern during solidification of a dilute binary alloy

The nonlinear dynamics equations of the time dependence of the perturbation amplitude of the solid/ liquid interface during unidirectional solidification of a dilute binary alloy are established. The solutions to these equations are obtained, and the condition of the initial steady state growth of the cellular and dendritic structure after the planar solid/liquid interface bifurcates (mGc> G) with the increase of the growth rate is given. The condition of the steady state growth of fine cellular and dendritic structure in the beginning after the coarse dendrites bifurcate ( mGc<Γw2 + G) under the rapid solidification is obtained. The relationship of the steady state cell and dendrite tip radius, the perturbation amplitude and wavelength at the solid/liquid interface is presented.     

DZ125合金超高周疲劳微观裂纹萌生机制

DZ125合金具有优良的综合性能表现,已被广泛应用于燃气涡轮高温部件的铸造。关于DZ125合金的疲劳问题研究已有较多文献报道,但从微观断口分析的角度系统阐述该合金超高周疲劳裂纹萌生及失效机制的研究则相对较少。通过研究发现,随着疲劳强度的降低,疲劳数据离散性有增大的趋势;较小的疲劳应力（小于220 MPa）所对应的疲劳寿命并未有明显增加,上述特征与疲劳微观裂纹萌生机制的改变直接相关。在高应力作用下,疲劳裂纹倾向于从材料的表面或次表面萌生,巨型二次裂纹成为其断口形貌的主要特征;在低应力状态下,材料内部的孔洞缺陷是疲劳裂纹萌生的主要区域,并严重影响材料的疲劳寿命。驻留滑移带（PSB）可导致表面粗糙区的形成,成为裂纹尖端的主要特征。主裂纹与其他二次裂纹存在竞争关系,并最终引起疲劳断裂的发生。基于Murakami公式,DZ125合金在裂纹萌生阶段的平均应力强度因子为3.15 MPa·m^1/2,裂纹快速扩展阶段的平均应力强度因子和材料的断裂韧性（K_IC）分别为7.72和15.70 MPa·m^1/2。     

Electrochemical preparation of V<Subscript>2</Subscript>O<Subscript>3</Subscript> from NaVO<Subscript>3</Subscript> and its reduction mechanism

Vanadium trioxide (V₂O₃) was directly prepared by NaVO₃ electrolysis in NaCl molten salts. Electrolysis products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The existing state and electrochemical behavior of NaVO₃ were also studied. The results indicated that V₂O₃ can be obtained from NaVO₃. VC and C were also formed at high cell voltage, high temperature, and long electrolysis time. During electrolysis, NaVO₃ was dissociated to Na⁺ and VO₃ ^? in NaCl molten salt. NaVO₃ was initially electro- reduced to V₂O₃ on cathode and Na₂O was released simultaneously. Na₂CO₃ was formed due to the reaction between Na₂O and CO₂. The production of C was ascribed to the electro-reduction of CO₃ ^2?. VC was produced due to the reaction between C and V₂O₃.     

Preparation of TiO2 photocatalyst loaded with V2O5 for O2 evolution

TiO₂ photocatalysts loaded with V₂O₅ were prepared via a modified hydrolysis process, and characterized by X-ray diffraction, transmission electron microscopy, Raman spectra and diffuse reflectance UV-Vis spectra measurements. The photocatalytic activity of V₂O₅/TiO₂ was investigated by employing splitting of water for O₂ evolution. The results indicate that V₂O₅ loading can pronouncedly improve the photocatalytic activity of TiO₂ with Fe³⁺ as an electron acceptor under UV or visible light irradiation. The optimum mass fraction of the loaded V₂O₅ is 8%, and the largest speed of O₂ evolution for 8%V₂O₅ (mass fraction) loaded TiO₂ catalyst is 118.2 μmol/(L·h) under UV irradiation, and 83.7 μmol/(L·h) under visible light irradiation.     

Vacuum degree effects on betavoltaics irradiated by <Superscript>63</Superscript>Ni with differently apparent activity densities

For many current betavoltaics, beta sources and PN junction energy conversion units are separated. The air gap between the two parts could stop part of decay beta particles, which results in inefficient performance of the betavoltaic. By employing ⁶³Ni with an apparent emission activity density of 7.26×10⁷ and 1.81×10⁸ Bq cm^?2, betavoltaic performance levels were calculated at a vacuum degree range of 1×10⁵ to 1×10^?1 Pa and measured at 1.0×10⁵ and 1.0×10⁴ Pa, respectively. Results show that betavoltaic performance levels improve significantly as the vacuum degree increases. The maximum output power (P _max) exhibits the largest change, followed by short-circuit current (I _sc), open-circuit voltage (V _oc), and fill factor. The vacuum degree effects on I _sc, V _oc, and P _max of the betavoltaic with low apparent activity density ⁶³Ni are more significant than those of the betavoltaic with high apparent activity density ⁶³Ni. Moreover, the improved efficiencies of the measured performances are larger than the calculated efficiencies because of the low ratio of I _sc and reverse saturation current (I ₀). The values of I ₀, ideality factor, and shunt resistance were estimated to modify the equivalent circuit model. The calculation results based on this model are closer to the measurement results. The results of this research can provide a theoretical foundation and experimental reference for the study of vacuum degree effects on betavoltaics of the same kind.