Mechanical properties and tribological behavior of ZrO<Subscript>2</Subscript> thin films deposited on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

A silane coupling reagent (3-mercaptopropyl)trimethoxysilane (abridged as MPTS) was self-assembled on a single-crystal Si substrate to form a two-dimensional organic monolayer (MPTS-SAM). The terminal –SH group in the MPTS-SAM film was in-situ oxidized to –SO₃H group to endow the film with good chemisorption ability. Then ZrO₂ thin films were deposited on the oxidized MPTS-SAM by way of the enhanced hydrolysis of aqueous zirconium sulfate (Zr(SO₄)₂·4H₂O) in the presence of aqueous HCl at 50 °C, making use of the chemisorption ability of the –SO₃H group. The thickness of the ZrO₂ films was determined with an ellipsometer, while their morphologies and corresponding friction forces were analyzed by means of atomic force microscopy. The hardness and elastic modulus of the ZrO₂ thin films were determined on a Nanoindentation II (MET) instrument. The macro-friction and wear behaviors of the ZrO₂ films sliding against an AISI-52100 steel ball were examined on a unidirectional friction and wear tester and the worn surface morphologies observed on a scanning electron microscope (SEM). As the results, the as-deposited ZrO₂ thin film at a deposition duration of 100 h is about 100 nm thick, it decreases to 48 nm after annealing at 500 °C and further decreases to 45 nm after heating at 800 °C. The as-deposited ZrO₂ film is relatively rougher, with the rms to be about 1.0 nm, while the ZrO₂ thin films heated at 500 and 800 °C have surface roughness rms of 0.76 nm and 0.68 nm, respectively. The ZrO₂ film annealed at 800 °C has a high hardness to elastic modulus (H/E) ratio (0.062) as compared to the as-deposited ZrO₂ film and the film annealed at 500 °C. Both the two annealed ZrO₂ films show excellent wear-resistance as they slide against AISI-52100 steel at a normal load below 2.0 N, while the one annealed at 800 °C has better wear-resistance. The differences in the friction and wear behaviors of the as-deposited ZrO₂ film, the ZrO₂ film annealed at 500 °C and that annealed at 800 °C are attributed to their different micro structures and compositions. Since the ZrO₂ films was well adhered to the underlying MPTS-SAM, it might find promising application in the surface-protection of single crystal Si and SiC subject to sliding at small normal load in microelectromechanical systems (MEMS).     

Development of a reduced relaxation function and comparison of stress relaxation for anatomically paired tendons

A new “standard nonlinear solid” reduced relaxation function has been developed to describe the measured relaxation responses of tendons with 3% and 4% strain levels. This new reduced relaxation function has been used in modeling tendon responses with the quasi-linear viscoelastic law. Unlike the reduced relaxation functions employed in previous studies, the present function closely fits the measured relaxation responses for both the short term of the first few seconds and the long term of 22 hours. The relaxation responses of the anatomically paired tendons were found to be more alike than those from different sites. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Keyoung Jin Chun received his B.S. degree in Mechanical Engineering from Pusan National University, Korea, in 1977. He then obtained his M.S. degree in Mechanical Engineering from Wayne State University, and his Ph.D. degree in Mechanics from Michigan State University in 1982 and 1986, respectively. Dr. Chun is currently the chief senior researcher at KITECH in Cheon-An, Korea. His research interests include biomechanics for senior and gerontechnology.     

Development and implementation of a high speed open loop control technique for micro-positioning of mechanical structures

A method has been developed for dynamic open loop control of a structure modelled as a single degree of freedom system with damping. The technique predicts the required input signal to the system such that a specified output motion is produced with minimal overshoot and ringing. Micropositioning implementation to a mechanical system consisting of a flexible beam driven by a piezoelectric crystal has shown promising results for controlled step and pulse outputs. Significant improvement in both rise time and dynamic control of the beam for a step output was demonstrated with respect to a previous closed loop control experiment on the same structure.     

机械密封用焊接金属波纹管失弹试验装置的研制

设计了机械密封用焊接金属波纹管失弹试验装置,得到工况下波纹管弹力变化值,为波纹管的结构设计提供了数据依据。采用新研制的波纹管失弹试验装置,实现了在高温下对失弹试验数据的连续测量;在ANSYS Workbench中对主要受力零件进行了有限元分析,得出结论：本套试验装置中,波纹管的失弹现象完全由波纹膜片应力松弛产生,与其他零部件应力松弛无关,证明了所设计试验装置的科学性与可行性。     

SLM激光快速成型金属零件的组织及力学性能分析

为了对SLM快速成型不锈钢零件的组织及力学性能进行分析与研究,用SLM制备了拉伸试样进行拉伸试验,对其断口进行电镜扫描,分析其断裂特点;利用SLM设备制备了金属立体,进行显微硬度的测试、金相组织分析。实验结果表明:SLM快速成型金属件具有良好的拉伸性能、拉伸试样为韧性断裂;零件内部具有良好的致密性、晶粒细小,显微硬度高于一般奥氏体不锈钢;内部组织结构均匀,具有定向凝固特征;成型件物相主要以奥氏体存在。SLM成型金属件具有良好的组织特性及力学性能,能够满足实际使用的要求。     

同心连接器的力学性能测试技术和系统研究

为了能快速测量同心连接器插拔过程中的力学性能和准确评价机械寿命,研制了一种同心连接器的力学性能测试系统。该系统主要由运动模拟的机械装置和传感测量与电机控制的测控子系统组成,具有四路同步自动测试能力;根据连接器测试标准分析系统的性能指标,提出一种直线运动与旋转运动相结合的测试方法,使测试条件更加符合连接器真实使用情况;同时设计出具有自适应能力的柔性夹具,减少安装误差对测试结果的影响;对运动模拟机构进行建模分析研究,在极限速度条件下确定插拔循环周期内直线与旋转运动配合时序。对连接器样品进行单次和多次插拔测试,分析数据得到了连接器的力学性能并对机械寿命评估验证,实验结果表明该系统满足测试要求且能得到预期效果。     

一重载高速机械臂的结构与控制同时设计

拟订了机械臂的工作原理,建立了机械臂的受控动力学方程,运用优化算法设计了PD控制器的增益,计算了机械臂在不同角度下的刚体动力学响应。为了确定合理的机械臂截面尺寸,运用有限元法建立了机械臂的弹性动力学方程,求解了不同截面尺寸下的机械臂弹性动力响应,评价了机械臂的弹性振动。实践证明,所确定的机械和控制设计方案满足设计要求。     

机械压力机PLC控制仿真软、硬件的研制

本文以西门子公司S7－200系列CPU216型PLC控制JA21－160型机械压力机为实例,指出了对机械压力机PLC控制进行仿真的必要性。建立了机械压力机PLC控制仿真板硬件系统,并对所编制的具有良好的综合性能的仿真软件的组成及功能进行了阐述。     

虚拟样机在农机产品研发中的应用

介绍虚拟样机在农机产品研发中的应用、测试方法及制约因素。     

基于Pro/E和ANSYS对转炉托圈的机械应力分析

介绍了转炉托圈在0°倾角时所受的外载荷,并描述了运用Pro/E软件对托圈进行建模和导入ANSYS软件的方法,然后,基于有限元理论,运用ANSYS软件对托圈进行机械应力分析,从而得到托圈的最大应力和应力集中的部位,分析结果可为转炉托圈设计提供理论依据。     

数控技术对机械制造业的影响与对策

重点分析机床数控技术普及的原因、特征及其对机械制造业的实际影响,指出相关企业风险与机遇并存的现状。针对数控机床普及的趋势,提出了转变观念、加快装备技术改造、储备数控人才和组建合理的生产模式等主张,对指导机械制造业良性发展具有实际意义。     

A simple formula for the dielectric relaxation time—temperature—pressure relationship of lubricating oils and its application to viscosity prediction

The dielectric constant and the loss factor for several lubricating oils were both measured within the frequency range of 100 Hz–1.5 MHz. Measurements were made at atmospheric pressure with varying temperature, and at fixed temperature with varying pressure. The temperature dependence of the dielectric relaxation time could be expressed by the Vogel—Fulcher—Tammann (VFT) equation. In order to express the dielectric relaxation time as a function of temperature and pressure, a pressure‐dependent term was introduced into the characteristic temperature of the VFT equation. The experimental relaxation time could then be represented by a simple formula. Moreover, high‐pressure viscosity was calculated from the dielectric relaxation data by introducing the pressure dependence of the bulk modulus. The predicted results showed fairly good agreement with the viscosity data.     

丙烯输送泵机械密封失效原因分析及改进

通过对丙烯输送泵机械密封使用情况的跟踪和性能参数的验算以及对其失效原因进行的分析,得出了温度过高、造成液膜相态不稳定是密封泄漏的主要原因,并相应采取适当减小端面比压、改善冷却和封液循环等措施,以降低密封端面温度,从而使密封性能和使用寿命均得到了较大提高。     

P-301A泵机械密封失效原因分析及改造措施

机械密封轴向装配尺寸设计不合理,导致动静环间端面比压过大,机械密封时常泄露,运行周期达不到要求。为了提高该泵机械密封的使用寿命,降低检修成本,从生产实际出发,对机械密封失效的原因进行了详细分析,并提出了具体的改造措施。     

Inverse identification of the mechanical parameters of a pipeline hoop and analysis of the effect of preload

To create a dynamic model of a pipeline system effectively and analyze its vibration characteristics, the mechanical characteristic parameters of the pipeline hoop, such as support stiffness and damping under dynamic load, must be obtained. In this study, an inverse method was developed by utilizing measured vibration data to identify the support stiffness and damping of a hoop. The procedure of identifying such parameters was described based on the measured natural frequencies and amplitudes of the frequency response functions (FRFs) of a pipeline system supported by two hoops. A dynamic model of the pipe-hoop system was built with the finite element method, and the formulas for solving the FRF of the pipeline system were provided. On the premise of selecting initial values reasonably, an inverse identification algorithm based on sensitivity analysis was proposed. A case study was performed, and the mechanical parameters of the hoop were identified using the proposed method. After introducing the identified values into the analysis model, the reliability of the identification results was validated by comparing the predicted and measured FRFs of the pipeline. Then, the developed method was used to identify the support stiffness and damping of the pipeline hoop under different preloads of the bolts. The influence of preload was also discussed. Results indicated that the support stiffness and damping of the hoop exhibited frequency-dependent characteristics. When the preloads of the bolts increased, the support stiffness increased, whereas the support damping decreased.     

Influence of pitch air-blowing and thermal treatment on the microstructure and mechanical properties of carbon/carbon composites

This paper discusses the optimization of pitch properties as a matrix precursor of C/C composites by subjecting the pitches to different pretreatments to promote polymerization of the molecular components of pitch, which could improve carbon yield and density of the resultant carbon materials. Two series of pitches were prepared by air-blowing of impregnating coal-tar pitches at temperatures between 523 and 573 K, and thermal treatment at temperatures between 673 and 703 K, in an inert atmosphere. Effects of pitch treatments on resultant coke texture and porosity were monitored by polarized light microscopy. Unidirectional laminar composites were prepared using the original and treated pitches and commercial PAN-based carbon fibres. Effects of pitch treatments on the main microstructural features of composites are determined by scanning electron microscopy and polarized light microscopy, and related to the mechanical properties of composites. Results show an improvement of the mechanical properties of composites in both series, particularly for pitch treatments at 523 K/air in the air-blown series, and at 698 K–5 h in the thermally treated one.     

The effect of CeF3 on the mechanical and tribological properties of Ni-based alloy

The Ni-based alloys with various proportions of CeF₃ as lubricant and active element were prepared by hot-pressing and sintering in an intermediate frequency inducing oven. The effects of CeF₃ addition on the tribological and some mechanical properties of the alloy were investigated on a pin-on-disk tribometer. The results indicated that the compressive strength and impact roughness as well as the tribological properties of the alloy were improved by adding 3 wt% CeF₃. It was supposed that CeF₃ can effectively act as an additive, which exhibits beneficial effects on the mechanical and tribological properties of Ni-based alloy.     

串联式干气密封的设计及其在液态烃泵上的应用

对液态烃泵用串联式干气密封的结构进行了优化，从理论上对影响干气密封性能的主要参数进行了研究。并设计制造出了适合轻烃类介质的串联式干气密封及其控制系统。工业运行获得成功，极大地提高了液态烃泵的性能及可靠性。     

Effect of Cl on microstructure and mechanical properties of in situ Ti/TiB MMCs produced by a blended elemental powder metallurgy method

A modified blended elemental powder metallurgy (MBEPM) method has been developed for the production of low-cost Ti alloys and in situ Ti/TiB MMCs for automobile components such as connecting rods and inlet and exhaust valves. The MBEPM method uses Ti sponge fines as raw material, which contain a substantial amount of Cl. The Cl refines the microstructure of the as-sintered Ti–6Al–4V alloys, with a reduced prior β-grain size and a reduced α-lath size and aspect ratio. However, the grain refining effect of Cl is much less pronounced in as-sintered Ti–6Al–4V–10%TiB MMCs. The Cl is present in the as-sintered microstructure in three forms: (1) shells consisting of fine NaCl particles in macropores; (2) cuboidal NaCl precipitates in the alloy matrix; and (3) Cl and Na segregated to prior β-grain boundaries. Increasing the Cl content increases the tensile ductility of both Ti–6Al–4V alloys and Ti–6Al–4V–10%TiB MMCs, but has little effect on strength.     

Effect of process parameters on the density and porosity of laser melted AlSi10Mg/SiC metal matrix composite

Laser melting of aluminium alloy—AlSi10Mg has increasingly been used to create specialised products in various industrial applications, however, research on utilising laser melting of aluminium matrix composites in replacing specialised parts have been slow on the uptake. This has been attributed to the complexity of the laser melting process, metal/ceramic feedstock for the process and the reaction of the feedstock material to the laser. Thus, an understanding of the process, material microstructure and mechanical properties is important for its adoption as a manufacturing route of aluminium metal matrix composites. The effects of several parameters of the laser melting process on the mechanical blended composite were thus investigated in this research. This included single track formations of the matrix alloy and the composite alloyed with 5% and 10% respectively for their reaction to laser melting and the fabrication of density blocks to investigate the relative density and porosity over different scan speeds. The results from these experiments were utilised in determining a process window in fabricating near-fully dense parts.