机械系统模糊可靠度的估计模型

对机械系统组成单元的含义作了新的定义,建立单元模糊可靠度及其置信区间的估计模型;建立了机械领域常见系统的模糊可靠度估计模型;通过对单元模糊可靠度的直接估计,利用所建立的估计模型可以快速方便地预测出系统的模糊可靠度.实例分析给出了估计模型的使用方法,并显示模型的有效性.     

Estimating chemical mechanical polishing pad wear with compressibility

A polishing pad is an important component in a chemical mechanical polishing (CMP) system. Few investigations have specialized in the variation of the characteristics of the pad as it undergoes wear. All of the information concerning a pad, such as compressibility and pad life, comes from the manufacturer. No acknowledged standard or instrument exists for determining a pad’s quality. This study obtained the variation of the compressibility (K) of major types of pad (single-layer pad and composite pad) with polishing time (pad wearing) by theoretical modeling and real experiments. The K of single-layer or composite pads changes due to wear, and the trends in the K values of the two types of pads are exactly opposite. A finite element method (FEM) is used here to show that the variation in K strongly affects the polishing process. Theoretically, the compressibility of a pad can be used to judge whether the pad is good for polishing or not.     

Estimating tool properties on the basis of acoustic emission

Estimation of the operational properties of metal-cutting tools on the basis of acoustic emission is considered.     

Theoretical analysis and experimental verification on the static properties of externally pressurized air-bearing pads with load compensation

Load compensation can lead to externally pressurized bearings with infinite stiffness at the operating conditions. Calculations and experiments carried out on these bearings are discussed in this paper for two types of circular bearing pads with compliant surfaces. The mathematics is amply treated in appendices, and the numerical procedures are illustrated in diagrams. The experimental set-up is explained.     

Estimating the functional properties of thin calcium-phosphate coatings on medical implants

Thin calcium-phosphate (CP) coatings were formed on the models of medical products by radio-frequency (RF) magnetron sputtering. Using microscope studies, the coatings were shown to be visually continuous without visible pores and cracks. The functional properties of thin CP coatings were estimated by the method based on the measurement of the disruptive electrical voltage in compliance with GOST (State Standard) 9.302. Thin CP coatings on specimens subjected to sand blasting endured shear loads better in comparison with bending ones.     

A study of material removal amount of sapphire wafer in application of chemical mechanical polishing with different polishing pads

The study mainly explores the fabrication mechanism for fabricating sapphire wafer substrate, by using chemical mechanical polishing (CMP) method. A slurry containing the abrasive particles of SiO₂ is used to contact with the sapphire substrate polish and to produce chemical reaction for removal of sapphire wafer substrate when CMP method is used. The study observes the changes of the removal amount of sapphire wafer substrate when the pattern-free polishing pad and hole-pattern polishing pad are used under different down forces, polishing velocities, abrasive particle sizes and slurry concentrations. Employing regression analysis theory, the study makes improvement of the equation of material removal rate (MRR) to be the material removal height per 30 minutes (MRRh), and develops a compensation parameter C_rv of the error caused by the volume concentration of slurry. The results of experimental analysis show that under a certain down force, if the polishing velocity is greater, the material removal amount will be greater. Generally speaking, the material removal amount of hole-pattern polishing pad is greater than that of pattern-free polishing pad. As to the relationship between abrasive particle size and slurry concentration, when particle size is smaller, the volume concentration of slurry will be higher, and the number of abrasives for polishing wafer will be greater. As a result, a better material removal depth can be acquired. Through the above analytical results, considerable help is offered to the polishing of sapphire wafer.     

Investigation of the mechanical properties of bone using ultrasound

This paper examines the serial use of ultrasonic velocity measurement to monitor fracture healing. New Zealand White rabbit tibiae were fractured using a constant-energy technique and the ultrasonic velocity along the bone measured in animals sacrificed at 16 day intervals up to 96 days from fracture. In parallel with these measurements the mechanical performance of the healed tibiae were determined using a three-point bending test. Regression analysis failed to show a sufficiently good correlation between ultrasonic velocity measurements and the bending properties of healing fractures for the method to be of use clinically.     

Tribological surfaces of organic brake pads

Despite the enormous amount of testing and development of automotive brakes and brake pad materials, rather little is known about their tribological contact situation on a microscopic level. The sliding of an organic brake pad against a grey cast iron rotor is very different from most tribological systems. When worn against the rotor, the complex structure and very inhomogeneous composition of the pads results in a particular surface structure, with large contact plateaus rising a few micrometers above the rest of the surface [Wear 232 (1999) 163; Wear 2000 (submitted for publication); Proceedings of the Nordtrib 2000, vol. 2 (2000), 358]. The present investigation involves a more comprehensive study of the formation, mechanical properties and composition of the tribological surfaces of such pads, using high resolution scanning electron microscopy, nanoindentation, energy dispersive X-ray analysis and three-dimensional profilometry using white light optical interferometry. The observations are discussed and correlated to observed friction phenomena.     

Real-time observations of mechanical stimulus-induced enhancements of mechanical properties in osteoblast cells

Osteoblast, playing a key role in the pathophysiology of osteoporosis, is one of the mechanical stress sensitive cells. The effects of mechanical load-induced changes of mechanical properties in osteoblast cells were studied at real-time. Osteoblasts obtained from young Wister rats were exposed to mechanical loads in different frequencies and resting intervals generated by atomic force microscopy (AFM) probe tip and simultaneously measured the changes of the mechanical properties by AFM. The enhancement of the mechanical properties was observed and quantified by the increment of the apparent Young's modulus, E(*). The observed mechanical property depended on the frequency of applied tapping loads. For the resting interval is 50s, the mechanical load-induced enhancement of E(*)-values disappears. It seems that the enhanced mechanical property was recover able under no additional mechanical stimulus.     

基于线性回归模型的机电产品再制造费用预测

针对再制造决策者在产品再制造成本发生前无法决策的问题,提出运用线性回归模型,建立产品零部件失效类型信息与产品再制造费用之间的线性关系;基于同类产品零部件失效类型信息以及同类产品再制造费用的统计,对产品的再制造费用进行事前预测,并根据各类零部件的质量属性,对产品再制造的预测费用进行修正,获得相对准确的产品再制造费用预测,并用预测费用与实际费用的相对误差描述再制造费用预测的准确性。     

Microstructure and mechanical properties of sheep horn

The sheep horn presents outstanding mechanical properties of impact resistance and energy absorption, which suits the need of the vehicle bumper design, but the mechanism behind this phenomenon is less investigated. The microstructure and mechanical properties of the sheep horn of Small Tailed Han Sheep (Ovis aries) living in northeast China were investigated in this article. The effect of sampling position and orientation of the sheep horn sheath on mechanical properties were researched by tensile and compression tests. Meanwhile, the surface morphology and microstructure of the sheep horn were observed using scanning electron microscopy (SEM). The formation mechanism of the mechanical properties of the sheep horn was investigated by biological coupling analysis. The analytical results indicated that the outstanding mechanical properties of the sheep horn are determined by configuration, structure, surface morphology and material coupling elements. These biological coupling elements make the sheep horn possess super characteristics of crashworthiness and energy absorption through the internal coupling mechanism. We suppose that these findings would make a difference in vehicle bumper design. Microsc. Res. Tech. 79:664–674, 2016. © 2016 Wiley Periodicals, Inc.     

Evaluation of abradable seal coating mechanical properties

Three proprietary plasma-sprayed coatings, based on Ni–graphite, Al–Si–graphite and Al–Si–polyester, were chosen for evaluation by the use of a (low speed) scratch tester, as a means of assessing the performance of abradable coatings. The scratch test behaviour was also correlated with the mechanical properties of the coatings (elastic modulus, microhardness and ultimate tensile strength). The results obtained were compared with those from industrial trials, to ascertain if the scratch test could be used as a relatively cheap and effective alternative to expensive engine trials. We have shown that the Progressive Abradability Hardness, abbreviated below as PAH, can be utilised as a measure of abradability in the scratch test, and can be related to the mechanical properties, in a manner consistent with engine test-bed findings. We have also found that the abradability and the PAH can change with scratch length due, we believe, to coating compression and densification ahead of the slider. In this work, the PAH has been related to coating hardness, ultimate tensile strength and elastic modulus.     

等离子弧熔覆成形零件的力学性能研究

介绍一种基于等离子弧熔覆的快速成形工艺.研究不同扫描方向对成形件抗拉强度和延伸率的影响,结果表明,零件的纵向抗拉强度和延伸率均高于横向.通过层间成形方向相互垂直的扫描方式,可以制作整体上各向同性的零件.零件致密度达99.27%,与激光熔覆成形相当.     

常用密封垫片的选型和安装

结合某炼油厂密封垫片的实际应用情况，对常用密封垫片的选型和安装问题进行了阐述。     

Effect of mechanical activation of ultra-high-molecular-weight polyethylene on its mechanical and triboengineering properties

The effect of mechanical activation of initial ultra-high-molecular-weight polyethylene powders on the pysicomechanical properties of the polymer is studied. Mechanical activation is found to raise the strain and strength properties, as well as the triboengineering characteristics of ultra-high-molecular-weight polyethylene. X-ray diffraction analysis, IR spectroscopy, and optical and electronic microscopy show that mechanoactivation of the initial powder defines the polymer’s structural organization.     

螺母机械性能国家标准浅析

本文分析了GB／T3098．2－2000《紧固件机械性能 螺母 粗牙螺纹》和GB／T3098．4－2000《紧固件机械性能 螺母 细牙螺纹》，阐明了该两项国家标准与被其代替的旧标准的主要区别。     

盘式制动衬片力学模型的特性分析

通过对盘式制动衬片的受力分析 ,建立盘式制动衬片表面受力的力学模型 ,并计算出总摩擦力的作用中心。通过对底板与摩擦材料之间的受力分析 ,说明在各种应力作用下 ,在制动过程中有可能出现制动不稳定状态 ,为了避免这一现象 ,应合理设计衬片的几何尺寸。同时对如何设计底板上抗剪力孔的位置进行简单的分析。定性的说明了由于摩擦热而引起底板的弯曲变形 ,对摩擦面受力情况的影响。     

Dynamic mechanical properties of photo resist thin films

Photo resist thin films have mainly been used and investigated for versatile applications of micro electronic mechanical systems because of its outstanding aspect ratio and attainable film thickness. An accurate structure properties derived from validated material characterization is required in engineering applications. In this work, dynamic responses of photo resist thin films are tested by a nanoindentation in association with a dynamic mechanical analysis, where the thin film is coated on a silicon wafer by spin coating. The results show that the storage modulus of the photo resist thin film remains constant at the beginning and then increases as the indentation depth increases. Meanwhile, the loss modulus increases as the indentation depth increases. Varying the film thickness shows that the substrate effect plays an important role in determining the dynamic properties of thin films. However, the results agree well with the bulk material when the amplitude of nanoindentation is relatively small. It illustrates the dynamic mechanical analysis can be an efficient method to characterize the viscoelastic properties of thin films, but proper attention on the test parameters is needed.     

Combined influences of mechanical properties and surface roughness on the tribological properties of amorphous carbon coatings

Carbon films (∼2 μm thick) with a range of mechanical properties and underlying substrate roughnesses were evaluated for delamination and wear under conditions of combined impact and sliding contact. One-side-coated and both-sides-coated titanium alloy pin and disk wear couples were assessed using a custom-made impact/sliding pin-on-disk apparatus in a colloid-based blood volume expansion medium. The normal stress distribution along the film/substrate interface upon impact loading by a smooth titanium alloy pin was modelled analytically for each coated system. For disk surface roughness centre-line average (R_a) values below 0.05 μm, the area of disk film delamination was shown to correlate with the presence of tensile stress at the film/substrate interface. The interfacial tensile stress was shown to occur when there was a film/substrate elastic modulus mismatch, either within or outside the perimeter of contact, depending on the direction of the film modulus deviation. We propose that the tensile stress promotes delamination by lifting the film locally from the substrate. With increased disk R_a, the area of disk coating loss tended to decrease, because the surface roughness improved the mechanical bonding of the composite system.     

Structure and mechanical properties of tribologically induced nanolayers

Ultra low wear rates are common for lubricated state-of-the-art mechanical devices used in machines and cars. The main paths of energy dissipation are heat and wear generation as well as a significant change of near-surface material within the range of a few hundred nanometers. Due to mechanical intermixing at the asperity level the involved materials change with respect to chemical composition, morphology and mechanical properties. By means of focused ion beam analysis the morphology of the near-surface material of tribologically stressed and unstressed samples was investigated. In addition, nanoindentation was applied to characterize the mechanical properties. In the presented study mechanical intermixing leads to nanocrystalline material which is softer than bulk material. Depending on the level of tribological stressing, the modified material exhibits smaller energy dissipation, thus lower friction and wear.