Method and surface roughness aspects for the design of DLC coatings

The design of coatings for highly loaded component contacts, such as bearings, gears and valve train components involves several important factors, including load, friction, lubrication, surface characteristics and material parameters. This paper presents an investigation of the influence of the material, coating thickness and surface roughness on tensional stress levels for coatings that are more compliant than the substrate material. Specifically the effect of multiple asperity contact is studied in three dimensions. The simulation is based on a finite element model where the load is applied as several interacting Hertzian pressure distributions.The results show that the surface structure, in combination with the elastic properties of the coating, has a large influence on the tensional stress level in the coating. The highest tensional stress level in the coating occurs when contact spots almost overlap neighbouring cells and at the same time the size of the contact spots is in the same order of magnitude as the coating thickness.     

Effective elastic properties of randomly distributed void models for porous materials

Many 2D analytical models are available for estimating the effective elastic properties of porous materials. Most of these models adopt circular voids of a uniform diameter in superlattice arrays, such as unit void or periodically positioned models. There are two principal issues in a realistic representation of porous materials: the random distribution of a statistically sufficiently large number of voids in the model, and the random distribution of the size and position of the voids. Numerical schemes such as the FEM or the BEM have also been presented to cater for regular patterned circular voids. However, due to the large number of elements needed to produce sufficient accuracy for the curved boundary of circular voids or modelling a statistically sufficient number of voids with a random distribution in both the void size and the position, no such model has yet been produced.Modelling based on an FEM approach using a simplified approximation for void geometry is proposed here for the calculation of the effective elastic properties of porous solids. A plane strain model of a square geometry is adopted for a 2D array of voids. This simplified square shape allows a large number of voids to be simulated with a random distribution for both void sizes and their locations. The problem of anisotropy, which arises from the square shape, is discussed. It is verified that along the two principal directions (parallel to the sides of the square voids), the elastic properties remain the same as those predicted by using a circular void geometry. This square-shaped approximation, with its reduced requirement for FE analysis, has the potential to be extended to 3-dimensional modelling for a realistic simulation of engineering materials.     

A systematic method for characterizing the elastic properties and adhesion of a thin polymer membrane

The elastic properties and adhesion of a thin silicone rubber membrane have been characterized. An effective instrumentation embodying a video-enhanced microscope, which meets force and displacement resolution of and 10 nm, was developed. It provides the capability of simultaneously measuring both the applied force and the resultant displacement of the thin polymer membrane. A linear theoretical elastic solution was applied to quantitatively interpret the measured central deflection of the membrane under a circular concentrical load. Young's modulus of the membrane can be easily determined once the applied force and the central deflection, together with the essential dimensions, are known. The membrane jumped into an adhesion contact when the punch approached the range of the inter-surface force across the punch-membrane gap. A pull-off event was observed at a nonzero contact circle when the tensile load reached a critical threshold. The experiment is basically consistent with a theoretical model based on linear elasticity and an energy balance. The new method can be used to measure mechanical behavior of prestressed ultra-thin biomembranes and thin walled biocapsules with a residual stress.     

An elastic deformation measurement method for helicopter based on double-IMUs/DGPS TRAMS

Because of the severe vibration during flight process, the elastic deformation caused by the weight of avionic devices which are placed in the head nacelle of the helicopter such as millimeter wave radar cannot be measured through the optical-imaging and accelerometer-induction method. In order to survey this elastic deformation in real-time, this paper proposes the double-IMUs/DPGS tightly-coupled relative attitude measurement system (TRAMS): double IMUs are comprised by the same accuracy grade inertial sensors; one IMU is assembled in the head nacelle, while the other is in the airframe; the double-IMUs tightly-coupled with the DPGS respectively can measure the attitudes (pitch, roll and heading) of the nacelle and helicopter airframe in high accuracy; the relative attitudes between the two single IMU/DPGS TRAMSs reflect the elastic deformation between the nacelle and airframe. The double-IMUs/DPGS TRAMS have been effectively verified through the ground experiment in a vehicle and two flight tests in a military helicopter. The results present satisfactory stability and repeatability. This system can be popularized to other dynamic deformation measurement backgrounds.     

Nonlinear free vibration of laminated composite plates on elastic foundation with random system properties

The present investigation is concerned with free vibration analysis of laminated composite plates resting on elastic foundation undergoing large amplitude oscillation with random system properties. The lamina material properties and foundation stiffness parameters are modeled as basic random variables for accurate prediction of the system behavior. The basic formulation of the problem is based on higher-order shear displacement theory including rotatory inertia effects and von Karman-type nonlinear strain displacement relations. A C⁰ finite element is used for descretization of the laminate. A direct iterative method in conjunction with first-order Taylor series based perturbation technique procedure is developed to solve random nonlinear generalized eigenvalue problem. The developed probabilistic procedure is successfully used for the nonlinear free vibration problem with a reasonable accuracy. Typical numerical results (second-order statistics) are obtained for the composite plates resting on Winkler and Pasternak elastic foundations with different support conditions, side-to-thickness ratio, aspect ratio, oscillation amplitude ratio, stacking sequences and foundation parameters for symmetric and anti-symmetric cross-ply and angle-ply laminates. The results are validated with existing available results and independent Monte Carlo simulation.     

Structure and water-lubricated tribological properties of Cr/a-C coatings with different Cr contents

The Cr containing amorphous carbon coatings (Cr/a-C) with varying Cr content were deposited using unbalanced magnetron sputtering. The results revealed that the chromium carbide nano-clusters were formed when the Cr content exceeded 4.9 at%. The critical load increased while the hardness decreased after the Cr element incorporation. Although the low Cr containing Cr/a-C coatings (≤4.9 at%) exhibited similar friction coefficient with a-C coatings, but the initial friction coefficient, running-in distance and wear rate of SUS440C balls all decreased. However, the Cr/a-C coatings with high Cr content (11.98–14.09 at%) would worsen the tribological properties because chromium carbides acted as abrasive wear particles during tribotests.     

Effect of asperity interactions on rough surface elastic contact behavior: Hard film on soft substrate

An improved elastic micro-contact model of rough surfaces accounting for asperity interactions is proposed. The contact behavior of a single asperity system is composed of a stiffer hemi-spherical asperity deformation and bellowing softer substrate deformation, which is then extended to rough surface contact including asperity interactions. Using the solution of substrate deformation, normal positions of individual asperities are adjusted during quasi-static contact, from which surface interactive forces are obtained. Analytical simulations are performed using the proposed rough surface contact model, whose results are compared to Greenwood-Williamson-based models and with experimental measurements.     

Investigation of the surface structure and elastic properties of calcium silicate hydrates at the nanoscale

This work is the first step towards the understanding of the structure of calcium silicate hydrate (C–S–H), the main constituent of cement paste, at the nanoscale. The first demonstration of atomic-resolution imaging of the (C–S–H) surface with an atomic force microscope (AFM) was performed.

C–S–H nanoparticles (60×30×5 nm³) were partially recrystallized by Ostwald ripening after long-term equilibrium in saturated calcium hydroxide solution of different concentration, leading to C–S–H of different calcium/silicon ratio (Ca/Si). The results of atomic resolution made possible the investigation of the C–S–H cell surface parameters. The surface layer structure depended on the calcium hydroxide concentration with which it equilibrated.

The change in structural properties perpendicular to the C–S–H layer was probed by modifying AFM for nanoindentation hardness measurements with a depth of indentation as low as 1 nm. The change in elastic modulus depending on the calcium/silicon ratio was evaluated and correlated in the change in structural parameters in this direction as estimated by X-ray diffraction.     

Tribological properties and vacuum ion-plasma methods of application of diamond and diamond-like coatings

Published data and results of the author’s studies of the tribological properties and methods of application of diamond and diamond-like coatings are examined. An explanation of the high antifriction properties of diamond and diamond-like coatings is proposed. The role of hydrogen in the coatings in providing the effect of ultralow friction is examined.     

The application and research of high-frequency ultrasonic reflection technique used in the measurement of small diameter’s tube cavity size

Based on the problems that the photoelectric detection method and the X-ray testing method cannot provide the ideal accuracy when they are applicated to detect the cavity of small workpiece with diameter Φ6 mm and the general probes cannot stretch to the internal of the workpiece, we propose a high-frequency ultrasonic reflection technique which is used to measure the cavity size of diameter tube. The method uses ultrasound to measure the thickness. It can extract information about the wall size of workpiece through signal processing, feature extraction and other methods. By using this information, we can measure the size of cavity. Compared with the test results showed by a venire caliper and screw micrometer, we can get the conclusion that the immersion focusing probe with center frequency of 10 MHz can accurately detect the cavity of the workpiece. The experiment shows that the method gives consideration to the accuracy and computational efficiency of the workpiece’s cavity parameters. It can get data supplely and effectively. There are other advantages of this method such as stable performance, easy installation, and lower power consumption and penetration ability. It is suitable for the precision measurement of the workpiece.     

Complex wear measurement on thin coatings by the cratering method

Ball cratering and rotating wheel tests are useful techniques for abrasive wear resistance evaluation of thin coatings. Nevertheless, such techniques involve significant experimental errors, coming from equipment deficiencies and changes in wear response depending on test parameters. In case of rotating wheel test, common instrumental errors are: geometry‐induced errors (curved or non‐horizontal sample surface), alignment errors (misalignment between ball/wheel rotation axis and sample stage) and optical measurement errors. In the present paper, errors due to crater dimension detection system (penetration depth or crater diameter) and equipment deficiencies (rotating axes misalignment and sample slope) were numerically analysed. A general expression for volume calculation was obtained, considering axes misalignment and sample slope, and experimentally validated by wear tests on Ti/TiN CAE‐PVD coatings and profilometer abraded volumes measurement. Results showed that axes misalignment and sample slope involve considerable errors in wear coefficient evaluation. However, errors can be corrected by the use of obtained expressions. Copyright © 2009 John Wiley & Sons, Ltd.     

超声振动辅助混粉电火花表面强化粗糙度研究

进行超声振动辅助混粉电火花表面强化实验,分析超声振动辅助混粉电火花表面强化过程中各因素,例如脉宽、脉间、峰值电流、混粉浓度和超声振动振幅等对强化层表面粗糙度的影响规律,研究结果表明,各因素对强化层表面粗糙度影响规律明显,研究结果可以对超声振动辅助混粉电火花表面强化的工艺参数优化提供依据,对进一步的理论和实验研究具有一定的指导意义.     

纳米陶瓷涂层磨削表面残余应力的研究进展

纳米陶瓷涂层材料具有高硬度和高耐磨性,采用超硬磨料的金刚石砂轮磨削是其最主要的加工方法,在磨削时容易出现表面残余应力而导致表面裂纹.目前,国外在纳米结构陶瓷涂层磨削表面残余应力的研究很少,我国正在对纳米陶瓷涂层材料超精密磨削后表面残余应力方面进行研究.介绍了纳米结构陶瓷涂层的研究背景,阐述了纳米结构陶瓷喷涂材料性能特点,分析了纳米结构陶瓷涂层的磨削研究动态和磨削表面残余应力的研究现状.分析研究表明,纳米结构陶瓷涂层的开发与研究将会受到越来越广泛的重视,其后续研究将是下一步的工作重点.     

Evaluation of wear and tribological properties of coatings rubbing against copper

A new crossed-cylinders tribo-tester is proposed. This tribo-tester can decrease the tendency of the chatter vibration. The tribological properties of coatings against copper is evaluated with this tribo-tester. The wear rate of TiN, TiC and TiCN rubbing against copper is higher than the substrate high speed tool steel: SKH51 (JIS). The catalytic action of copper for oxidation of Ti-based coatings is a main reason of this high wear rate of TiN, TiC and TiCN rubbing against copper. The wear rate of CrN rubbing against copper is in a very low level because CrN shows the excellent oxidation resistance and Cr₂O₃ film formation decreases the wear loss of CrN coating.     

青年与老年手指甲表面形貌、成分与力学性能的实验分析

应用红外光谱仪、场发射扫描电镜、差示扫描热量仪、原位纳米力学测试系统对青年(20~25岁)与老年(70~75岁)指甲的表面结构、形貌、水含量及力学性能进行了实验分析。结果表明:与青年组成员指甲相比,老年组成员指甲的PO 2、C-O、CH 2与CONH基团的峰位向高波数移动;老年组成员指甲表面比青年组成员指甲粗糙并表现出明显的纵向纹理;尽管其总含水量与青年组成员指甲相当,但老年组成员指甲结合水的含量比青年组成员指甲的低;老年组成员指甲的硬度与约化弹性模量均高于青年组成员指甲相应对比量,因此,老年组成员指甲在划痕实验中显示出更好的耐磨性,但在较大载荷时出现明显的裂纹。     

Influence of low friction coatings on the scuffing load capacity and efficiency of gears

The influence of multilayer composite surface coatings on gear scuffing load carrying capacity, gear friction coefficient and gearbox efficiency is discussed in this work.The deposition procedures of molybdenum disulphide/titanium (MoS₂/Ti) and carbon/chromium (C/Cr) composite coatings are described.Tests reported in the literature, such as Rockwell indentations, ball cratering, pin-on-disc and reciprocating wear, confirm the excellent adhesion to the substrate and the tribological performance of these coatings, suggesting they can be applied with success in heavy loaded rolling–sliding contacts, such as those found in gears.FZG gear scuffing tests were performed in order to evaluate the coatings anti-scuffing performance, which both improved very significantly in comparison to uncoated gears. These results in conjunction with the friction power intensity (FPI) scuffing criterion allowed the determination of a friction coefficient factor X_SC to include the coating influence on the friction coefficient expression.The composite coatings were also applied to the gears of a transfer gearbox and its efficiency was measured and compared at different input speeds and torques with the uncoated carburized steel gears. Significant efficiency improvement was found with the MoS₂/Ti coating.     

Measurement of elastic constants of limited-size piezoelectric ceramic sample by ultrasonic method

Measurement of material elastic constants for limited-size samples by ultrasonic method is described and validated. Based on acoustic microscope technology, the material elastic constants are determined by longitudinal wave and leak surface wave velocities simultaneously measured by developed ultrasonic system with a line-focus PVDF transducer. In this paper, the elastic constants of limited-size Cr₂O₃ doping on 0.2 PZN–0.8 PZT piezoelectric ceramic wafer sample are determined and the measurement errors are analyzed. The experimental results show this ultrasonic system can be used for measurement of material elastic constants for limited-size samples with high measurement precision, and the relative errors for Poisson’s ratio and Young’s module measurements are, respectively, less than 1% and 3%. It can satisfy the requirement of engineering and science research. Furthermore, it is suitable to measure elastic constants of both isotropic and anisotropic materials by ultrasonic method with help of developed ultrasonic system.     

Experiences from scratch testing of tribological PVD coatings

The use of PVD coatings in tribological applications becomes more and more widespread. Thus also the need to fully understand the relationships between the intrinsic properties of the coating, the properties of the coating/substrate composite and the tribological performance of the composite in different tribological systems becomes increasingly pressing. One of the tools available for tribological characterization of coatings and coating/substrate composites is scratch testing. In the current paper, Uppsala University presents a selection of results from many years of scratch testing of PVD coated components. Applications range from adhesion assessment and coating quality determination to estimation of coating fracture resistance. Examples in the form of scratch studies of PVD coatings on various high speed steels and tool steels - including failure mode anaiysis in situ SEM - are given.     

Artificial neural network-based prediction technique for wear loss quantities in Mo coatings

Mo coated materials are used in automotive, aerospace, pulp and paper industries in order to protect machine parts against wear and corrosion. In this study, the wear amounts of Mo coatings deposited on ductile iron substrates using an atmospheric plasma-spray system were investigated for different loads and environment conditions. The Mo coatings were subjected to sliding wear against AISI 303 counter bodies under dry and acid environments. In a theoretical study, cross-sectional microhardness from the surface of the coatings, loads, environment and friction test durations were chosen as variable parameters in order to determine the amount of wear loss. The numerical results obtained via a neural network model were compared with the experimental results. Agreement between the experimental and numerical results is reasonably good.