On the evaluation of adhesion of coatings by automatic scratch testing

Automatic scratch testing is an expedient technique for comparatively evaluating the cohesive failure load and adhesion failure load of thin coatings on various substrates. In combination with SEM examination of the scratch track, this technique has been used herein to detect and evaluate various effects on coating strength and adhesion. For soft Triballoy T-800 and Stellite SF-6 cobalt-base coatings on 4340 low alloy steel, adhesion was found to be strong and failure was found to be cohesive in the coating. In the presence of a plated chromium interlayer, pre-existing cracks lowered substantially the cohesive failure load, which was also lowered by an increase in the coating deposition pressure. The spacing of transverse cracks within the coating was found in all cases to decrease with increasing applied normal load. In soft aluminum coatings on depleted uranium (DU)-0.75% Ti alloy specimens, alloying aluminum with magnesium or zinc enhanced the coating strength and adhesion. In (Al-Mg) coatings on this substrate, a smoother surface led to a lower friction coefficient and a higher adhesion failure load. In hard, thin TiN coatings on 17-4 PH steel, a lower bias voltage applied to the substrate yielded higher cohesive and adhesion failure loads. In hydrogenated amorphous SiC thin coatings on 4340 steel, loss of hydrogen by annealing converted the residual compressive stresses into tensile stresses and lowered both the cohesive and the adhesion failure loads. Finally, automatic scratch testing proved helpful in determining delamination loads in multilayer TiN/Ti/TiN coatings on DU-0.75% Ti alloy.     

Mucoadhesive films inside the colonic tube: performance in a three-dimensional world

A self-propelling colonoscopic device moving inside the colonic tube should be able to periodically grip safely to the colonic wall as well as to manipulate the generated friction. The feasibility of achieving high grip and friction manipulation by covering the device with mucoadhesive films is experimentally tested. More precisely, the frictional behaviour of mucoadhesive films inside the colonic tube is tested in vitro in porcine colon. It appears that mucoadhesive films generate significantly higher friction than conventional materials (ANOVA p=0, 95% CIs=−3.04, −2.14). The geometry of the film plays a role as well. When holes are, for instance, present in the film geometry and are large enough so that the colonic tissue can wrap their borders, friction can be significantly increased (ANOVA p=0, 95% CIs=−2.53, −1.26). By altering the contact area or the film geometry, friction manipulation can be achieved. Moreover, a simple theoretical model is developed and experimentally verified (R=0.92). The model can be used to estimate the level of the friction generated by three-dimensional configurations of mucoadhesive films as a function of their geometric characteristics and the material properties of the colon.     

A combined analytical‐experimental investigation of friction in cylinder liner inserts under mixed and boundary regimes of lubrication

It is necessary to develop an analytical solution in order to combine predictions with measured tribological parameters and fundamentally understand the mechanism of lubrication in a typical region of engine cycle, using tribometric studies. This paper deals with the development of such a representative approach. An analytical, rather than a numerical approach is expounded, as it is shown to suffice for the purpose of precise time‐efficient predictions, which conform well to the measurements. The effect of surface topography, material and operating conditions are ascertained for the representative case of top compression ring—cylinder liner contact at the top dead centre reversal in transition from the compression to power stroke. Stainless steel uncoated surface used as press fit cylinder liners for niche original equipment manufacturer applications are compared with those furnished with a Nickel‐Silicon Carbide wear‐resistant coating of choice in high performance motorsport. © 2017 The Authors Lubrication Science Published by John Wiley & Sons Ltd.     

Comparison of tribological properties of various carbon plastics under water-lubricated sliding friction

Carbon plastics based on polyphenylene sulfide matrix and carbon fabric have been synthesized using various technological procedures. Comparative triboengineering test results are cited for pure polyphenylene sulfide, carbon plastics on its base, and carbon plastics of grade FUT and UGET. Carbon plastics based on polyphenylene sulfide show higher wear resistance as compared to FUT and UGET. Carbon plastics based on polyphenylene sulfide with slight addition of C₆₀ fullerene show even higher wear resistance.     

Experimental and numerical investigation of thermal characteristics of a novel concentric type tube heat exchanger with turbulators

In this study, the heat transfer performance and friction characteristics of a novel concentric tube heat exchanger with different pitches of helical turbulators were investigated experimentally and numerically for a Reynolds number range from 3000 to 14 000. An experimental system was established to obtain experimental data. The numerical simulations were performed by using a three dimensional numerical computation technique, a commercial CFD computer code. Then, the heat transfer performance and friction characteristics of several helical turbulators were compared. The experimental, numerical and empirical correlation results were in a good agreement with each others. As a result, the heat transfer enhancements using turbulators were 2.91, 2.41, 2.18 and 1.99 times better than the smooth tube for pitch distances of p = 20, 40, 60 and 80 mm, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

屏蔽电机轴承选择浅析

结合屏蔽电机实际运行工况,针对水润滑材料碳化硅、硅化石墨、碳石墨、浸渍石墨的不同特点,对屏蔽电机常用轴承材料的性能进行了对比论述,并对该轴承材料的适用工况进行了概括,对不同工况下屏蔽电机轴承材料的选择给出了建议。     

平衡抛武器制动机构设计与实现

单兵有限空间发射的武器,大都采用平衡抛发射结构.本设计为提高发射过程的安全性和可靠性,在对现有制动技术总结基础上,利用薄壁圆环的径向收缩变形和摩擦环的摩擦吸能原理,设计出一种新的平衡抛制动机构.文中通过数值模拟和样机动态试验,验证了该制动机构的可靠性和安全性均有明显提高.为此类武器的设计提供了技术参考.     

大直径桩的荷载传递机理

由于大直径桩的承载力高、变形小，与普通中、小直径桩存在明显差异。因此，不宜用中小直径桩计算理论来分析大直径桩。采用有限元法模拟大直径桩的荷载传递并进行分析，得到的结果与试验研究相符。     

Mechanical characterization of spot friction stir welded joints in aluminum alloys by combined experimental/numerical approaches: Part II: Macromechanical studies

This is part II of a two part paper summarizing material characteristics of Spot Friction Stir Welded (SFW) lap joints in aluminum alloy 6111 at the macromechanical and micromechanical levels. In this paper, modal vibration testing and static flexure testing at the macromechanical level combined with numerical finite element models have been used to indirectly determine the elastic moduli of the base metal and weld zone. It was observed that the modal frequencies (and the corresponding apparent stiffness) of the joint oscillate at low amplitudes with increasing processing time. For each vibration mode, the amplitude of the oscillation in the frequency vs. processing time is only a few percent of the mean frequency, while the corresponding lap shear strength increases monotonically by a factor of about 8 as the processing time increases. Comparison of predicted modal frequencies and static load–displacement response of SFW joints with the corresponding measured responses seem to indicate that the weld zone is not as stiff as the base metal. Parametric studies to determine the effect of weld zone measurements on the modal frequencies have been carried out using finite element models.     

Adaptive Precision Control of Permanent Magnet Linear Motors

This paper describes an adaptive control scheme developed for precision control of DC permanent magnet linear motors (PMLM). A sliding surface is defined on which a self‐tuning version of robust control capable of achieving tight set‐point regulation is developed, where the control gains are tuned using an adaptive algorithm. Parameter and states convergence properties of the adaptive controller are derived based on the control law formulated. Finally, simulation study and a real‐time experiment are provided to evaluate the performance of the proposed control system.