Lubrication performance of finite journal bearings considering effects of couple stresses and surface roughness

To inspect the performance characteristics of finite journal-bearing systems, the combined effects of couple stress due to a Newtonian lubricant blended with additives and the presence of roughness on journal-bearing surfaces are studied in this article. Basing on the Stokes theory and Christensen’s stochastic model, the stochastic generalized Reynolds equation is deduced. The film pressure distribution equation is numerically solved by using the conjugate gradient method of iterations. According to the results, the couple stress effects can raise the film pressure of the lubricant fluid, improve the load-carrying capacity and reduce the friction parameter, especially at high eccentricity ratio. The surface roughness effect is dominant in long bearing approximation and the influence of transverse or longitudinal roughness to the journal bearing is in reverse trend. In general, the critical value of length-to-diameter is 1.1.     

Pressure profiles measured within lubricated contacts in presence of dented surfaces. Comparison with numerical models

In this paper, dented contacts have been studied in an EHL ball on disk device under pure sliding conditions. Dents with diameter of half the Hertzian contact radius were positioned in the center of the contact. The measured pressure profiles, obtained from Raman microspectrometry, are very different from those expected. A huge pressure peak is observed at the place where the lubricant leaves the dent, leading to very high pressure gradients. The effect of the dent shoulders is also visible. These results are discussed and compared to numerical ones. Finally, some consequences on life prediction of dented surfaces are presented.     

Sliding wear evaluation of hot isostatically pressed (HIPed) thermal spray cermet coatings

The aim of this study was to investigate the potential of applying hot isostatic pressing (HIPing) as a post-treatment to thermally sprayed wear resistant cermet coatings. The relative performance of the as-sprayed and hot isostatically pressed functionally graded WC-NiCrBSi coatings was investigated in sliding wear conditions. Coatings were deposited using a high velocity oxy-fuel (HVOF)—JP-5000 system, and HIPed without any encapsulation at temperatures of 850 and 1200 °C. The influence of post-treatment temperature on the coating's wear resistance was thus investigated. Sliding wear tests were carried out using a high frequency reciprocating ball on plate rig using steel and ceramic balls under two different loads. Results are discussed in terms of microstructural investigations, phase transformations, mechanical properties, and residual stress investigations. The results indicated significant alteration of the coating microstructure, brought about by the coating post-treatment, particularly when carried out at the higher temperature of 1200 °C. As a consequence, developments in the coating mechanical properties took place that led to higher wear resistance of the HIPed coatings.     

Effect of shot noise and secondary emission noise in scanning electron microscope images

The effect of shot noise and emission noise due to materials that have different emission properties was simulated. Local variations in emission properties affect the overall signal‐to‐noise ratio (SNR) value of the scanning electron microscope image. In the case in which emission noise is assumed to be absent, the image SNRs for silicon and gold on a black background are identical. This is because only shot noise in the primary beam affects the SNRs, irrespective of the assumed noiseless secondary electron emission or backscattered electron emission processes. The addition of secondary emission noise degrades the SNR. Materials with higher secondary electron yield and backscattering electron yield give rise to higher SNR. For images formed from two types of material, the contrast of the image is lower. The reduction in image signal reduces the overall image SNR. As expected, large differences in δ or η give rise to higher SNR images.     

机械零件的接触应力计算

传递动力的高副机构、如摩擦轮、凸轮齿轮、链轮传动、滚动轴承、滚动螺旋等,都有接触强度问题,自然也涉及到接触应力。在此对接触应力作较为全面的讨论。     

微型涡喷发动机辐板热变形故障分析

研究了某微型涡喷发动机在研制中出现的辐板热变形故障,应用湍流换热计算公式 计算了辐板上的换热系数等有关参数,应用有限元素法计算了辐板的稳态温度场、机械 应力和热应力。基于上述的计算,分析了辐板热变形,并对辐板结构的改进提出了建议。     

镱薄膜应力传感器的工艺研究

介绍了镱薄膜应力传感器的工艺设计和制造过程,通过传感器的静态,动态标定及材料测试,验证了新的工艺设计和制造过程是正确可行的。     

7310E滚子冷镦模寿命的设计工艺

采用 6 5 Nb预压应力组合模具作为 GCr1 5 - 731 0 E滚子冷镦模。对模件施与不同的加工及热处理工艺 ,使模具具有更加优良的性能及配合。模具平均寿命提高 4～ 5倍 ,效益可观 ,有一定的推广应用价值。     

应力测试中的误差分析

从应变片、应变仪、记录仪和数据处理系统 4个环节分析了机械应力实测过程中所产生的误差及产生误差的原因。针对各种误差 ,结合实际情况 ,得出了使误差降到最小程度的具体措施 ,阐明了保证测试数据准确性的实际意义。