球径规值对角接触球轴承凸出量和接触角的影响

根据轴承内部滚动体与沟道的接触几何关系,推导了轴承实际凸出量的通用计算方法。在此基础上,针对实际生产过程两种操作方法(定游隙和变游隙),分析了滚动体直径变化对轴承凸出量和接触角的影响并推导了通用计算公式。研究表明,在定游隙情况下,滚动体直径变化对轴承凸出量和接触角的影响较小;而在变游隙情况下,上述影响较大。     

The effect of tape overwrap angle and head radius on head/tape spacing and contact pressure in linear tape recording

Linear tape recording devices typically employ contact recording to minimize head/media magnetic spacing and thus maximize recording density. Successful contact recording is a delicate balance between spacing and contact pressure. If an air bearing develops, spacing will exceed the 100 nm upper limit for current high recording density devices. Conversely, high contact pressure can lead to head wear or tape damage. Most recording heads produced today for linear tape devices consist of one or more cylindrical wafer sections that are bonded together to form a rigid structure. Each individual tape bearing surface is cylindrical with straight edges. The tape is held over the head contact surface by tape guides so that the tape is wrapped sharply around the edges where cylindrical surface and flat surface meet. Overwrap angle is defined as the angle between the tape after it leaves the head and a tangent to the cylindrical head surface at the edge where cylindrical surface and flat surface meet. This paper will use one-dimensional finite element modeling to explore how overwrap angle and bump radius affect head/tape spacing and contact pressure. The effects of tape stiffness, tape tension, and tape velocity will be investigated. Feasible combinations of overwrap angle and bump radius will be presented which minimize head/tape separation, yet keep contact pressure within bounds.     

Modeling the edge contact effect of finite contact lines on subsurface stresses

Finite contact line conditions lead to subsurface stress distributions determined by the free boundaries. Combined with a correction procedure, Semi-Analytical Methods (SAMs) accurately include the free boundary effects, and represent a rapid alternative to the Finite Element Method (FEM) for contact pressure calculation. This paper extends the free boundary correction procedure to the evaluation of surface and subsurface stresses from SAMs. The investigation integrates a validation based on a two-level factorial comparison confronting the stress distributions established with the developed procedure to results obtained from FEM models. The comparison examines three dimensionless factors, and shows that the stress distributions are evaluated with a high level of precision. The model also offers evaluation more than 125 times faster than FEM simulations.     

双列角接触球轴承的游隙与接触角

通过对双列角接触球轴承轴向游隙、径向游隙、接触角关系的推导换算,分析影响接触角的各因素,采取合理可行的方法保证接触角。     

Edge contact effect on thermal elastohydrodynamic lubrication of finite contact lines

Minimum lubricant film thickness and maximum pressure every so often appear close to roller ends. This study combines the Boussinesq–Cerruti half-space equations with a free boundary correction procedure for precise modeling of edge contact conditions. The thermal EHL model developed associates this representation to a standard finite difference of the energy equation, and to a modified finite difference expansion of the Couette term of the Reynolds equation. To complete the model, the Carreau expression describes the shear-thinning response of the lubricant. The investigation includes different roller profile corrections. The results show that a large radius crowning modification combined with a rounding of the corners constitutes the most effective profile adjustment.     

Neutralizing the effect of the angle variations on the drop detachment in automatic GMAW system

Two forces play the main role on the drop detachment in gas metal arc welding process: the electromagnetic and gravitational forces. Since in an automatic pipeline system, the welding angle varies from 0° to 180° in each pass, the total force will vary, so the drop detaching will not remain invariable during the welding time. In the previous works Doodman Tipi (Int J Adv Manu Technol 50:137?C147, 2010 [1]), Doodman Tipi (Int J Adv Manu Technol 50:149?C161, 2010 [2]), the angle variation effects on the metal transfer was studied on both transfer modes (free flight and short circuit). In this paper, the effect of the input parameters on the drop detaching is studied. Also, a welding current pattern is presented in order to neutralize the effect of the angle variation around the pipe. Furthermore, suitable patterns for other parameters (arc voltage, travel speed, and electrode speed) are introduced to keep constant the molten electrode volume, heat input, voltage to current relation, and energy density. This would guarantee stabilization of the other welding specifications. Finally, several experimental and simulation examples illustrate to achieve the regular detachment using the presented method, and results are compared with the un-neutralized case.     

Stress drop and contact stiffness measured from stick-slip experiments on PMMA-PMMA friction

We present results from an extensive stick-slip study on PMMA-PMMA dry friction, where we studied the influence of a wide range of normal stresses, loading velocities and roughnesses of the sliding surfaces. In this paper we focus (a) on the analysis of a residual coefficient of friction, i.e., shear stress measured at the end of the slip phase divided by the corresponding normal stress, and (b) on the contact stiffness measured by plotting the relative displacement between sample against the shear stress during the stick phase. It is shown that the residual coefficient of friction (i) decreases as normal stress increases, (ii) shows a slight increase when the roughness of the sliding surfaces increases and (iii) does not vary according to the loading velocity. The contact stiffness proved independent of loading conditions and of the roughness of the sliding surfaces. These results are interpreted in terms of asperity interlocking. This revised version was published online in July 2006 with corrections to the Cover Date.     

Role of contact frequency on the wear rate of steel in discontinuous sliding contact conditions

This work presents a novel approach of sliding ball-on-disk wear tests where the disc material is investigated. Each part of the wear track on the disc is in discontinuous contact with the counterbody. The contact frequency at each part of the wear track on the disc with the counterbody is defined by the rotation frequency of the disc. The sliding speed is however a function of both the rotation frequency and wear track diameter. In this work, the effect of the contact frequency on friction and wear was investigated on carbon steel in discontinuous sliding contact with corundum balls. Various sliding speeds were used while maintaining the contact frequency at a fixed value, and various contact frequencies were applied at constant sliding speeds.The wear rate of the disk material is shown to depend not only on the usual wear test parameters, namely sliding speed and contact load, but also on contact frequency. Moreover, contact frequency is shown to be a key factor determining the wear mode even at constant sliding speed and load. At contact frequencies above 9 Hz, the dominant wear mechanism is oxidational wear, while at frequencies below 4 Hz the dominant wear mechanism is adhesive wear. This transition from adhesive to oxidational wear takes place together with a change in the type of debris generated and in the value of the coefficient of friction.The validity of the Garcia-Ramil-Celis model proposed earlier for discontinous sliding contact conditions, is demonstrated for the case of carbon steel disks sliding against a chemically inert counterbody.     

A study of the effect of radial clearance,contact angle and contact pressure on the wear of boundary-lubricated bearing bronze

In the course of work directed towards the development of an international standard on the measurement of the tribological properties of bearing materials, the influence of radial clearance, contact angle and contact pressure on the wear of boundary-lubricated bearing bronze Cu5Sn5Pb5Zn in contact with plain carbon steel rings was studied. It was found that under all experimental conditions wear proceeds via the build-up of a thin transferred layer of bronze on the mating steel surface. Neither wear rate nor process surface roughness depend on radial clearance or contact angle. However, the friction-time diagram is found to react to a change in test conditions. From such diagrams the time necessary to attain equilibrium friction can be found. It is shown that this time bears no relation at all to the time needed to adapt the stationary bronze specimen to the radius of the mating steel ring. It is also concluded that the contact pressure does not influence the wear process.     

小角度X射线衍射法研究夹层复合材料和长程有机大分子材料

对具有大层间距的累托石-尼龙夹层复合材料和具有长周期有序排列的脂质材料等进行了小角度X射线衍射分析。结果表明,通过调整X射线衍射仪的光路系统,适当控制入射X射线和散射线的强度,即使在极小的角度区域范围内,仍可清晰地分辨X射线衍射峰。对于日本理学D Max -rB型转靶X射线衍射仪,使用如下的光路系统:DS =1 2°,SS =1 6°,RS =0 .15mm ,可获得清晰结果。     

Accurate surface tension measurement of glass melts by the pendant drop method

A pendant drop tensiometer, coupled with image digitization technology and a best-fitting algorithm, was built to accurately measure the surface tension of glass melts at high temperatures. More than one thousand edge-coordinate points were obtained for a pendant glass drop. These edge points were fitted with the theoretical drop profiles derived from the Young-Laplace equation to determine the surface tension of glass melt. The uncertainty of the surface tension measurements was investigated. The measurement uncertainty (σ) could be related to a newly defined factor of drop profile completeness (Fc): the larger the Fc is, the smaller σ is. Experimental data showed that the uncertainty of the surface tension measurement when using this pendant drop tensiometer could be ±3 mN∕m for glass melts.     

Effect of slot edge defects on the head/tape spacing

The effect of slot edge defects on the performance of the head/tape interface is studied for single and double module heads. A number of typical edge defects was created artificially on a glass replica of an actual head, and three-wavelength interferometry was used to study spacing changes caused by these defects. The results show that head edge defects have a small influence on the flying behavior of tape with the effects being localized to the immediate defect area.     

轮齿压力角对齿面接触强度的影响分析

运用赫兹接触理论,分析了轮齿压力角对齿轮接触强度的影响,得出了轮齿强度随压力角的变化规律。发现轮齿压力角的增大,齿面接触正应力和工作剪应力均减小,对提高齿轮强度和防止齿面点蚀极为有利,为重载齿轮的设计提供了理论依据。     

Effects of the impact angle variations on the erosion rate of glass in powder blasting process

Sandblasting, a conventional technique which is used for paint or scale removing, deburring, and glass decorating, has recently been developed into a powder blasting technique for brittle materials capable of producing micro-structures larger than 100 m. This article describes an investigation of the effects of the impact angle of particles, the scanning times, and the standoff distance on the surface roughness, the weight-loss rate of samples with no mask, and the wall profile and over-etching of samples with different mask patterns in powder blasting of soda-lime glass. The parameters are the various impact angles between 50 and 90°, the scanning times of a nozzle up to 40, and the standoff distances between 70 and 100 mm. The widths of the mask pattern are 0.2 mm, 0.5 mm, and 1 mm. The powder used is Al2O3 sharp particles, WA#600. The mass flow rate of powder during the erosion test is constant at 175 g/min and the blasting pressure of the powder is 0.2 Mpa. After a series of necessary experiments are performed, the results are investigated and analysed. As a result, a fundamental basis is established that can be applied to powder blasting to produce micro-mechanical parts of glass.     

风力发电机偏航轴承载荷分布及接触角数值解法研究

基于赫兹弹性接触理论,推导了滚子与轴承内外圈接触变形时的接触刚度,建立了偏航轴承受复杂载荷时受力平衡的非线性方程组,井运用带有松弛因子的牛顿-拉夫逊法求解非线性方程组,得到了承载时偏航轴承各滚子的接触应力和接触角.最后,用经典理论公式和有限元方法对此方法计算结果进行了验证,证明了文中计算方法的正确性,为兆瓦级风力发电机轴承的设计计算提供了参考依据,具有一定的工程应用价值.     

Plasmonic effect of silver nanoparticles on the upconversion emissions of Sm3+-doped sodium-borosilicate glass

The effect of the localized surface plasmon resonance (SPR) on optical absorption and photoluminescence of Sm³⁺-doped sodium borosilicate glass containing reduced silver nanoparticles (NPs) is reported (Ag⁺ → Ag⁰). The interaction of ultraviolet light by metallic NPs and its effect on the optical properties of samarium in proposed glass were investigated by absorption and photoluminescence spectra analysis. The existence of the NPs was pursued by transmission electron microscopy technique, revealing the existence of Ag NPs with average size of ∼8–14 nm. The largest enhancement was achieved for emission at 561 nm. Such improvements were attributed and discussed by enhanced electric field around metallic NPs and energy transfer (ET) between Sm³⁺ ions and silver NPs.     

基于任意声矢量传感器阵列的角度和频率估计算法

提出了一种基于任意声矢量传感器阵列下联合角度和频率估计新方法.将矢量传感器阵输出的信号进行建模分析表明此信号具有平行因子四线性模型特征.利用四线性分解的唯一性条件,从分解得到的矩阵中联合估计出声源的参数.该算法首先应用平行因子四线性分解算法估计出频率矩阵和方位矩阵,然后根据频率矩阵和方位矩阵的结构特点及最小二乘方法进行声源参数的计算.该方法与传统算法相比,无需多维谱峰搜索及参数配对,并具有更高的估计精度,在工程上有一定的应用价值.计算机仿真和实验结果验证了该方法的有效性.     

Effect of cavosurface angle beveling on the exposure angle of enamel prisms in different cavity sizes

The quality of the micromechanical retention between the enamel prisms exposed through acid etching and adhesive system can be influenced by the relationship between the angle of the exposed enamel prisms and the external surface/restorative material. Therefore, the aim of the present study was to determine the influence of the enamel cavosurface beveling in different cavity sizes on the angle relation between enamel prisms and the restorative material. For this research, 30 human permanent molars were used and divided into three groups according the isthmus aperture of class I cavities (1/4, 1/3, and 1/2 of the intercuspal distance). Cavosurface angle beveling was performed in each tooth buccal or palatal/lingual side, and a resin composite restoration was placed. Each restored tooth was sectioned in buccal/palatal direction followed by analysis in scanning electron microscope. Means of the angles observed between enamel prisms and the restorative material were registered and statistically analyzed by Kruskal‐Wallis test. Results showed higher mean angle values for beveled groups when comparing with the values observed in the unbeveled margins (p < .05) regardless of the isthmus aperture, being 1/4 (beveled = 48.36°; unbeveled = 20.71°), 1/3 (beveled = 39.75°; unbeveled = 29.15°), and 1/2 (beveled = 37.02°; unbeveled = 26.34°). It was also observed that in some unbeveled cavities, there were the presence of laterally exposed enamel prisms (0°), mainly in more conservative cavities. It was concluded that the presence of higher angles values occurred in the samples with beveled margins, without presence of laterally exposed enamel prisms.     

Effect of microrelief on the contact shakedown of fixed joints

Under the conditions of cyclic loading at fixed joints, the repeated mutual slip of the contacting surfaces is observed in the contact zone, fretting appears, and the wear and destruction of the assembly elements occurs. The existing methods for overcoming fretting are aimed at reducing its intensity. The finite element analysis of fixed joints of smooth contact surfaces and surfaces with relief under the conditions of cyclic loading of junctions makes it possible to reveal the regions of mutual slip and, to determine the parameters of the microrelief, which contribute the most to the onset of contact shakedown. The method for improving the resistance to fretting in friction units based on achieving the conditions for the onset of contact shakedown using microrelief is implemented for fixed joints of a hard-alloy cutter pick and a drilling bit rolling cutter, as well as for an abutting joint of the rotor impeller shrouds of a universal gas distributor.     

Influence of material parameters on the hydrostatic bulging of a circular diaphragm

The plastic bulging of pressurized circular membranes is examined with particular attention to the effect of material parameters on the inherent inhomogeneity of the test. A rigid-viscoplastic behaviour based on flow-theory of plasticity is considered for materials with transversely isotropic properties. The numerical calculations display the effects of strain-hardening, strain-rate hardening and yield surface shape on the bulging pressure, the strain-distribution and the bulge shape. Comparisons with available experimental data are also presented.