THE SURFACE EFFECT ON THE TENSILE STRENGTH OF MICROMACHINED POLYSILICON FILMS FOR MEMS

In order to accomplish reliable mechanical design of MEMS, the influences of surface roughness and octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on the mechanical properties of micromachined polysilicon films for MEMS are investigated. Surface effect on the fracture properties of micromachined polysilicon films is evaluated with a new microtensile testing method using a magnet-coil force actuator. Statistical analysis of the surface roughness effects on the tensile strength predicated the surface roughness characterization of polysilicon films being tested and the direct relation of the mechanical properties with the surface roughness features. The fracture strength decreases with the increase of the surface roughness. The octadecyltrichlorosilane self-assembled monolayers coating leads to an increase of the average fracture strength up to 32.46%. Surface roughness and the hydrophobic properties of specimen when coated with OTS films are the two main factors influencing the tensile strength of micromachined polysilicon films for MEMS.     

Coupling vibration of vehicle-bridge system

By applying the sinusoidal wave mode to simulate the rugged surface of bridge deck, accounting for vehicle-bridge interaction and using Euler-Bernoulli beam theory, a coupling vibration model of vehicle-bridge system was developed. The model was solved by mode analyzing method and Runge-Kutta method, and the dynamic response and the resonance curve of the bridge were obtained. It is found that there are two resonance regions, one represents the main resonance while the other the minor resonance, in the resonance curve. The influence due to the rugged surface, the vibration mode of bridge, and the interaction between vehicle and bridge on vibration of the system were discussed. Numerical results show that the influence due to these parameters is so significant that the effect of roughness of the bridge deck and the mode shape of the bridge can‘ t be ignored and the vehicle velocity should be kept away from the critical speed of the vehicle_     

Wind tunnel simulation of wind loading on a solid structure of revolution

The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the surface were obtained, and the relationships between the roughness Reynolds number and pressure distributions were analyzed and discussed. The results show that increasing the surface roughness can significantly affect the pressure distribution, and the roughness Reynolds numbers play an important role in the change of flow patterns. The three flow patterns of subcritical, critical and supercritical flows can be classified based on the changing patterns of both the mean and the fluctuating pressure distributions. The present study suggests that the wind tunnel results obtained in the supercritical pattern reflect more closely those of full-scale solid structure of revolution at the designed wind speed.     

CAPILLARY EFFECT ON VERTICALLY EXCITED SURFACE WAVE IN CIRCULAR CYLINDRICAL VESSEL

In a vertically oscillating circular cylindrical container, singular perturbation theory of two-time scale expansions was developed in inviscid fluids to investigate the motion of single free surface standing wave including the effect of surface tension. A nonlinear slowly varying amplitude equation, which incorporates cubic nonlinear term, external excitation and the influence of surface tension, was derived from potential flow equation. The results show that, when forced frequency is lower, the effect of surface tension on mode selection of surface wave is not important. However, when forced frequency is higher, the surface tension can not be neglected. This proved that the surface tension causes free surface returning to equilibrium location. In addition, due to considering the effect of surface tension, the theoretical result approaches to experimental results much more than that of no surface tension.     

VIBRATION AND ACOUSTIC RADIATION FROM SUBMERGED STIFFENED SPHERICAL SHELL WITH DECK-TYPE INTERNAL PLATE

Based on the motion differential equations of vibration and acoustic coupling system for thin elastic spherical shell with an elastic plate attached to its internal surface, in which Dirac-δ functions are employed to introduce the moments and forces applied by the attachment on the surface of shell, by means of expanding field quantities as Legendre series, a semi-analytic solution is derived for the vibration and acoustic radiation from a submerged stiffened spherical shell with a deck-type internal plate, which has a satisfactory computational effectiveness and precision for an arbitrary frequency range. It is easy to analyze the effect of the internal plate on the acoustic radiation field by using the formulas obtained by the method proposed. It is concluded that the internal plate can significantly change the mechanical and acoustic characteristics of shell, and give the coupling system a very rich resonance frequency spectrum. Moreover, the method can be used to study the acoustic radiation mechanism in similar structures as the one studied here.     

SURFACE EFFECT ON NANOSIZED VOID GROWTH IN A RIGID-PERFECTLY PLASTIC MATERIAL

The influence of the surface effect on the nanosized spherical void growth in a rigidperfectly plastic material is analyzed and the mechanism of the nanosized void growth with high triaxiality is given. Based on the Rice and Tracey model for a macro void growth, the present model is proposed to account for the nanosized void growth under a uniform remote strain rate field with consideration on the surface effect. It is concluded that the surface effect yields an evident resistant influence on the nanosized void growth. That is, this influence decays as the void radius increases. With high triaxiality, the nanosized void growth is divided into two stages： the initial stage and the mature stage. At the first stage, the void grows slowly and the influence of surface effect is relatively weak, whereas at the second stage, the influence is significant and the void grows drastically.     

Scattering of Tollmien-Schlichting waves by localized roughness in transonic boundary layers

The laminar-turbulent transition in boundary-layer flows is often affected by wall imperfections, because the latter may interact with either the freestream perturbations or the oncoming boundary-layer instability modes, leading to a modification of the accumulation of the normal modes. The present paper particularly focuses on the latter mechanism in a transonic boundary layer, namely, the effect of a two-dimensional(2 D) roughness element on the oncoming Tollmien-Schlichting(T-S) modes when they propagate through the region of the rapid mean-flow distortion induced by the roughness. The wave scattering is analyzed by adapting the local scattering theory developed for subsonic boundary layers(WU, X. S. and DONG, M. A local scattering theory for the effects of isolated roughness on boundary-layer instability and transition: transmission coefficient as an eigenvalue. Journal of Fluid Mechanics, 794, 68–108(2006)) to the transonic regime, and a transmission coefficient is introduced to characterize the effect of the roughness. In the sub-transonic regime, in which the Mach number is close to, but less than, 1, the scattering system reduces to an eigenvalue problem with the transmission coefficient being the eigenvalue; while in the super-transonic regime, in which the Mach number is slightly greater than 1, the scattering system becomes a high-dimensional group of linear equations with the transmission coefficient being solved afterward. In the largeReynolds-number asymptotic theory, the K′arm′an-Guderley parameter is introduced to quantify the effect of the Mach number. A systematical parametric study is carried out,and the dependence of the transmission coefficient on the roughness shape, the frequency of the oncoming mode, and the K′arm′an-Guderley parameter is provided.     

EFFECT OF SURFACE ENERGY ON DISLOCATION-INDUCED FIELD IN HALF-SPACE WITH APPLICATION TO THIN FILM-SUBSTRATE SYSTEMS

In this work the elastic field of an edge dislocation in a half-space with the effect of surface energy has been obtained. The elastic field is then used to study the image force on the dislocation, the critical thickness for dislocation generation in epitaxial thin films with strain mismatch and the yielding strength of thin films on substrates. The results show that the image forces on the dislocation deviate from the conventional solutions when the distance of the dislocation from the free surface is smaller than several times of the characteristic length. Also due to the effect of surface energy, the critical thickness for dislocation generation is smaller than that predicted by the conventional elastic solutions and the extent of the deviation depends on the magnitude of mismatch strain. In contrast, the effect of surface energy on the yielding strength for many practical thin films can be neglected except for some soft ones where the characteristic length is comparable to the thickness.     

Spinodal surface instability of soft elastic thin films

When the thicknesses of thin films reduce to microns or even nanometers, surface energy and surface interaction often play a significant role in their deformation behavior and surface morphology. The spinodal surface instability induced by the van der Waals force in a soft elastic thin film perfectly bonded to a rigid substrate is investigated theoretically using the bifurcation theory of elastic structures. The analytical solution is derived for the critical condition of spinodal surface morphology instability by accounting for the competition of the van der Waals interaction energy, elastic strain energy and surface energy. Detailed examinations on the effect of surface energy, thickness and elastic properties of the film show that the characteristic wavelength of the deformation bifurcation mode depends on the film thickness via an exponential relation, with the power index in the range from 0.749 to 1.0. The theoretical solution has a good agreement with relevant experiment results.     

Generation of unsteady waves by concentrated disturbances in an inviscid fluid with an inertial surface

The surface waves generated by unsteady concentrated disturbances in an initially quiescent fluid of infinite depth with an inertial surface are analytically investigated for two- and three-dimensional cases. The fluid is assumed to be inviscid, incompressible and homogenous. The inertial surface represents the effect of a thin uniform distribution of non-interacting floating matter. Four types of unsteady concentrated disturbances and two kinds of initial values are considered, namely an instantaneous/oscillating mass source immersed in the fluid, an instantaneous/oscillating impulse on the surface, an initial impulse on the surface of the fluid, and an initial displacement of the surface. The linearized initial-boundary-value problem is formulated within the framework of potential flow. The solutions in integral form for the surface elevation are obtained by means of a joint Laplace-Fourier transform. The asymptotic representations of the wave motion for large time with a fixed distance- to-time ratio are derived by using the method of stationary phase. The effect of the presence of an inertial surface on the wave motion is analyzed. It is found that the wavelengths of the transient dispersive waves increase while those of the steady-state progressive waves decrease. All the wave amplitudes decrease in comparison with those of conventional free-surface waves. The explicit expressions for the freesurface gravity waves can readily be recovered by the present results as the inertial surface disappears.     

Passive vibration absorber effect on the machining surface quality of a flexible workpiece

This paper presents a study of the vibratory behaviour of a flexible workpiece subject to a milling end operation. Indeed, this vibratory behaviour is critical, especially when the excitation frequency is near to the resonance. For this reason, passive vibration suppression is considered in order to attenuate the dynamic response of the milled workpiece and decrease the dynamic effect on the resulting machined surface roughness and flatness. In order to confirm the efficiency of the passive vibration suppression, the vibratory behaviour and the quality (roughness and flatness) of a machined surface are studied without and with passive absorber (TMD) using a finite-element model.     

磨合表面形貌特征参数的提取及分析

在销-盘式摩擦磨损试验机上对船用柴油机活塞环-缸套材摩擦副进行磨合磨损试验,采用光学显微镜对不同磨损阶段的磨损表面形貌进行观察分析,应用小波分析和奇异值分解提取磨损表面统计特征的低频特征参数和高频特征参数.结果表明:低频特征参数和高频特征参数刻画了磨合表面的形貌特征,可以作为磨合表面的特征参数;低频特征参数反映了磨合表面的接触面积,其值愈大,接触面积愈大;高频特征参数反映了磨合表面的粗糙度,其值愈大,粗糙度愈小.     

表面粗糙度对微细管内气体流动特性的影响

采用了表面粗糙度粘性系数模型对微细管内的气体流动进行数值模拟，以研究微管内壁表面粗糙度对微管内气体流动的影响。运用本文改进的表面粗糙度粘性系数模型，数值模拟与实验数据十分吻合。计算结果表明，进出口压力一定时，表面粗糙度对流场的压力、密度及温度分布的影响不大，但是对速度场的影响十分显著，表面粗糙度使气体流动速度减小，并使壁面附近的速度梯度减小，从而使通过管道的气体质量流量减小，在微管内的气体流动中，表面粗糙度的影响是不能被忽略的。     

粗糙表面滑动轴承非牛顿介质润滑的计算

分析了轴承润滑中非牛顿介质的流变特性以及轴承表面形貌对润滑效果的影响,推导出了修正的雷诺方程,在方程中用差分粘度和第一正应力差函数表征非牛顿介质的流变特性,采用流量因子表征表面形貌的作用.结果表明:差分粘度的变化是影响润滑结果的主要因素,它取决于不同介质的动态参数和剪切频率范围,非牛顿介质润滑的承载力并非总高于或低于牛顿介质;在动载荷条件下,第一正应力差效应使油膜压力明显增大;影响流量因子的2个因素为表面形貌的粗糙度和纹理,但其作用远小于非牛顿介质流变特性的影响.     

表面粗糙度对摩擦尖叫噪声特性的影响

采用不同结构刚度的测量装置,对光滑表面和喷砂处理表面进行滑动摩擦噪声对比试验,研究不同粗糙度表面在不同试验装置上的摩擦尖叫噪声特性及其对摩擦尖叫噪声的影响和作用机理.结果表明:摩擦表面粗糙度和磨损情况对摩擦尖叫噪声的产生及演变具有重要的影响,表面粗糙度越大的喷砂处理表面能更明显地抑制界面摩擦尖叫噪声的产生.本试验条件下,磨屑堆积和黏着剥落等磨损特征对应的黏着撕裂作用更易引起摩擦力高频成分的产生并导致较高强度的尖叫噪声,而喷砂处理的粗糙表面能减轻这些界面因素的形成,削弱摩擦力高频成分,抑制摩擦尖叫噪声的产生.     

接触表面不平度对摩擦尖叫噪声的影响

针对摩擦尖叫的间歇性特点,建立了考虑摩擦接触表面不平度的3自由度摩擦自激振动机理模型.应用数值方法分析了接触表面不平度倾角对系统稳定性及瞬态动力学特性的影响,并进行了基于销-盘装置的摩擦尖叫噪声试验研究.结果表明:系统的稳定性主要取决于系统自身的耦合特性,但也与摩擦特性和接触表面不平度倾角的综合作用有关.当接触表面不平度倾角增大时,系统趋向不稳定,会激发尖叫噪声.     

DIFFERENCE BETWEEN ARTIFICIAL AND COMMERCIAL PIPES IN TRANSITION ZONE1)

管路沿程损失是教学中要讲的内容。其中在过渡粗糙区,人工管和商业管的沿程损失系数存在差异。本文对此差异做了初步分析。从学生对此差异的理解和表面粗糙度的含义两方面探讨了表面粗糙度对此差异的影响。量化探讨表面粗糙度在过渡粗糙区的作用仍是个问题。     

表面粗糙度对Glidcop和Q345低周疲劳寿命影响的试验研究

为考察表面粗糙度对弥散增强铜合金Glidcop和低合金钢Q345疲劳寿命的影响,对两种材料都加工了不同粗糙度等级的试样,在常温下进行了应力控制的低周疲劳试验,并对断后的试样进行了扫描电镜观察。结果表明,两种材料共有的现象是:粗糙表面削弱了低周疲劳性能,随着表面粗糙度的增大,低周疲劳寿命呈下降趋势;表面粗糙度对主裂纹的形成时间有影响。不同的现象是:低周疲劳寿命与表面粗糙度的关系Glidcop为线性,而Q345则为幂函数;Glidcop的断口有轻微颈缩,疲劳辉纹明显,Q345的主裂纹沿着试样的径向和周向同时扩展,大粗糙度下辉纹支离破碎。因此,表面粗糙度对疲劳寿命的影响既表现出共同的现象,又呈现为材料相关性。本文的结果将为这两种材料制成的承受低周疲劳构件的表面粗糙度选取提供参考。     

基于表面粗糙度影响的摩擦声发射特性研究

接触表面粗糙度是影响摩擦的重要因素之一,而摩擦为复杂的动态过程,在线测量非常困难.为了研究表面粗糙度对摩擦的影响,利用声发射技术对不同粗糙度表面的摩擦过程进行了检测.研究结果表明：摩擦系数随着表面粗糙度的增大而增大,但当粗糙度增至一定程度时,摩擦系数随着表面粗糙度的增大而减小;声发射信号各参数（振铃计数、振幅、能量）随表面粗糙度的变化规律与摩擦系数随粗糙度的变化规律一致;声发射信号各参数与表面粗糙度存在密切的对应关系,因此,用声发射技术实时监测摩擦过程是可行的.     

偶件表面粗糙度对碳纤维增强尼龙复合材料摩擦学性能的影响

在栓-盘摩擦磨损试验机上考察了干摩擦条件下偶件表面粗糙度对碳纤维增强尼龙（PA1010）复合材料摩擦学性能的影响,采用不迩显微镜观察分析了偶件表面转移膜的形貌。结果表明,碳纤维能够明显提高PA1010的耐磨性能,当碳纤维增强相的质量分数为10%和20%时,增强PA1010复合材料的磨损率比非增强PA1010的降低3～6倍。这是由于碳纤维起到了承载作用并具有较强的抗犁削能力所致,磨损表面形貌光学显微分析表明：磨损前后偶件表面形貌发生了明显的变化;当偶件表面粗糙度Ra处于0.11～0.13um范围内时,复合材料的摩损率最低;随Ra值的增大或减小微切削和转移膜疲劳脱落加剧致使复合材料的磨损率快速增大。