共查询到19条相似文献,搜索用时 140 毫秒
1.
毛细力诱发的粘附现象在自然界和工农业生产中广泛存在,例如微机电系统、微纳米自组装、油气驱替等.本文系统研究了两根微梁的毛细粘附行为,包括梁剥离过程中液桥的形貌以及剥离力-位移变化规律.试验发现,微梁在毛细力作用下的剥离部分经历了液膜粘附和液滴粘附两个阶段.考虑两个阶段的液桥形状特征,分别建立系统的能量泛函,采用变分原理推导了考虑毛细力的微梁剥离的非线性微分方程和边界条件.基于Matlab 编程求解方程,得到了剥离力-位移曲线,理论计算与试验结果具有很好的一致性.另外,参数研究表明,接触角和表面张力系数对液膜粘附的微梁剥离影响显著,而对液滴粘附的剥离影响较小;微梁刚度对两个阶段的剥离都有明显影响.本文的试验结果和理论分析对于实际工程中微结构的定量设计具有一定参考价值. 相似文献
2.
相对湿度对材料表面粘附力影响的研究 总被引:1,自引:0,他引:1
利用自制微摩擦及粘附力测试装置考察了在微载荷条件下,相对湿度对Si(100)材料表面粘附力的影响,分析了在大气环境中水分子的毛细作用力和范德华力对粘附力的贡献,并以BET吸附模型为基础推导出考虑湿度影响的粘附力计算公式.结果表明:在微载荷条件下,相对湿度对材料表面的粘附力影响十分显著,随着相对湿度升高粘附力增加,特别是相对湿度RH在40%~80%之间时,粘附力变化最为显著;当相对湿度RH小于20%时,范德华力大于水的毛细作用力且占主导地位;当相对湿度RH大于20%后,水分子的毛细作用力不断增加,同时范德华力因水膜的存在而降低,水的毛细作用力占主导地位. 相似文献
3.
研究了红外探测器中红外焦平面列阵的象元—BST铁电薄膜微桥在红外辐射作用下输出信号的分析方法.将BST铁电薄膜微桥结构简化为一块微米尺度的夹层板,中间是BST铁电薄膜,在极化模式下工作.微桥的上表面接收辐射脉冲信号.由于微桥十分微小,可以认为红外辐射在板面上均匀分布,又由于板的平面尺寸比厚度大得多,可以认为热传导只在板厚的方向进行.采用适当的力-电-热耦合的控制方程和非线性的本构方程,得到了铁电薄膜微桥在红外辐射作用下的的力、热、电输出信号的解析解,并将计算结果与实验结果作了比较. 相似文献
4.
主要介绍了PDMS(polydimethylsiloxane,聚二甲基硅氧烷)-碳纤维复合仿生粘附材料的制备工艺及其粘附性能的测试方法,并测试了该材料在几种不同基底下的法向和切向粘附力。实验结果显示,硅、钛、氧化硅、氮化硅基底中,粘附材料在氮化硅表面的法向粘附力最高(8.24N/cm~2),在硅表面的切向粘附力最高(2.22N/cm~2)。粘附力的大小受基底接触角、粗糙度等多种物理特性的共同影响。本文通过对粘附力与基底的接触角和粗糙度间关系的讨论,为PDMS-碳纤维复合材料今后的应用提供了理论依据。 相似文献
5.
为了确定微纳米尺度金属薄膜的拉伸分叉点,本文使用磁控溅射镀膜技术,在PI(聚酰亚胺)基底上沉积500nm厚的铜薄膜,制作薄膜/基底结构拉伸试件。在单轴拉伸作用下,通过测量拉伸加载过程中铜薄膜的电阻变化情况,得到薄膜电阻随应变变化的关系,并与理论推导的结果进行对比分析,从而确定了塑性阶段理论曲线与实验曲线分离的点,即铜薄膜的分叉点。以此为基础,研究了铜薄膜在单轴拉伸作用下的分叉行为。研究结果表明,沉积于PI基底上的微纳米尺度铜薄膜在单轴拉伸下,经过弹性变形阶段后,很快就发生分叉,然后产生破坏,而塑性变形阶段和局部化阶段较短;弹性阶段薄膜的电阻变化速率很小,塑性阶段薄膜的电阻变化速率稍有增大,而当薄膜表面开始出现微裂纹后,电阻变化速率急剧增大。 相似文献
6.
7.
8.
硅微谐振式加速度计是一种高精度的惯性传感器,它通过谐振梁刚度随惯性力的变化检测输入加速度的大小。为了得到较高的标度因数,国内外的研究机构普遍使用微机械杠杆机构来放大惯性力,但实验中微机械杠杆往往达不到理想的放大倍数,尤其是多级杠杆对力的放大作用非常有限。结合国内加工条件,微机械杠杆力放大机构的模型被合理简化,使用有限元分析运动模态的方法,分别计算微机械杠杆、检测质量支撑梁以及谐振梁的刚度,并按此仿真计算结果估算微机械杠杆的力放大倍数。通过理论推导、ANSYS仿真和对微机械杠杆实验的结果验证了这种方法的正确性。为分析微机械杠杆实际的力放大效果提供了一种实用方法,并基于此方法提出通过提高输出刚度来提高微机械杠杆力放大倍数的方法。通过对杠杆结构的优化,可将原有3.9倍的杠杆放大倍数提高到7.0倍。 相似文献
9.
建立不同金属厚度的金瓷试件梁有限元力学模型,分析界面处应力分布,利用真实口腔修复体的金属和瓷的力学参数,分别对常用的三种不同厚度为基底的金属梁试件进行了瓷层以0.2mm为梯度进行加厚,计算各梁的界面应力和位移,同时也对力学性能较好的金属层和瓷层一组进行了全瓷梁应力、位移计算分析.为了更加真实的反映计算结果,部分试件的数值分析与实验进行了比较.通过分析比较,结果显示金瓷界面处应力较大,是脱剥瓷常发生部位;金属层较薄的烤瓷体有更高的韧性,力学性能较金属基底厚的有更强的抗脱瓷能力;金属作为基底大大提高了试件的抗弯曲能力,比全瓷梁更增强了试件破坏能力. 相似文献
10.
11.
Since heat flux increases sharply yet cooling space in microelectronic and chemical products gradually decreases, a micro heat pipe has been an ideal device for heat transfer for high heat-flux products, and its performance depends largely on its capillary limit. This study proposed an integrated utilization of the advantages of lower backflow resistance to working fluid in trapezium-grooved-wick micro heat pipes and greater capillary force in sintered-wick micro heat pipes; first the factors that are crucial to both types’ heat transfer performances were analyzed, and then mathematical modeling was built for capillary limit of a micro heat pipe with the compound structure of sintered wick on trapezium-grooved substrate, and finally heat transfer limits for micro heat pipes with a trapezium-grooved wick, a sintered wick and with a compound structure were tested through experiments. Both the theoretical analysis and experimental results show that for a micro heat pipe with proposed compound structure, its capillary limit is superior to that of a micro heat pipe with a simplex sintered wick or trapezium-grooved wick. 相似文献
12.
13.
Slug flow is one of the representative flow regimes of two-phase flow in micro tubes. It is well known that the thin liquid film formed between the tube wall and the vapor bubble plays an important role in micro tube heat transfer. In the present study, experiments are carried out to clarify the effects of parameters that affect the formation of the thin liquid film in micro tube two-phase flow. Laser focus displacement meter is used to measure the thickness of the thin liquid film. Air, ethanol, water and FC-40 are used as working fluids. Circular tubes with five different diameters, D = 0.3, 0.5, 0.7, 1.0 and 1.3 mm, are used. It is confirmed that the liquid film thickness is determined only by capillary number and the effect of inertia force is negligible at small capillary numbers. However, the effect of inertia force cannot be neglected as capillary number increases. At relatively high capillary numbers, liquid film thickness takes a minimum value against Reynolds number. The effects of bubble length, liquid slug length and gravity on the liquid film thickness are also investigated. Experimental correlation for the initial liquid film thickness based on capillary number, Reynolds number and Weber number is proposed. 相似文献
14.
A micro scale Timoshenko beam model is developed based on strain gradient elasticity theory. Governing equations, initial conditions and boundary conditions are derived simultaneously by using Hamilton's principle. The new model incorporated with Poisson effect contains three material length scale parameters and can consequently capture the size effect. This model can degenerate into the modified couple stress Timoshenko beam model or even the classical Timoshenko beam model if two or all material length scale parameters are taken to be zero respectively. In addition, the newly developed model recovers the micro scale Bernoulli–Euler beam model when shear deformation is ignored. To illustrate the new model, the static bending and free vibration problems of a simply supported micro scale Timoshenko beam are solved respectively. Numerical results reveal that the differences in the deflection, rotation and natural frequency predicted by the present model and the other two reduced Timoshenko models are large as the beam thickness is comparable to the material length scale parameter. These differences, however, are decreasing or even diminishing with the increase of the beam thickness. In addition, Poisson effect on the beam deflection, rotation and natural frequency possesses an interesting “extreme point” phenomenon, which is quite different from that predicted by the classical Timoshenko beam model. 相似文献
15.
16.
A size-dependent Reddy–Levinson beam model is developed based on a strain gradient elasticity theory. Governing equations and boundary conditions are derived by using Hamilton’s principle. The model contains three material length scale parameters, which may effectively capture the size effect in micron or sub-micron. This model can degenerate into the modified couple stress model or even the classical model if two or all material length scale parameters are taken to be zero respectively. In addition, the present model recovers the micro scale Timoshenko and Bernoulli–Euler beam models based on the same strain gradient elasticity theory. To illustrate the new model, the static bending and free vibration problems of a simply supported micro scale Reddy–Levinson beam are solved respectively; the results are compared with the reduced models. Numerical results reveal that the differences in the deflection, rotation and natural frequency predicted by the present model and the other two reduced Reddy–Levinson models are getting larger as the beam thickness is comparable to the material length scale parameters. These differences, however, are decreasing or even diminishing with the increase of the beam thickness. This study may be helpful to characterize the mechanical properties of small scale beam-like structures for a wide range of potential applications. 相似文献
17.
In micro channels, slug flow becomes one of the main flow regimes due to strong surface tension. In micro channel slug flow, elongated bubble flows with the thin liquid film confined between the bubble and the channel wall. Liquid film thickness is an important parameter in many applications, e.g., micro heat exchanger, micro reactor, coating process etc. In the present study, liquid film thickness in micro square channels is measured locally and instantaneously with the confocal method. Square channels with hydraulic diameter of Dh = 0.3, 0.5 and 1.0 mm are used. In order to investigate the effect of inertial force on the liquid film thickness, three working fluids, ethanol, water and FC-40 are used. At small capillary numbers, liquid film at the channel center becomes very thin and the bubble interface is not axisymmetric. However, as capillary number increases, bubble interface becomes axisymmetric. Transition from non-axisymmetric to axisymmetric flow pattern starts from lower capillary number as Reynolds number increases. An empirical correlation for predicting axisymmetric bubble radius based on capillary number and Weber number is proposed from the present experimental data. 相似文献
18.
A micro scale nonlinear beam model based on strain gradient elasticity is developed.Governing equations of motion and boundary conditions are obtained in a variational framework.As an example,the nonlinear vibration of microbeams is analyzed.In a beam having a thickness to length parameter ratio close to unity,the strain gradient effect on increasing the natural frequency is predominant.By increasing the beam thickness,this effect decreases and geometric nonlinearity plays the main role on increasing the natural frequency.For some specific ratios,both geometric nonlinearity and size effects have a significant role on increasing the natural frequency. 相似文献
19.
A simple methodology is proposed for measuring the dynamic flexural strength of brittle materials. The proposed technique
is based on 1-point impact experimental setup with (unsupported) small beam specimens. All that is needed is a measurement
of the prescribed velocity as a boundary condition and the fracture time for a failure criterion, both to be input in a numerical
(FE) model to determine the flexural strength. The specimen was modeled numerically and observed to be essentially loaded
in bending until its final inertial failure. The specimen’s geometry was optimized, noting that during the very first moments
of the loading, the specimen length does not affect its overall response, so that it can be considered as infinite. The use
of small beam specimens allow large scale testing of the flexural strength and comparison between static and dynamic loading
configurations. Preliminary experiments are presented to illustrate the proposed approach. 相似文献