Liquid flow under adhesive forces

The flow of viscous liquid near the surface of rigid bodies is complex and depends on adhesive interactions that have been little studied.     

A study of the physical adhesive state between solids

The force required to separate two adhering bodies (needles with plates) was measured for various materials. The contact pressure was controlled by the heat expansion of a liquid. The adhesion force obtained from a load of less than 5 mgf was a constant value depending on the type of material. It was found that the adhesive energy was affected largely by temperature and could be expressed by an Arrhenius relation. From the results obtained the Hamaker constant was estimated to be (1– 3) × 10⁻¹² erg.     

Microstructural aspects determining the adhesive wear of tool steels

In many machining applications, adhesion of the workpiece to the tool is a major problem. Adhesion may be reduced by changing the microstructure of the tool steel, e.g. by increasing the carbide content. The present work deals with the influence of some microstructural parameters in the adhesive wear of tool steels. The investigations were conducted using six model alloys based on the powder metallurgy high speed steel AISI M4, all of which had the same martensitic matrix composition after heat treatment. The alloys had MC carbide contents which varied between 0 and 25 mol% in 5 mol% increments. Ball-on-disc experiments were carried out in ambient air at room temperature using austenitic stainless steel and aluminum balls as counterfaces. Wear tracks on the disks were characterized using both a scanning electron microscope and an optical profiler. The results show that two main parameters determine the adhesive wear behavior: the carbide content and the distance between carbides.     

空间反射镜胶粘结固紧结构优化设计

为了设计合理的空间反射镜胶粘结结构,对某空间反射镜中的胶层进行了等效刚度建模,并对反射镜组件进行了热弹性分析,通过与试验结果对比,验证了模型的有效性,同时发现初始设计不满足设计指标要求.综合分析了结构粘合剂泊松比、粘结位置、胶层宽度和胶层厚度等因素对反射镜面形误差的影响,找出影响离焦误差的因素,进而提出了一种优化的胶层粘结方案,并进行了反射镜组件的动静态刚度分析和热尺寸稳定性分析.计算结果表明:优化的粘结方案,不仅满足设计指标要求而且有效防止了偏心粘结造成的胶层分布不均匀对系统的影响.     

Similarity considerations in adhesive contact problems

The classical ‘JKR’ solution for the force required to separate two elastic spheres is independent of the elastic moduli. We demonstrate that this remarkable simplification is a rigorous consequence of the quadratic character of the spherical profile and hence that it must also apply exactly to more general quadratic profiles such as the contact of two ellipsoids. The same feature is also responsible for the fact that Bradley's ‘rigid sphere’ solution depends only on the interface energy and not on the detailed character of the adhesive force law.     

全自动钉排涂胶机的设计

主要介绍用于建筑装璜业的钉排加工的自动涂胶机的结构设计。该涂胶机可以完成自动上料、双面刷胶、自动输送、切断的全部功能,是一个自动化程度较高的生产设备。该设备的应用可以提高生产效率、提高产品质量,减少污染,对于该行业生产水平的提高有很大的实际意义,也填补了该技术领域的缺欠。     

Patterned wafer bonding using ultraviolet adhesive

The process of patterned wafer bonding using ultraviolet (UV) adhesive as the intermediate layer was studied. By presetting the UV adhesive guide-layer, controlling the thickness of the intermediate layer (1– 1.5 μm), appropriate pre-drying temperature (60°C), and predrying time (6 min), we obtained the intermediate layer bonding of patterned quartz/quartz. Experimental results indicate that patterned wafer bonding using UV adhesive is achieved under room temperature. The process also has advantages of easy operation, low cost, and no plugging or leakage in the patterned area after bonding. Using the process, a microfluidic chip for red blood cell counting was designed and fabricated. Patterned wafer bonding using UV adhesive will have great potential in the fabrication of microfluidic chips.     

Environmental effects on the formation process of adhesive wear particles

Three kinds of experiments have been conducted to study the effect of environmental molecules on the formation process of adhesive wear particles. First, the growth process of transfer particles was continuously observed by scanning electron microscope. It was understood that the growth of the transfer particles was due to the continuous conversion of the disc surface material into transfer particles. Next, wear tests between a Sn pin and Sn disc were conducted in an oxygen environment from 7 × 10⁻³ Pa to 1.0 × 10⁵ Pa. The size and hardness of wear particles and the wear volume increased with increasing oxygen pressure. Wear tests between Sn and Sn were also conducted while Au metals were sputter-deposited onto the friction surface. The deposition of Au had the same effect on the size and hardness of the wear particles as the oxygen atmosphere. In general, the hardness of metals is increased by the small amount of impurity atoms in them. The inclusion of oxygen or gold atoms on the surface and in the transfer particle is supposed to have the same effect of enhancing the shear strength of the interface and the transfer particles. This is the possible mechanism of the continuous shear fracture within the bulk which results in the growth of transfer particles.     

Effect of the rate of repeat traversal on adhesive wear

An experimental study of the effect of the rate of repeat traversais on the adhesive wear of selected metal combinations at sliding speeds of around 10 mm s^?1 is described. Using a pin-on-disk geometry the time for repeat traversals was varied by conducting wear tests in which the pin traced either a circular wear track or a spiral wear track on the rotating disk, the time between repeat traversais being 6 s in the first case and in the range 450–10000 s in the second case.At low loads, typically between 5 and 20 g, metals undergo a mild form of adhesive wear, either burnishing or a regime in which wear debris is predominantly oxide. At high loads, above 1000 g, severe metal transfer occurs, the surfaces become rough and the debris is predominantly metallic. In neither of these two load ranges is there a difference between the tests using circular and spiral tracks.However, at intermediate loads varying the time between repeat traversals has a significant effect with oxide-forming metals. The spiral wear track tests gave a reduction of almost two orders of magnitude in the wear coefficient accompanied by lower friction coefficients and much smoother surfaces presumably because the oxide layer functioned more effectively. Using gold, which forms no oxide layer, severe wear is encountered even at very low loads (2 g). Varying the time for repeat traversals has no effect.No effects attributable to the fatiguing of the metal surfaces were noted.     

应变胶粘剂对应变计和传感器性能的影响

简要介绍应变胶粘剂对应变计和传感器性能的影响，并提出改进应变胶粘剂以提高应变计及传感器的各种性能。     

新型方舱大板胶粘剂的研制及其性能研究

方舱是指控系统的主要装载平台,而胶粘剂是方舱生产中复合型关键原料,我所结合自身产品需要研制环氧类方舱大板胶粘剂.分析其固化机理,进行胶粘剂拉伸剪切强度、180.剥离强度、大板高低温贮存、整舱日照热效应试验,并将其与国外某些胶粘剂相关性能进行比较,结果表明该胶粘剂具有良好的力学和环境适应性性能,适用于方舱生产.该胶黏剂具有良好的经济效益和社会效益,今后将进一步推广应用到民用市场.     

即贴型单层带通FSS的传输特性

以狭缝阵列为例,利用模匹配法计算分析,并结合实验,针对即贴型频率选择表面(FSS)与介质板的复合结构进行研究,分析了不同厚度的聚酰亚胺基底膜和粘合胶层的影响,并深入研究了不同复合方式下的频率响应.结果表明,即贴型FSS结构中,基底膜与粘合胶层等细节的影响不可忽略,影响程度与复合方式和介质厚度均密切相关.复合结构中应当含有粘合胶层,避免空气间隙的影响.仅当基底膜和粘合胶层的介电常数小于介质板或与之相近,采用合适的复合方式,并且介质板厚度为基底膜和粘合胶层厚度的10倍以上,才能使基底膜和粘合胶层对复合结构传输特性的影响降至最低.一系列厚度的介质单侧加载时的FSS结构频率响应测试结果与计算结果的对比表明粘合工艺的缺陷会导致即粘型FSS结构的传输性能发生变化.FSS的设计中应当全面考虑上述因素的影响.     

导电胶导电性能的实验研究

当今微机电系统电路板焊接点已可采用导电胶替代传统工艺所用的锡铅合金来进行电气连通.但是导电胶的固化温度和固化时间对导电胶的导电性有很大的影响.本论文通过实验,研究了固化温度与固化时间之间的关系以及最终固化完成后对导电性能的影响.导电胶层的厚度对其固化性能也有一定的影响,实验得出导电胶层厚度可以做得薄些.同时还通过固化冷却到室温后电阻变化的研究和初步温度循环中电阻变化的研究,得出其固化的最佳工艺应是当固化过程进行到导电胶电阻值基本不变化时即停止固化的结论,也就是要避免固化过度.     

Multiscale analysis on two-dimensional nanoscale adhesive contacts

Nanoscale adhesive contacts play a key role in micro/nano-electro-mechanical systems as the dimension of the components come to nanometer.Experimental studies on nanoscale adhesive contacts are limited by some uncertain factors and the cost of experiments is too high.Besides,nanoscale textured surfaces are difficult to process and nanoscale adhesive contacts of textured surfaces are still lack of investigation.By using multiscale method,which couples molecular dynamics simulation and finite element method,two-dimensional nanoscale adhesive contacts between a rigid cylindrical tip and an elastic substrate are investigated.For the contacts between the rigid cylindrical tip and smooth surface,Von Mises stress distributions,the maximum Von Mises stresses,and contact forces are compared for different radii to show the size effects and adhesive effects.The phenomena of hysteresis are observed and more obvious as the radii of the tip increase.The influences of indentation depth and indentation speed are also discussed.Then two series of textured surfaces are employed,and the influences of the texture asperity shape,asperity height,and asperity spacing on contact forces are studied.The contact forces comparisons show that textured surfaces can reduce contact forces effectively in the range of the two series.Contact forces of textured surfaces increase as the asperity heights increase,and textured surfaces with smaller asperity spacing will get higher contact forces.Contact forces may be controlled through textured surfaces in the future.The obtained results will help to improve contact condition and provide theory basis for texture design.     

Calculation of characteristics of discrete adhesive contact

The mathematical model of discrete contact between real engineering surfaces has been proposed. The model takes into account the adhesion between surfaces in contact. The analytical expressions for calculating the deformation of a contact and the real (physical) contact area have been obtained. The dimension-less criterion for estimating the influence of adhesive forces on the contact characteristics has been proposed. The effect of various factors on the above characteristics has been analyzed. It has been shown that, at the nanoscale level (asperities of nanoscale size), especially under low contact loads, the influence of adhesive forces is significant.     

The adhesive scarf joint in pure bending

The stress distribution in a scarf joint subjected to pure bending, and with arbitrary angle of scarf, is analyzed as a two dimensional elasticity problem in plane stress. Both the adherend and the adhesive are assumed to be elastic and isotropic. The two adherends may have differing moduli of elasticity. Numerical results are given.     

Alleviation of the adhesive protrusion problem at the bonding interface of free-standing microstructures

The vertically allocated free-standing SU-8 microstructures are typically bonded to a glass cover by the usage of uncrosslinked SU-8 adhesives. Such a phenomenon can easily cause SU-8 protrusion and eventually result in the SU-8 cantilever to be immovable. Traditional methods are sensitive to the bonding conditions and have a short bondable thickness of SU-8 adhesives. In this study, we propose an approach, that is, improved structural features, to alleviate the protrusion problem while extending the bondable thickness for the freestanding SU-8 microstructures in an enclosed channel. We used concave and moat microstructures as solutions of the improved structural features. We investigated the influence of both microstructures on the bonding quality and compared the bondable thickness with the previous one. THB-151N was used in another example to demonstrate the availability of our method. The bonding quality at the interfaces was evaluated by SEM images and direct inspection through a transparent glass cover. The bonding method is advantageous to other microfluidic systems, particularly those with long narrow channels.

     

Dentin bond strength and nanoleakage of the adhesive interface after intracoronal bleaching

This study evaluated dentin bond strength (BS) and nanoleakage of non‐ and pre‐etched dentin immediately (T₀,), 7 days (T₇), and 14 days (T₁₄) after bleaching. Bovine incisors (150) were selected and half of them submitted to intrapulpal dentin etching (e). Non‐ and pre‐etched dentin were subjected to the following (n = 15): no bleaching/control (C); 35% carbamide peroxide (CP); 35% hydrogen peroxide (35% HP); 25% hydrogen peroxide (25% HP); and sodium perborate (SP). Bleaching agents were applied to the pulp chamber four times within a 72‐h interval. Afterwards, pulp chamber dentin was prepared for the BS test at different evaluation times (n = 5): T₀, T₇, and T₁₄. Composite blocks were built on pulp chamber and sectioned in slices. Slices were reduced to an hour‐glass shape with a cross‐sectional area of 0.8 mm² and submitted to microtensile BS test. Two additional specimens for each group were prepared for nanoleakage evaluation by transmission electron microscopy (TEM). Results were analyzed by ANOVA (two‐way) and Dunnett's test (p < .05). BS decreased immediately after intracoronal bleaching for both sound and pre‐etched dentin (p < .05). At T₁₄, the BS of non‐etched bleached dentin increased for all groups, whereas the pre‐etched SPe group presented BS similar to the Ce. Nanoleakage within the hybrid layer was perceptible immediately after bleaching, although a decrease in nanoleakage was observed for all groups at T₁₄. Adhesive restorations should be performed 7–14 days after bleaching, according to the bleaching agent used. Intracoronal bleaching should be performed preferably with sodium perborate if previous dentin etching is applied.     

Models of adhesive contact between rough elastic solids

Adhesion of rough elastic solids is considered. Roughness is simulated by the Winkler–Fuss nonlinear elastic layer, which can be stretched. Mechanical properties of the layer are determined by statistical theories of adhesive contact between nominally flat rough surfaces. The contact of solids is described by the nonlinear boundary integral equations with non-monotonic operators, whose solutions determine reduction of effective thickness of the rough layer, nominal contact stresses, nominal contact regions and relation between applied force and approach of solids. The theoretical background and numerical implementation of the models are given. Both a full model and its simplified version are analyzed.