Adhesion of Elastic Thin Films: Double Peeling of Tapes Versus Axisymmetric Peeling of Membranes

The mechanism of detachment of thin films from a flat smooth rigid substrate is investigated. In particular, analytical solutions in closed form are proposed for the double peeling of an elastic tape as well as for the axisymmetric peeling of a membrane. We show that in the case of double peeling of an endless elastic tape, a critical value of the pull-off force is found, above which the tape is completely detached from the substrate. In particular, as the detachment process advances, the peeling angle is stabilized on a limiting value, which only depends on the geometry of the tape, its elastic modulus and on the interfacial energy $\Updelta\gamma$ . This predicted behavior agrees with the “theory of multiple peeling” and clarifies some aspects of this theory. Moreover, it is also corroborated by experimental results (work in progress) we are carrying out on a standard adhesive tape adhered to a smooth flat poly(methyl methacrylate) surface. In the case of the axisymmetric adhering membrane, a different behavior is observed. In such case, the system is always stable, and the detached area monotonically increases with the peeling force, i.e., the elastic membrane can sustain in principle any applied force. Results are validated by a fully numerical analysis performed with the aid of a finite element commercial software.     

L形碳纤维增强复合材料/铝合金胶接复合构件剥离应力建模与分析

针对承受剥离载荷的L形碳纤维增强复合材料(Carbon fiber reinforced plastic/polymer,CFRP)/铝合金胶接复合构件,以微元受力平衡方程为基础,建立胶层平均剥离应力的二维分布方程。在方程中引入基材的弯曲刚度系数,描述背材与基材均为刚性材料的情况下胶层剥离应力的分布规律。其应力分布曲线为拉压应力交替作用的阻尼调和函数,周期与峰值由胶接件构型尺寸与材料性能参数决定。通过CFRP/铝合金剥离试验及三维有限元模拟对理论模型进行对比验证,结果的总体趋势与数值吻合程度较好,并分析不同方法获得的剥离应力分布状态之间的差异及其产生的原因。基于胶接复合构件的理论模型与三维有限元模型,研究基材厚度改变对剥离应力分布的影响,发现伴随着CFRP板厚度的增加,剥离应力的峰值明显下降,在剥离前沿的应力集中现象得到改善。     

Modeling and analysis of curved beams with debonded piezoelectric sensor/actuator patches

In this paper, a mathematical model for thin-walled curved beams with partially debonded piezoelectric actuator/sensor patches is presented for investigating the effect of debonding of the actuator/sensor on their open- and closed-loop behaviors. The actuator equations and the sensor equations of the curved beam in perfectly bonded and debonded regions are derived. In the perfect bonding region, the adhesive layer is modeled to carry constant peel and shear stresses; while in the debonding area, it is assumed that there is no peel and shear stress transfer between the host beam and the piezoelectric layer. Both displacement continuity and force equilibrium conditions are imposed at the interfaces between the bonded and debonded regions. Based on the model and the sensing equation of the sensor, a closed-loop vibration control for the curved beams is performed. To obtain the frequency response from the presented model, a solution scheme for solving the complex governing equations is given. Using this model and the solution scheme, the effects of the debonding of actuator and sensor patches on open- and closed-loop control are investigated through an example. The results show that edge debonding of the piezoelectric patch has a significant side effect on the closed-loop control of the curved beams.     

Machining with applied chip tension—Part II: Experiments

Machining with applied chip tension is the basis of a process, strip peeling, for making small batches of metal special strip products. An approximate slip-line field numerical analysis of the process, related to the matrix method, is presented which shows how pulling stress and its direction affect chip thickness and curvature and tool forces. Pulling parallel to, or within 5° of, the rake face produces straight chips but results in less reduction of chip thickness and tool forces than pulling at more than 5° to the rake face. In the latter case chips are formed curled and are subsequently plastically straightened by the pulling force. Chip failure by plastic straightening and other causes is discussed and it is recommended that the pulling direction should be between 5 and 20° from the rake face. Influences of rake angle and friction stress are also considered.     

消除薄壁零件车削颤振的加工实践

通过分析薄壁零件结构特点和技术要求,在车床上借助辅助工装,采取负压和胶带粘附的措施,有效地解决了车削薄壁零件的颤振问题,成功地加工出符合要求的零件,并将其广泛应用到实际生产中。实践证明,采用负压和胶带粘附方式消除车削颤振是切实可行的,且具有安全可靠、操作简便、成本低廉的优势。     

Chromium oxide coatings applied to magnetic tape heads for improved wear resistance

This paper reports on an investigation of the wear of chromium oxide based very thin films. Linear data tape Advanced Digital Recording (ADR™) heads coated with 20- and 40-nm thick chromium oxide films have been tested subject to temperature/humidity matrix of 10 to 40°C/10 to 80% in order to assess the wear behaviour of the coating as a function of environment. The tested heads were analysed at various stages of wear, by use of optical microscopy (OM), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). The results show that the most severe damage occurs at the highest relative humidity (80% RH) and for a given humidity, at the lowest temperature (10°C). Inversely, stain transferred from the tape to the head surface predominates at the lowest humidity (10% RH). Stain therefore appears to protect the coating against wear with the degree of protection increasing with the temperature.The wear process differs according to the coating thickness. This is attributed to the location of the maximum subsurface stress with respect to the coating/substrate interface. It is shown that this maximum stress occurs below the interface for 20 nm and at the interface for 40 nm thick coatings. This correlates to different observed wear modes.     

Investigation on overlap joining of AZ61 magnesium alloy: laser welding, adhesive bonding, and laser weld bonding

This paper presents the research on weldability of magnesium alloy AZ61 sheets by overlap laser welding, adhesive bonding, and laser seam weld bonding processes. Microstructures and mechanical properties of the joints are investigated. In overlap laser welding, the joint fractures at the interface between the sheets and maximum shear strength can reach 85% of that of the base metal. Off-center moment during tensile shear test can lead to the strength loss, while the weld edge can also influence the strength as a cracking source. Adhesive bonded joint can offer high tensile shear failure force but low peel strength. Laser weld bonded joint offers higher tensile shear failure force than either laser welded joint or adhesive bonded joint does, and the improved failure load is due to combined contribution of the weld seam and the adhesive. The weld seam can block the adhesive crack propagation, and the adhesive improves the stress distribution, so they can offer a synergistic effect.     

Interactions at the head–tape interface of a linear tape system

In this study, tape cycling experiments were performed using two different experimental metal particle media in combination with a Travan™ linear tape system. The aim was to investigate the effect of head/tape contact on the tribological properties and signal performance of the system. A combination of cycling at extreme environmental conditions, use of experimental media, and cycling beyond the normal limit of operation ensured a worst-case scenario for the head–tape interactions. Auger electron spectroscopy (AES) and atomic force microscopy (AFM) were used to characterize the chemical and physical surface changes that occurred on and in the head surfaces. X-ray photoelectron spectroscopy (XPS) was used to identify the chemical changes that occurred at the media surface and these changes were correlated to variation in signal dropout rate. Measurements were made as functions of number of cycles.The cycling experiments for the two different tapes were performed at conditions of 32°C, 80% RH and 5°C, 10% RH and transfer of material from the media to the head was observed at each condition for both tape types. The degree of material transfer was influenced by the environmental operating conditions, but was governed by localized heating effects, such as those originating from active magnetoresistive (MR) elements and frictional interactions between the head and media. XPS analyses of the surface of the media revealed a reduction of nitrogen with increasing number of cycles indicating binder depletion. Significant differences in elemental concentrations were also detected between areas corresponding to regions directly under the cartridge belt compared to those off belt.     

镁合金激光胶接焊接头微观及力学性能

采用激光胶接焊焊接镁舍金，利用现代测试手段分析接头的微观组织特征，并分别研究激光焊、胶接和激光胶接焊3种接头在相同工艺参数下的剪切力和抗剥离力，在较好的工艺参数下，激光胶接焊焊缝成形良好。在激光热源的作用下，焊缝区内胶层受热分解并以气体形式逸出焊缝，并未影响焊缝的组织熔舍；焊缝边缘附近胶层炭化裂解，存在胶层失效区，虽减小胶层的承载面积，但该区域很窄，对接头的实际承载能力影响不大。激光胶接焊接头剪切力最大，胶接接头次之，激光焊接接头剪切力最小；激光胶接焊接头的抗剥离力远大于胶接接头的抗剥离力。激光胶接焊有效提高接头的实际承载能力，因此具有很大的发展潜力。     

考虑弯曲效应的混元胶接单搭接头应力模型

混元胶接接头是利用多种不同剪切弹性模量的胶层来传递被粘物载荷的单搭接头。它兼具胶层连续性连接和降低端头应力集中等优点,因此能充分利用被粘物材料性能(如复合材料)以提高接头强度。以典型双元胶接接头为对象,考虑加载作用线偏心引起的弯曲效应和胶层剥离正应力,建立被粘物为各向同性的线弹性双元胶接接头应力解析模型。理论模型中的胶层切应力、剥离正应力和上被粘物纵向正应力与精细有限元模型吻合得较好,证实了理论模型的正确性。参数研究中确定了影响混元胶层应力分布的关键耦合参数。     

Structural and Chemical Evolution of the Near-Apex Region of an Atomic Force Microscope Tip Subject to Sliding

Atomic force microscopy and molecular dynamics simulation are used to study the nanoscale wear of a silicon dioxide tip sliding on a copper substrate. Wear is characterized in terms of structural and chemical evolution of the system where the latter is possible experimentally using atom probe tomography of the slid tips. Comparison of the experimentally observed and simulation-predicted wear reveals that adhesive wear is dominant in the short sliding distances of the simulation at any applied load, while the sliding distances in the experiments are long enough to observe load-induced transitions between adhesive-dominated and abrasive-dominated wear.     

Analysis of adhesive behaviour of human skin in vivo by an indentation test

Indentation testing is a widely used technique to quantify the elastoplastic properties of materials. However, it also allows the analysis of the adhesive force between a substrate and an indenter. In this paper, in order to contribute to the understanding of the human skin behaviour, an elastic adhesive theory has been applied to a steel/skin in vivo contact. The human skin adhesive behaviour is investigated by varying different parameters; namely the normal load, the indentation speed, the contact time and the indenter geometry. Under controlled experimental conditions, this in vivo skin study results in the characterisation of the skin adhesive behaviour.     

Surface roughness and the friction and adhesion of elastomers

When certain elastomers are traversed over clean counterfaces true interfacial sliding is not apparent. Relative motion is achieved by propagation of Voltara or macroscopic dislocations. These dislocations, which are known as Schallamach waves, can be readily observed provided that one of the contacting pair is transparent. It has been possible to account for the energy dissipated during this process, and hence the frictional force, in terms of the energy required to peel the interface apart at the front of the dislocation. The level of this energy dissipation was studied in direct peeling experiments and was found to be a marked function of peeling velocity and surface roughness. The influence of surface topography in peeling and friction experiments was considered in some detail. In peeling, changes in roughness greatly modified the adhesion process, whereas the frictional force was relatively unchanged by the introduction of surface roughness.     

Rolling friction and adhesion between smooth solids

Rolling friction has been explained in terms of crack propagation through an adhesive joint. The contact between a smooth cylinder and flat has been regarded as an adhesive junction bounded by two cracks moving in the same direction at the same speed, one crack continually opening and one closing. Propagation of these cracks requires a force which is calculated from crack theory and shown to be equal to the friction.The theory has been verified experimentally using glass cylinders rolling on smooth rubber. Results show that rolling friction is closely connected with peel adhesion. Moreover, this adhesion interpretation of rolling friction between smooth surfaces explains several observations: (a) the existence of a static rolling friction, (b) the unusually high value of friction and its independence from load and roller radius, (c) the marked effect of lubricant or dust.     

基体表面的分数维对电弧喷涂层结合强度的影响

研究了不同喷砂角度下２０钢基体表面的粗糙度和分数维的变化及其对电弧喷涂层结合强度的影响,结果发现,不同角度喷砂处理对２０钢基体表面的平均粗糙度影响不大,而基体表面的分数维则受喷砂角度的影响。并且存在一个最优喷砂角度,此时基体表面形貌的分数维最大,电弧喷涂层的结合强度值也最大。     

Failure mode maps in the thin film scratch adhesion test

The scratch test has been used to assess thin coating adhesion for some time now. In this test a diamond indenter is drawn across the coated surface under an increasing load (either stepwise or continuous) until at some load, termed the critical load, L_c a well-defined failure event occurs; if this failure event represents coating detachment then the critical load can be used as a qualitative measure of coating-substrate adhesion. However, it is well known that a range of possible failure modes can occur and only some of these are dependent on adhesion. Other failure modes which depend on plastic deformation and fracture within the coating, rather than any adhesive failure at the coating substrate interface, may be just as useful in the assessment of coating quality particularly for tribological applications. In this paper the load regimes in which the main adhesion-related failure modes (spallation and buckling) occur as a function of coating thickness will be presented for thermally grown oxide and sputtered nitride coatings. The origin of the observed failure modes and the use of the scratch test to assess coating/substrate adhesion in a more quantitative fashion is discussed in the light of these observations.     

Adhesion Mechanics between Nanoscale Silicon Oxide Tips and Few-Layer Graphene

Finite element method (FEM) simulations of the adhesive contact between a nanoscale tip and a silicon oxide substrate covered with graphene were performed, modelling experimental atomic force microscopy pull-off measurements. Simulations showed a slight increase in the pull-off force as layer number increased. This small enhancement was within reported experimental error, agreeing with the experimental findings of layer-independent adhesion forces. Pull-off forces did not vary with the elastic strain in the system for a given number of layers, but were influenced by the greater adhesive stresses for tip–graphene interaction compared with tip–substrate interactions. FEM simulations were also performed on suspended graphene and showed that the adhesive forces increased slightly beyond one layer of graphene, but then varied little from two to four layers of graphene. The results indicate that while there is some local delamination of the graphene sheets from the substrate, the adhesive stresses between the graphene layers in multilayer graphene effectively prevent out-of-plane mechanical deformation of the graphene layers that could result from tip–graphene interactions. Thus, the increased pull-off forces observed beyond one monolayer results from a change in the amount of material between the tip and substrate, or in this case the number of graphene layers, thus increasing the van der Waals force between tip and graphene.     

Lateral motion and edge wear of magnetic tapes

Lateral motion and edge wear are measured on magnetic tape, and the relationship between tape edge wear and tape lateral motion is investigated. Instrumentation for measuring tape edge force is described. Tape edge force is measured at the tape guiding position using a force-calibrated cantilever spring and a linear optical probe. Typical measurements of tape lateral motion are given as a function of tape tension, tape direction, and path position. A technique for measuring tape edge wear is introduced and wear measurements are presented as a function of load and the number of passes.     

Topographic effects on adhesive force mapping of stretched DNA molecules by pulsed-force-mode atomic force microscopy

Adhesive interaction between a tip and a sample surface was examined on a microscopic scale by pulsed-force-mode atomic force microscopy (PFM-AFM). The signal measured by monitoring pull-off force is influenced by various factors such as topography, elasticity, electrostatic charges, and adsorbed water on surfaces. Here, we focus on the topographic effects on the adhesive interaction. To clarify the topographic influence, the adhesive force measurement of a stretched DNA molecule with a smaller radius of curvature than that of a tip was carried out at low relative humidity (RH) with an alkanethiol-modified tip. The experimental conditions such as low RH and the use of the alkanethiol-modified tip were required to minimise the influence of water capillary force on hydrated DNA strands. The hydrophobic modification of a substrate surface was also important to minimise the adsorbed water effect. The DNA molecules were stretched on the substrate surfaces by an immobilisation process called a dynamic molecular combing method. The two-component vapour-phase surface modification with an alkylsilane mixed with a silane derivative containing an amino end group enhanced the DNA adsorption due to the electrostatic interaction. The experimental results for the topographic effects on the adhesive force mapping were reproducible.     

The dissipation of energy in the friction of rubber

The sliding of rubber over glass when waves of detachment are responsible for the relative motion at the interface has been studied. The frictional force and the velocity and frequency of the waves were recorded for various sliding conditions. In a separate experiment, the work required to peel apart and then re-adhere unit area of rubber-glass interface was measured as a function of peeling velocity. Assuming that the passing of a wave corresponds to a peeling and re-adhering of the contact area, the work of adhesion is calculated from the friction observations and compared with the values measured directly. The good correlation which is found indicates that in these circumstances the frictional energy dissipation may be accounted for in terms of the net work of adhesion.