磁场力及膜曲率对磁敏感薄膜-基底界面 黏附性能的影响与调控

界面黏附和脱黏的可调控在攀爬装置、黏附开关、机械抓手等方面具有重要的应用需求. 针对磁敏感薄膜-基底界面, 开展了薄膜初始曲率及外加磁场对界面黏附性能影响机制的研究. 首先实验制备了具有初始曲率的磁敏感薄膜, 分别开展了具有初始曲率的磁敏感薄膜-基底界面撕脱实验及理论研究, 研究了薄膜初始曲率、弯曲刚度和外加磁场强度对界面黏附性能的影响规律. 实验和理论结果一致表明: 具有初始曲率的磁敏感薄膜-基底界面黏附力随薄膜初始曲率的增大而减小, 而外加磁场能够有效提高界面黏附力;相比于初始零曲率薄膜-基底界面稳态撕脱力与薄膜弯曲刚度无关, 薄膜弯曲刚度减弱了具有初始曲率薄膜-基底界面的稳态撕脱力. 进一步从能量角度分析了界面等效黏附性能, 揭示了薄膜弯曲能、磁场势能、界面黏附能的相互竞争机制. 最后, 基于本文的实验及理论结果, 提出了一种磁场和薄膜初始曲率协同调控的简易机械抓手, 可连续实现物体的拾取、搬运和释放功能. 本文结果不仅有助于理解多场调控的界面可逆黏附机制, 对界面黏附可控的功能器件设计亦提供了一种新方法.      

Peeling behavior of a bio-inspired nano-film on a substrate

A peeling model is proposed to analyze the peeling properties of bio-mimetic nano-films using the finite element method (FEM) and theoretical approach. The influences of the nano-film’s adhesion length, thickness, elastic modulus, roughness and peeling angle on the peeling force were considered as well as the effect of the viscoelastic behavior. It has been found that the effective adhesion length, at which the peeling force attained maximum, was much smaller than the real length of nano-films; and the shear force dominated in the case of smaller peeling angles, whereas, the normal force dominated at larger peeling angles. The total peeling force decreased with an increasing peeling angle. Two limiting values of the peeling-off force can be found in the viscoelastic model, which corresponds to the smaller and larger loading rate cases. The effects of nano-film thickness and Young’s modulus on peeling behaviors were also discussed. The results obtained are helpful for understanding the micro-adhesion mechanisms of biological systems, such as geckos.     

Molecular dynamics simulation of peeling a DNA molecule on substrate

Molecular dynamics (MD) simulations are performed to study adhesion and peeling of a short fragment of single strand DNA (ssDNA) molecule from a graphite surface. The critical peel-off force is found to depend on both the peeling angle and the elasticity of ssDNA. For the short ssDNA strand under investigation, we show that the simulation results can be explained by a continuum model of an adhesive elastic band on substrate. The analysis suggests that it is often the peak value, rather than the mean value, of adhesion energy which determines the peeling of a nanoscale material.The project supported by the Distinguished Young Scholar Fund of NSFC (10225209) and key project from the Chinese Academy of Sciences (KJCX2-SW-L2)     

Peeling experiments of ductile thin films along ceramic substrates – Critical assessment of analytical models

Two types of peeling experiments are performed in the present research. One is for the Al film/Al₂O₃ substrate system with an adhesive layer between the film and the substrate. The other one is for the Cu film/Al₂O₃ substrate system without adhesive layer between the film and the substrate, and the Cu films are electroplated onto the Al₂O₃ substrates. For the case with adhesive layer, two kinds of adhesives are selected, which are all the mixtures of epoxy and polyimide with mass ratios 1:1.5 and 1:1, respectively. The relationships between energy release rate, the film thickness and the adhesive layer thickness are measured during the steady-state peeling process. The effects of the adhesive layer on the energy release rate are analyzed. Using the experimental results, several analytical criteria for the steady-state peeling based on the bending model and on the two-dimensional finite element analysis model are critically assessed. Through assessment of analytical models, we find that the cohesive zone criterion based on the beam bend model is suitable for a weak interface strength case and it describes a macroscale fracture process zone case, while the two-dimensional finite element model is effective to both the strong interface and weak interface, and it describes a small-scale fracture process zone case.     

微纳米尺度膜/基结构界面性能的实验研究

为了研究铜膜/有机玻璃结构的界面性能,首先对沉积在有机玻璃基底上300nm厚的铜膜进行了单轴压缩实验,部分区域的薄膜因屈曲而脱离基底。选择在膜/基粘接良好区域、膜/基脱粘区域分别进行等位移纳米压痕实验。利用膜/基粘接良好区域处硬度/弹性模量与压痕位移的关系来确定膜/基结构的临界脱粘位移。基于宏观力学中表征界面性能的能量法,利用两个区域等位移的塑性功差值来确定界面能量释放率。研究结果表明:当压痕位移约450nm时,膜/基结构开始出现界面脱粘,实验测得铜膜/有机玻璃结构的界面能量释放率值在6.81~10.32J/m2之间。     

EXPERIMENTAL INVESTIGATIONS OF STRENGTH,TOUGHNESS AND FAILURE MECHANISM OF THE METAL/EPOXY/METAL ADHESIVE SYSTEM

本文系统地开展了金属/环氧/金属胶结体系的强韧机理及失效行为实验研究,针对铝合金圆棒与铝合金圆棒通过环氧树脂胶层的各种斜截面方向粘结,实验观测了该体系的拉伸变形和失效行为,测量了界面失效载荷对胶层厚度和粘结界面倾斜角的依赖关系;通过引入胶结界面平均正应力、平均剪应力、平均正应变、平均剪应变等概念,可对界面失效强度进行测量,获得界面强度与界面粘结角度以及胶层厚度的关系,进而获得了铝合金/环氧胶层/铝合金体系的强度失效面以及胶结界面的断裂能和胶结体系的能量释放率.上述研究结果为深入认识金属胶结体系的强韧性能和失效机制提供了科学依据,对金属胶结体系的优化设计和性能评判具有重要指导意义.研究结果表明,铝合金/环氧胶层/铝合金体系的拉伸失效总体呈弹脆性破坏特征,失效表现为胶层粘结界面的断裂,失效强度和界面断裂能在胶层厚度为百微米量级时表现出强烈的尺度效应：界面粘结强度随着胶层厚度的减小而显著增大,临界状态的平均正应力和平均剪应力在强度破坏面上近似位于同一圆上,界面断裂能随着胶层厚度的减小而显著减小;与此同时,界面失效强度和界面断裂能也密切依赖于界面粘结角度.     

Strain energy release rate for interfacial cracks in hybrid beams

The finite element modeling and fracture mechanics concept were used to study the interfacial fracture of a FRP-concrete hybrid structure. The strain energy release rate of the interfacial crack was calculated by the virtual crack extension method. It is shown that the crack growth has three phases, namely, cracking initiation, stable crack growth and unstable crack propagation. The effects of geometric and physical parameters of the hybrid beam on the energy release rate were considered. These parameters include Young’s moduli of the FRP, the concrete and the adhesive, thickness of the FRP plate and adhesive, and the distance of FRP plate end from the beam end. The numerical results show that the energy release rate of the interfacial crack is influenced considerably by these parameters. The present investigation can contribute to the mechanism understanding and engineering design of the hybrid structures.     

DETERMINATION OF INTERFACIAL MECHANICAL PARAMETERS FOR AN Al/EPOXY/Al2O3 SYSTEM BY USING PEEL TEST SIMULATIONS

Peel test measurements and simulations of the interfacial mechanical parameters for the Al/Epoxy/Al2O3 system are performed in the present investigation. A series of Al film thicknesses between 20 and 250 microns and three peel angles of 90, 135 and 180 degrees are considered. Two types of epoxy adhesives are adopted to obtain both strong and weak interface adhesions. A finite element model with cohesive zone elements is used to identify the interfacial parameters and simulate the peel test process. By simulating and recording normal stress near the crack tip, the separation strength is obtained, Furthermore, the cohesive energy is identified by comparing the simulated steady-state peel force and the experimental result. It is found from the research that both the cohesive energy and the separation strength can be taken as the intrinsic interfacial parameters which are dependent on the thickness of the adhesive layer and independent of the film thickness and peel angle.     

壁虎粘附微观力学机制的仿生研究进展

本文针对壁虎粘附系统最小单元的真实形状, 类似于有限尺寸纳米薄膜的铲状纤维, 综述了对其微观粘附力学机制主要影响因素的多个研究, 主要考虑了有限尺寸纳米薄膜长度、厚度、撕脱角等对撕脱力的影响; 物体表面粗糙度以及环境湿度等对粘附的影响因素; 包括实验、理论及数值模拟的研究及结果比较. 最后给出仿生粘附力学方向仍然存在的主要科学问题及进一步的研究展望.     

硅表面电沉积MoS2薄膜及其微观摩擦性能研究

以单晶硅片为基片,采用电化学沉积工艺通过阴极还原硫代钼酸根制备MoS2薄膜,利用光学显微镜、扫描电子显微镜、X射线衍射仪、俄歇电子能谱仪以及原子力显微镜表征薄膜结构,并研究其微观摩擦磨损性能.结果表明:所制备的薄膜为纳米/亚微米厚度,表面光滑致密,结构为非晶态,由钼、硫和氧元素构成;微米厚度的薄膜表面粗糙度增加,薄膜易开裂,结合性差;沉积MoS2薄膜的硅表面的最小摩擦力约为原始硅表面的1/2;沉积MoS2可以使硅表面的粘着能减少50%左右,从而使其微观摩擦力降低.     

The ultratough peeling of elastic tapes from viscoelastic substrates

The peeling of an elastic thin tape from a flat smooth viscoelastic substrate is investigated. Based on a Green function approach and on the translational invariance, a closed form analytical solution is proposed, which takes into account the viscoelastic dissipation in the substrate material.We find that peeling is prevented from taking place, only when the external force is smaller than the one predicted by Kendall's formula for elastic tapes on rigid substrates. However, we also find that, regardless of the value of the applied force, steady state detachment may occur when the elastic tape is sufficiently stiff. In this case, the constant peeling velocity can be modulated by properly defining the geometrical parameters and the material properties of tape and viscoelastic foundation. On the other hand, for relatively high peeling angles or compliant tapes a threshold value of the peeling force is found, above which the steady-state equilibrium is no longer possible and unstable detachment occurs.The present study contributes to shed light on the behavior of pressure sensitive adhesives in contact with viscoelastic substrates like the human skin. At the same time, it can be considered a first step towards a better understanding of the effect of viscoelastic dissipation on the fracture behavior of solids.     

Analysis of the adhesive contact of confined layers by using a Green's function approach

The authors develop a numerical procedure to analyze the adhesive contact between a soft elastic layer and a rough rigid substrate. The solution of the problem, which belongs to the class of the free boundary problems, is obtained by calculating the Green's function which links the pressure distribution to the normal displacements at the interface. The problem is then formulated in the form of a Fredholm integral equation of the first kind with a logarithmic kernel, and the boundaries of the contact area are calculated by requiring that the energy of the system is stationary. The methodology is relatively simple and easy to implement in a numerical code. It has been utilized to analyze the adhesive properties of a confined layer in contact with a wavy rigid substrate as a function of thickness, applied stress or penetration. It is shown that reducing the thickness of the slab reduces the effective energy of adhesion, i.e. the work needed to separate the bodies, but nevertheless increases the adherence force between the slab and the substrate. However, thinning the slab also increases the confinement of the system and therefore increases the negative hydrostatic pressure in the layer. This, in turn, may produce cavitation. When this happens the rupture of the adhesive bond does not occur through interfacial crack propagation but, by the growth of new interfacial voids or cavities.     

切应力协同下受热过冷层流液膜的破断特性

针对界面切应力协同下受热过冷层流液膜流动的破断过程, 建立了不同气液流向下的临界液膜厚度和最小润湿量的理论模型, 分析了不同驱动力作用下, 接触角、流体温度、界面切应力和壁面热流密度对液膜破断特性的影响. 研究表明: 临界液膜厚度和最小润湿量均随壁面热流密度的增加而增大; 重力驱动下的接触角影响在不同热流密度下有所不同, 流体温度在不同驱动力下对最小润湿量的影响截然相反; 同向切应力驱动下临界液膜厚度和最小润湿量随切应力增加而减小; 在重力和切应力协同驱动下, 同向切应力对最小润湿量的影响与重力和切应力所起作用的相对大小有关, 反向切应力使得临界液膜厚度和最小润湿量有所增大.      

Analytical Model and Experimental Verification of the Interfacial Peeling Strength of Electrodes

Background

The interfacial peeling strength of lithium-ion battery electrodes is a very important mechanical property that significantly affects the electrochemical performance of battery cells.

Objective

To characterize the interfacial peeling strength of an electrode, an analytical model based on the energy balance principle is established by considering the state of charge (SOC), the energy release rate, the tensile stiffness, and the peeling angle.

Methods

Uniaxial tensile tests and 180-degree peeling tests are conducted to determine the Young’s modulus and the interfacial peeling strengths of electrodes at different SOCs, respectively. The experimental data serve as a validation of the accuracy of the analytical model.

Results

The interfacial peeling strength of the electrode shows a strong reliance on many factors. Specifically, the interfacial peeling strength increases with the SOC and the energy release, and decreases with the peeling angle. When the tensile stiffness of the active layer equals that of the current collector, the interfacial peeling strength has a maximum value.

Conclusions

By comparing with experimental data of the 180-degree peeling test, the model prediction shows excellent agreement at different SOCs, and the analytical model established in this paper can be used to guide and assess the interfacial properties of electrodes for industry.

     

Adhesion and friction of an elastic half-space in contact with a slightly wavy rigid surface

The paper deals with the estimation of the pressure distribution, the shape of contact and the friction force at the interface of a flat soft elastic solid moving on a rigid half-space with a slightly wavy surface. In this case an unsymmetrical contact is considered and justified with the adhesion hysteresis. For soft solids as rubber and polymers the friction originates mainly from two different contributions: the internal friction due to the viscoelastic properties of the bulk and the adhesive processes at the interface of the two solids. In the paper the authors focus on the latter contribution to friction. It is known, indeed, that for soft solids, as rubber, the adhesion hysteresis is, at least qualitatively, related to friction: the larger the adhesion hysteresis the larger the friction. Several mechanisms may govern the adhesion hysteresis, such as the interdigitation process between the polymer chains, the local small-scale viscoelasticity or the local elastic instabilities. In the paper the authors propose a model to link, from the continuum mechanics point of view, the friction to the adhesion hysteresis. A simple one-length scale roughness model is considered having a sinusoidal profile. For partial contact conditions the detached zone is taken to be a mode I propagating crack. Due to the adhesion hysteresis, the crack is affected by two different values of the strain energy release rate at the advancing and receding edges respectively. As a result, an unsymmetrical contact and a friction force arise. Additionally, the stability of the equilibrium configurations is discussed and the adherence force for jumping out of contact and the critical load for snapping into full contact are estimated.     

Analytical and experimental study of a circular membrane in adhesive contact with a rigid substrate

The problem that is addressed here is that of a pressurized circular membrane in adhesive contact with a rigid substrate. A closed-form membrane analysis is developed for the JKR, DMT and Maugis regimes, which describes the relationships between adhesion energy, pressure, contact radius and contact force. The JKR–DMT transition is studied for this case of membrane contact by introducing an appropriate dimensionless parameter. Experiments are conducted with smooth and structured acrylate layers on a PET carrier film contacting a glass substrate using an apparatus based on moiré deflectometry to measure the contact radius and slope of these thin transparent films. They demonstrate that this analysis predicts the contact radius well. The adhesion energy extracted from the analysis of the measured pressure-contact radius response is constant during unloading but appears to increase during pressurization.     

Quantitative characterization of the interfacial adhesion of Ni thin film on steel substrate: A compression-induced buckling delamination test

A compression-induced buckling delamination test is employed to quantitatively characterize the interfacial adhesion of Ni thin film on steel substrate. It is shown that buckles initiate from edge flaws and surface morphologies exhibit symmetric, half-penny shapes. Taking the elastoplasticity of film and substrate into account, a three-dimensional finite element model for an edge flaw with the finite size is established to simulate the evolution of energy release rates and phase angles in the process of interfacial buckling-driven delamination. The results show that delamination propagates along both the straight side and curved front. The mode II delamination plays a dominant role in the process with a straight side whilst the curved front experiences almost the pure mode I. Based on the results of finite element analysis, a numerical model is developed to evaluate the interfacial energy release rate, which is in the range of 250–315 J/m² with the corresponding phase angle from −41° to −66°. These results are in agreement with the available values determined by other testing methods, which confirms the effectiveness of the numerical model.     

干燥环境下表面黏附性能调控研究进展

实现黏附可控是解决微/纳机械产品黏附失效问题和发展先进黏附材料及新型微操作/微装配技术等的有效途径. 基于该研究背景,针对干燥不带电系统,对近年来发展的几类黏附调控方法进行了综述,从表面改形、材料改性及外场控制三方面介绍了织构、涂层/薄膜和复合材料、速度、温度、外力和磁场在黏附调控方面的研究进展,分析和总结了各类方法的黏附调控机理、关键影响因素和特点,并指出了应用领域,介绍了多手段复合调控黏附方法的最新研究成果. 最后,探讨了当前黏附调控方面存在的问题和未来可能的发展方向.      

用侧向力显微镜对不同非晶态GeSbTe薄膜的摩擦性能研究

采用侧向力显微镜研究了磁控溅射方法制备的GeSbTe薄膜在大气环境中的纳米级摩擦性能,考虑了相对湿度、扫描速度及表面粗糙度对其摩擦性能的影响,对比不同成分的GeSbTe薄膜的摩擦特性.结果表明:在相对湿度较大时,扫描速度对针尖和GeSbTe薄膜之间的摩擦力影响很大;在其它条件相同、外加载荷较大时,同一载荷下的摩擦力与表面粗糙度呈线性关系,但在外加载荷较小的情况下,二者呈现非线性变化规律;相对湿度对Ge2Sb2Te5薄膜和针尖的粘附力影响较GeSb2Te4薄膜弱,且粘附力使得摩擦系数减小;在同一相对湿度下,由于薄膜成分的变化导致硬度不同,其对薄膜的摩擦性能也有一定影响.