Interface Between an Old Concrete and a Bonded Overlay: Debonding Mechanism

The ageing of concrete structures creates the need for their repair. The thin bonded overlay technique is widely used; it is particularly suitable for the repair of large concrete areas. It is appropriate for slabs on grade (mainly industrial floors), pavements, bridge decks, walls and tunnels. Toppings and linings are similar applications. The aim of the overlay may be to smooth a damaged surface, and/or to improve the mechanical capacity of a structure by increasing its thickness, or to provide additional cover for corrosion protection.The durability of such repairs or overlays depends on the durability of their bond with the base structure; it is usually the critical aspect. Work, carried out in Laboratoire Matériaux et Durabilité des Constructions (Laboratory for building Materials and Constructions Durability) in Toulouse, France, is part of a larger programme started in 1990. The programme objective is to achieve a thorough knowledge of the debonding mechanisms of an overlay. Design rules and practical recommendations eliminating or drastically reducing durability hazards are expected to be developed. The work reported here focuses on the debonding propagation along an interface, notably the major influence of the interlocking between the two faces of the debonding interface. The study relies on finite elements modelling and on the comparison with experiments.Having evidenced the major role of interlocking in the example of a crack propagation, the paper focuses on the actual case of an interface. Debonding propagates in mixed mode, mode I combined with mode II, bringing an extra degree of complexity. Beyond the problem of the mixed mode, an important issue is how interlocking changes while debonding propagates. Indeed, mode I debonding opening damages interlocking for both mode I and mode II. A mode II slip has the same coupled effect on interlocking. A very significant problem is taking into account the coupling of mode I and II displacements to evaluate the actual value of the interlocking at any step of the propagation.The involved parameters have been identified and a method is proposed to take into account the coupling. The comparison with experimental results is promising. This research opens a new approach on the mechanism of the propagation of a debonding along an interface. The next step will consider evolution of the interlocking in the case of fatigue loading.     

First principles simulation of a ceramic /Metal interface with misfit

The relaxed atomic structure of a model ceramic/metal interface, 222MgO/Cu, is simulated, including lattice constant mismatch, using first principles local-density functional theory plane wave pseudopotential methods. The 399-atom computational unit cell contains 36 O and 49 Cu atoms per layer in accordance with the 7/6 ratio of MgO to Cu lattice constants. The atomic layers on both sides of the interface warp to optimize the local bonding. The interface adhesive energy is calculated. The interface electronic structure is found to vary appreciably with the local environment.     

Multi-scale plasma simulation by the interlocking of magnetohydrodynamic model and particle-in-cell kinetic model

Many kinds of simulation models have been developed to understand the complex plasma systems. However, these simulation models have been separately performed because the fundamental assumption of each model is different and restricts the physical processes in each spatial and temporal scales. On the other hand, it is well known that the interactions among the multiple scales may play crucial roles in the plasma phenomena (e.g. magnetic reconnection, collisionless shock), where the kinetic processes in the micro-scale may interact with the global structure in the fluid dynamics. To take self-consistently into account such multi-scale phenomena, we have developed a new simulation model by directly interlocking the fluid simulation of the magnetohyrdodynamics (MHD) model and the kinetic simulation of the particle-in-cell (PIC) model. The PIC domain is embedded in a small part of MHD domain. The both simulations are performed simultaneously in each domain and the bounded data are frequently exchanged each other to keep the consistency between the models. We have applied our new interlocked simulation to Alfvén wave propagation problem as a benchmark test and confirmed that the waves can propagate smoothly through the boundaries of each domain.     

Charge interaction in layered systems with spatial dispersion

The potential electrostatic energy of a charge near the surface of a metal with a metal or a dielectric coating (adsorbate), on the interface between metal (semimetal) and insulator (electrolyte) and in layered thin-film sandwich-type systems (MIS structures) has been calculated. The influence of the metal and the dielectric epitaxial coatings of the metal surface upon the interaction of charges is investigated. Taking into account the spatial dispersion effects, it is shown that in thin films surrounded by a medium with a large dielectric constant, the Coulomb repulsion between electrons decreases.     

Effect of Er:YAG laser energy on the morphology of enamel/adhesive system interface

The aim of this study was to evaluate in vitro the influence of Er:YAG laser energy variation to cavity preparation on the morphology of enamel/adhesive system interface, using SEM. Eighteen molars were used and the buccal surfaces were flattened without dentine exposure. The specimens were randomly assigned to two groups, according to the adhesive system (conventional total-etching or self-etching), and each group was divided into three subgroups (bur carbide in turbine of high rotation, Er:YAG laser 250 mJ/4 Hz and Er:YAG laser 300 mJ/4 Hz) containing six teeth each. The enamel/adhesive system interface was serially sectioned and prepared for SEM. The Er:YAG laser, in general, produced a more irregular adhesive interface than the control group. For Er:YAG laser 250 mJ there was formation of a more regular hybrid layer with good tag formation, mainly in the total-etching system. However, Er:YAG laser 300 mJ showed a more irregular interface with amorphous enamel and fused areas, for both adhesive systems. It was concluded that cavity preparation with Er:YAG laser influenced on the morphology of enamel/adhesive system interface and the tissual alterations were more evident when the energy was increased.     

Multi-scale plasma simulation by the interlocking of magnetohydrodynamic model and particle-in-cell kinetic model

Many kinds of simulation models have been developed to understand the complex plasma systems. However, these simulation models have been separately performed because the fundamental assumption of each model is different and restricts the physical processes in each spatial and temporal scales. On the other hand, it is well known that the interactions among the multiple scales may play crucial roles in the plasma phenomena (e.g. magnetic reconnection, collisionless shock), where the kinetic processes in the micro-scale may interact with the global structure in the fluid dynamics. To take self-consistently into account such multi-scale phenomena, we have developed a new simulation model by directly interlocking the fluid simulation of the magnetohyrdodynamics (MHD) model and the kinetic simulation of the particle-in-cell (PIC) model. The PIC domain is embedded in a small part of MHD domain. The both simulations are performed simultaneously in each domain and the bounded data are frequently exchanged each other to keep the consistency between the models. We have applied our new interlocked simulation to Alfvén wave propagation problem as a benchmark test and confirmed that the waves can propagate smoothly through the boundaries of each domain.     

Co元素对硬质合金基底金刚石涂层膜基界面结合强度的影响

采用基于密度泛函理论的第一性原理平面波赝势方法, 研究了硬质合金刀具基底黏结相Co元素对金刚石涂层膜基界面结合强度的影响机理. 借助Materials Studio软件建立了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型, 采用CASTEP仿真软件计算了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型的最优稳定结构. 通过仿真计算, 获得了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型的界面结合能、电荷密度图及Mulliken重叠布居数. 经对比分析后发现, 硬质合金基底中磁性元素Co的存在能转移金刚石涂层膜基界面处W元素及C元素的电荷, 从而使膜基界面处的原子因失电荷而相斥, 这直接导致了金刚石涂层膜基界面间距变大, 使得金刚石涂层膜基界面结合能降低.     

An exact result for bimetallic interface energies

An exact result is derived for the interface energy of a jellium interface. An approximate model of the bimetallic interface is then used to find approximate values of the adhesive energies of jellium interfaces and specific metal pairs.     

金属-半导体超晶格中界面电荷的生成机理

采用LMTO ASA能带计算方法，研究(Si₂)₃ (2Al) ₆ (001),(Ge₂)₃ (2Al) ₆ (001),(Ge₂)₃ (2Au) ₆ (001)和(Ge₂)₃ (2Ag) ₆ (001)超晶格中半导体界面电荷Qss的生成机理，结 关键词： Schottky势垒 界面电荷     

Theoretical assessment of the errors involved in ultrasonic location and sizing of molten weld pools

Ultrasonic transit times may be used to locate the interface between molten weld metal and parent plate as a weld is formed. These transit times will lead to errors in interpretation of the location of the weld interface if account is not taken of the variation of ultrasonic velocity with temperature. We assess the magnitude of these errors using a theoretical model based on the Green's function to obtain the temperature distribution at any time and then convert the temperatures into elastic constants through empirical fits to high temperature data. A ray tracing method and a semi-analytical approach are used to estimate the effects of the changes in elastic constants on the ray paths and transit times. From these theoretical predictions we conclude that the location errors incurred by assuming ultrasonic velocities appropriate to cold metal are less than 0.5 mm for a 3.5 mm radius weld in austenitic steel or in iron. Experimental values tend to be larger than this, possibly suggesting that the solid-liquid interface is not as perfect as in the theoretical model. Under all of the conditions investigated, predicted errors are smaller with compression waves than with shear waves.     

Fracture Mechanics Studies of Adhesion in Biological Systems

A fracture mechanics based methodology for quantifying adhesive interactions between soft solids, or between a soft solid and a rigid substrate, is reviewed. An emphasis is placed on the application of these techniques to the characterization of adhesive interactions in biological systems. Results from experiments involving the adhesion of gelatin hydrogels to hydrophilic and hydrophobic substrates are described as an illustration of the application of these methods. In these experiments a hemispherical gelatin cap is brought into contact with a flat surface. Separation of the two materials is described in terms of crack propagation along the gelatin/substrate interface. Simultaneous measurements of the applied load, the resulting displacement, and the contact area between the two materials enable us to determine the elastic modulus of the cap, in addition to the crack driving force, or energy release rate. The adhesive behavior of the interface is quantified by the relationship between the energy release rate and the crack velocity. Analogies are made to information obtained from contact angle measurements, and from measurements made with the Israelachvili surface forces apparatus.     

Prestressed FRP and interface slip effect on interfacial stresses analysis: the new FRP sheets rigidity model

This paper presents an improved bi-material beam theory with adhesive interface and the new prestressed-fiber reinforced polymer (FRP) – model, which has been applied to the study the problem of interfacial stresses. This work explicitly considers the interfacial slip effect on the structural performance by including both the effect of adherend shear deformations and the fiber volume fraction of the prestressed laminates. This new method needs only one differential equation to determine both shear and normal interfacial stress, which is one aspect that has not been taken into account by the previous studies in the literature. A parametrical study is carried out to show the effects of some design variables, e.g., stiffness and thickness of adhesive layer and FRP plate.     

铁磁绝缘层对正常金属/铁磁绝缘层/正常金属/p波超导结隧道谱的影响

在正常金属/铁磁绝缘层/正常金属/自旋三重态p波超导隧道结中,考虑到铁磁绝缘层的磁散射和粗糙界面散射,运用Bogoliubov-de Gennes(BdG)方程和Blonder-Tinkham-Klapwijk(BTK)理论模型,研究了铁磁绝缘层对隧道结微分电导的影响.研究表明:(1)对于px波,粗糙界面散射和磁散射都能使零偏压电导峰变低,能隙处凹陷升高;随着磁散射的增强,谱线的尖锐峰消失,宽峰逐渐变为凹陷;(2)对于py波,粗糙界面散射和磁散射都能使零能凹陷上移,能隙峰变低,随着粗糙界面散射的增强,两能隙峰间距减小;随着中间正常金属层厚度的增加,能隙内电导随外加偏压呈现振荡行为,能隙外电导仅与普通势垒有关;(3)对于px+ipy波,随着粗糙界面散射的增强,零偏压电导峰被压低,双凹陷处的值逐渐增大为小的能隙峰,而磁散射并不改变谱线中各凹陷处的电导值.     

Nonlinear evolution equations for surface plasmons for nano-focusing at a Kerr/metallic interface and tapered waveguide

Maxwell's equations for a metallic and nonlinear Kerr interface waveguide at the nanoscale can be approximated to a (1+1) D Nonlinear Schrodinger type model equation (NLSE) with appropriate assumptions and approximations. Theoretically, without losses or perturbations spatial plasmon solitons profiles are easily produced. However, with losses, the amplitude or beam profile is no longer stationary and adiabatic parameters have to be considered to understand propagation. For this model, adiabatic parameters are calculated considering losses resulting in linear differential coupled integral equations with constant definite integral coefficients not dependent on the transverse and longitudinal coordinates. Furthermore, by considering another configuration, a waveguide that is an M–NL–M (metal–nonlinear Kerr–metal) that tapers, the tapering can balance the loss experienced at a non-tapered metal/nonlinear Kerr interface causing attenuation of the beam profile, so these spatial plasmon solitons can be produced. In this paper taking into consideration the (1+1)D NLSE model for a tapered waveguide, we derive a one soliton solution based on He's Semi-Inverse Variational Principle (HPV).     

Optical properties of gold metal clusters: A time-dependent local-density-approximation investigation

The optical response of free and matrix-embedded gold metal clusters Au_N is investigated in the framework of the time-dependent local-density-approximation (TDLDA). The characteristics of the surface plasmon resonance are carefully analyzed as a function of the model parameters and the particle radius. The strong influence of the frequency-dependence of the 5d core-electron dielectric function in the vicinity of the interband threshold is emphasized. The size evolution of the Mie-frequency in free gold clusters exhibits a noticeable blue-shift trend as the particle size decreases, much stronger than in silver clusters. The width and shape of the resonance, essentially ruled by the decay via the interband transitions, are found closely correlated to the imaginary component of the core-electron dielectric function. In presence of a surrounding matrix the blue-shift trend is largely rubbed out. Agreement with recent experimental results on size-selected gold clusters embedded in an alumina matrix may be achieved by taking into account the porosity effects at the metal/matrix interface. The comparison with the predictions of classical models is also provided. Received: 9 March 1998 / Revised: 5 June 1998 / Accepted: 3 July 1998     

金属/有机界面势垒对单层有机电致发光器件发光效率的影响

基于高场下电荷的注入过程及激子的解离和复合过程,建立了单层有机发光器件电致发光(EL)效率的理论模型。计算表明：(1)当金属／有机界面势垒高度大于0．3eV时,器件的EL效率很低,降低金属／有机界面势垒可以显著提高器件的EL效率;(2)在较低偏压下,注入过程对器件的电致发光效率起主要作用,但在高偏压下复合过程起支配作用。这一模型可以阐明注入和复合过程对有机发光器件EL效率的影响,对选择发光材料、优化器件结构和提高器件EL效率具有指导意义。     

Theoretical and experimental research on nonlinear spring models of a bonding interface

<正>The nonlinear boundary conditions on a bonding interface between two solids of a longitudinal or shear horizontal(SH) wave under normal incidence were explored.By applying the second-order perturbation method,the nonlinear spring models are rigorously developed in the limit of small thickness to wavelength ratio.Numerical results agree well with the exact solutions obtained by continuous boundary conditions.The nonlinear spring model for longitudinal wave is verified by measuring the nonlinearity of a wedge-shaped bonding structure of steel or aluminum substrates.The experimental results reveal that the above model is rather accurate and as the impedance ratio of adherend to adhesive increases,the model becomes more accurate.     

Interfacial electrostatic phenomena in polyimide Langmuir–Blodgett films in electron tunneling devices

Nanometric electrostatic space charges exist at the metal/molecular film interface due to the displacement of excessive electrons from metal to molecular films. As a result, surface potential is built across the films on metal. The distributions of the displaced electrons and the electronic density of states in films can be determined using the surface potential built. The current–voltage characteristic of tunneling device using polyimide Langmuir–Blodgett films is discussed with taking into account the space charge.     

Investigation of adhesive–dentin interfaces using Raman microspectroscopy and small angle X‐ray scattering

Human dentin specimens were treated with two different etch‐and‐rinse adhesives, Single Bond 2 (SB2) and Prime & Bond NT (PBNT), and two composite resins, TPH and P60. Cross‐sectional samples, approximately 1 mm thick, were analyzed with Raman line mapping and imaging across the dentin–adhesive–composite interface. The integrated intensities of selected bands associated with adhesive, organic material, composite and hydroxyapatite of dentin were calculated to determine the distribution of adhesive infiltration into demineralized dentin. The results were compared with the enamel‐adhesive composite interface. The demineralized zone was smaller in the enamel‐adhesive interface than in the dentin–adhesive interface. The region of collagen‐adhesive crosslinking was wider in the PBNT adhesive than in the SB2 adhesive. However, a gap at the dentin–PBNT composite interface, which was not observed at the dentin–SB2 composite interface, might compromise the dentin–restoration bond. K‐means cluster analysis of the Raman images confirmed the findings. The ultrastructure of the dentin–resin interface was studied using scanning electron microscopy. Small‐angle X‐ray scattering was also applied to reveal and quantify fine‐scale structural features. SB2 adhesive was found to diffuse more into demineralized dentin along with greater nanosized aggregations in the hybrid layer. Copyright © 2011 John Wiley & Sons, Ltd.