A Zener–Stroh crack at the interface of a thin film bonded to a substrate

A Zener–Stroh crack can nucleate at the interface of a multi-layered structure when a dislocation pileup is stopped by the interface which works as an obstacle. During the entire fracture procedure of a crack, Zener–Stroh crack mechanism controls the initial stage, or the first phase of crack initiation and propagation. In our current research, stress investigation on a Zener–Stroh crack initiated at the interface of a thin film bonded to a half plane substrate has been carried out. With the application of dislocation-based fracture mechanics, the micro crack is simulated by the distributed dislocations along the crack line. To eliminate the contradictory oscillation phenomenon for the stress field near the interfacial crack tip, a contact zone behind the crack tip is introduced. The physical problem is thus formulated into a set of non-linear singular integral equations. Through careful examination of the crack singularities at the crack tips for different configurations, the formulated integral equations are solved with numerical methods developed in our research. The contact zone length, the stress fields near the crack tip and the stress intensity factors of the crack are evaluated accordingly. Numerical examples based on practical engineering structures are provided to discuss the influence of the key parameters, such as the thickness of the film, and the Dundurs constants, on the fracture behaviour of the crack.     

Perturbation method for the solution of a Zener–Stroh crack with a slightly curved configuration

This paper investigates the Zener–Stroh crack with curved configuration in plane elasticity. A singular integral equation is suggested to solve the problem. Formulae for evaluating the SIFs and T-stress at the crack tip are suggested. If the curve configuration is a product of a small parameter and a quadratic function, a perturbation method based on the singular integral equation is suggested. In the method, the singular integral equation can be expanded into a series with respect to the small parameter. Therefore, many singular integral equations can be separated from the same power order for the small parameter. These singular integral equations can be solved successively. The solution of the successive singular integral equations will provide results for stress intensity factors and T-stress at the crack tip. It is found that the behaviors for the solution of SIFs and T-stress in the Zener–Stroh crack and the Griffith crack are quite different. This can be seen from the presented comparison results.     

On the fracture behavior of a Zener–Stroh crack with plastic zone correction in three-phase cylindrical composite material

With crack tip plastic zone correction, stress investigation on the fracture behavior of a Zener–Stroh crack in three-phase composite was carried out. A Zener–Stroh crack (in the matrix phase) is near a circular inclusion, with the three-phase cylindrical composite model used to represent the composite material. In the solution procedure, the crack is simulated as a continuous distribution of edge dislocations. The Dugdale model of small scale yielding is used to introduce a thin strip of yielded plastic zone each crack tip. The physical problem is formulated into a set of singular integral equations, using the solution for a three-phase model with a single dislocation in the matrix phase as the Green’s function. The singular integral equations are solved numerically for the plastic zone sizes and crack tip opening displacements using Erdogan and Gupta’s method with some iterative numerical procedures.     

An interfacial arc-shaped Zener–Stroh crack due to inclusion–matrix debonding in composites

Stress analysis has been carried out for a curved interfacial Zener–Stroh crack between a circular inclusion and an infinite matrix due to interface debonding in a composite. Using the distributed dislocation technique, the physical problem is formulated into singular integral equations of the 2nd kind. With the Jacobi polynomials and Gauss-Legendre integration methods, the integral equations are discretized and solved numerically. The stress intensity factors and energy release rates of the curved crack are evaluated accordingly. In the numerical examples, the effects of half debonding angle, the Dundurs’ constants, and the loading ratio ${{b_{x}^{T}}/{b_{y}^{T}}}$ on the stress intensity factors and the energy release rates are analyzed in detail. It is found that the stress intensity factors are greatly affected by the half debonding angle, the Dundurs’ constant β and the loading ratio ${{b_{x}^{T}}/{b_{y}^{T}}}$ , while the influence of Dundurs’ constant α is relatively small especially when the loading ratio is close to zero.     

Cooperative effects at the interface of nanocrystalline metal–organic frameworks

Controlling the chemistry at the interface of nanocrystalline solids has been a challenge and an important goal to realize desired properties. Integrating two different types of materials has the potential to yield new functions resulting from cooperative effects between the two constituents. Metal–organic frameworks (MOFs) are unique in that they are constructed by linking inorganic units with organic linkers where the building units can be varied nearly at will. This flexibility has made MOFs ideal materials for the design of functional entities at interfaces and hence allowing control of properties. This review highlights the strategies employed to access synergistic functionality at the interface of nanocrystalline MOFs (nMOFs) and inorganic nanocrystals (NCs).

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Characteristic times of oxygen mass transfer at the liquid metal–vapour interface

The interactions of liquid metals and alloys with the environment mostly depends on the thermodynamic properties of the liquid surface. In fact, the surface tension is strongly influenced by the presence in the surrounding atmosphere of reactive gases through solution, adsorption mechanisms and/or surface reactions. In particular, oxygen, which shows a high surface activity towards a large number of metallic systems, is the most important contaminant of liquid metals and alloys.Theoretical approaches for estimating the oxygen mass transfer at the liquid–vapour interface under inert atmosphere and vacuum have been developed already in order to relate the observed physical properties to the real surface composition data.In the present work a model of the interfacial transport of a liquid metal–oxygen system under Knudsen conditions that foresees the temporal evolution of the interfacial composition is presented. The diffusion characteristic times for reaching steady-state conditions are evaluated in order to define two system sizes depending on the different oxygen transport mechanisms in the liquid phase.An experimental study of the interface evolution is at present under way and preliminary results show a satisfactory agreement with theoretical studies.     

Monolayer studies of sugar- and nucleoside-terminated dendrimers at the air–water interface

Sugar- and adenosine-terminated dendrimers, [1,2-o-Isopropylideneribosyl-(G₁-12acid), -(G₂-36acid)] and [Adenosyl-(G₁-12acid), -(G₂-36acid)], were synthesized using Newkome's dendrimer synthetic method. Langmuir and Langmuir–Blodgett (LB) monolayers of these dendrimers have been constructed and characterized at the air–water interface and on solid substrates by measuring surface pressure–molecular area (Π–A) isotherms, atomic force microscopy (AFM), ellipsometry and contact angle measurement. Π–A isotherms and AFM images showed that these dendrimers formed stable and homogeneous monolayers without aggregation on pure water surface. The first and second generation of sugar-terminated dendrimers show molecular areas of 647 and 1359 Ų, respectively. Ellipsometry measurement indicates that the thickness of both the first and the second generation of sugar-terminated dendrimers were about 10 Å. This reflects a flat orientation of both molecules at the air–water interface. On the other hand, the first generation of adenosine-terminated dendrimer shows an area of 105.6 Ų per molecule with a thickness of 16 Å, and for the second generation, the area was 738.4 Ų with a thickness of 27 Å. These results suggested that adenosine-terminated dendrimers maintain a spherical form at the air–water interface. It was found that small difference in the structure of thymine and uracil in the subphase critically affects the interaction of the molecules and conformation of the dendrimers at the interface.     

Frictional stresses at the disc–jaw interface during the standardized execution of the Brazilian disc test

An attempt to more accurately describe the boundary conditions of the standardized Brazilian disc test is presented. Specifically addressed is the problem of quantitatively relating the radial pressure with the tangential (frictional) stresses generated at the disc–jaw interface according to a physically acceptable law. A novel approach is proposed based on the notion that friction is directly related to the mismatch between the tangential components of displacement of the disc and jaw along their common interface due to the different deformability of the two materials. The surface displacements in both jaw and disc are determined using the complex potentials method, and the difference between their tangential components along the common contact arc is calculated. This difference in combination with the radial contact pressure tends to generate relative lateral displacements between the disc and jaw that are counterbalanced by frictional forces. The distribution of friction stresses along the contact rim obtained from the present approach fulfils all physical and intuitive imposed conditions. In addition, it is strongly skewed, attaining its maximum value at two-thirds distance from the centre of the contact arc, in good agreement with the earlier results based on a completely different approach.     

Physicochemical interaction at the MnSi1.71–1.75/Mo interface

Diffusion processes at the interface between higher manganese silicide (HMS) MnSi_1.71–1.75 and Mo at elevated temperatures have been studied by microstructural analysis and X-ray microanalysis. The results demonstrate the formation of a reaction diffusion zone at the HMS/metal interface. The compositions of the phases identified in intermediate layers are consistent with phase equilibria in the ternary system Mn-Mo-Si, and their electrical and thermal conductivity is high enough not to create an energy barrier in the contact zone with the semiconductor. The thermal expansion mismatch between the phases in contact may degrade the bonding between the layers.     

Infrared nanoscopy of dirac plasmons at the graphene-SiO₂ interface

We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO(2) substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage.     

Textured mullite at muscovite–kaolinite interface

Mullite crystallization was carried out by the inter-reaction of alternate layers of muscovite and kaolinite minerals. The nucleation and growth of mullite anisotropic crystals take place along the muscovite plane and specific structural relationships are observed, which confirm a topotactic effect with the high temperature form of muscovite. The [001]_mull axis is oriented parallel to [010]_musc, [310]_musc and axes. The mullite orientation is fully completed in a temperature range between the ternary eutectic at 985 °C and the ternary transition point at 1140 °C, of the SiO₂–Al₂O₃–K₂O system, which strongly suggests an influence of a small quantity of liquid phase at the interface. Along the kaolinite–muscovite interface, the realisation of highly textured ceramics can be achieved.     

BEM analysis of crack onset and propagation along fiber–matrix interface under transverse tension using a linear elastic–brittle interface model

The behavior of the fiber–matrix interface under transverse tension is studied by means of a new linear elastic–brittle interface model. Similar models, also called weak or imperfect interface models, are frequently applied to describe the behavior of adhesively bonded joints. The interface is modeled by a continuous distribution of linear-elastic springs which simulates the presence of a thin adhesive layer (interphase). In the present work a new linear elastic–brittle constitutive law for the continuous distribution of springs is introduced. In this law the normal and tangential stresses across the undamaged interface are, respectively, proportional to the relative normal and tangential displacements. This model not only allows for the study of crack growth but also for the study of crack onset. An important feature of this law is that it takes into account the variation of the fracture toughness with the fracture mode mixity of a crack growing along the interface between bonded solids, in agreement with previous experimental results. The present linear elastic–brittle interface model is implemented in a 2D boundary element method (BEM) code to carry out micromechanical analysis of the fiber–matrix interface failure in fiber-reinforced composite materials. It is considered that the behavior of the fiber–matrix interphase can be modeled by the present model although, strictly speaking, there is usually no intermediate material between fiber and matrix. A linear-elastic isotropic behavior of both fiber and matrix is assumed, the fiber being stiffer than the matrix. The failure mechanism of an isolated fiber under transverse tension, i.e., the onset and growth of the fiber–matrix interface crack, is studied. The present model shows that failure along the interface initiates with an abrupt onset of a partial debonding between the fiber and the matrix, caused by presence of the maximum radial stress at the interface, and this debonding further develops as a crack growing along the interface.     

Effect of bovine serum albumin on the functionality and structure of catanionic surfactant at air–buffer interface

Interaction of bovine serum albumin (BSA) with the solvent spread monolayer of a catanionic surfactant, octadecyltrimethylammonium dodecylsulfate, (C₁₈TA⁺DS^?) at the air–buffer interface was investigated by measuring the surface pressure with time and change in surface area. Dipalmitoylphosphatidylcholine (DPPC) was used as reference. Kinetics of BSA desorption from the interface to the buffer subphase, that of C₁₈TA⁺DS^? and DPPC through their interaction with BSA, were also studied at different BSA concentrations (in the subphase) and surface pressures. Surface pressure (π)–area (A) isotherms (at pH = 5.4, μ = 0.01, T = 298 K) revealed that the coacervate/DPPC monolayer becomes expanded in the presence of BSA at low π while their protein bound species are released into the subphase at high π. Film morphology, studied by epifluorescence microscopy (EFM) and atomic force microscopy (AFM), reveals that the sizes of the domains of both DPPC and coacervate decrease in the presence of BSA. Presence of BSA in the coacervate and DPPC monolayer was supported from AFM data analysis.     

Determination of the thickness of the surface microlayer from which aerosols are formed by burst of gas bubbles at the liquid–gas interface

The surface diameters of gas bubbles at the liquid–gas interface whose burst leads to the formation of aerosol from a thin surface microlayer of thickness 1 μm and less have been determined experimentally. Precisely the anomalous concentrations of such a microlayer are responsible for the fractionation of substances in the process of ocean–atmosphere exchange.     

A study of the heat-removal process at the semiconductor–ceramics interface in solar cells by the laser thermal-wave method

The influence of the solder layer between a semiconductor solar cell and heat-removing ceramics on the nonstationary heat-transfer processes has been investigated by the laser thermal-wave method. A theoretical model taking into account the presence of additional thermal resistance and thermal capacitance at the soldered junction is proposed. Different soldering modes are considered. It is shown that the laser thermal- wave methods within the developed model allow one to correctly estimate the thermophysical properties of multilayer structures.