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This paper presents an analytical description of frictional contact hysteresis behavior between two flat rough surfaces in partial and gross slip. Couplings between shear and normal forces in the contact interface are included by considering spherical asperities in oblique contact. In the oblique contact, the relation between shear and normal interface forces is determined using asperities tangential friction forces and Hertzian normal contact forces. The Mindlin elastic spherical contact solution is modified in this study using the rod contact model leading to higher maximum tangential friction force and pre-slip limit compared to the classical solution. Based on the proposed modified Mindlin spherical contact solution, this paper develops a modified two rough interface (MTRI) model using the multi-asperity contact theory. The MTRI model provides accurate estimates of the contact interface behavior in an explicit form by including the oblique contact effects and the rod solution. In obtaining the hysteresis behavior of two flat rough interface contact, the contact regions associated with the pre-slip and sliding state at different tangential loading phases, i.e., virgin loading, unloading, and reloading, are determined. Then by the integration of pairs of asperities contact forces over the contacting regions at each state, restoring forces of contacting surfaces are obtained. The proposed MTRI model predictions are validated against experimental observations and found to be in good agreement.

For solid-fluid interaction, one of the phase-density equations in diffuse interface models is degenerated to a “0=0” equation when the volume fraction of a certain phase takes the value of zero or unity. This is because the conservative variables in phase-density equations include volume fractions. The degeneracy can be avoided by adding an artificial quantity of another material into the pure phase. However, nonphysical waves, such as shear waves in fluids, are introduced by the artificial treatment. In this paper, a transport diffuse interface model, which is able to treat zero/unity volume fractions, is presented for solid-fluid interaction. In the proposed model, a new formulation for phase densities is derived, which is unrelated to volume fractions. Consequently, the new model is able to handle zero/unity volume fractions, and nonphysical waves caused by artificial volume fractions are prevented. One-dimensional and two-dimensional numerical tests demonstrate that more accurate results can be obtained by the proposed model.

A dynamic magneto-viscoelastic interface model is proposed to study the effective magneto-mechanical responses of magnetorheological nanocomposites filled with carbon nanotubes. It is incorporated with the fundamental micromechanics principles, microstructural magnetic and mechanical coupling, and computational homogenization procedures. The field-dependent effective dynamic stiffness and damping of randomly dispersed, chain-structured nanocomposites are investigated with the consideration of imperfect interfacial conditions among nanofillers, micro-particles and the matrix. Comparisons are performed between the model prediction and experimental data for a specific type of Fe particle-reinforced elastomer nanocomposites filled with multi-walled carbon nanotubes to demonstrate the capability of the proposed model framework.

The performance of film cooling is influenced by many parameters, and the nonuniform flow caused by the internal cooling system is found to largely affect the film cooling, which further complicates the in-hole flow and draws new difficulties in predicting the cooling performance. In this study, we find a very interesting phenomenon that there always exists an in-hole interface, on which distributions of many parameters, including the velocity and kinetic energy, are seldom affected by the mainstream. The existence of this specific interface can be observed for both cylindrical and shaped film cooling holes under most operating conditions. The theoretical analysis of this interface is conducted in this study based on the characteristic decomposition of the Navier–Stokes equation, and this interface is named as the characteristic interface. Theoretical analysis and numerical observations suggest the film cooling system can be simplified to two weakly coupled regions separated by this interface. It also explains why existing source term models for film cooling may fail. Based on these findings, a new prediction model is developed, which uses the convolutional neural networks (CNN) model to predict the boundary conditions on the characteristic interface. The new model outperforms existing source term models and yields similar accuracy as full-mesh computational fluid dynamics (CFD), while reducing the computational cost by one order of magnitude. This model is further evaluated in large eddy simulation (LES), showing moderate success. To sum up, the current work reports the characteristic interface phenomenon in the film cooling hole, based on which a new and efficient prediction model is developed and verified.

The dynamics of a thin layer of liquid, between a flat solid substrate and an infinitely-thick layer of saturated vapor, is examined. The liquid and vapor are two phases of the same fluid, governed by the diffuse-interface model. The substrate is maintained at a fixed temperature, but in the bulk of the fluid the temperature is allowed to vary. The slope $\varepsilon$ of the liquid/vapor interface is assumed to be small, as is the ratio of its thickness to that of the film. Three asymptotic regimes are identified, depending on the vapor-to-liquid density ratio $\rho_{v}/\rho_{l}$. If $\rho_{v}/\rho_{l}\sim1$ (which implies that the temperature is comparable, but not necessarily close, to the critical value), the evolution of the interface is driven by the vertical flow due to liquid/vapor phase transition, with the horizontal flow being negligible. In the limit $\rho_{v}/\rho_{l}\rightarrow0$, it is the other way around, and there exists an intermediate regime, $\rho_{v}/\rho_{l}\sim\varepsilon^{4/3}$, where the two effects are of the same order. Only the $\rho_{v}/\rho_{l}\rightarrow0$ limit is mathematically similar to the case of incompressible (Navier--Stokes) liquids, whereas the asymptotic equations governing the other two regimes are of different types.

A Diffuse Interface Model (DIM) is employed to model droplet impact on a heated solid surface. The DIM uses an especially constructed solid wall boundary condition which enables simulations with different wetting conditions of the solid surface. The model is also extended to include the effects of surface roughness on the behavior of the contact line dynamics. Multiple simulations are carried out to demonstrate the capabilities of the presented model. The simulation results demonstrate the influence of the wetting properties of the solid, with a higher cooling rate for hydrophilic than for hydrophobic wetting conditions. Surface roughness of the solid surface increases the cooling rate of the solid by enhancing the heat transfer between solid and fluid.

The onset of frictional motion is mediated by the dynamic propagation of a rupture front, analogous to a shear crack. The rupture front nucleates quasi-statically in a localized region of the frictional interface and slowly increases in size. When it reaches a critical nucleation length it becomes unstable, propagates dynamically and eventually breaks the entire interface, leading to macroscopic sliding. The nucleation process is particularly important because it determines the stress level at which the frictional interface fails, and therefore, the macroscopic friction strength. However, the mechanisms governing nucleation of frictional rupture fronts are still not well understood. Specifically, our knowledge of the nucleation process along a heterogeneous interface remains incomplete. Here, we study the nucleation of localized slip patches on linear slip-weakening interfaces with deterministic and stochastic heterogeneous friction properties. Using numerical simulations, we analyze the process leading to a slip patch of critical size for systems with varying correlation lengths of the local friction strength. Our deterministic interface model reveals that the growth of the critical nucleation patch at interfaces with small correlation lengths is non smooth due to the coalescence of neighboring slip patches. Existing analytical solutions do not account for this effect, which leads to an overestimation of global interface strength. Conversely, when the correlation length is large, the growth of the slip patch is continuous and our simulations match the analytical solution. Furthermore, nucleation by coalescence is also observed on stochastic interfaces with small correlation length. In this case, the applied load for a given slip patch size is a random variable. We show that its expectation follows a logistic function, which allows us to predict the strength of the interface well before failure occurs. Our model and observations provide new understanding of the nucleation process and its effect on the static frictional strength., International Journal of Solids and Structures, 225, ISSN:0020-7683, ISSN:1879-2146

An interface model of homogenization was proposed, this model considers the influence of the inclusions size of the micrometre range on the elastic properties of composites. The appearance of surface strains and shear stresses at the interphase boundary is associated with the "sticking" of the matrix to the surface of the inclusions. The effective modulus of elasticity of a composite is the sum of two terms: a constant part in the form of a modulus of elasticity of a bulk material, and a variable part that is caused by a shift at the interphase boundary and depends on the particles size. Absolute of particles sizes were considered by introducing within the interfacial model empirical elasticity modulus of the composite with the one basic particle size. The results of the calculation are in good agreement with the experimental data for Young's modulus of polymer composites with spherical particles.

A novel constitutive framework suitable for material interfaces undergoing large deformations in a geometrically exact setting was developed in Ottosen et al. (2016). In contrast to previous works, it permits the description of arbitrary material anisotropies by fulfilling all fundamental balance laws in physics as well as the principle of material objectivity. This paper deals with an efficient finite element implementation of the aforementioned framework in terms of the natural basis vectors. To be more precise, a different, more compact and more direct derivation of this framework is outlined first. It relies on the variational structure of the underlying problem. Subsequently, the aforementioned finite element approximation is elaborated which is finally embedded into a computational homogenization scheme. This scheme allows the analysis of the influence of the novel interface model on the resulting macroscopic (effective) material response. It is shown by numerical examples that the interaction of bulk energies and interface energies leads, in a very natural manner, to a complex size effect. It includes the frequently observed “the smaller the stiffer” relation, but also the less often observed “the smaller the softer” relation. However, since the overall response is usually a superposition of such relations, the effective properties cannot generally be characterized by one of the aforementioned limiting relations.

This study focuses on the shear-friction behaviour of concrete interfaces (joints) with rubber between concrete segments or rings from the perspective of experiment and theoretical analysis. A number of direct shear concrete specimens with and without rubber cushions were tested under conditions of different normal loads. The shear test results of the concrete interfaces without rubber show that the slip or shear displacements can be divided into elastic and perfectly plastic phases. The post-peak shear strengths hold almost a constant with increasing shear slip, which can be described by the Coulomb frictional law. However, when concrete interface is pasted with rubber, the slip failure behaviour of the interfaces under pressure-shear loads is more appropriately characterized by hyperbolic failure criterion. The shear tests of the interfaces with rubber show that rubber materials significantly reduce the shear strength of the interfaces, which indicate that thin rubber can accommodate the mechanical response of the tunnel concrete lining, particularly by reducing the stress level of concrete segments surrounding joints due to the rubber material pasted to the joints. An elasto-plastic constitutive model for describing the three-dimensional mechanical behaviour of concrete joint with rubber is developed and also verified by means of the shear tests of concrete joints with rubber mentioned above. The predictions by the present interface model are well in agreement with the shear tests.

Publisher Copyright: © 2021 The Author(s) This paper presents a two-dimensional interface model for timber-concrete contacts, that has been developed based on the empirical observations from a set of friction tests and additional micromechanical assumptions. In tangential direction, the interface model accounts initial bonding and debonding between the surfaces, different static and kinetic friction as well as smooth transition between them, effects of load reversal, pressure-dependence in friction and sticking stiffness and slip softening over increasing cumulative slip. In normal direction, simple linear cohesive and pressure-overclosure behaviour is assumed. The model has been formulated in cohesive-frictional interface framework, coupling damage-based cohesive behaviour with elastoplasticity-based frictional behaviour. The model has been tested in various cases and verified by comparison on a set of 27 tests on timber-concrete contact pairs under cyclic loading with varying normal pressure and multiple different material pairs. The interface model is able to capture relevant parts of the experimentally observed tangential behaviour, indicating suitability to present timber-concrete interface behaviour under cyclic loading. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

A layer-substrate, or coating-substrate, interface can be mathematically formed by jointing a homogeneous half-space and a layer of another material or even the same material. The physical formation of the interface may be complex due to coating processing and material mismatching properties. In general, the coating and substrate may be imperfectly bonded to each other, and the their interface can be described by models of imperfect interfaces subjected to the dislocation-like, force-like, spring-like, and frictionlessly interfacial conditions. This paper presents a coupled dislocation-like and force-like interface model for the elastic fields caused by pressure and shear tractions applied on the surface of such a layer-substrate system. The model is solved analytically by employing the Papkovich–Neuber potentials, where six displacement and stress jumping coefficients are utilized to reflect the discontinuity at the interface. The derived analytical equations can be used as the basic solutions for solving contact problems involving a layer-substrate material system and an arbitrarily shaped indenter. The sliding contact of a spherical indenter and a layered flat is further investigated. The pressure, loading curve, as well as the stresses, for the system with different layers are analyzed with respect to different jumping coefficients.

We present a convex-splitting scheme for the fourth order parabolic equation derived from a diffuse interface model with Peng-Robinson equation of state for pure substance. The semi-implicit scheme is proven to be uniquely solvable, mass conservative, unconditionally energy stable andL∞convergent with the order of. The numerical results verify the effectiveness of the proposed algorithm and also show good agreement of the numerical solution with laboratory experimental results.

When a tensile brittle film is moderately bonded to elastic substrates interface can debond and exhibit complex debonding morphology after formation of a mud-crack pattern. The experimentally observed debonding morphology significantly depends on the film thickness and the mud-crack pattern. In this paper we propose a continuum approach to simulate the evolution of complex debonding front in the mud-crack film. This approach combines the phase field microelasticity model for multiple mud-like crack problem and the cohesive interface model for tracking arbitrary interface debonding front. Using the simulation, how the mud-crack pattern and the anisotropic stress lead to anisotropic interface debonding are revealed. The film thickness dependent debonding morphology observed in experiment is recovered and the mechanism of its formation is discussed based on fracture mechanics.

First-principle calculation is carried out on Al2O3(012)/SiC(310) interface model. It can be concluded from the electronic density and population analysis that Al-C and O-Si located at grain boundary primarily contribute to the interface bonding strength and creep resistance property. The electronic charges in grain boundaries and grains are compared with each other. And the valence electrons are found to be redistributed. The relationship of all kinds of chemical bonds in grains and grain boundary of the interface model is analyzed. Also the toughening mechanism of Al2O3/SiC multi-phase ceramic tool materials is explained in nano-scale.

The interface between constituents of a multiphase material exhibits properties different from those of the bulk and can lead to major alternation of the material response. Interface effects are particularly important for multiphase nano-materials where the area-to-volume ratio is significantly large. In this contribution, we study the influence of a degrading general interface. That is, we allow for the initiation and accumulation of damage on a generalized interface accounting for both jumps of the displacement and the traction across the interface. The applicability of the proposed framework is demonstrated through several numerical examples. We present a parametric study on the influence of a broad range of interface material parameters on the overall behavior of various microstructures subject to volumetric loading and unloading. The numerical results illustrate that the resistance along the interface plays a key role in the resulting damage mechanism and could potentially prevent the detachment of the inclusion from the matrix regardless of the resistance across the interface or bulk material parameters. This behavior is observed and shown for both two- and three-dimensional examples. Moreover, the size-effect due to the general interface model is examined and compared against other interface models. Finally, the influence of the boundary conditions on the effective response and damage initiation of several microstructures is studied.

The interface of the ternary boride hard cladding material consists of hard phase (Mo2FeB2) and bonding phase (α-Fe). In this paper, on the basis of the ideal interface model of Mo2FeB2 (100)/α-Fe (001) built with the molecular dynamics software, the Mo2FeB2 (100)/α-Fe (001) interface models with micro-cracks parallel with the interface, normal to the interface, and inclined to the interface have been built separately. The interface bonding energies of these four different interface models have been calculated, which shows that the interface model with the micro crack inclined to the interface has the biggest interface bonding energy, while the interface model with the micro crack parallel with the interface has the smallest bonding energy, the interface crack will be the most easily to propagate. The change rule of bonding energy of the interface model with the micro crack parallel with the interface with different lengths has been simulated and analyzed.

International audience; In this paper a spring-like micromechanical contact model is proposed, aiming to describe the mechanical behavior of two rough surfaces in no-sliding contact under a closure pressure. The contact region between two elastic bodies is described as a thin damaged interphase characterized by the occurrence of non-interacting penny-shaped cracks (internal cracks). By combining a homogenization approach and an asymptotic technique, tangential and normal equivalent contact stiffnesses are consistently derived. An analytical description of evolving contact and no-contact areas with respect to the closure pressure is also provided, resulting consistent with theoretical Hertz-based asymptotic predictions and in good agreement with available numerical estimates. Proposed model has been successfully validated through comparisons with some theoretical and experimental results available in literature, as well as with other well-established modeling approaches. Finally, the influence of main model parameters is addressed, proving also the model capability to catch the experimentally-observed dependence of the tangent-to-normal contact stiffness ratio on the closure pressure.

There have already been several interface models for the analyses of thin interfacial layers in bonded materials. To distinguish their corresponding advantages or limitations, a comparative study is carried out, and a new constitutive-based interface model is proposed. Through numerical examinations, the limitations of typical models are clarified. It is found that the new interface model is an efficient and accurate model, by which both the traction and the displacement jumps across the modelled interface with the thickness of zero are allowed, and the stresses within the interfacial layer can also be analyzed.

Interfacial tractions generated at the interface in two-layered nanobeams are studied through the stress-driven nonlocal theory of elasticity and an interface model. The model uses a layerwise description of the problem and satisfies the continuity conditions at the interface. The size-dependency are incorporated into formulation through a nonlocal constitutive law which defines the strain at each point as an integral convolution in terms of the stresses in all the points and a kernel. The Bernoulli-Euler beam theory is used separately for each layer to describe kinematic field, and to derive size-dependent system of coupled governing equations. The displacement components within the layers are derived and the interfacial tractions are obtained through the interfacial constitutive relations. Results are presented for the interfacial shear and normal tractions, exhibiting a different behavior at the nano-scale compared to those of the layered beams with large-scale dimensions including different maximum interfacial tractions and the location where maxima occur. A superior resistance of nanobeams against debondings and delaminations due to the interfacial normal tractions compared to that of the beams with large-scale dimensions is observed. The formulation and the understandings presented here are expected to stimulate further researches on multilayered nanobeams, including their interfacial fracture mechanics.

In the present study a method is presented for simulations of droplet collisions in three spatial dimensions under non-isothermal conditions using a Diffuse Interface Model, which is based on the non-isothermal Navier–Stokes–Korteweg equations combined with the Van der Waals equation of state. This particular Diffuse Interface Model can only be used for a single component fluid and the temperature needs to be close to the critical point of the fluid to prevent the interfacial thickness from being too small compared to the size of the computational domain. Results are produced with a numerical method based on the finite-volume approach in combination with a Total Variation Diminishing time-integration scheme. Simulations of droplet collisions show the existence of multiple collision regimes for which the energy transfer and dissipation processes during the collisions are studied in detail.

Realistic assessment of existing masonry structures requires the use of detailed nonlinear numerical descriptions with accurate model material parameters. In this work, a novel numerical-experimental strategy for the identification of the main material parameters of a detailed nonlinear brick-masonry mesoscale model is presented. According to the proposed strategy, elastic material parameters are obtained from the results of diagonal compression tests, while a flat-jack test, purposely designed for in-situ investigations, is used to determine the material parameters governing the nonlinear behaviour. The identification procedure involves: a) the definition of a detailed finite element (FE) description for the tests; b) the development and validation of an efficient metamodel; c) the global sensitivity analysis for parameter reduction; and d) the minimisation of a functional representing the discrepancy between experimental and numerical data. The results obtained by applying the proposed strategy in laboratory tests are discussed in the paper. These results confirm the accuracy of the developed approach for material parameter identification, which can be used also in combination with in-situ tests for assessing existing structures. Practical and theoretical aspects related to the proposed flat-jack test, the experimental data to be considered in the process and the post-processing methodology are critically discussed.

Recent experimental studies involving Fabric Reinforced Cementitious Matrix (FRCM) strengthening systems externally applied to structural supports have underlined important aspects characterizing their response. In particular, failure mechanisms quite different from the ones emerged in case of traditional Fiber Reinforced Polymers (FRP) have been observed. These mechanisms particularly underline the role of additional phenomena to necessarily consider for the study and the development of theoretical models/design formulas specific for FRCMs. Aim of the present paper is to analyze the role of different aspects characterizing the behavior of FRCM strengthening systems externally applied on structural supports. Among these, it is mainly considered the role of the upper mortar layer, and, in particular, the influence of its possible damage state during the interaction mechanism between the reinforcement and the matrix. With this aim, a simple theoretical model is here presented. It accounts for the interaction between the reinforcement and the mortar matrix at the level of interface, by considering both the de-bonding and the tensile failure of mortar phenomena, which generally affect the resistant mechanism of FRCMs. The results presented in the paper underline the role of the different components of the strengthening system and their influence both in terms of local and global response.

We study the contribution of surface piezoelectricity to the interaction between a screw dislocation and a hexagonal piezoelectric bimaterial interface. The screw dislocation suffers a finite discontinuity in the displacement and in the electric potential across the slip plane, and meanwhile is subjected to a line force and a line charge at its core. The surface piezoelectricity is incorporated by using an extended version of the continuum-based surface/interface model of Gurtin and Murdoch. An elementary solution in terms of the exponential integral is obtained. In addition, we present an explicit and concise expression of the image force acting on the piezoelectric screw dislocation. Several special cases are discussed in detail to demonstrate and validate the obtained solution. The associated problem of a piezoelectric screw dislocation interacting with a circular inclusion with surface piezoelectricity is also solved. The dislocation can be located either in the surrounding matrix or in the circular inclusion.

The present study proposes a dynamic constitutive material interface model that includes non-associated flow rule and high strain rate effects, implemented in the finite element code ABAQUS as a user subroutine. First, the model capability is validated with numerical simulations of unreinforced block work masonry walls subjected to low velocity impact. The results obtained are compared with field test data and good agreement is found. Subsequently, a comprehensive parametric analysis is accomplished with different joint tensile strengths and cohesion, and wall thickness to evaluate the effect of the parameter variations on the impact response of masonry walls.

The convergence of a peridynamic model for solid mechanics inside heterogeneous media in the limit of vanishing nonlocality is analyzed. It is shown that the operator of linear peridynamics for an isotropic heterogeneous medium converges to the corresponding operator of linear elasticity when the material properties are sufficiently regular. On the other hand, when the material properties are discontinuous, i.e., when material interfaces are present, it is shown that the operator of linear peridynamics diverges, in the limit of vanishing nonlocality, at material interfaces. Nonlocal interface conditions, whose local limit implies the classical interface conditions of elasticity, are then developed and discussed. A peridynamics material interface model is introduced which generalizes the classical interface model of elasticity. The model consists of a new peridynamics operator along with nonlocal interface conditions. The new peridynamics interface model converges to the classical interface model of linear elasticity.

This paper deals with the accurate modelling of unreinforced masonry (URM) behaviour using a 3D mesoscale description consisting of quadratic solid elements for masonry units combined with zero-thickness interface elements, the latter representing in a unified way the mortar and brick–mortar interfaces. A new constitutive model for the unified joint interfaces under cyclic loading is proposed. The model is based upon the combination of plasticity and damage. A multi-surface yield criterion in the stress domain governs the development of permanent plastic strains. Both strength and stiffness degradation are captured through the evolution of an anisotropic damage tensor, which is coupled to the plastic work produced. The restitution of normal stiffness in compression is taken into account by employing two separate damage variables for tension and compression in the normal direction. A simplified plastic yield surface is considered and the coupling of plasticity and damage is implemented in an efficient step by step approach for increased robustness. The computational cost of simulations performed using the mesoscale masonry description is reduced by employing a partitioning framework for parallel computation, which enables the application of the model at structural scale. Numerical results are compared against experimental data on realistic masonry components and structures subjected to monotonic and cyclic loading to show the ability of the proposed strategy to accurately capture the behaviour of URM under different types of loading.

Interface between matrix/coating or coating/coating in fact represents a very complicate thin interfacial layer. So interface model is necessary to avoid the difficulty on considering such a complicate thin layer in analysis. Classic interface model and cohesive model have been widely used in stress analysis of coating materials, though they cannot represent the effect of very thin interfacial layer accurately. A complete interface model has been deduced from the equivalent constitutive of interfacial layer in this paper. It is found that both classic interface model and cohesive model sometimes cannot give correct analysis results, while the complete interface model can always give a correct result. Moreover, the stress parallel to interface within the interfacial layer can also be analyzed by the new model. Besides, this model can also be used to describe the equivalent properties of interfacial layer, thereby, can provide a quantitative characterizing method for interfacial layer itself.

A discontinuous approach aimed at modeling the brittle fracture behavior of mesoscopic 100Cr6 (SAE 52100) steel specimens is presented in this work. The proposal accounts for explicitly considering carbide particles and martensitic matrix in a metallographic image based mesoscale model. Two-dimensional numerical tests are carried out for the mesoscale specimens including a temperature dependent elastoplastic matrix dealing with the martensitic/austenitic phases and the embedded elastic carbide particles. A fracture damage-based interface constitutive rule is then employed for modeling the brittle behavior occurring at the joint between both the carbides-to-matrix and the matrix-to-matrix interfaces. The soundness and capability of the proposed formulation dealing with the quench cracking phenomenon is demonstrated. Experimental tensile test results on a 100Cr6 steel in its martensitic phase, at room and high temperature, are employed and the evaluation of microcracks formation during a High-Speed-Quenching test is also discussed. Fil: Said Schicchi, Diego. Stiftung Institut für Werkstofftechnik; Alemania Fil: Caggiano, Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería ; Argentina. Universitat Technische Darmstadt; Alemania Fil: Benito, Santiago. Ruhr Universität Bochum; Alemania Fil: Hoffmann, Franz. Stiftung Institut für Werkstofftechnik; Alemania

International audience; The proposed study aims to derive an imperfect interface model which couples finite strain and damaging. The governing equations are obtained via an asymptotic approach within the finite strain theory. Theoretical findings have been numerically validated within an original application to brick/mortar interfaces in masonry walls in shear loading conditions.

The effects of mortars joints in masonry substrate reinforced with FRP is investigated from the numerical point of view. The analysis has been conducted by means of a new interface model specifically developed to reproduce the debonding process occurring between an elastic thin body in adhesion with a cohesive support material, as concrete or masonry. The model accounts for mode I and mode II of failure, considering the effect of the in-plane deformation of the interface, i.e. the possible elongation or confinement of the material constituting the interface. Numerical results are compared with experimental evidences showing the good performances of the proposed model in investigating the transferring phenomena in heterogeneous interfaces and, in particular, in studying the influence of the presence of mortar joints in the masonry texture in the debonding process.

We consider problems involving singularities such as point force, point moment, edge dislocation and a circular Eshelby?s inclusion in isotropic bimaterials in the presence of an interface incorporating surface/interface elasticity under plane strain deformations and derive elementary solutions in terms of exponential integrals. The surface mechanics is incorporated using a version of the continuum-based surface/interface model of Gurtin and Murdoch. The results indicate that the stresses in the two half-planes are dependent on two interface parameters.

A thermodynamically consistent diffuse interface model is developed for two-phase flows with phase transition. Inside the liquid-vapor mixing layer, the Cahn-Hilliard equation governing the evolution of liquid/vapor species explicitly includes the phase transition between the two species. In the present model, the specific Helmholtz free energy of the binary mixing fluid as well as other thermodynamic functions consists of a classical part (ideal mixing free energy plus a double-well potential of the mass fraction) and a nonclassical part consisting of the gradient of mass fraction. The nonclassical chemical potential is defined in a manner similar to the classical chemical potential. According to the present model, there exists a (conserved) nonclassical stress tensor in the mixing fluid, which is a distributed form of the surface tension across the mixing layer. Using the principle of entropy increase, it is observed that the rate of local phase transition is proportional to the local generalized chemical potential, and a system of transport equations of the mixing fluid is derived. This system of equations can be reduced to that of Guo and Lin [“A thermodynamically consistent phase-field model for two-phase flows with thermocapillary effects,” J. Fluid Mech. 766, 226 (2015)] except for the formula on chemical potential. The present diffuse-interface model will also be reduced to the general classical sharp interface model when the mixing layer collapses to a sharp surface.

The Jackson’s factors of three low Miller-index crystal planes of Mg2Si were calculated with a rough interface model by using a growth unit of coordination polyhedron instead of atom. The Jackson’s factors of the {1 0 0}, {1 1 0} and {1 1 1} planes were obtained to be 2.53, 1.27 and 3.80, respectively. The physical meaning of using coordination polyhedron to calculate the Jackson’s factor was interpreted reasonably. The thermodynamic possibility of growing units onto a solid/liquid interface was linked to the microscopic appearance of crystal planes and to the macroscopic shape of Mg2Si crystals formed.

This paper presents a new interface model to simulate the cyclic bond-slip behavior of steel reinforcing bars embedded in concrete. A multi-surface plasticity formulation is used to model two major inelastic deformation mechanisms occurring in bond slip. One is the crushing and shearing of the concrete between the bar ribs, and the other is the sliding between the concrete and bar surfaces. These two mechanisms are represented by different yield surfaces and nonassociated flow rules. The flow rules account for the shear dilatation of the interface induced by the wedging action of the bar ribs and crushed concrete particles. The interface model has been implemented in a finite element analysis program and has been validated with experimental data. The model is easy to calibrate and is able to reproduce the bond-slip behavior of bars under a wide range of confinement situations, including bar pullout and concrete splitting failures.

The dispersion relation of the infinite long rod model with a weak interface has been deduced via wave equation of the guided waves and boundary spring interface model. The dispersion characteristics of the rigid interface and the slip interface are calculated, while the effect of different axial stiffness coefficient is also discussed. The results suggest that the phase velocity of the slip interface decreases slowly with increasing frequency at the low frequency of the L (0,1) mode. As for the weak interface, when the axial coefficient Kt is in the particular range of [10 10 ,10 14 ]pa/m, the interface turns from the slip interface to the rigid interface. That shows the value of axial coefficient Kt is an essential prerequisite for the non-destructive evaluation to evaluate the interface cementation degree.

A viscoelastic interface model is proposed to study the effective mechanical responses of nanocomposites filled with carbon nanotubes. It is incorporated with the Mori–Tanaka method and the elastic-viscoelastic correspondence principle. The effective dynamic stiffness and damping of randomly oriented nanocomposites are investigated with the consideration of imperfect interfacial condition between the filler and matrix as well as the concentration and aspect ratio of fillers. Comparisons are performed between the model-based simulation and the experimental data for a specific type of multi-walled carbon nanotube reinforced elastomer nanocomposites to demonstrate the potential of the proposed framework.

Highlights? Modeling thin interface with solid finite elements with very high aspect ratio. ? A scalar damage model can be used to describe bond degradation due to slip. ? The technique can model the bond-slip behavior of rebars embedded in concrete. ? Densification of the finite elements in the interface region is not required. ? Discrete constitutive relations and contact elements are not necessary. The use of standard solid finite elements with a very high aspect ratio is proposed to model the behavior of thin interface regions between distinct components of composite structural members. It is shown that these elements present the same kinematics as the Continuous Strong Discontinuity Approach (CSDA) and can be used to describe bond stresses between components, even when the thickness of the interface region tends to zero. A scalar damage model consistent with the CSDA is presented to describe bond degradation due to slip. The technique is successfully applied to model the bond-slip behavior of reinforcing bars embedded in concrete.

The interfacial energy and diffusion phenomenon of the Al2O3(012)-SiC (011) interface model are studied based on molecular dynamics. The interfacial energy increases firstly until reaches its maximum 0.459J/m2at the temperature of 1500K and then decreases. The relationship of diffusion coefficients for each kind of atoms is C>Si>O>Al. Diffusion coefficients of atoms increase at first and then decrease as the temperature goes up. This indicates the diffusion mechanism has been changed during the temperature rising process.

The introduced resonant accelerometer makes use of the equivalent electrostatic stiffness to sense the acceleration. The sensitivity can be adjusted by changing the applied sensing voltage. But the no-linearity problem between the output frequency and applied acceleration is difficult to calculate the sensitivity and analysis its influence directly. When the stiffness of the fold beam is much smaller than the vibrating beam, the analytic sensitivity expression is given. The relationship between the sensitivity and the structure critical dimension is easily obtained in the design stage. A resonant accelerometer with sensitivity of 62Hz/g is designed and fabricated by bulk-silicon dissolved processes. The experiment finds there is the critical dimension loss in the fabrication process, which makes the sensitivity change; the same frequency disturbance will influence the closed-loop phase equilibrium. The equivalent interface model is built for the signal processes in the future. The frequency modulation and re-modulation is suggested to eliminate the disturbance. Vacuum package should be adopt to enlarge the weaken output signal.

We present some mathematical analyses of a recently proposed stochastic implicit interface model for an elastic surface immersed in an incompressible viscous fluid subject to fluctuation forces. We derive suitable a priori estimates and establish the well-posedness of pathwise solutions and provide uniform control on the solutions in probability.

Many experimental studies have pointed out that failures or remarkable losses of strength may occur in sand–structure interfaces when they are subjected to cyclic rotational shear. This work introduces an interface model based on the Generalized plasticity theory to describe the effects of cyclic rotational shear on the mechanical behavior of sand–structure interfaces. The simulative capabilities of the model are then presented for various stiffness boundary conditions.

In the framework of numerical analysis of joined bodies, the present paper is devoted to the constitutive modeling, via an interface kinematic formulation, of mechanical behaviour of internal adhesive layers. The proposed interface constitutive model couples a cohesive behaviour, based on the damage mechanics theory, with a frictional one, defined in a non-associative plasticity framework. Namely, the interface formulation follows the transition of the adhesive material from the sound elastic condition to the fully cracked one. This formulation is able to model, by means of a specific interpretation of the damage variable and in a relevant mathematical setting, the interface intermediate mechanical properties, during the microcracks spreading process up to the discontinuity surface formation (macrocrack). The constitutive modeling is performed in fully compliance with the thermodynamic principles, in order to ensure the thermodynamic consistency requirement. In the present work, various monotonic and cyclic loading conditions are examined in order to show the main features of the constitutive formulation as well as several significant differences with respect to other existing models. Computational efficiency of the interface constitutive model is tested in a numerical application by FEM resolution strategy approach.

A computational model, in which the effects of high temperature on steel and concrete’s properties and the composite action and interfacial properties between steel tube and concrete core were considered, was developed using ABAQUS program. Based on a damage model of concrete at ambient condition and tested stress versus strain curves of fire-damaged concrete, a new damage model of concrete after exposure to high temperatures was developed to consider the influence of high temperatures on the damage of concrete. By introducing the damage model of fire-damaged concrete, the reasonable equivalent stress-strain relations of confined concrete and a modified steel tube-concrete interface model into the ABAQUS FE model, the mechanical behaviors of the fire-damaged CFT columns and connections were simulated precisely and verified by some relative test results.

The classical theory of the crystallography of martensitic transformations developed in the 1950s is based on the notion that the interface between the parent and product phases is an invariant plane of the shape deformation. Underlying this hypothesis is the expectation that such interfaces do not exhibit long-range strain, and the geometric theory is an algorithm for finding invariant planes, the orientation relationship and transformation displacement. In the context of ferrous alloys, the classical theory has been applied successfully to transformations with {295} habit planes, but is less satisfactory for {575} for example. A new model of martensitic transformations has been presented recently based on dislocation theory, incorporating developments in the understanding of the topological properties of interfacial defects. Topological arguments show that glissile motion of transformation dislocations, or disconnections, can only occur in coherent interphase interfaces. Hence, the interface in the model comprises coherent terraces with a superimposed network of disconnections and crystal dislocations. It is demonstrated explicitly that this defect network accommodates the coherency strains, and that lateral motion of the disconnections across the interface effects transformation in a diffusionless manner. Moreover, it is shown that a broader range of habit planes is predicted on the basis of the semi-coherent interface model than the invariant plane notion. In the case of ferrous alloys, it will be shown that a range of viable solutions arise which include {575}.

The paper presents a nonlocal elastic damage-frictional interface model. The reason to introduce nonlocal mechanical features inside the constitutive relations is justified by the fact that there are several circumstances, in which the interface displays inside an extended process zone with microstructural spatial interactions. Typically, spatial bridging mechanical effects can be effectively modeled by integral (strongly nonlocal) stress-strain relations. The paper develops an elastic nonlocal model with local isotropic damage and the relations are constructed following a thermodynamical consistent approach.

The spreading of a liquid droplet on a smooth solid surface in the partially wetting regime is studied using a diffuse-interface model based on the Cahn--Hilliard theory. The model is extended to include non-90$^{\circ}$ contact angles. The diffuse-interface model considers the ambient fluid displaced by the droplet while spreading as a liquid. The governing equations of the model for the axisymmetric case are solved numerically using a finite-spectral-element method. The viscosity of the ambient fluid is found to affect the time scale of spreading, but the general spreading behaviour remains unchanged. The wettability expressed in terms of the equilibrium contact angle is seen to influence the spreading kinetics from the early stages of spreading. The results show agreement with the experimental data reported in the literature.

A discontinuous model aimed at modeling ductile fracture for metals is presented. The effect of microvoid nucleation, growth and coalescence on the inelastic response of structural metals is modeled through a suitable interface proposal for cracking analysis. The discontinuos proposal is completely conceived within the general framework of fracture mechanics and porous plasticity concepts. The porosity affects the strength parameters and softening rules defining the failure initiation and post-cracking response of the interface. To demonstrate the soundness and capability of the proposed formulation, a comparative study against numerical simulations obtainable from a classical well-known continuous approach for capturing ductile fracture, based on finite element analysis, is presented. Fil: Said Schicchi, Diego. Stiftung Institut für Werkstofftechnik; Alemania Fil: Caggiano, Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The conditions for grain boundary (GB) structural transitions are determined from a diffuse interface model that incorporates structural disorder and crystallographic orientation. A graphical construction and numerical calculations illustrate the existence of a first-order GB order–disorder transition below the bulk melting point. When thermodynamic conditions permit their existence, disordered GB structures tend to be stable at higher temperatures and are perfectly wet by liquid at the melting point, while ordered grain boundaries are meta-stable against preferential melting. We calculate GB phase diagrams which are analogous to those for liquid–vapor phase transitions.