Elastic Interface Research Articles

Topological electromagnetic and elastic states in phoxonic crystal cavity arrays

AbstractIn this paper, we investigate the topological characteristics of the phoxonic crystal (PxC) arrays. For the PxC system, the electromagnetic transverse electric mode and the elastic in‐plane mode are considered. The PxC possesses the photonic and phononic bandgaps simultaneously. Based on the bandgaps, we design the PxC cavity which can confine the electromagnetic and elastic waves. The interaction strength between the neighboring PxC cavities can be tuned by changing the distance between these cavities. The PxC cavity arrays with the topologically non‐trivial and trivial phases are obtained. We combine the PxC arrays with the topologically non‐trivial and trivial phases together. The electromagnetic and elastic topological interface states can be simultaneously observed at the interface of the PxC cavity arrays.

Analysis of shape, orientation and interface properties of Mo[formula omitted]C precipitates in Fe using ab-initio and finite element method calculations

We study the Mo2C precipitate, a carbide commonly used for secondary hardening in steels, and its interface to the Fe matrix using a combination of ab-initio density functional theory and finite element simulations. For Mo2C and Fe, the elastic properties as a function of temperature are determined and different interfaces of the carbide to the matrix are characterized. With finite element simulations that use the derived elastic properties and interface energies as input, the energy contributions from elasticity and creep are evaluated. Combining the results from atomic to micro scale allows to explain the specific needle shape of these precipitates that has been reported experimentally. For one selected interface, also the full elastic properties are determined with ab-initio methods and compared to the Grimsditch-Nizzoli approach, where we find good agreement. Our study shows how a combination of the ab-initio and the finite element method may be used to characterize and understand the micro-mechanical effects of precipitates.

Thermally rounded depinning of an elastic interface on a washboard potential.

The thermal rounding of the depinning transition of an elastic interface sliding on a washboard potential is studied through analytic arguments and very accurate numerical simulations. We confirm the standard view that well below the depinning threshold the average velocity can be calculated considering thermally activated nucleation of defects. However, we find that the straightforward extension of this analysis to near or above the depinning threshold does not fully describe the physics of the thermally assisted motion. In particular, we find that exactly at the depinning point the average velocity does not follow a pure power law of the temperature as naively expected by the analogy with standard phase transitions but presents subtle logarithmic corrections. We explain the physical mechanisms behind these corrections and argue that they are nonpeculiar collective effects which may also apply to the case of interfaces sliding on uncorrelated disordered landscapes.

FEM Benchmark Problems for Cracks with Spring Boundary Conditions Under Antiplane Shear Loadings

A new analytical solution in the form of asymptotic series is proposed and studied for Mode III crack problems with spring boundary conditions, which are, in the mathematically-oriented literature, referred to as Robin boundary conditions. Under the assumption of antiplane shear loading, the corresponding elastic problem reduces to the Laplace equation for the out-of-plane displacement. Numerical solutions for benchmark problems are obtained, applying the Finite Element Method, to verify this asymptotic approximation. In particular, two problems are studied, Neumann–Robin and Dirichlet–Robin. Both are used to define a partially damaged adhesive interface in which the Linear Elastic Interface Model is applied. The numerical solution is obtained using the software FEniCS, for which the variational formulation of the problem is developed. Then, it is compared to the analytical expressions proposed for the problem, computing a normalized error. Finally, a convergence analysis is presented. Several parameters, such as the stress singularity or another error measure, are used to analyse two different ways to refine the mesh.

A Cloud-Optimized Transport Protocol for Elastic and Scalable HPC

Amazon Web Services (AWS) took a fresh look at the network to provide consistently low latency required for supercomputing applications, while keeping the benefits of public cloud: scalability, elastic on-demand capacity, cost effectiveness, and fast adoption of newer CPUs and GPUs. We built a new network transport protocol, scalable reliable datagram (SRD), designed to utilize modern commodity multitenant datacenter networks (with a large number of network paths) while overcoming their limitations (load imbalance and inconsistent latency when unrelated flows collide). Instead of preserving packets order, SRD sends the packets over as many network paths as possible, while avoiding overloaded paths. To minimize jitter and to ensure the fastest response to network congestion fluctuations, SRD is implemented in the AWS custom Nitro networking card. SRD is used by HPC/ML frameworks on EC2 hosts via AWS elastic fabric adapter kernel-bypass interface.

Chromatography and oil displacement mechanism of a dispersed particle gel strengthened Alkali/Surfactant/Polymer combination flooding system for enhanced oil recovery

In recent years, a newly developed dispersed particle gel (DPG) has attracted significant attention because of its excellent properties and a good application prospect in an enhanced oil recovery process. The preparation method is convenient and easy to scale up for the field application. The dispersed particle gel with sizes ranging from submicron to micron can block the high permeability layers by accumulating in large pore spaces or directly plugging small pore throats. Furthermore, the dispersed particle gels can achieve in-depth profile control due to the elastic deformation and migration into the reservoir's porous media. These characteristics have demonstrated great potential for the dispersed particle gels to strengthen the alkali/surfactant/polymer combination flooding system. The polymers used are the principal sources of viscosity in the system; the surfactant and alkaline produce the synergistic effect by generating the ultralow oil-water interfacial tension. The added dispersed particle gel has a synergistic viscosity increase effect, temperature tolerance, and thermal stability. However, the combined flooding system suffers from the surfactant loss and chromatographic separation that affect the chemical components' synergistic effect for enhanced oil recovery. In this paper, the chromatography separation effects linked to a new method of oil displacement mechanism based on the dispersed particle gel strengthened Alkali/Surfactant/Polymer as a novel combination flooding system was investigated. The addition of dispersed particle gel in the Alkali/Surfactant/Polymer combination flooding system could interleave in the system's network structure and increase the viscosity stability by strengthening the flooding system to improve the oil recovery capacity. The novel dispersed particle gel strengthened alkali/surfactant/polymer flooding systems have a high displacement efficiency and a better-swept volume capacity considering the oilfield requirement for the enhanced oil recovery process. The effects of polymer, surfactant, alkaline, and dispersed particle gel concentration on the combination flooding system were evaluated, furthermore the impact of external factors on the system such as salinity; aging time was described. The results showed that the effects of external factors aging time and salinity slightly affected the system's interfacial reduction capacity. The increase in interface elasticity produced significantly favorable effects on system stability. For the displacement mechanism, when the dispersed particle gel strengthened alkali/surfactant/polymer combination flooding system moved in a porous medium, the dispersed particle gel passed through the pore throat directly or by deformation depending on the system's pressure variation.Furthermore, the phase separation was formed due to the combined component's effects, resulting in the differential migration between the systems, which led to different degrees of chromatographic separation phenomenon to affect the displacement mechanism. As we can see in the micro visualization simulation experiment, the residual oil interacted with Alkali molecules and form the in-situ surfactant, which makes the remaining oil emulsified, as well the surfactant adsorbed by DPG particles, make the crude oil emulsified and get enhanced. The chromatography and micro visualization experiments results of the dispersed particle gel strengthened alkali/surfactant/polymer combination flooding system indicated a favorable application of the system in an enhanced oil recovery process.

Elastic fingering in two-dimensional Stokes flow

Mode coupling is used to study two-dimensional Stokes flows produced by suction or injection flux, in which two fluids react upon contact, forming an elastic interface. The interplay of viscous and elastic effects reveals the formation of nonlinear suction-driven patterns having near-cusp structures.

Effect of preparation procedure on properties of egg white protein and the fibrous microparticle stabilized complex emulsions.

This study, three different procedures were used for preparation of egg white protein (E) and egg white protein fibrous microparticle (EM) complex emulsions, to modify the interfacial and aqueous composition. According to the adding order of EM and E during emulsification, the emulsions were named as type I (EM and E mixed firstly, followed by emulsification), type II (emulsified with EM firstly, followed by the addition of E) and type III (emulsified with EM firstly, followed by the addition of E). The particle size, creaming stability at various salt concentration, elastic module (G'), and lipid oxidation degree were investigated. The results showed that, EM at interface is beneficial for improving salt resistance of the complex emulsions, while E was more effective in terms of preventing oxidation of oil, attributed to the possibility to form continuous elastic interface film. The type III complex emulsion at EM:E ratio of 2:1 showed both improved creaming and oxidation stability, behaving the potential to be used as carrier of lipo-nutrients.

Vibrations of double-nanorod-systems with defects using nonlocal-integral-surface energy-based formulations

We report suitable surface energy-nonlocal-integral and -differential models for investigating mechanical behavior of a nanosystem consists of double parallel nanorods with defects. By visualizing the locally caused defects by appropriate linear springs, the equations of motion that display longitudinal vibrations of the defected nanosystem are derived accounting for nonlocality and surface energy effects. For the nanosystem at hand with a single defect in each nanorod, there would exist four coupled-integro-partial differential equations with eight boundary conditions. By evaluating the exact nonlocal-surface energy-based modes associated with fixed–fixed and fixed-free defected nanorods according to the nonlocal-differential-based model, Galerkin method is implemented to assess the longitudinal frequencies. The capabilities of the nonlocal-integral-based model in capturing the natural frequencies of the nonlocal-differential-based model for the defected nanosystem with fixed–fixed and fixed-free ends are revealed. The roles of the nonlocality, surface energy, nanorod diameter and length, location and mechanical constants of defects as well as the constant of the elastic interface layer on the free vibration are explained.

Improved Oil Recovery in Carbonates by Ultralow Concentration of Functional Molecules in Injection Water through an Increase in Interfacial Viscoelasticity.

Injection of sea water is the most common practice to displace oil in porous media in subsurface formations. In numerous studies, conventional surfactants at concentrations in a range of one weight percent have been proposed to be added to the injected water to improve oil recovery. Surfactants accumulate at the oil-water interface and may reduce the interfacial tension by three orders of magnitude or more, resulting in higher oil recovery. Recently, we have proposed the addition of ultralow concentration of a non-ionic surfactant to the injected water to increase interface viscoelasticity as a new process. The increase in interface viscoelasticity increases oil recovery from porous media. This alternative approach requires only a concentration of 100 ppm (two orders less than the conventional improved oil recovery) and therefore is potentially a much more efficient process. In this work, we present a comprehensive report of the process in an intermediate-wet carbonate rock. There is very little adsorption of the functional molecules to the rock surface. Because the critical micelle concentration is low (around 30 ppm), most of the molecules move to the fluid-fluid interface to form molecular structures, which give rise to an increase in interface elasticity. We also demonstrate that interface elasticity has a non-monotonic behavior with the salt concentration of injected brine, and an optimum salinity exists for maximum oil recovery.

Reliable and Tunable Elastic Interface States in Soft Metamaterials

Tunable elastic interface states in soft materials have been successfully observed in experiments recently, which provides great application potentials in dynamic vibration energy‐harvesting devices or mechanical control of soft robotics. However, the generation of the proposed tunable elastic interfacial states relies on two differently deformed soft periodic phononic crystals, and complicated mechanical loadings and external installations are inevitable, which are indeed difficult to generate and manipulate. Herein, the dynamically adjustable elastic localized states are implemented in a more reliable and convenient way, which is readily modulated simply through compressing or stretching a mirror‐symmetric metamaterial composite simultaneously. The primitive cell of the soft periodic structures is inspired by the symmetry‐broken hexagonal boron nitride structure. Repeatable and reversible frequency shift and switch on–off characteristics of the interface states are observed during the dynamical regulation process, which is used in the dynamic elastic filter or divider devices. The feasibility of utilizing mirror operation to produce the interface states is clearly demonstrated, which effectively reduces the geometry and configuration design during the manufacturing process. The mirror method is also generalized to other periodic photonic and phononic crystals for the generation of additional multiple tunable interface states.

An Estimation Approach for the Effective Elastic Modulus of Lightweight Bulk Filling Material with Compressible Inclusions and Imperfect Interfaces.

In this study, an approach is developed to estimate the density and effective elastic modulus of a lightweight bulk filling material made up of expanded polystyrene (EPS) and cement-reinforced clay (matrix). First, a representative volume element (RVE) is composed of cell A (an EPS and matrix) and cell B (matrix only). Then, an elastic interface is introduced to describe the discontinuity of displacement at the interface between EPS beads and matrix. Third, an Eshelby compliance tensor is modified in cell A to include the effects of imperfect interface and the compressibility of EPS beads. Finally, the approach for the density and effective elastic modulus of the EPS beads mixed cement-reinforced clay is verified with experimental data. The compressibility ratio of lightweight clay is compared under different confining pressures and curing times. It is found that the imperfect interface has salient impacts on the effective elastic modulus with the increase of volume fraction of inclusions. The interface parameters (α and β) vary with curing time and confining pressure. At the same curing time, the parameter α is almost constant regardless of confining pressure but the parameter β changes with confining pressure. The compressibility ratio is smaller for longer curing time if the confining pressure is constant.

2D numerical model for studying frictional sliding

The onset of frictional motion couples complex spatiotemporal dynamics of discrete contacts with different orders of magnitude at time and length scales. In order to reveal how these individual scales affect the frictional sliding, we establish a 2D multiscale spring-block model for the frictional sliding at an elastic slider-rigid interface. In this model, the rupture of frictional interface is described by three different types of locally microscopic motion: pinned, sliding and dislocated states. By using realistic boundary conditions, our numerical results can precisely reproduce the loading curves found in previous experiments. The precursor events, corresponding to a discrete sequence of rapid crack-like fronts propagating partially in the contact zone, can also be shown in our simulation. From the analysis of the microscopic motion, we characterize the evolution of the real contact area and the corresponding interface motion at the mesoscale level, and show that the evolution corresponds to four distinct and inter-related phases: detachment, fast and slow slip motion, as well as the rest of slip. These mesoscale behaviors are completely consistent with the existing experimental results and their physical mechanisms can be explained by the detailed information of the numerical simulation. The study is established on a bottom-up multiscale model which provides a comprehensive picture about the complex spatiotemporal dynamics of frictional sliding.

Heterogeneous FE model for single lap shear tests on FRP reinforced masonry curved pillars with spike anchors

A 3D-FE heterogeneous approach is proposed to reproduce experimental single lap shear tests performed on curved masonry prisms reinforced either at the intrados or extrados with FRP strips fixed to the masonry surface by both epoxy resin and an anchor device placed in the middle of the strip. Bricks and mortar are modeled with a concrete damage plasticity material exhibiting softening, whilst for both the FRP and spike a linear-elastic behavior is assumed. An elastic uncoupled cohesive interface between FRP/substrate and anchorage/substrate is also introduced in the model to properly reproduce experimental stiffness and damage diffusion inside masonry. The model is benchmarked against four sets of single lap shear tests performed by the authors at the University of Florence, Italy. A good match between experimental evidences and numerical predictions is obtained. Sensitivity analyses are finally performed in order to furnish a prediction of the delamination strength also in cases not studied experimentally.

A fiber optic sensor platform for smart hydrogel event detection

Abstract Stimuli-responsive hydrogels have emerged as innovative materials for sensors and actuators, and there is a need to develop a low-cost, simple, but sensitive sensor to detect hydrogel response events to external stimuli. This paper demonstrates a fiber optic sensor platform that can detect external stimulant events of a smart hydrogel. A tapered resonant fiber sensor was fabricated using arc-induced optical fiber tapering and liquid-based gold coating on the tip of the fiber sensor. Poly N-isopropylacrylamide (pNIPAAm)-based temperature-sensitive hydrogel was selected as a model sensing material. The sensing mechanism employs the volume change of the hydrogel when the external temperature induces the phase transition of the hydrogel. To implement this concept in the proposed fiber sensor, we have developed a reliable approach to create bilayered hydrogel and elastic polymer with the tapered fiber sensor. By embedding the fiber sensor in a thin elastic polymer layer and creating a strong bonding between the hydrogel and the elastic layer through porous elastic polymer interface, the sensor operates reliably over cyclic thermal experiments. The results indicate that our sensor can detect the threshold events of the hydrogel, where its maximum volume changes occur during external temperature changes. We envisage that similar platforms can be extended to other smart hydrogels and their optical sensing applications.

Numerical study of interface cracking in composite structures using a novel geometrically nonlinear Linear Elastic Brittle Interface Model: Mixed-mode fracture conditions and application to structured interfaces

Interface cracking is one of the most prominent failure modes in fibre reinforced polymer (FRP) composites. Recent trends in high-tech applications of FRP composites exploit the limits of the load bearing capacity, generally encompassing the development of notable nonlinear effects from geometrical and material signatures. In this investigation, we present a comprehensive assessment of the new Linear Elastic Brittle Interface Model (LEBIM) in geometrically nonlinear applications undergoing mixed-mode fracture conditions. This interface model for triggering fracture events is formulated through the advocation of continuum-like assumptions (for initial non-zero interface thickness) and allows the incorporation of the potential role of in-plane deformation effects. The performance of the present interface model is demonstrated through the simulation of specimens with mixed-mode delamination, with special attention to its application in samples equipped with structured interfaces. Predictions exhibit an excellent agreement with experimental data, validating the proposed methodology.

A consistent finite displacement and rotation formulation of the Linear Elastic Brittle Interface Model for triggering interlaminar damage in fiber-reinforced composites

In this study, a novel procedure enabling the computation of the relative displacements (normal δn, shear δss and in-plane δsl) that are needed to evaluate a traction-separation law (TSL) under finite displacement and rotation hypotheses within the framework of interface modelling is investigated. This kind of procedure is required when rigid body motions appear along the interface that links two solids or along an adhesive joint. The implementation of this procedure into a general purpose Finite Element (FE) code is also described. In this context, the displacements associated with a coordinate system with an axis coincident with the midplane of an interface in presence of rigid body motions are obtained for two types of element formulations: cohesive elements and continuum or solid elements. In particular, the FE commercial code ABAQUS® is used to perform two dimensional analyses. Firstly, normal and shear relative displacements, δn and δss respectively, are calculated using the strain field for COH2D4 cohesive elements. Secondly, relative displacements are determined for standard continuum elements by means of the plane strain elements CPE4. In the second case, a description of the element enhancement is detailed, using an enriched displacement field thanks to the computation of the in-plane jump δsl. Subsequently, some representative benchmark problems involving 1-element tests with prescribed node displacements are shown in order to validate the proposed procedure. Finally, the Horizontal Drum Peel test which includes finite displacements and rotations is modelled together with the Linear Elastic Brittle Interface Model (LEBIM). This test allows the fracture toughness of a bonded joint to be evaluated.

Peak instability in an elastic interface ferrofluid

The instability of an elastic interface separating a ferrofluid and a nonmagnetic fluid subjected to an applied magnetic field perpendicular to the initially undisturbed interface is investigated in the effectively two-dimensional environment of a vertical, rectangular Hele-Shaw cell. By using a third-order mode-coupling perturbative scheme, and considering that the elastic interface has a curvature-dependent bending rigidity, the emergence of elastic ferrofluid peaks is detected at the onset of nonlinearities. In this context, the approximate profile of the interface is obtained. It is also shown that the morphology of the resulting peaks is sensitive to changes in a dimensionless magnetoelastic number (relative measure of magnetic and elastic forces), as well as in a bending rigidity fraction parameter, which expresses variations in the bending rigidity with the local interface curvature.

In-plane loading of a bonded rigid disc inclusion embedded at a pre-compressed elastic interface: The role of non-linear interface responses

The paper examines the in-plane loading of a bonded rigid disc inclusion of finite thickness that is embedded at a smooth pre-compressed elastic interface composed of two halfspace regions. The in-plane loading induces a pure translation of the inclusion without rotation. The paper first develops estimates for the in-plane elastic stiffness of the disc inclusion. Upon de-bonding of the inclusion-elastic medium interfaces, the peak force is established by considering a Coulomb friction response of fully debonded interfaces. When the detached interface exhibits dilatant processes the displacement-dependent peak force at the detached surfaces can be estimated using a work-plastic energy dissipation relationship. When the bonded faces of the inclusion exhibit an elasto-plastic response, the force–displacement response of the in-plane loaded inclusion can exhibit a transition from the fully bonded response to partial detachment. The analysis of this problem is achieved using a computational approach that accounts for the development of failure and separation at the pre-compressed interface.

Stick–slip behaviour of mortar–rock interface under high loading rate

A modified push-out method was used to explore the bond characteristics of the mortar–rock interface in an anchor system at different loading rates. Under a high loading rate (≥ 1·12 × 10−4 s−1), stick–slip behaviour, which is usually used to describe the mechanism of earthquakes, was observed at the mortar–rock interface for the first time in this experimental research. The test results showed that the load–displacement curve under a high loading rate included four stages: elastic deformation, interface softening, residual friction and stick–slip oscillation. A micro-mechanical model of bond–slip at the mortar–rock interface was also developed. A series derivation revealed the relationships among the dilatancy stress of the mortar–rock interface, the loading rate and the stress drop of stick–slip. The mechanism of stick–slip behaviour at the mortar–rock interface was theoretically established. The modified visco-elastoplastic constitutive model established to describe the stick–slip characteristics of a mortar–rock interface was verified with experimental results using Abaqus software.