Imperfect Interface Research Articles

Circumferential SH wave in piezo-reinforced composite structure with imperfect interface bonding

The present study fundamentally focuses on analyzing the limitations and transference of circumferential shear horizontal (CSH) waves in a four-layered compounded cylinder. The geometrical structure consists of cylinders of infinite length composed of self-reinforced (SR), fibre-reinforced (FR), piezo-magnetic (PM), and piezo-electric(PE) materials. In order to make the structure sensitive to the application pertaining to sensors and actuators, the PM and PE cylinders have been categorically placed in the outer part of the geometry. Whereas in order to provide stiffness and stability to the structure, the inner part consists of SR and FR materials. The common boundary between each of the cylinders has been essentially considered as imperfectly bounded. At the interface of PE and PM media, mechanical, electrical, magnetic, and inter-coupled types of imperfections have been exhibited. The closed-form of dispersion relation has been deduced for two contrast cases i.e. electrically open magnetically short (EOMS) and electrically short and magnetically open (ESMO) circuit conditions. Dispersion curves have been plotted to illustrate the salient features of parameters like normalized imperfect interface parameters, initial stresses, and radii of the concentric cylinders. The comparative effect of each one of these parameters on the phase velocity of the wave has been enlisted and marked individually. Every graph has been presented with two successive modes for a comprehensive understanding. This theoretical study may be implemented to improvise the performance of surface acoustic wave (SAW) sensors, actuators, and Piezo-cables in the form of Piezo-polymer sensors consisting of piezo-electric quartz, piezo-composite concentric cylinders, and coaxial piezo-cables.

Lightweight cement pastes with hollow glass microspheres: Analytical estimation of elastic parameters

An analytical model is presented for estimation of the elastic parameters of lightweight cement pastes with hollow glass microspheres (HGMS). The microspheres consist of a siliceous spherical outer shell filled with gas, providing a density modification agent for the cement paste. The obtained lightweight cement paste is used for cementing deep wells where it is necessary to guarantee the integrity of the cement sheath to avoid fluid migration, contain the rock mass and protect the casing. The proposed micromechanical model, compared to other alternatives, results in an easy-to-use approach for obtaining an estimation of the elastic parameters of the HGMS lightweight cement. The elastic parameters are necessary for the design of the cement sheath and the analysis of its performances. The model input parameters are the elastic parameters of the cement matrix and the microspheres, as well as microspheres dimensions and volume fraction, which are easy to obtain. The model predictions are compared to experimentally evaluated elastic parameters of lightweight cement pastes. A good compatibility between predictions and experimental data is obtained, even when assuming a perfectly bounded interface between the microspheres and the cement matrix.The model also permits to take into account an imperfect interface between the microspheres and the cement matrix improving the model predictions with respect to the experimental results. The model presents an engineering tool to design lightweight cement slurries with hollow microspheres and to estimate their mechanical contribution to a cement sheath for drilling operations.

Effective properties of centro-symmetric micropolar composites with non-uniform imperfect contact conditions

In this work, the homogenization theory is addressed within the framework of three-dimensional linear micropolar composite materials with centro-symmetric constituents and non-uniform imperfect interface conditions. The imperfect contact conditions are modeled like a generalization of the spring model, where tractions and coupled stresses are continuous, but displacements and microrotations are discontinuous across the interface. The jumps in displacement and microrotation components are proportional to the interface traction and coupled stress components in terms of a partition of different spring-factor-type interface parameters, respectively. The two-scale asymptotic homogenization method (AHM) is developed, through series expansions for displacements and micro-rotations, to find the analytical statement of the local problems on the periodic cell and the corresponding effective coefficients. In particular, centro-symmetric multi-laminated micropolar composites with non-uniform imperfect contact conditions are studied, and their corresponding effective properties are explicitly declared. Numerical results show the effects of the interface partition lengths, the non-uniform imperfection values, and the constituent’s fraction volumes on the effective properties of centro-symmetric bi-laminated composite with isotropic constituent materials. We also analyze and discuss the effective behaviors illustrated in the results. In general, the effective properties are always affected by a non-uniform imperfect interface, and they are bounded between those achieved when the contact conditions are perfect and imperfect uniform. The reported formulas and data may be helpful as benchmarks for checking other experimental and numerical results.

Estimating macroscopic conductivity of randomly elliptic inclusion model with imperfect interfaces

The paper introduces some solutions for computing the effective conductivity of randomly elliptic inclusion with imperfect interfaces in two-dimensional space. Based on the coated-ellipse inclusion model and the polarization approximation, one can determine the effective conductivity of the ellipse inclusions with the approximation for lowly conducting imperfect interface (ALI) and the approximation for highly conducting imperfect interface (AHI). Some solutions, including the equivalent inclusion approximations (ALI and AHI), differential approximations (DAs), Hamilton–Crosser approximations (HAs), and fast Fourier transformation (FFT) method will be applied to determine the effective conductivity of the randomly ellipse model with AHI and ALI in two-dimensional space. The ALI and AHI results agree well with DA, HA, and FFT results showing the effectiveness of the methods.

Experimental characterization and modelling of adhesive bonded joints under static and non-monotonic fracture loading in the mode II regime

Understanding and predicting the behaviour of bonded joints under different loading conditions is certainly an aspect of primary importance. Although numerous experimental studies have been carried out over the last few decades, the shear behaviour of bonded joints under cyclic loading has not been investigated in detail. To fill this gap, an extensive experimental and numerical program of double lap shear bonded joints has been carried out. The double lap shear joints were tested under static and cyclic loading to evaluate and compare the influence of external forces on the adhesive performance. The results are discussed in terms of the force-displacement relationship, shear stress, stiffness, residual displacement, and initial damage. Finally, a method is presented for predicting the actual behaviour of double lap shear bonded joints under different loading conditions using an imperfect interface model with damage evolution. The numerical results are in good agreement with the experimental results for all loading conditions. This work has provided and validated an interesting design tool for adhesive structures.

Influences of upsetting on the propagation characteristic of the elastic wave in the countersunk head riveted joints

The countersunk head riveted joints (CHRJ) have extensive use in the aerospace and marine industry. When testing the CHRJ with ultrasonic technology, the signal near the initial pulse cannot be used to detect near-surface defects due to the blind zone of the ultrasonic testing (UT). Moreover, the presence of clutters between the first and second bottom echoes can significantly affect the effectiveness of the UT. Therefore, it is crucial to investigate the propagation characteristic of ultrasonic waves in the CHRJ. The relationship between the interface stiffness and the upsetting length was obtained because of the multi-interface feature of the CHRJ. The propagation characteristic of ultrasonic waves in the CHRJ was investigated using the finite element simulation based on the spring model of the imperfect interface. The simulation results showed that shank echoes would generate at the surface of the rivet shank when the elastic wave propagates in the shank of the CHRJ. The shank echoes would propagate obliquely downward and reflect repeatedly on the surface of the rivet shank. Furthermore, the amplitude of the first shank echo would decrease with the increase of the upsetting length due to the increase of contact stress and deformation. To verify the simulation results, the experiments were carried out using the piezoelectric ultrasonic transducer, and the experimental results matched well with the simulation results. This paper can provide a reference for the ultrasonic testing of defects in the CHRJ.

Linear spring model to analyse the effect of interfacial imperfection on the propagation and attenuation of Love-type waves in viscoelastic-FGPM bedded structure

This article is dedicated to analyse the propagation and attenuation behaviour of Love-type waves in an imperfectly bonded viscoelastic-functionally graded piezoelectric material (FGPM) layered structure. The linear spring model is adopted to portray the interfacial imperfection. The wave solutions in the FGPM substrate are approximated using Wentzel–Kramers–Brillouin (WKB) approximation technique. Dispersion relation is obtained and found to be complex in nature, when traction-free and electrically short conditions are taken into account. Numerical example and computations have been presented to analyse the dispersion equation. The pronounced effects of different parameters such as gradient coefficients, layer’s width, interfacial imperfection, and dissipation factor on the phase velocity, as well as attenuation coefficient of the Love-type wave have been illustrated graphically. Obtained results may be used to achieve better performance of surface acoustic wave (SAW) devices and Love-wave sensors.

A multiscale homogenization model on thermal conductivity of bio-based building composite considering anisotropy, imperfect interface and moisture

Bio-based materials are considered as one of the solutions to reduce energy consumption in buildings due to their excellent thermal insulation properties. However, previous studies often do not consider multiple complex microstructural characteristics in one model. In this study, a novel iterative multi-scale homogenization model was developed to predict the effective thermal conductivity of bio-based materials. This model is based on micro-geometric features at three scales and considers plant fiber orientation and shape, imperfect contact, moisture, and different pores’ size. Further, the model was verified by comparison with finite element models and experimental data from the literature. The results show that the present model demonstrates reliable predictions on the scale of binder, plant fiber, and bio-based composites. The application on hemp verified the accuracy of the imperfect contact in the model, while the application on wheat straw showed the non-negligibility of moisture. Additionally, this study also has good applicability to other plant fibers. In conclusion, this model links microstructure and macroscopic behavior, which can effectively predict and evaluate the thermal conductivity of a wide range of bio-based materials, and thus contribute to reducing building energy consumption.

The effect of memory and stiffness on energy ratios at the interface of distinct media

PurposeThis paper aims to study the energy ratios of plane waves on an imperfect interface of elastic half-space (EHS) and orthotropic piezothermoelastic half-space (OPHS).Design/methodology/approachThe dual-phase lag (DPL) theory with memory-dependent derivatives is employed to study the variation of energy ratios at the imperfect interface.FindingsA plane longitudinal wave (P) or transversal wave (SV) propagates through EHS and strikes at the interface. As a result, two waves are reflected, and four waves are transmitted, as shown in Figure 2. The amplitude ratios are determined by imperfect boundaries having normal stiffness and transverse stiffness. The variation of energy ratios is computed numerically for a particular model of graphite (EHS)/cadmium selenide (OPHS) and depicted graphically against the angle of incidence to consider the effect of stiffness parameters, memory and kernel functions.Research limitations/implicationsThe energy distribution of incident P or SV waves among various reflected and transmitted waves, as well as the interaction of waves for imperfect interface (IIF), normal stiffness interface (NSIF), transverse stiffness interface (TSIF), and welded contact interface (WCIF), are important factors to consider when studying seismic wave behavior.Practical implicationsThe present model may be used in various disciplines, such as high-energy particle physics, earthquake engineering, nuclear fusion, aeronautics, soil dynamics and other areas where memory-dependent derivative and phase delays are significant.Originality/valueIn a variety of technical and geophysical scenarios, wave propagation in an elastic/piezothermoelastic medium with varying magnetic fields, initial stress, temperature, porosity, etc., gives important information regarding the presence of new and modified waves.

Design of Two-Dimensional Transient Circular Thermal Cloaks with Imperfect Interfaces

In this paper, analytic modeling for the design of a transient thermal invisibility cloak with imperfect interfaces is presented together with numerical simulations. In contrast to steady-state conditions, it is shown that an object can only be made partially invisible under a transient-state condition with either ideal or imperfect interfaces. The thermal visibility of an object to the external region can be optimally suppressed under certain conditions referred to as the "weak invisibility conditions" for the transient response, which are different from the "strong invisibility conditions" that can completely conceal an object in a steady state. In the formulation, a homogeneous metamaterial with constant volumetric heat capacity and constant anisotropic conductivity tensor is employed. It can be demonstrated that the interface's bonding conditions will have a significant effect on the design of metamaterials. Two typical types of imperfect interfaces, referred to as low-conductivity- and high-conductivity-type interfaces, are considered. Conditions, that render an object mostly undetectable, are analytically found and expressed in simple forms under quasi-static approximations. Within the quasi-static limit, the thermal localization in the target region can be tuned with the anisotropy of the conductivity tensor. Thermal shielding or concentrating effects in the target region are exemplified based on finite element simulations to demonstrate the manipulation of heat flux in the target region. The present findings make new advances in theoretical fundamentals and numerical simulations on the effect of the imperfect interface in the transient regime and can serve as guidelines in the design of thermal metamaterials through the entire conduction process.

Single-crystalline van der Waals layered dielectric with high dielectric constant.

The scaling of silicon-based transistors at sub-ten-nanometre technology nodes faces challenges such as interface imperfection and gate current leakage for an ultrathin silicon channel1,2. For next-generation nanoelectronics, high-mobility two-dimensional (2D) layered semiconductors with an atomic thickness and dangling-bond-free surfaces are expected as channel materials to achieve smaller channel sizes, less interfacial scattering and more efficient gate-field penetration1,2. However, further progress towards 2D electronics is hindered by factors such as the lack of a high dielectric constant (κ) dielectric with an atomically flat and dangling-bond-free surface3,4. Here, we report a facile synthesis of a single-crystalline high-κ (κ of roughly 16.5) van der Waals layered dielectric Bi2SeO5. The centimetre-scale single crystal of Bi2SeO5 can be efficiently exfoliated to an atomically flat nanosheet as large as 250 × 200 μm2 and as thin as monolayer. With these Bi2SeO5 nanosheets as dielectric and encapsulation layers, 2D materials such as Bi2O2Se, MoS2 and graphene show improved electronic performances. For example, in 2D Bi2O2Se, the quantum Hall effect is observed and the carrier mobility reaches 470,000 cm2 V-1 s-1 at 1.8 K. Our finding expands the realm of dielectric and opens up a new possibility for lowering the gate voltage and power consumption in 2D electronics and integrated circuits.

Dynamic response of an elliptic cylinder inclusion with imperfect interfaces subjected to plane SH wave

Underground chambers or tunnels often contain inclusions, the interface between the inclusion and the surrounding rock is not always perfect, which influences stress wave propagation. In this study, the imperfect interface and transient seismic wave were represented using the spring model and Ricker wavelet. Based on the wave function expansion method and Fourier transform, an analytical formula for the dynamic stress concentration factor (DSCF) for an elliptical inclusion with imperfect interfaces subjected to a plane SH-wave was determined. The theoretical solution was verified via numerical simulations using the LS-DYNA software, and the results were analyzed. The effects of the wave number (k), radial coordinate (ξ), stiffness parameter (β), and differences in material properties on the dynamic response were evaluated. The numerical results revealed that the maximum DSCF always occurred at both ends of the elliptical minor axis, and the transient DSCF was generally a factor of 2–3 greater than the steady-state DSCF. Changes in k and ξ led to variations in the DSCF value and spatial distribution, changes in β resulted only in variations in the DSCF value, and lower values of ωp and β led to a greater DSCF under the same parameter conditions. In addition, the differences in material properties between the medium and inclusion significantly affected the variation characteristics of the DSCF with k and ξ.

Homogenization of a class of singular elliptic problems in two-component domains

This paper deals with the homogenization of a quasilinear elliptic problem having a singular lower order term and posed in a two-component domain with an ε-periodic imperfect interface. We prescribe a Dirichlet condition on the exterior boundary, while we assume that the continuous heat flux is proportional to the jump of the solution on the interface via a function of order ε γ . We prove an homogenization result for − 1 < γ < 1 by means of the periodic unfolding method (see SIAM J. Math. Anal. 40 (2008) 1585–1620 and The Periodic Unfolding Method (2018) Springer), adapted to two-component domains in (J. Math. Sci. 176 (2011) 891–927). One of the main tools in the homogenization process is a convergence result for a suitable auxiliary linear problem, associated with the weak limit of the sequence { u ε } of the solutions, as ε → 0. More precisely, our result shows that the gradient of u ε behaves like that of the solution of the auxiliary problem, which allows us to pass to the limit in the quasilinear term, and to study the singular term near its singularity, via an accurate a priori estimate.

Three-dimensional tractive rolling contact analysis of functionally graded coating-substrate systems with interfacial imperfection and frictional anisotropy

Three-dimensional tractive rolling contact analysis of functionally graded coating-substrate systems with interfacial imperfection and frictional anisotropy

A Theoretical Study to Investigate the Impact of Bilayer Interfacial Modification in Perovskite Solar Cell

The interfacial defects or imperfections in the multilayer perovskite solar cells (PSCs) are detrimental for efficient and stable devices. To produce highly efficient and stable PSCs, a bilayer between the interfaces of electron‐transport material/perovskite and perovskite/hole‐transport material can be useful for suppressing recombinations at these interfaces. To passivate the interfacial defects at the perovskite/SnO2and perovskite/Spiro‐OMeTAD for three absorber materials (CsPbI3, FAPbI3,and Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3), a thin layer of WO3and poly‐bathocuproine interfacial layer is explored using solar cell capacitance simulation in 1D. The optimized device photovoltaic performances significantly improve using bilayers. The power conversion efficiency for the FAPbI3‐based PSCs in bilayer configuration is more than 12% as compared to pristine, whereas open‐circuit voltage is improved by over 13%. The enhancement in device performance is attributed to the reduction of interfacial defects at both the electron transport layer/perovskite and perovskite/hole transport layer interfaces. The proposed interface modification strategy provides a novel approach for fabricating efficient perovskite devices.

A Single-Variable Zigzag Approach to Model Imperfect Interfaces in Layered Beams

The flexibility of the bonds between the adjacent layers of multi-layered systems and their degradation or the presence of delaminations strongly affect mechanical response and final collapse. The formulation of accurate and efficient models able to capture the complex local distributions of stresses and displacements, which arise due to the layered structure and imperfect bonding, is of great importance for the design and verification of the systems. In this paper a novel and effective “single-variable zigzag” theory is formulated to analyze beams with homogeneous layers made of the same material and imperfect interfaces, which allow sliding between the layers. The primal variable is a fictitious bending displacement, which is derived in order to define all other kinematic and static quantities in terms of it. The “zigzag” technique describes multilayer systems with imperfect interfaces as equivalent single-layers, so that the problem is governed by equations similar to those of the classical theories for homogeneous beams; the “single-variable” formulation facilitates the implementation into numerical schemes and eliminates well-known numerical problems. Explicit solutions are straightforwardly derived for simply supported beams subjected to uniform and sinusoidal transverse loads. The results for some exemplary structural elements confirm the accuracy and efficiency of the approach. The study is preliminary to the single-variable reformulation and numerical implementation of the zigzag models for laminates with elastic mismatch between the layers.

Effect of imperfect interface on the effective properties of elastic micropolar multilaminated nanostructures

AbstractIn this paper, the problem of a heterogeneous elastic micropolar nanostructure with a periodic structure subject to imperfect contact conditions is analyzed through the two‐scale asymptotic homogenization method (AHM). The imperfect interface is modeled as a generalization of the well‐known spring model; that is, the homogeneous imperfect interface is described by the following conditions: tractions and coupled stress are continuous, but displacements and microrotations are discontinuous across the imperfect interface. The jumps in displacements and microrotations are proportional to the interface traction and coupled stress components, respectively. In particular, micropolar multilaminated nanocomposites with centro‐symmetric isotropic constituents and imperfect contact conditions are studied. From AHM, the solutions for the displacement and microrotation fields are found by means of two‐scale series expansions depending on a local (microscopic) variable and a global (macroscopic) variable. The local problem statements and the corresponding effective properties are explicitly described. The formulation depends on the constituent physical properties, the imperfection parameters, the cell length in the y3‐direction, and the phase's volume fractions. Numerical results are illustrated and discussed. We concluded that the effective moduli are affected by the imperfections and the cell length in the y3‐direction.

Piezoelectric performance of lead-free PDMS/CNT/BaTiO3 piezocomposites with imperfect interphases and CNT agglomerations

Three-dimensional (3D) printable lead-free piezocomposites offer scalable and environmentally friendly solutions in many engineering applications. Typically, the composite system consists of polymeric matrices reinforced with active polycrystalline particles, and possibly nanoadditives. The presence of interfacial inclusion/matrix damage could not only compromise the structural integrity of the component but also significantly alter its ability to act as functional smart materials. In addition, both the agglomeration of the nanoadditives, such as carbon nanotubes (CNTs), and the degree of polarization could also affect the electromechanical behavior of the composite. In this paper, we develop a computational micromechanical model for the study of the influence of three types of internal defects on the piezoelectric performance of such composites. We investigate the influence of (a) the texture of the active phase, which is linked to the degree of polarization; (b) the effect of agglomerations of the CNTs; and (c) the presence of damage in the inclusion/matrix interphase region. Performance is assessed through the macroscopic response in various figures of merit. This work provides numerical evidence that the effective piezoelectric constants related to normal strain modes are strongly affected by the presence of damage in the interphase. Instead, the piezoelectric constant related to the shear strain remains unchanged by interfacial damage. Near the percolation threshold of the CNTs, piezocomposites exhibit a notable improvement in the piezoelectric response compared to the composite without nanomodification, as noted in previous works. Interestingly, this trend also applies in the presence of interfacial damage, and it is described in this work. The piezoelectric performance also depends on the texture of the active particles. We find, under some simplifications, the optimal orientation for the crystallites, and we find how the texture changes the performance in the presence of damage. Regarding energy harvesting applications, optimal energy conversion efficiency has been observed for polycrystalline inclusions that resembles a highly oriented single crystal and CNT volume fraction of 60 of percolation threshold. This is a quite surprising result since the optimal is usually expected for volume fractions very close to percolation and active inclusions with some orientational dispersion. The optimal CNT volume fraction depends on the presence of interfacial damage. Under perfect interface conditions, the energy conversion efficiency is improved with the presence of CNT agglomerations. Under imperfect interface conditions, there is no enhancement due to the addition of CNT.

Stacking Interactions and Photovoltaic Performance of Cs2AgBiBr6 Perovskite

Elpasolite Cs2AgBiBr6 also known as double perovskite has been touted in recent years as a promising alternative to the lead‐based perovskite for light harvesting. Its structure and properties mainly stem from the replacement of Pb2+ cation with a pair of aliovalent silver (Ag+) and bismuth (Bi3+) cations. Although the elpasolite Cs2AgBiBr6 exhibits improved stability, its photophysical properties and device performance are inferior to those of the Pb‐based perovskites. To date, numerous efforts have been geared toward the development of efficient Cs2AgBiBr6 solar cells. However, the indirect, wide bandgap and high exciton binding energy of Cs2AgBiBr6 have limited such efforts. This has been attributed to its low (zero) electronic dimensionality (0D), formation of small polaronic states, and interfacial imperfections with charge transporting layers. In this review, the different aspects of the elpasolite Cs2AgBiBr6 in relation to compositional and interlayer interactions in solar cell are discussed, and its suitability for photovoltaic application is assessed, accompanied by potential measures to further advance its performance. An alternate application of Cs2AgBiBr6 in photocatalysis, which takes advantage of its less toxicity and better stability, is also discussed.

Propagation of Rayleigh Wave in Sandy Media with Imperfect Interface

In the present study, the propagation of Rayleigh wave in a sandy layer overlying a sandy semi-infinite media is investigated, with the interface considered imperfect. Expressions for displacement components are obtained. The dispersion frequency equation is derived using suitable boundary conditions. In particular cases, when interface is perfect and elastic media replace sandy media are also discussed. The effects of imperfectness and sandy parameter on the Rayleigh waves’ phase velocity are investigated using MATLAB software. The theoretical results obtained may find useful applications in geophysics, civil engineering and soil mechanics