Imperfect Bond Research Articles

Estimating equivalent elastic properties of frozen clay soils using an XFEM-based computational homogenization

This study addresses the challenge of estimating the elastic properties of heterogeneous frozen clay soils by introducing a comprehensive approach that combines analytical and numerical models. The frozen clay soil is treated as a mixture composed of frozen clay-water composites and nonclay mineral inclusions. An inversion algorithm is employed to deduce the elastic properties of the matrix (clay-water composites) of two artificially frozen sandy clay samples with known temperature-dependent elastic properties. Subsequently, a two-dimensional numerical simulation using the eXtended Finite Element Method (XFEM) is conducted to carry out numerical homogenization by considering the imperfect bond among frozen clay-water composites and nonclay minerals. The numerical homogenization model offers insights into the temperature-dependent behavior of the interface stiffness parameter. The numerical homogenization results are compared with conventional numerical homogenization approaches like the FEM, which rigidly defines the bonding between inclusions and the matrix. The comparison indicates that the neglect of imperfect bonds among clay-water composites and nonclay minerals will lead to unrealistic outcomes in cases with a high fraction of inclusions. This integrated approach advances the understanding and prediction of elastic properties of frozen clay soils by considering their heterogeneous nature.

Effect of Bonding Type on the Failure of Reinforced Concrete Beam Strengthened with In-Situ High Performance Fibre Reinforced Concrete Layer

High performance fibre reinforced concrete (HPFRC) materials with tensile hardening behaviour can effectively be used for strengthening reinforced concrete beams. A perfect bond between the original and the reinforcing layer cannot be formed, the load-bearing capacity and ductility of the strengthened beam can significantly be affected by the interfacial bond strength between the contacting surfaces. In this paper, beam retrofitting with cast in-situ strengthening type is examined. The purpose of this experimental study is to investigate the impact of the different bond types on the load-bearing capacity, ductility, and failure mode of the strengthened beams in the case of cast in-situ strengthening. Twenty-four beam tests were performed with untreated and rough surfaced beams, with or without connecting elements. The effect of the bond type proved to be significant regarding the failure mode in the case of compression side strengthening, stronger bond resulted in higher load bearing capacity and ductility, too. When tensile side reinforcement was investigated no average increment was experienced in the maximal force and ductility due to the stronger bond. Based on the results, it can be concluded that the generally applied analytical models that assume perfect connection may lead to exaggerated results in the case of a compressed side HPC-strengthened beam. Therefore, it is necessary to develop a model that considers the effect of the imperfect bond.

Characterization of the Mechanical, Biodegradation, and Morphological Properties of NBR/Biopolymer Blend, Integrated with a Risk Evaluation.

Biopolymer blends have attracted considerable attention in industrial applications due to their notable mechanical properties and biodegradability. This work delves into the innovative combination of butadiene-acrylonitrile (referred to as NBR) with a pectin-based biopolymer (NGP) at a 90:10 mass ratio through a detailed analysis employing mechanical characterization, Fourier transform infrared (FTIR) analysis, thermogravimetric analysis (TGA), and morphology studies using SEM. Additionally, biopolymer's biodegradability under aerobic and anaerobic conditions is tested. The study's findings underscore the superior tensile strength and elongation at break of the NGP/NBR blend in comparison to pure NBR, while also exhibiting a decrease in puncture resistance due to imperfect bonds at the particle-matrix interfaces, necessitating the use of a compatibilizer. In anaerobic conditions, evaluation of biodegradable properties reveals 2% and 12% biodegradability in NBR and NGP/NBR blend, respectively. The degradation properties were also aligned with TGA results highlighting a lower decomposition temperature for NGP. Additionally, this research integrates the application of a conditional value-at-risk (CVaR)-based analysis of the blend's tensile properties to evaluate the uncertainty impact in the experiment. Under risk, a significant enhancement in the tensile performance (by 80%) of the NGP/NBR blend was shown compared to pure NBR. Ultimately, the study shows that adding pectin to the NBR compound amplifies the overall performance of the biopolymer significantly under select criteria.

Strengthening aluminum matrix composite with additively manufactured 316L stainless steel lattice reinforcement: Processing methodology, mechanical performance and deformation mechanism

This study investigates various processing approaches, interface characteristics, and mechanical properties of an aluminum (Al) matrix composite reinforced with additively manufactured (AM) 316L stainless-steel (SS) lattice. The AM-316L-SS lattice, boasting a 30 % infill density, was fabricated using the laser powder bed fusion technique. The Al-matrix was integrated with the AM-316L-SS reinforcement through experimentation involving pre-stirring of the molten Al under pressurized and unpressurized die-casting conditions. A well-bonded interface, with cohesive regions, was obtained in the pre-stirred structures. In contrast, regions of decohesion were displayed in cast structures without pre-stirring, leading to the presence of pores and the manifestation of imperfect bond interfaces. Compression tests conducted on the sound composite demonstrated enhanced mechanical properties, with a compressive strength of approximately 163 MPa, significantly higher than that of the pure Al-matrix (approximately 80 MPa). Localized interface cracking was initiated by stress gradients and plastic deformation, leading to microcrack propagation into the Al-matrix.

The Elastic Properties of Dilute Solid Suspensions with Imperfect Interfacial Bonding: Variational Approximations Versus Full-Field Simulations

The Elastic Properties of Dilute Solid Suspensions with Imperfect Interfacial Bonding: Variational Approximations Versus Full-Field Simulations

Modelling equivalent elastic properties of imperfectly bonded soil-rock mixtures using an XFEM-based computational homogenization

In this paper, a two-dimensional computational homogenization model is utilized to investigate the elastic stiffness properties of soil-rock mixtures (S-RMs). The medium is idealized as a periodic environment. Consequently, a Representative Elementary Volume (REV) containing rock aggregates within the soil matrix is adopted at the meso-scale level to estimate the homogenized properties at the macro-scale. Using the eXtended Finite Element Method (XFEM), an imperfect interface stiffness coefficient is put forward to consider the cohesiveness between rock and soil without altering the underlying regular mesh. Experimental data of S-RMs in normal and frozen conditions, which are retrieved from the literature, are employed to calibrate and validate the model for varying interface stiffness parameters. The changes in the interfacial bonding are assumed dependent on the temperature and the developed computational tool was used for modelling elastic properties of S-RMs by considering the imperfect bond at normal and frozen conditions. The consistency of the results for the REVs with the randomly distributed rock aggregates with different sizes and grading curves is investigated. Also, the effects of the number of rock aggregates and variations in the interface stiffness parameters on the effective stiffness predictions are discussed and compared with the rigid bond models.

Electric–elastic analysis of multilayered two-dimensional decagonal quasicrystal circular plates with simply supported or clamped boundary conditions

A three-dimensional (3D) electric–elastic analysis of multilayered two-dimensional decagonal quasicrystal (QC) circular plates with simply supported or clamped boundary conditions is presented through a state vector approach. Both perfect and imperfect bonds between the layers are considered by adjusting the parameter sets in the model. Governing equations for the plates subjected to electric or elastic load on the bottom surfaces are derived using the state equations and the propagator matrix method. We explicitly obtain the analytical solution by writing the physical variables as Bessel series expansions and polynomial functions with respect to the radial coordinate. The solution is validated by comparing the numerical results with the 3D finite element analysis. The basic physical quantities of the plates in the phonon, phason, and electric fields are computed in the numerical examples. Result shows that the QC layers as coatings decrease the deflection in the phonon and phason fields of plates. The phonon–phason coupling elastic modulus and piezoelectric constant produce positive and negative effects on the magnitudes of stresses. Besides, compliance coefficients of the weak interface in the phonon field contribute more to the variations than those in the phason field.

Interfacial microstructures and properties of hyper-eutectic Al–21Si / hypo-eutectic Al–7.5Si bimetallic material fabricated by liquid–liquid casting route

Abstract. The bimetal casting process using the liquid–liquid technique was developed to produce a high-quality hyper-eutectic Al–21Si / hypo-eutectic Al–7.5Si alloy bimetal material. Microstructure and microhardness were investigated as a function of the time interval between pouring hypo-eutectic and hyper-eutectic alloys. A bimetal material was successfully fabricated using a liquid–liquid casting technique with a 10 s time interval in a permanent mould casting. A unique structure comprised of hyper-eutectic Al–21Si, hypo-eutectic Al–7.5Si and a eutectic interface of 70 µm thickness was obtained. This structure totally differs from that obtained using a higher time interval above 10 s that showed an imperfect interface bond due to the shrinkage cavity and formation of oxides. The hardness variation from the upper zone of 117.5 HV to the lower zone of 76 HV corresponded to the variation in Si and the content of other alloying elements. The proposed total solidification time control method is a promising approach for the successful fabrication of liquid–liquid bimetal material.

Stabilization policy and indeterminacy in a small open economy

This paper studies the (de)stabilizing effects of income tax rules in a two-sector small open economy with production externalities. The paper shows that in the model with positive sector-specific externalities in the investment sector and negative sector-specific externalities in the consumption sector (or positive aggregate investment externalities), a regressive income tax rule can stabilize such an economy against indeterminacy, whereas a progressive income tax rule can increase the tendency for indeterminacy to occur. This paper also studies two variants that consider an imperfect world bond market and an endogenous labor supply, respectively, and shows that the qualitative results stated above remain valid. Moreover, increasing the level of sector-specific investment externalities can decrease (increase) the minimal level of tax progressivity required for indeterminacy if the investment externalities are below (above) a certain critical value and if the negative externalities in the consumption sector are taken as given.

Stoneley waves with spring contact and evaluation of the quality of imperfect bonds

In this paper, the propagation of Stoneley waves along the interface between two orthotropic elastic half-spaces is investigated. The half-spaces are compressible or incompressible and they are in spring contact with each other. The main aim of the paper is to derive secular equations and formulas for the ratios of displacement components at the interface and to show that Stoneley waves are a good tool for evaluating the quality of imperfect bonds modeled as spring contacts. First, the secular equation and the formulas for the displacement-component ratios for the compressible case (two half-spaces are compressible) are derived. Then, those for the incompressible cases (one or both half-spaces are incompressible) are obtained by using the incompressible limit method. The obtained secular equations reveal that, while Stoneley waves are non-dispersive for the welded contact and the sliding contact, they are dispersive for the spring contact. Employing the obtained secular equations and formulas for the displacement-component ratios, two particular examples are carried out for determining the spring constants from the measured values of the displacement-component ratios and the wave velocity. It is shown that the ratios of displacement components at two sides of the interface are the best choice for evaluating the quality of imperfect bonds.

Two-dimensional hygrothermal modelling of masonry walls accounting for imperfections at the masonry joint

Hygrothermal models are important tool for assessing the risk of moisture-related decay mechanisms such as freeze-thaw in historic masonry structures. There are several sources of uncertainty when modelling masonry, related to material properties, boundary conditions, quality of construction and twodimensional interactions between mortar and unit. This paper examines one potential source of uncertainty; the imperfect nature of mortar joints. This interface may feature hairline cracks or imperfect bonds which can be modelled as a fracture. This will alter the rate of liquid transport into and out of the wall and impede the liquid transport between mortar and masonry unit. This means that the “effective” liquid transport of the wall system will be different then if measured properties of the bulk material were modelled. A detailed methodology for modelling the interface as a fracture is presented including material property definition. Two-dimensional DELPHIN models of masonry walls were created to simulate this interaction with varying levels of fracture widths (apertures). A series of hygrothermal simulations were performed to demonstrate change in moisture profile from the baseline condition. A significant increase in moisture absorption was found. This was dependent on aperture size, material and the relative size of the masonry modelled.

Localized and overall interaction effects of irregular interfacial bonds and elastic edge restraints for sandwich and functionally graded multilayer circular plates with normal/shear tractions

In the present article, interactions of the effects of the interfacial bond’s irregularity, shear and normal tractions, and flexible edge supports on the distributions of the lateral deflections and stress of the laminated/sandwich circular plates are investigated, for the first time. To widen the applicability of the research, the layers are assumed to be functionally graded ones. A layerwise model that unlike the traditional layerwise theories, not only guarantees continuity of the transverse stress components but also takes into account the discontinuity of all of the displacement components at the imperfect or damaged bonds between layers is proposed. The governing equations are derived based on the principle of minimum potential energy and solved based on the Maclaurin transformation analytical method. Results are enhanced through a three-dimensional elasticity correction. Results reveal that while compliance of the edge restraint has a significant role on the magnitude of the global displacements, amount of the discontinuities in the displacement components at the mutual interfaces is mainly affected by both the local and global (mean) bond stiffness. Furthermore, while both the compliance of the elastic edge restraint and irregularity of the bonds increase the stress and displacement components, each combination of these parameters may specifically lead to magnifications of the stresses in a particular layer of the plate.

Cubic B20 helimagnets with quenched disorder in magnetic field

We theoretically address the problem of cubic B20 helimagnets with a small concentration $c\ensuremath{\ll}1$ of defect bonds in external magnetic field $\mathbf{H}$, which is relevant to mixed B20 compounds at small dopant concentrations. We assume that the Dzyaloshinskii-Moriya interaction and the exchange coupling constant are changed on imperfect bonds which leads to distortion of the conical spiral ordering. In a one-impurity problem we find that the distortion of the spiral pitch is long ranged and it is governed by the Poisson equation for an electric dipole. The variation of the cone angle is described by the screened Poisson equation for two electric charges with the screening length being of the order of the spiral period. We calculate corrections to the spiral vector and to the cone angle at finite $c$. The correction to the spiral vector is shown to be independent of $H$. We demonstrate that diffuse neutron scattering caused by disorder appears in the elastic cross section as power-law decaying tails centered at magnetic Bragg peaks.

UiO-66-Type Metal-Organic Framework with Free Carboxylic Acid: Versatile Adsorbents via H-bond for Both Aqueous and Nonaqueous Phases.

The metal-organic framework (MOF) UiO-66 was synthesized in one step from zirconium chloride and isophthalic acid (IPA), together with the usual link material, terephthalic acid (TPA). UiO-66 with free -COOH can be obtained in a facile way by replacing up to 30% of the TPA with IPA. However, the chemical and thermal stability of the synthesized MOFs decreased with increasing IPA content used in the syntheses, suggesting an increase in the population of imperfect bonds in the MOFs because of the asymmetrical structure of IPA. The obtained MOFs with free -COOH were applied in liquid-phase adsorptions from both water and model fuel to not only estimate the potential applications but also confirm the presence of -COOH in the MOFs. The adsorbed amounts of several organics (triclosan and oxybenzone from water and indole and pyrrole from fuel) increased monotonously with increasing IPA content applied in MOF synthesis (or -COOH in the MOFs). The favorable contribution of free -COOH to adsorption can be explained by H-bonding, and the direction of H-bonds (adsorbates: H donor; MOFs: H acceptor) was confirmed by the adsorption of oxybenzone in a wide pH range. The versatile applications of the MOFs with -COOH in adsorptions from both polar and nonpolar phases are remarkable considering that hydrophobic and hydrophilic adsorbents are generally required for water and fuel purification, respectively. Finally, the presence of free -COOH in the MOFs was confirmed by liquid-phase adsorptions together with general Fourier transform infrared analyses and decreased chemical and thermal stability.

A New Approach to Thermal Analysis of a Multilayered Cylindrical Structure With Imperfect Bonds and Internal Heat Source

In the present research, a new and straightforward mathematical model, named augmented state-space method, is introduced to solve the heat conduction equation for a multilayered orthotropic hollow cylinder with bonding imperfection in the presence of heat source. Since such problems including heat source are inherently inhomogeneous and complex, augmented state-space method converts these inhomogeneous equations into homogeneous ones. The transient solution will be achieved by present method based on laminate approximation theory in the Laplace domain, and then the solutions obtained are retrieved into the time domain by applying the numerical Laplace transform inversion. All material properties can be considered to vary continuously within the cylinder along the radial direction with arbitrary grading pattern. Based on the proposed method, the solution of heat conduction problem can be also obtained for general boundary conditions which may be included various combinations of arbitrary temperature, flux, or convection. Due to lack of any data on the transient thermal analysis corresponding to problems with imperfect bonds in the cylindrical coordinate system (r,θ), comparison is carried out with the available results for the three-layer semi-circular annular region with perfect bonds in the literature. Finally, the influence of orthotropy and interface imperfection on the distribution of the temperature field for three-layer hollow cylinder, in which the second layer is made of orthotropic functionally graded material (FGM), will be visualized.

An Improved Micromechanical Framework for Saturated Concrete Repaired by the Electrochemical Deposition Method considering the Imperfect Bonding

The interfaces between the deposition products and concrete are not always well bonded when the electrochemical deposition method (EDM) is adopted to repair the deteriorated concrete. To theoretically illustrate the deposition healing process by micromechanics for saturated concrete considering the imperfect interfaces, an improved micromechanical framework with interfacial transition zone (ITZ) is proposed based on our recent studies. In this extension, the imperfect bonding is characterized by the ITZ, whose effects are calculated by modifying the generalized self-consistent model. Meanwhile, new multilevel homogenization schemes are employed to predict the effective properties of repaired concrete considering the ITZ effects. Moreover, modification procedures are presented to reach the properties of repaired concrete with ITZs in the dry state. To demonstrate the feasibility of the proposed micromechanical model, predictions obtained via the proposed micromechanical model are compared with those of the existing models and the experimental data, including results from extreme states during the EDM healing process. Finally, the influences of ITZ and deposition product on the healing effectiveness of EDM are discussed based on the proposed micromechanical model.

Percolation and jamming in random sequential adsorption of linear k-mers on square lattices with the presence of impurities

Percolation and jamming of linear k-mers (particles occupying k adjacent sites) on two-dimensional square lattices with impurities have been studied by numerical simulations and finite-size scaling analysis. The model offers a simplified representation of the problem of percolation in amorphous solids, where the presence of defects in the system is simulated by introducing a fraction of imperfect bonds ρ, which are considered forbidden for deposition. The dependence of percolation and jamming thresholds on the concentration of defects was investigated for different values of k, ranging from 2 to 64. The results obtained show that: for each fixed value of k, percolation can occur when ρ is smaller than a certain value ; and in the range , the percolation threshold is practically independent of the fraction of defects. The behavior of as a function of k indicates that the percolation of linear k-mers on square lattices is impossible even for an ideal lattice if . Critical exponents were also calculated to show that the universality class corresponding to ordinary percolation is preserved.

Spiral magnets with Dzyaloshinskii-Moriya interaction containing defect bonds

We present a theory describing spiral magnets with Dzyaloshinskii-Moriya interaction (DMI) subject to bond disorder at small concentration $c$ of defects. It is assumed that both DMI and exchange coupling are changed on imperfect bonds. Qualitatively the same physical picture is obtained in two models which are considered in detail: B20 cubic helimagnets and layered magnets in which DMI leads to a long-period spiral ordering perpendicular to layers. We find that the distortion of the spiral magnetic ordering around a single imperfect bond is long-range: values of additional turns of spins decay with the distance $r$ to the defect as $1/r^2$ being governed by the Poisson's equation for electric dipole. At finite concentration of randomly distributed imperfect bonds, we calculate correction to the spiral vector. We show that this correction can change the sign of spin chirality even at $c\ll1$ if defects are strong enough. It is demonstrated that impurities lead to a diffuse elastic neutron scattering which has power-law singularities at magnetic Bragg peaks positions. Then, each Bragg peak acquires power-law decaying tails. Corrections are calculated to the magnon energy and to its damping caused by scattering on impurities.

Phase-lag heat conduction in multilayered cellular media with imperfect bonds

We present a theoretical framework to study the thermal responses of one-dimensional multilayered systems, functionally graded solid media, and porous materials. The method for thermal analysis resorts to non-Fourier heat conduction theories including three-phase-lag, dual-phase-lag, and hyperbolic heat conduction. The graded media are modeled as multilayered systems displaying finite numbers of layers. For each homogenous layer, the differential equations of heat conduction describing the wave-like three-phase-lag are solved in closed-form in the Laplace domain. Solutions accounting for proper interfacial and boundary conditions are first presented to describe the thermal behavior of heterogeneous solids and porous media. Transient temperature and heat flux are obtained in time domain via fast Laplace inversion. We then apply the solutions obtained with each heat conduction theory to one-dimensional media and compare their thermal behavior. Finally, maps are presented to visualize the thermal responses of cellular materials, functionally graded cellular materials, and multilayered systems. For the latter, particular attention is devoted to investigate the impact of key attributes defining graded media, such as layer bond imperfections and material heterogeneity.

Effects of Mass Layer Stiffness and Imperfect Bonding on a Quartz Crystal Microbalance

We study free vibrations of a crystal plate of AT-cut quartz carrying a thin mass layer operating as a quartz crystal microbalance for mass sensing. The mass layer is imperfectly bonded to the crystal plate with its interface described by the so-called shear-slip model that allows a discontinuity of the interface displacement. The effect of mass layer in-plane shear stiffness is also considered. The equations of anisotropic elasticity are used for the crystal plate with the omission of the small elastic constant <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">56</sub> . The mass layer is governed by the plane-stress equations of elasticity. An analytical solution is obtained using Fourier series, from which the resonant frequencies and vibration mode shapes are calculated. The effects of the mass layer in-plane shear stiffness, imperfect interface bonding on resonant frequencies and energy trapping are examined.