Thickness Of Adhesive Layer Research Articles

The effective characteristics and electroelastic state of active composite elements

For rods in which the piezoelectric and elastic layers are perpendicular to the rod axis and the lamination has a periodic structure, formulae for the effective characteristics of inhomogeneous material are obtained and the equations that describe the electroelastic state are constructed by the asymptotic method of homogenization. Such active composite elements are known as stacks. As an example, the electroelastic state of stacks executing forced harmonic vibrations under the action of an electrical load is calculated, the effective characteristics of material are found, and both the slowly varying state described by the rod theory and the rapidly varying state caused by the inhomogeneity of the layered structure are calculated. The effect of the thickness of weak adhesive layers on the electromechanical coupling coefficient, characterizing the stacks as energy convertors, is investigated.

Effect of Adhesive Thickness on Transverse Low-Speed Impact Behavior of Adhesively Bonded Similar and Dissimilar Clamped Plates

This study investigates the effect of adhesive thickness on the transverse low-speed impact behavior of adhesively bonded similar (Al–Al, St–St) and dissimilar (Al–St, St–Al) clamped plates using the three-dimensional explicit finite element method. The contact force and plastic dissipation histories are studied for various impact energies and adhesive thicknesses. The residual plastic strains in both adhesive layer and the two plates increase with increasing impact energy. The central transverse deflections become maximal in Al–Al, moderate in Al–St, St–Al and minimal in St–St bonded plates. The back plates of all configurations deform noticeably. The stiff steel plate results in a shorter contact time, a higher contact force, a lower plastic dissipation energy and the impact energy is absorbed by the adhesive layer rather than by the front and back plates, whereas Al–Al plates dissipate it as much as the adhesive layer. The total contact time gets longer with increasing impact energy. St–St bonded plates experience larger damaged regions in both plates and adhesive layer than those in Al–Al bonded plates. The adhesive thickness has only a minor effect on the magnitude of the contact force and contact time, whereas a stiffer (St) front or back plate affects considerably the contact force and total contact time. Increasing the adhesive thickness decreases apparently residual plastic strains in plates and the adhesive layer, the central transverse deflection. A thick adhesive layer results in a minor increase in the kinetic energy of impactor, a shorter total contact time, a lower plastic dissipation energy and smaller damaged areas on the back faces of the lower plate, along the adhesive–plate interfaces.

雰囲気制御IH-FPP処理による改質層形成機構に及ぼす投射粒子の影響

Basic mechanisms of generating a surface modified layer formed by a previously developed atmospheric controlled IH-FPP system, consisting of induction heating system and fine particle peening system, were investigated. Three types of specimen treated at 900°C in argon with Cr, Al2O3 and Cu shot particles were prepared. Surface microstructures of the treated commercial-grade pure iron were characterized with a scanning electron microscope (SEM), an energy dispersive X-ray spectrometer (EDX) and an X-ray diffraction analysis (XRD). When treatment was carried out using Cr particles, the transferred layer and the diffused layer of the shot-particle element formed at the treated surface. This was because the radius of Cr atom was almost the same as that of the Fe, thus forming a solid solution in the substrate. Conversely, when the treatment was applied using chemically stable Al2O3 particles, a transferred layer only was observed. In the case of Cu particles, adhesion occurred due to the low melting temperature of Cu particles, resulting in the formation of a thick adhesive layer such as that generated by thermal spraying. These results suggest that the characteristics of the modified layer, generated by the atmospheric controlled IH-FPP treatment system, can be controlled by varying the shot particles and other processing parameters.

Possibilities and limits of adhesive layer thickness optical evaluation

The uniform adhesive layer thickness belongs to the key criterions of the bonded joint formation. On the basis of long-term laboratory findings it was evaluated as one of basic effects on the strength changes. This fact leads to the objective evaluation necessity and to the technical practice respecting. The carried out laboratory experiments are indicative of the incongruity between the expected adhesive layer thickness and the real value determined in the bonded joint square cut using the microscope.

Terahertz spectroscopy on adhesive bonds

Especially in the aerospace and automotive industries, adhesive joints continually gain importance. They hold the potential to replace conventional fastening methods by offering distinctive advantages over competing techniques, such as being cost-effective and very flexible in terms of material compatibility and surface conditions. Due to the strong demand for adhesive bonding, many technologies have been applied to study the characteristics and, especially, the integrity of adhesive bonds. If non-destructive testing is required, the choice of measuring tools narrows down considerably. In this paper, we propose terahertz time-domain spectroscopy as a non-destructive tool for the analysis of adhesive layers. We demonstrate that specialized data extraction schemes enable the contact-free determination of the adhesive layer thickness, the refractive index and the absorption coefficient from THz measurements, and show experimentally obtained data on three different material systems.

Dynamics of Piezoelectric Smart Beams Using a Three-Parameter Elastic Foundation Model

Piezoelectric patches are usually externally bonded to host structures as sensors and/or actuators. The performance and integrity of this type of smart structures are determined by the interface stresses within the adhesive layer. In this study, the dynamic behavior of a piezoelectric smart beam is analyzed using a novel three-parameter elastic foundation model. Closed-form solutions of the deformations, interfacial stresses, strain transfer, and sensing charge output are obtained. The new interfacial stress solutions overcome the inherent shortcomings in the existing two-parameter elastic foundation model by not only satisfying the zero shear stress boundary condition at the free edge, but also correctly predicting two different peeling stress distributions along the piezoelectric patch/adhesive interface and the host beam/adhesive interface. When the thick adhesive layer is used, the present three-parameter elastic foundation model exhibits high accuracy; while the existing two-parameter elastic foundation model significantly overestimates the response of the smart beam.

Static failure analysis of axially loaded aluminium–epoxy butt joints

The present work is concerned with the study of the influence of adhesive layer thickness on the mechanical strength of axially loaded aluminium–epoxy butt joints. The main goal is to predict the rupture force using model equations that combine enough mathematical simplicity to allow their usage in engineering problems with the capability of describing a complex non-linear mechanical behaviour (three-dimensional state of stress; possibility of cohesive failure, of adhesive failure or mixed failure, depending on the geometry of the joint, on the adhesive strength and on the interaction between surfaces). The predicted values of the rupture force for different values of the thickness of the adhesive layer are compared with experimental data, showing a good agreement.

Effect of Adhesive Layer Thickness and Drug Loading on Estradiol Crystallization in a Transdermal Drug Delivery System

The effects of adhesive layer thickness and drug loading on estradiol crystallization were studied in a drug-in-adhesive patch. Patches containing different estradiol loadings (1.1% and 1.6% w/w) in different thicknesses (45, 60, and 90 μm) were prepared by coating of a homogenous mixture of adhesive solution and the drug on a siliconized release liner by a film applicator. After drying, the film was laminated on a Poly(ethylene terephthalate) backing layer and cut into appropriate size. Release tests were performed using thermostated Chien-type diffusion cells. Cross-section of the patches was observed by optical microscopy. Scanning electron microscopy was done for surface analysis of the patches after drug release test. Crystal formation was not expected in the adhesive layer based on the linear free-energy relationship formalisms however; crystalline regions were observed in different locations through the thickness of the patches. These regions were significantly more discontinuous in 45 μm samples which elucidated the effective role of adhesive layer thickness in drug crystallization. Extensive crystallization observed for thicker patches was attributed to the strong crosslinking capability of estradiol hemihydrate. Drug release study confirmed some of the crystallization results. No significant increase was observed in the burst release with increasing in thickness from 45 to 60 μm which can be attributed to the severe increase in the crystallization extent. Also, formation of a crystalline layer near the releasing surface and more discontinuous pattern of the crystals in some samples was confirmed by investigation of the drug release curves.

Influence of Layer Thickness on Cohesive Properties of an Epoxy-Based Adhesive—An Experimental Study

Cohesive laws are determined for different layer thicknesses of an engineering adhesive. The shape of the cohesive law depends on the adhesive layer thickness. Of the two parameters of the cohesive law—the fracture energy and the strength—the fracture energy is more sensitive to thickness variation than the strength. The fracture energy in peel mode (Mode I) increases monotonically as the thickness is increased from 0.1 to about 1.0 mm. At an adhesive thickness of 1.5 mm, the fracture energy is slightly lower than for a 1.0 mm adhesive thickness, indicating a maximum between 1.0 and 1.5 mm. In shear mode (Mode II), the thickness dependence is not as strong, but an increasing trend in fracture energy with increasing adhesive thickness is evident. A slight decrease in strength with increasing adhesive thickness is found in both loading modes.

Controlling the Morphology of Gold Films on Poly(dimethylsiloxane)

Gold films on poly(dimethylsiloxane) (PDMS) have applications in stretchable electronics, tunable diffraction gratings, soft lithography and as neural interfaces. The electrical and optical properties of these films depend critically on the morphology of the gold. Therefore, we examine qualitatively and quantitatively the factors that affect the morphology of the gold film. Three morphologies can be produced controllably: microcracked, buckled, and smooth. Which morphology a gold film will adopt depends on the film stress and the growth mode of the film. The factors that affect the film stress and growth mode, and thus the morphology, are as follows: deposition temperature, film thickness, elastic modulus, adhesion layer thickness, surface properties of the PDMS, and mechanical prestrain applied during deposition. We discuss how the different components of the film stress and growth mode of the film affect the morphology.

Elastic analysis of interfacial stresses for the design of a strengthened FRP plate bonded to an RC beam

In this paper, the problem of interfacial stresses in RC beams strengthened with bonded composite laminates is analyzed using linear elastic theory. It explicitly considers the interface slip effect on the structural performance by including both the effect of the adherend shear deformations and the time-dependent deformations (such as shrinkage and creep). This new method needs only one differential equation to determine both shear and normal interfacial stress whereas the others solutions need two differential equations. Closed-form solutions are derived for plated RC beams simply supported at both ends and verified through direct comparisons with existing results. A parametrical study is carried out to show the effects of some design variables, e.g., thickness of adhesive layer and FRP plate.

Durability of Wet Bond of Hybrid Laminates to Cast-in-Place Concrete

Wet bond is a chemical bond developed to connect fiber-reinforced polymer (FRP) stay-in-place formwork to cast-in-place concrete for a composite action. Curing of chemical adhesive and fresh concrete occurs simultaneously in wet bond. Since FRP-concrete composite structure so designed is strongly dependent on the bond between FRP and concrete, a durable bond is of paramount importance. This paper presents a study on durability performance of wet bond exposed to sustained low temperature, freeze-thaw cycles, and wet-dry cycles. Single lap pull-off tests were conducted to evaluate the effect of exposure on bond. It was found that both first crack load and ultimate load of wet bond were reduced in comparison to dry bond. This reduction was more severe in first crack load than in ultimate capacity and was associated with voids, thickness, and surface of adhesive layer. The epoxy in wet bond had reached comparable degree of cure to dry bond and even gained a higher Tg . Environmental exposures did not show mor...

TEM characterization of a silorane composite bonded to enamel/dentin

Objectives The low-shrinking composite composed of combined siloxane–oxirane technology (Filtek Silorane, 3M ESPE, Seefeld, Germany) required the development of a specific adhesive (Silorane System Adhesive, 3M ESPE), in particular because of the high hydrophobicity of the silorane composite. The purpose of this study was to characterize the interfacial ultra-structure at enamel and dentin using transmission electron microscopy (TEM). Methods Non-demineralized/demineralized 70–90 nm sections were prepared following common TEM specimen processing procedures. Results TEM revealed a typical twofold build-up of the adhesive resin, resulting in a total adhesive layer thickness of 10–20 μm. At bur-cut enamel, a tight interface without distinct dissolution of hydroxyapatite was observed. At bur-cut dentin, a relatively thin hybrid layer of maximum a few hundreds of nanometer was formed without clear surface demineralization. No clear resin tags were formed. At fractured dentin, the interaction appeared very superficial (100–200 nm). Distinct resin tags were formed due to the absence of smear plugs. Silver-nitrate infiltration showed a varying pattern of both spot- and cluster-like appearance of nano-leakage. Traces of Ag were typically detected along some part of the enamel–adhesive interface and/or between the two adhesive resin layers. Substantially more Ag-infiltration was observed along the dentin–adhesive interface of bur-cut dentin, as compared to that of fractured dentin. Conclusions The nano-interaction of Silorane System Adhesive should be attributed to its relatively high pH of 2.7. The obtained tight interface at both enamel and dentin indicates that the two-step self-etch adhesive effectively bridged the hydrophilic tooth substrate with the hydrophobic silorane composite.

Bond Thickness Effects upon Dynamic Behaviour in Adhesive Joints

The influence of adhesive layer thickness on the dynamic behaviour of the single-lap adhesive joints is investigated in this paper. The ABAQUS finite element analysis (FEA) software was used to predict the frequency response functions (FRFs) of the single-lap adhesive joints of different thickness of the adhesive layer. As a reference, the FRFs of a cantilevered beam without joint were investigated as well. It is clear that the FRFs of the four beams are close to each other within the frequency range 0~1000 Hz. It is also found that the composite damping of the single-lap adhesive joint increases as the thickness of the adhesive layer increases.

Debonding Analysis along a Softening FRP-Concrete Interface between Two Adjacent Cracks in Plated Beams

External bonding of fibre reinforced polymer (FRP) composites has become a common way for strengthening concrete members. The performance of the interface between FRP and concrete is one of the key factors affecting the behaviour of the strengthened structure. For this FRP-concrete structure, there are two types of debonding failures: plate end debonding and intermediate crack (IC) induced debonding. This paper presents an analytical solution for the second type debonding failures in FRP-concrete bonded joint model where the FRP plate is subject to tension at both ends. Both the strengthened beam and strengthening FRP are modeled as two linearly elastic Euler–Bernoulli beams bonded together through a thin adhesive layer. The debonding process of the FRP–concrete interface is discussed in detail, and closed-form solutions of bond slip, interface shear stress, and axial force of FRP in different stages are obtained. Parametric studies are further carried out to investigate the effect of the thickness of adhesive layer on the bond behavior of FRP–concrete interface.

Finite difference three-dimensional solution of stresses in adhesively bonded composite tubular joint subjected to torsion

Traditionally, the adhesive layer in adhesively bonded joints is simplified as having constant shear and peel stresses across the thickness. In this study, it is modeled as a separate 3D elastic body without the uniform stress assumption. The stress state in an adhesively bonded fiber-reinforced composite tubular joint subjected to a torsional load is theoretically analyzed. A finite difference method is utilized to solve the system of equilibrium equations. The solution is validated by comparison with data found in the literature. The effects of fiber orientation, composite laminate stacking sequence, overlap length, adhesive layer thickness, and adhesive stiffness on the shear and peel stress distribution are evaluated and presented. The results show that all the six stress components are present and they vary considerably across the adhesive layer thickness; 3D analysis is desired, especially for general laminated composite adherends.

Adhesive interface layer effects in PZT-induced Lamb wave propagation

In PZT-induced acousto-ultrasound techniques, the adhesive layer between aPZT and a host structure significantly affects sensor signals. However, its effectshave been barely studied so far. A numerical model is essential to fundamentallyunderstand the role of the adhesive interface. Using the hybrid spectral element, theeffects of the adhesive bond-line layer on the Lamb wave generation and receptionwere modeled and compared with available test data for validation of the hybridspectral element. The validations were conducted with different adhesive layerthicknesses. The trends in simulation results agreed well with the experiments.Parametric studies are presented to understand the adhesive layer effects. In thesestudies, adhesive thickness and stiffness, and PZT diameter and thickness, areselected as parameters. The physics of the adhesive layer are then discussed.

Optimum thickness of joints made of GFPR pultruded adherends and polyurethane adhesive

This paper presents results of experimental and numerical investigations on double-lap joints composed of pultruded GFRP profiles and polyurethane adhesive subjected to quasi-static axial tensile loading. The objective was to investigate the effect of the joint geometry on the structural response of adhesively-bonded joints and, in particular, to seek for experimental evidence of an optimum adhesive layer thickness. The influence of the adhesive thickness (0.3-10.0 mm) and the overlap length (50-200 mm) on the joint behavior was investigated. It was found that there is an optimum adhesive thickness of approximately 1.0 mm and joint strength consistently increases with the overlap length. (C) 2009 Elsevier Ltd. All rights reserved.

Bond–slip models for double strap joints strengthened by CFRP

This paper presents the results of a series of tension tests on CFRP bonded steel plate double strap joints. The main aim of this research is to provide detailed understanding of bond characteristics using experimental and numerical analysis of strengthened double strap joints under tension. A parametric study has been performed by numerical modelling with the variables of CFRP bond lengths, adhesive maximum strain and adhesive layer thicknesses. Finally, bond-slip models are proposed for three different types of adhesives within the range of the parametric study.

Simplified Impedance Model for Adhesively Bonded Piezo-Impedance Transducers

The electromechanical impedance technique employs surface-bonded lead zirconate titanate piezoelectric ceramic patches as impedance transducers for structural health monitoring and nondestructive evaluation. The patches are bonded to the monitored structures using finitely thick adhesive bond layer, which introduces shear lag effect, thus invariably influencing the electromechanical admittance signatures. This paper presents a new simplified impedance model to incorporate shear lag effect into electromechanical admittance formulations, both one-dimensional and two-dimensional. This provides a closed-form analytical solution of the inverse problem, i.e. to derive the true structural impedance from the measured conductance and susceptance signatures, thus an improvement over the existing models. The influence of various parameters (associated with the bond layer) on admittance signatures is investigated using the proposed model and the results compared with existing models. The results show that the new mod...