Bond Layer Research Articles

Use of CFRP Overlays to Strengthen Welded Connections under Fatigue Loading

This study evaluates the performance of various methods to prevent and repair fatigue damage in welded connections, a recurring problem that affects a significant number of steel bridges. Experimental tests and analytical simulations were carried out to investigate the fatigue performance of coverplate specimens in which the welded connections were reinforced with carbon-fiber reinforced polymer (CFRP) overlays. Specimens were loaded in three-point bending induced by a cyclic load to evaluate the change in fatigue-crack initiation life of the welded connections caused by the attachment of the CFRP overlays. Test results showed that when bond between the CFRP overlays and the steel was maintained, the reduction in stress demand was sufficient to extend the fatigue life of the welded connections from AASHTO fatigue-design Category E’ in the unreinforced configuration to the infinite fatigue life range. Test results also showed that the fatigue strength of the bond layer was drastically improved by introducing breather-cloth material within the bond layer.

Study of stress in tensile nitrogen-plasma-treated multilayer silicon nitride films

The authors conducted a physico-chemical analysis of tensile sequential-nitrogen-plasma-treated silicon nitride films, which function as stressor liners in complementary metal oxide semiconductor (CMOS) technologies. These films are made of stacked nanometer-thick, plasma-enhanced, chemical vapor-deposited layers which were individually treated with N2-plasma, to increase stress. This study allowed us to monitor the evolution of the films’ chemical composition and stress as a function of process parameters such as deposition and post-N2-plasma duration. Consistent with secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM) and other physico-chemical analysis results, it was shown that the elementary component of the films can be modeled with a bi-layer consisting of an untreated slice at the bottom that is covered by a more tensile post-treated film. In addition, we observed that longer plasma treatments increase residual stress, SiN bond concentration and layer density, while reducing hydrogen content. The stress increase induced by the plasma treatment was shown to correlate with the increase in SiN bonds following a percolation mechanism that is linked to hydrogen dissociation. Kinetics laws describing both SiN bond generation and stress increase are proposed and it is demonstrated that stress increase follows first-order kinetics.

An Alternative Cu-Based Bond Layer for Electric Arc Coating Process

A Cu-Al alloy has been used as bond coat between a carbon steel substrate and a final coating deposit obtained by applying the twin wire electric arc spraying coating technique. The presence of a copper-based material in the composite system can change the overall temperature profile during deposition because copper exhibits a thermal conductivity several times higher than that of the normally recommended bond coat materials (such as nickel-aluminum alloys or nickel-chromium alloys). The microstructures of 420 and 304 stainless steels deposited by the electric arc spray process have been investigated, focusing attention on the deposit homogeneity, porosity, lamellar structure, and microhardness. The nature of the local temperature gradient during deposition can strongly influence the formation of the final coating deposit. This study presents a preliminary study, undertaken to investigate the changes in the temperature profile which occur when a Cu-Al alloy is used as bond coat, and the possible consequences of these changes on the microstructure and adhesion of the final coating deposit. The influence of the thickness of the bond layer on the top coating temperature has also been also evaluated.

Nanoindentation strain-rate jump tests for determining the local strain-rate sensitivity in nanocrystalline Ni and ultrafine-grained Al

Abstract

Coupling layer corrections in pulse echo time‐of‐flight measurements in solids revisited.

It is well known that to extract highly accurate phase velocities from pulse echo ultrasonic time‐of‐flight measurements, one must take into account the influence of the medium used to acoustically couple the transducer (or buffer rod) to the sample being measured. This correction is typically on the order of 0.1% and is usually achieved by fitting experimental data to a scalar transmission line model in which echoes undergo phase shifts upon transmission through or reflection from the various boundaries. Fitting data to such a model involves varying two free parameters, the thickness of the coupling bond layer and the speed of sound in the sample. When performing the fit, one must make a choice between multiple solutions corresponding to different bond lengths and sample sound speeds. This talk will quantify the importance of the couplant correction in selected cases and discuss the error introduced to the extracted velocities by selecting a “wrong” fit to the data. Additionally, criteria and methods for...

Nonlinear Nondestructive Testing and Evaluation: Harmonic Imaging of Kissing Bonds and Micro Damage

Recent advances in harmonic imaging of industrial materials are reviewed. The conventional ultrasonic testing, which is based on acoustic impedance mismatch between contact materials, fails to detect kissing bonds, micro damage and micro defects within a bond layer of dissimilar materials. To the contrary, the nonlinear ultrasonic method, in particular higher harmonic method, makes use of higher harmonics excited at disordered structures mentioned above under incidence of large amplitude of tone-burst waves of a fixed frequency. This review is composed of three parts; key concept of nonlinear ultrasonics, instruments for higher harmonic imaging and harmonic images of kissing bonds, nonmetallic inclusions in metal, creep damage, microcracks in SiC/Ti composite, and weld boundaries. The higher harmonic imaging could be indispensable technique for quality assurance of bonded interfaces of dissimilar materials in near future.

Review of matrix metalloproteinases' effect on the hybrid dentin bond layer stability and chlorhexidine clinical use to prevent bond failure.

This review describes the relationship between dentin collagen hybrid bond layer degradation and the Matrix Metalloproteinases (MMPs) after their release by acid etch and rinse adhesives and self etching bonding adhesives that can reduce the bond stability over time. MMP-2, MMP-8 and MMP-9 are indicated as the active proteases that breakdown the collagen fibrils in the hybrid bond layer. Phosphoric acid in the acid etch and rinse bonding process and acid primers in the self etch process are implicated in the release of these proteases and their activation by several non-collagen proteins also released from dentin by the etching. MMPs are released in saliva by salivary glands, by cells in the gingival crevices to crevicular fluid and by pulpal odontoblasts cells to the dentinal fluids. These sources may affect the hybrid layer also. Evidence of the bond strength deterioration over time and the ability of Chlorhexidine to prevent bond deterioration by inhibiting MMP action are discussed. Dentin Bonding procedure utilizing Chlorhexidine for different application times and concentrations are being developed. The application of 2% Chlorhexidine to the phosphoric acid etch surface after rinsing off the acid is the only procedure that has been clinically tested for a longer period of time and shown to prevent bond strength degradation so far. The adoption of this procedure is recommended as means of improving bond stability at this time.

Ten‐years degradation of resin–dentin bonds

The purpose of this study was to evaluate the durability of resin-dentin bonds in 10-yr water-storage testing. Resin-dentin bonded bulk specimens were prepared using six commercially available resin adhesives. The resin-dentin bonded specimens were stored in water for 24 h (control group) or for 10 yr (experimental groups). After each storage period, the specimens were sectioned to make specimen beams and then subjected to a microtensile bond test. After the bond test, fractured surfaces were examined by scanning electron microscopy (SEM). In addition, interfacial observation of silver nanoleakage was performed using the backscatter electron mode of SEM. The bond strengths of four of the six adhesive systems tested decreased significantly after 10 yr. However, no significant bond-strength reduction was recorded for the other two systems. The interfacial observations showed water tree propagation in the bonding resin layer as a typical morphological change after aging for five of the six adhesives tested. Water tree propagation may be a symptom of degradation in the resin bonding layer of resin-dentin bonds.

Morphology and surface chemistry of kissing bonds in adhesive joints produced by surface contamination

Kissing bonds (KBs) or zero volume debonds are interfacial defects in which the substrate and adhesive are in intimate contact or couple through a weak bond or thin layer of contaminant. These KBs can dramatically alter the failure strength of the joint causing premature failure. Adhesive bonds containing a layer of Frekote 700NC, artificial sweat and cutting oil lubricant were produced on chromic acid etched aluminium substrates. All the joints with contaminants were examined using analytical field emission scanning electron microscope (FESEM) fitted with energy dispersive X-ray spectrometer (EDS) and also wavelength dispersive spectrometer (WDS). Photoacoustic Fourier transform infrared spectroscopy (FTIR) and mechanical testing were also performed. These methods were used to investigate whether such joints qualified as KBs. FESEM revealed changes in morphology and surface/interface chemistry related to the corresponding contaminants. Elemental distribution from EDS showed migration of artificial sweat and absorption of oil contaminant into the adhesives particularly when curing at elevated temperature while mould release agent (Freekote 700NC) remained at the metal/adhesive interface or within the interphase. FTIR revealed the presence of contaminants including comprehensive information of chemical interaction of the adhesives and contaminants within the interphase. Further understanding of the effect of various contaminants on wetting of contaminated substrates was obtained by contact angle measurement. A direct relationship was discovered amongst the reduction in surface energy of the substrate contaminated with Frekote, morphological changes and a reduction in joint strength, showing that Frekote is a potential contaminant in the production of kissing bonds.

A Randomized Clinical Evaluation of a One- and Two-step Self-etch Adhesive Over 24 Months

To evaluate the performance of All Bond SE used in a one- or two-step protocol in a 24-month randomized clinical study. Thirty-three patients with two similarly sized non-carious cervical lesions participated in this study. A total of 66 restorations were placed, half using the one-step All Bond SE protocol (SE-1) and the other half using the two-step All Bond SE protocol (SE-2). The restorations were evaluated at baseline and after 6, 12 and 24 months following the modified USPHS criteria and analyzed by the McNemar's test and Fisher's exact test (alpha = 0.05). After 24 months, six SE-1 and four SE-2 restorations were rated as Bravo in marginal discoloration The retention rates for SE-1 and SE-2 were 84.8% and 90.9%, respectively, after 24 months. Compared to baseline, the retention rate for SE-1 was statistically lower. All Bond SE used in the one- or two-step protocol resulted in high retention rates after 24 months.

Shear horizontal guided wave modes to infer the shear stiffness of adhesive bond layers

This paper presents a non-destructive, ultrasonic technique to evaluate the quality of bonds between substrates. Shear-horizontally polarized (SH) wave modes are investigated to infer the shear stiffness of bonds, which is necessarily linked to the shear resistance that is a critical parameter for bonded structures. Numerical simulations are run for selecting the most appropriate SH wave modes, i.e., with higher sensitivity to the bond than to other components, and experiments are made for generating-detecting pre-selected SH wave modes and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the shear stiffness modulus of a bond layer at different curing times between a metallic plate and a composite patch, such assembly being investigated in the context of repair of aeronautical structures.

Thermal Stresses Around Two Collinear Interface Cracks between a Nonhomogeneous Bonding Layer and One of the Two Dissimilar Elastic Half-Planes Under Uniform Heat Flux

In composite materials, in which two dissimilar elastic half-planes are bonded by a nonhomogeneous elastic layer, two collinear cracks are situated at the interface between the nonhomogeneous elastic layer and one of the two dissimilar half-planes. The stress intensity factors are solved under uniform heat flux normal to the cracks. The material properties of the bonding layer vary continuously from the lower half-plane to the upper half-plane. The boundary conditions are reduced to dual integral equations using the Fourier transform technique. In order to satisfy the boundary conditions outside the cracks, the differences in temperature and displacements at the crack surfaces are expanded in a series of functions that vanish outside the cracks. The unknown coefficients in each series are evaluated using the Schmidt method. The stress intensity factors were calculated numerically for selected crack configurations.

Development and Testing of High-temperature Piezoelectric Wafer Active Sensors for Extreme Environments

Development of high-temperature piezoelectric wafer active sensors (HT-PWAS) using high-temperature piezoelectric material for harsh environment applications is of great interest for structural health monitoring of high-temperature structures such as turbine engine components, airframe thermal protection systems, and so on. This article presents a preliminary study with the main purpose of identifying the possibility of developing PWAS transducers for high-temperature applications. After a brief review of the state of the art and of candidate high-temperature piezoelectric materials, the article focuses on the use of gallium orthophosphate (GaPO4) samples in pilot PWAS applications. The investigation started with a number of confidence-building tests that were conducted to verify GaPO4 piezoelectric properties at room temperature and at elevated temperatures in an oven. Electromechanical (E/M) impedance measurements and material characterization tests (scanning electron microscopy, X-ray diffraction, energy dispersive spectrometry) were performed before and after exposure of HT-PWAS to high temperature; it was found that GaPO4 HT-PWAS maintain their properties up to 1300°F (∼705°C). In comparison, conventional PZT sensors lost their activity at around 500 F (∼260°C). Subsequently, HT-PWAS were fabricated and installed on metallic specimens in order to conduct an in situ evaluation of their high-temperature performance. A series of in situ tests were performed using the E/M impedance and pitch-catch methods; the tests were conducted in two situations: (a) before and after exposure to high temperature and (b) inside the oven. The experimental results show that the fabricated HT-PWAS can survive high oven temperatures up to 1300°F (∼705°C) and still present piezoelectric activity. The article also discusses fabrication techniques for high-temperature PWAS applications, including the wiring of the sensor ground and signal electrodes, bond layer adhesive selection, and preparation.

First principle conductance calculation of zigzag, armchair and mixed geometries of S–6C–4H–S structures

We investigated ballistic transport properties of armchair (AC), zigzag (ZZ), mixed, rotated-AC and rotated-ZZ geometries of small molecules made of 2S, 6C & 4H atoms which exhibit sp–sp 2 hybridization. Well-tested first principle scattering states formalism implemented in Quantum Espresso package has been employed to perform the calculations. The chains made of 6C-atoms with 1S-atom at each end and 4H-atoms attached to different C-atoms have been relaxed. This resulted in AC, ZZ, mixed geometry structures. Differences in transmission coefficient ( T) curves of AC, ZZ and mixed molecules suggest geometry dependence of conductance and are in accordance with the previously reported results for AC and ZZ nanoribbons. In addition, our computed results for rotated-AC and rotated-ZZ suggest that the angle between electrode surface layers and molecular axis plays dominant role, compared to the role of angle between S–C bond and electrode surface layers, in determining conduction through the structure. The structures with molecular axis perpendicular to electrode surface layers yield higher conductance values.

Analysis of Mesoscopic Interfacial Mechanics of RC Beams Strengthened with FRP

Concrete is assumed as a three-phase composite material composed by aggregate, mortar matrix and the bond layer between them in mesoscopic. The damage constitutive relationships of the composed materials are determined. A local meso-model of reinforced concrete (RC) beams strengthened with hybrid FRP was established to investigate the crack propagation and failure modes. The results show that the deformation, damage and failure of the concrete occurred near the ends of the interface.

Thermal stability studies of plasma sprayed yttrium oxide coatings deposited on pure tantalum substrate

Plasma sprayed Yttrium oxide is used for coating of crucibles and moulds that are used at high temperature to handle highly reactive molten metals like uranium, titanium, chromium, and beryllium. The alloy bond layer is severely attacked by the molten metal. This commonly used layer contributes to the impurity addition to the pure liquid metal. Yttrium oxide was deposited on tantalum substrates (25 mm × 10mm × 1mm thk and 40 mm × 8mm × 1mm thk) by atmospheric plasma spray technique with out any bond coat using optimized coating parameters. Resistance to thermal shock was evaluated by subjecting the coated specimens, to controlled heating and cooling cycles between 300K to 1600K in an induction furnace in argon atmosphere having ≤ 0.1ppm of oxygen. The experiments were designed to examine the sample tokens by both destructive and non-destructive techniques, after a predetermined number of thermal cycles. The results upto 24 thermal cycles of 25 mm × 10mm × 1mm thk coupons and upto 6 cycles of 40 mm × 8mm × 1mm thk coupons are discussed. The coatings produced with the optimized parameters were found to exhibit excellent thermal shock resistance.

Input of atomic layer deposition for solid oxide fuel cell applications

The development of a new generation of solid oxide fuel cells (SOFCs) operating at lower temperatures with competitive performances requires the use of high-quality thin layers, either as electrolytes, electrodes or interlayers, such as catalysts, diffusion barriers, bond or protective layers. Atomic layer deposition (ALD) is a sequential chemical vapour deposition (CVD) technique allowing processing of one mono-atomic layer after another, conformal, adherent and homogeneous nano-scaled films which are often crystalline as-deposited without the need of high-temperature annealing treatments. Moreover, the scalability of ALD offers an important prospect for industrial applications. In this work, the literature dealing with ALD applied to SOFCs is thoroughly analysed, showing the present achievements as well as the numerous advantages of this technique. New developments for the future are currently in progress extending the potential use of ALD to other high-temperature devices such as proton electrolyte fuel cells, high-temperature water electrolysis, HTWE (with reversed SOFC-type systems) and molten carbonate fuel cells (MCFCs).

A Hybrid Joining Technology for Aluminum/Zinc Coated Steels in Vehicles

Currently, in the automotive industry, joining of the aluminum alloys with the steel is a crucial problem to be solved. Conventional joining techniques including resistance spot and gas metal arc welding are not acceptable for those applications due to a number of metallurgical problems. The investigation was carried out to develop the hybrid joining process combining the resistance spot welding and brazing. In this study, an attempt was made to apply hybrid process to the joining of dissimilar sheet metals, Al-Mg-Si (6000 series) alloy and low carbon steel sheet. Hybrid process (resistance spot weld/brazing) using filler metal was found to be effective to overcome the incompatibility between aluminum alloy and steel. Although hybrid joining process of Al alloy sheet and steel sheet did not produce acceptable bond strength, it was proved to have reasonable interfacial bond layer if the optimal process condition was applied.

Optical Power Transmission Through Adhesive and Bonding Layers

In this paper, we analyze the optical power transmission in structures that include a low-index intermediate layer and sources with a wide angular distribution. Special attention is paid to the angular average of the transmission coefficient, which can be cast in a universal form for two practically relevant classes of source layers. Due to the so-called frustrated total internal reflection, the structure transparency is highly sensitive to the intermediate layer thickness and index contrast. We show that the transmission coefficient for isotropic radiation may remain low even for optically thin low-index intermediate layers, so that the usual comparison between the optical thickness and the wavelength is no longer a reliable criterion. Calculations are presented for exemplary structures, such as a semiconductor scintillator bonded to a photodiode. The angular dependence of the transmission coefficient is shown to satisfy a simple and universal sum rule.

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...