Durability Of Adhesive Bonds Research Articles

Microencapsulated markers for damage detection in adhesive joints

ABSTRACTThe durability of adhesive bonds is not only affected by the quality of the bonding procedure but also by aging processes which influence the bond performance negatively on a long time scale. Especially the building industry, where safety related joints are increasingly boned with adhesives, demands new quality assurance methods. Therefore, appropriate monitoring techniques for developing cracks or critical stresses are essential.A new approach for in situ monitoring of transparent/opaque adhesives will be presented in this paper. Microcapsules, filled with special dyes, are embedded into adhesive systems. Upon breakage through cracks or exceedance of certain stress levels within the adhesive seam, the capsules release their liquid cores which leads to a detectable color change and, thus, enables non-destructive condition monitoring of the bond. In order to examine the feasibility of the approach, microcapsules are formed via interfacial polymerization. Microscopy techniques such as optical or scanning electron microscopy allow to study the capsule morphology, shape and dimensions (size and wall thickness) in dependence to the preparation procedure. Thereupon, the durability and release behavior are investigated with thermal analyses (differential scanning calorimetry and thermogravimetric analyses). Atomic force-based nanoindentation measurements give an insight into the size-dependency of mechanical properties like stiffness and burst forces.Finally, the principle of health monitoring is evaluated by dispersing the prepared capsules in the adhesive systems.Apart from the experimental examinations, numerical simulations of the crack propagation within the adhesive matrix are performed to demonstrate the effect of different microcapsule sizes and capsule walls on the fracture behavior.This preliminary study demonstrates the basic feasibility of the approach, but there is still a great need for investigations in order to employ the concept for industrial purposes.

Effects of silane surface functionalization on interfacial fracture energy and durability of adhesive bond between cement paste and epoxy

Epoxy adhesives are experiencing widespread use in concrete structures. However, a common concern regarding the adhesive joints in the infrastructure is their durability when exposed to harsh environments, most particularly, high levels of moisture. This work recognizes that adhesive bond between epoxy and substrate resists applied loads by a combination of chemical (hydrogen) bonds and mechanical interlock. Given the complexity of the stress-transfer mechanism this work focused exclusively on the chemical bond component between epoxy and cement paste, while the mechanical interlock was minimized through polishing of the cement paste substrate. A beam adhesion test method with notched interface was developed to assess the durability of chemical bonds between the adherents when aged by water immersion; surface functionalization of cement paste substrate was additionally explored as means of improving the chemical bonding and adhesion along the interface. Test results indicated that interfacial fracture energies were improved in both dry and conditioned groups with silane surface treatment. Analysis of interfacial failure modes with respect to the analytical crack kink criterion revealed that interphase region between epoxy and cement paste is characterized with higher fracture toughness than the cement paste substrate. The study lays groundwork for improvement in the durability of adhesive joints in related infrastructure through bottom-up interface design.

Adhesives for Achieving Durable Bonds with Acetylated Wood.

Acetylation of wood imparts moisture durability, decay resistance, and dimensional stability to wood; however, making durable adhesive bonds with acetylated wood can be more difficult than with unmodified wood. The usual explanation is that the acetylated surface has fewer hydroxyl groups, resulting in a harder-to-wet surface and in fewer hydrogen bonds between wood and adhesive. This concept was evaluated using four different adhesives (resorcinol–formaldehyde, emulsion polymer isocyanate, epoxy, and melamine–formaldehyde) with unmodified wood, acetylated wood, and acetylated wood that had been planed. Strikingly, acetylation did not hinder adhesive bonds with a waterborne resorcinol–formaldehyde adhesive that bonded equally well to both unmodified and acetylated yellow poplar. An epoxy adhesive bonded better to the acetylated wood than to the unmodified wood, in contrast to an emulsion polymer isocyanate, which gave less durable bonds to acetylated than to unmodified wood. Planing of the acetylated wood surface prior to bonding reduced bond durability for the epoxy adhesive and increased the amount of surface hydroxyl groups, as measured using X-ray photoelectron spectroscopic analysis of the trifluoroacetic anhydride-treated wood. These experiments showed that wood modification is useful in understanding wood-adhesive interactions, in addition to determining how to develop adhesives for acetylated woods.

Durability of adhesive bonds to tooth structure involving the DEJ.

The importance of the Dentin Enamel Junction (DEJ) to the durability of adhesive bonds to tooth structure is unclear. In fact, no investigation has been reported on contributions of the DEJ to the fatigue resistance of the bonded interface. In this study, the durability of adhesive bonds to tooth structure involving the DEJ was quantified and compared to that of adhesive bonds to enamel only, not including the DEJ. Two different configurations of enamel bonding were considered, including when tensile stress is focused on the outer enamel (occlusal configuration) or the inner decussated enamel (decussated configuration). The resistance to failure for all bonded interfaces was assessed under both static and cyclic loading to failure. Results showed that the durability of the bonded interfaces was primarily a function of their resistance to crack initiation and growth. The bonded interface strength involving the DEJ was significantly (p ≤ 0.05) greater than that of bonds to enamel only with occlusal configuration, under both static and cyclic loading. While the fatigue strength of bonds involving the DEJ was approximately 20% greater than that for enamel bonds with occlusal configuration (7.7MPa) it was lower than that of enamel with the decussated configuration. The DEJ deterred cracks from extending readily into the dentin but it did not prevent fatigue failure. These results suggest that the durability of bonds to enamel are most dependent on the enamel rod decussation and that the DEJ plays a minor role.

Can long-term dentine bonding created in real life be forecasted by parameters established in the laboratory?

Tooth-coloured plastic dental fillings secured by adhesives to tooth structures are widely used to fix decayed teeth. Whereas laboratory tests demonstrate rapid deterioration of the ability of the adhesives to stick to dentine, clinical studies show that these fillings are relatively durable. This discrepancy suggests that the parameters used for simulating bond degradation in the laboratory setting do not correlate well with clinical outcomes. The present study examined the long-term tensile bond strength of resin composite fillings performed in real life and under different laboratory-simulated bonding conditions to identify parameters that may be used to forecast the durability of adhesive bonds created in dentine. Fillings placed in vivo were subjected to different periods of intraoral function. In vitro specimens were bonded based on whether simulated pulpal pressure (SPP) or thermomechanical cycling was implemented, and how long the completed fillings were stored in water. Thermomechanical cycling used in combination with long-term water ageing are useful in forecasting the decline in strength of resin-dentine bonds created in vivo. These parameters should be adopted for future evaluations. Conversely, the use of SPP does not appear to be a significant parameter in the simulation of long-term clinical deterioration of bond integrity.

Novel adhesion promotion of aluminium for aerospace environments

This study focuses on analysing the durability of adhesive bonds formed in samples of Aluminium 6063, Titanium Nitride deposited Al 6063 and Anodized Al 6063 using epoxy adhesive Weicon A. Two types of studies are performed, first, samples of Aluminium 6063, Titanium Nitride deposited Al 6063 and Anodized Al 6063, are bonded by an epoxy adhesive Weicon A. Second, the samples are bonded by the adhesive with reinforcement of Ca2SiO4 nanoparticles in different proportions. The samples are examined using the scanning electron microscopy to study the morphology of the coating. A lap shear test is performed to determine the strength of the adhesive after the specimens were subjected to harsh chemical environments. A thermogravimetric analysis is performed on the adhesive to understand the effect of nanoparticles in the thermal stability in the Weicon A. It is understood from the tests that the titanium nitride coated Al 6063 samples bonded with Weicon A exhibited greater bond strength and also retained the strength when exposed to harsh environments. The inclusion of calcium silicate nano-particles showcased a considerable reduction in the bond strength. The thermal stability of Weicon A seems to be unaffected by the inclusion of calcium silicate nanoparticles.

Influence of Electrolytical Oxidising of Silumine Surfaces on the Quality of Bonding with Epoxy Resin

Abstract The article presents the preparation process of AC-AlSi12 aluminum alloy surface by application of anodic oxidation method. The method enables the formation of a porous oxide layer (Al2O3) which generates the substrate of durable adhesive bond with an epoxy resin. It also presents the influence of the form of silicon precipitates in the modified alloy upon anodizing process, uniform structure and thickness of the oxide layer as well as the topography of its surface which is expected to improve adhesion of the resin and silumin. The paper describes how the position of oxidized surface against the negative electrode influences the coating structure. The studied silumins are intended to form the material for casting of 3 dimensional objects whose parts will change the distribution of electric field strength that may cause non-uniform structure of the coating.

Effect of carbodiimide on the fatigue crack growth resistance of resin–dentin bonds

Recent studies have shown that ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) inactivates endogenous dentin proteases, thereby preventing collagen degradation and improving the durability of adhesive bonds to dentin. Bond durability is routinely assessed by monotonic microtensile testing, which does not consider the cyclic nature of mastication. ObjectiveTo characterize the effect of an EDC pretreatment on the fatigue crack growth behavior of resin–dentin bonds. MethodsBonded interface Compact Tension (CT) specimens were prepared using a three-step etch-and-rinse adhesive and hybrid resin–composite. Adhesive bonding of the treated groups included a 1min application of an experimental EDC conditioner to the acid-etched dentin. The control groups did not receive EDC treatment. The fatigue crack growth resistance was examined after storage in artificial saliva for 0, 3 and 6 months. ResultsThere was no significant difference in the immediate fatigue crack growth resistance of the EDC-treated and control groups at 0 months. However, after the 3 and 6 months storage periods the EDC-treated groups exhibited significantly greater (p≤0.05) fatigue crack growth resistance than the control specimens. SignificanceAlthough the EDC treatment maintained the fatigue crack growth resistance of the dentin bonds through 6 months of storage, additional studies are needed to assess its effectiveness over longer periods and in relation to other cross-linking agents.

One-year Adhesive Bond Durability to Coronal and Radicular Dentin Under Intrapulpal Pressure Simulation.

To evaluate the microtensile bond strength (μTBS) of different adhesives to coronal vs radicular dentin after one year of storage in artificial saliva and under intrapulpal pressure (IPP) simulation. Roots of 36 freshly extracted premolars were sectioned 5 mm apical to the cemento-enamel junction and pulp tissue was removed. Buccal enamel and cementum were trimmed to obtain standardized flat dentin surfaces. Specimens were divided into three groups (n=12/group) according to the adhesive strategies utilized: a two-step etch-and-rinse adhesive; a two-step self-etch adhesive; and a single-step self-etch adhesive. Adhesives and resin composite were applied to coronal and radicular dentin while the specimens were subjected to IPP simulation. After curing, specimens were stored in artificial saliva at 37°C in a specially constructed incubator while the IPP was maintained for either 24 hours or one year prior to testing. Bonded specimens were sectioned into sticks with a cross section of 0.8 ± 0.01 mm(2) and subjected to μTBS testing. Data were statistically analyzed using multi-way analysis of variance (ANOVA) with repeated measures; one-way ANOVA tests; and Bonferroni post hoc test (p<0.05). Failure modes were determined using a scanning electron microscope at 100× magnification. ANOVA results revealed a statistically significant effect for the adhesive strategy (p<0.001) and storage period (p<0.001) as well as for their interaction (p=0.024) on the μTBS. However, dentin substrate and its interactions revealed no significant effects. For both dentin substrates, the two-step self-etch adhesive revealed statistically significantly higher μTBS values than did the other two adhesives after 24 hours and one year of storage. After one-year storage, a significant decrease in bond strength values of all tested adhesives occurred with both dentin substrates. Modes of failure were mainly adhesive and mixed. Adhesives were not sensitive to structural differences between coronal and radicular dentin even after one year of storage under IPP simulation. However, all tested adhesive systems strategies were sensitive to storage.

Nanosilica-toughened polymer adhesives

High-performance adhesives are of great importance to achieving strong and durable adhesive bonds in a wide range of applications. This article presents an investigation of the use of nano-sized silica particles to improve the fracture toughness of polymer adhesives, focusing on the effects of particle size, matrix ductility and adhesive thickness. The results reveal that the performance of nano-silica as a toughening additive depends strongly on the matrix’s ductility and adhesive thickness. With merely 2.1vol% nano-silica, the fracture toughness of an epoxy has been improved from 0.19 to 1.34kJ/m2, representing a 605% improvement. Microscopy studies show that this improvement is attributed to the formation of a dilatation zone, approximately 2–3μm thick, which dissipates energy. The nanoparticles in general produce a higher adhesive toughening effect than their micron-sized peers. A significant toughening effect has been made by dispersing the nanoparticles in a relative ductile matrix, while such an effect was not observed for the micro-sized particles.

Monitoring and damage detection of adhesive bonds with micro-encapsulated markers

The quality and durability of adhesive bonds are affected by aging processes. Therefore, appropriate monitoring for early damage detection is essential for such bonds. For these reasons, we set out to develop an adhesive-based joining technology that makes early detection of potential defects in adhesive bonds possible. In this method, various dyes are added to the adhesive used, which indicate, if the specific load is exceeded. These dyes are micro-encapsulated through different methods, producing capsules of different sizes and wall thicknesses. When an adhesive bond is damaged or overloaded, the capsule would break and the dye would be released. The released colors can be detected optically or with suitable measurement systems. To demonstrate this technology, various experiments were carried out. Firstly, changes in adhesive properties were checked through thermal analysis and then pure substance specimens were produced and tested as means of comparison. Finally, the formulated adhesives were used to produce specimens for compressive shear tests, using glass and aluminium. The advantage of this technology by comparison to conventional nondestructive testing methods is the possibility to detect defects in adhesive bonds before the durability of the adhesive bond itself is affected.

Surface treatment of aluminium automotive sheet: Mythology and technology

The use of aluminium automotive sheet to save weight, fuel and carbon emissions is increasing as EU OEMS strive to reach progressively tougher targets and from the need to avoid fleet average penalty payments. Surface finishing of structural sheet for alloys like AA5754 generally involves cleaning and pretreatment followed by roll coating with a lubricant. For alloys supplied for body panels like AA6016 and its variants, surface treatments can include a mechanical texturing treatment followed by cleaning and pretreatment with a stabilising treatment and then spray coating with a dry film lubricant. Surface finishing capacity in the EU is now available on six finishing lines with an estimated total capacity of about 350 kt/year. This is just about in balance with present demand, but the capacity of the existing lines will soon be exceeded by the rapidly increasing demand. Further finishing lines will be required to keep pace with the increasing demand. There is a difficult balance to achieve between cost and finishing process complexity and the demanding requirements of formability, adhesive bond durability and surface appearance specified by the automotive companies in the EU. It is important to understand the need and value of each of the finishing treatments considered to be essential for automotive sheet supply in the EU compared to the less stringent requirements applied in North America and Japan. The complex microstructural and technological issues surrounding surface finishing and sheet performance will be analysed and discussed in detail and opportunities identified. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Quantification of Endogenous Matrix Metalloprotease 8 (MMP‐8) in Dentinal Cavity Walls

Inhibition of matrix metalloproteinase (MMP) activity is expected to increase the long‐term stability and durability of resin‐based restorations by preventing degradation of denuded collagen fibrils in the hybrid layer. Endogenous MMP‐8, released by adhesive procedures, can hydrolyse collagen fibrils at resin/dentin interfaces compromising adhesive bond durability. In this study, occlusal surfaces of n=4 extracted non‐carious human molar teeth (&lt;2 days from extraction, stored −80°C) were removed using a low‐speed diamond saw. 2×4×2mm cavity was prepared on the dentinal surface, leaving surrounding dentinal walls of 1mm thickness. Cavity walls were then acid‐etched with 38% phosphoric acid, pulverized using a liquid nitrogen analytic mill, demineralized in 1% phosphoric acid, suspended in extraction buffer (100mM Tris‐HCl pH 7.6, 0.1mM ZnCl2, 100mM CaCl2, 200mM NaCl, 1% Triton X‐100) and centrifugally concentrated. The results of our study showed that an average of 0.238pg MMP‐8/mg dentin is present as measured by ELISA. This study is the first of its kind to identify endogenous levels of MMP‐8 present in a single‐tooth dentin sample. This information will contribute to the design of specific, clinical inhibition of endogenous MMP activity in dentinal cavity walls to prolong the longevity of resin‐based restorations.

Fatigue of the resin–enamel bonded interface and the mechanisms of failure

The durability of adhesive bonds to enamel and dentin and the mechanisms of degradation caused by cyclic loading are important to the survival of composite restorations. In this study a novel method of evaluation was used to determ.ine the strength of resin–enamel bonded interfaces under both static and cyclic loading, and to identify the mechanisms of failure. Specimens with twin interfaces of enamel bonded to commercial resin composite were loaded in monotonic and cyclic 4-point flexure to failure within a hydrated environment. Results for the resin–enamel interface were compared with those for the resin composite (control) and values reported for resin–dentin adhesive bonds. Under both modes of loading the strength of the resin–enamel interface was significantly (p≤0.0001) lower than that of the resin composite and the resin–dentin bonded interface. Fatigue failure of the interface occurred predominately by fracture of enamel, adjacent to the interface, and not due to adhesive failures. In the absence of water aging or acid production of biofilms, the durability of adhesive bonds to enamel is lower than that achieved in dentin bonding.

Additives for enhancing the drying properties of adhesives for corrugated boards

Adhesives play a fundamental role in many modern technologies, and adhesive failure can have catastrophic consequences. It is, therefore, valuable to understand the factors important for the production of a good durable adhesive bond. The additives are also used to enrich the properties. The objective of this paper is to increase the drying speed of the starch adhesive by adding suitable additives and thereby increasing the production speed of corrugated board manufacturing. The other functional additives that could be incorporated in minor amounts for better drying speed are studied and selected. Their properties such as drying speed, strength, viscosity and pH are tested. The results from the tests are compared and the best additive for fast drying is selected.

Bond Durability of Adhesives Containing Modified-monomer With/Without-fluoride After Aging in Artificial Saliva and Under Intrapulpal Pressure Simulation

To evaluate the dentin bond strength durability of adhesives containing modified-monomer with/without-fluoride after storage in artificial saliva and under intrapulpal pressure simulation (IPPS). The occlusal enamel of 48 freshly extracted teeth was trimmed to expose midcoronal dentin. Roots were sectioned to expose the pulp chamber and to connect the specimens to the pulpal-pressure assembly. Specimens were assigned into four groups (n=12) according to adhesive system utilized: a two-step etch-and-rinse adhesive system (SB, Adper Single Bond 2, 3M ESPE), a two-step self-etch adhesive system (CSE, Clearfil SE Bond, Kuraray Medical Inc), and two single-step self-etch adhesives with the same modified monomer (bis-acrylamide)-one with fluoride (AOF, AdheSE One F, Ivoclar-Vivadent) and the other without (AO, AdheSE One, Ivoclar-Vivadent). Bonding was carried out while the specimens were subjected to 15-mm Hg IPPS. Resin composite (Valux Plus, 3M ESPE) buildups were made. After curing, specimens were aged in artificial saliva and under 20-mm Hg IPPS at 37°C in a specially constructed incubator either for 24 hours or six months prior to testing. Bonded specimens (n=6/group) were sectioned into sticks (n=24/group) with a cross section of 0.9 ± 0.01 mm(2) and subjected to microtensile bond strength (μTBS) testing using a universal testing machine. Data were statistically analyzed using two-way analysis of variance (ANOVA) with repeated measures, one-way ANOVA tests, and a t-test (p<0.05). Failure modes were determined using a scanning electron microscope. The μTBS values of SB and CSE fell significantly after six-month storage in artificial saliva and under IPPS, yet these values remained significantly higher than those for the other two adhesives with modified monomers. There was no significant difference in the bond strength values between fluoride-containing and fluoride-free self-etch adhesive systems (AOF and AO) after 24 hours or six months. Modes of failure were mainly adhesive and mixed. Based on the results of this study, 1) Fluoride addition did not affect dentin bond durability; and 2) despite the fact that the single-step adhesive system with modified monomer showed stability, bond strengths associated with these systems remained lower than those of multistep adhesive systems.

Characterization of the durability of adhesive bonds

ABSTRACTThe deterioration of adhesive bonds as a result of exposure to aggressive service environments is a problem for both metallic and composite bonded joints in aircraft structures. In this context airworthiness issues arising from the in service growth of small naturally occurring defects in adhesively bonded repairs has led to the need to develop a fracture mechanics based approach for setting the inspection intervals associated with the growth of such naturally occurring defects. This involves issues associated with both durability and damage tolerance that are associated with such small defects because it is well known that, for metals, the use of long crack data can lead to erroneous non‐conservative estimates. As such a means for assessing the issues related to such small naturally occurring defects is urgently needed. In this context the Boeing Wedge test, and its related variants, plays a central role in not only qualitatively assessing environmental performance but also in ranking surface treatments. However, this method has the problem that the initial defect introduced during wedge testing may not be representative of the small initial defects that can arise in service. Thus the relative ranking of various surface treatments obtained using wedge tests may be misleading. To this end, the paper presents a simple fracture mechanics based method that has the potential to account for the discrepancy in the initial defect size. This approach resembles crack growth laws developed to account for the growth of both long and short cracks in metals, environmentally enhanced crack growth in metals and delamination growth in composites.

The Influence of Solvent Content in Liquefied Wood and of the Addition of Condensed Tannin on Bonding Quality

Liquefi ed wood (LW) is a promising natural material that can be used as a part of the adhesive formulation. However, adhesive bonds made of LW only, have low durability. The aim of this study was, therefore, to increase the durability of adhesive bonds containing LW. LW was obtained with liquefaction of black poplar wood in ethylene glycol (EG) as the solvent and sulphuric acid (SA) as the catalyst. An optimal time of 120 minutes and a wood/EG mass ratio of 1:3 was defi ned for liquefaction at 180 °C. After liquefaction, the EG was evaporated in order to achieve a low solvent content LW with a fi nal mass ratio of 1:1. A hydroxyl number for 1:3 and 1:1 LW was determined in order to examine the reduction of hydroxyl groups. Four different adhesive mixtures were prepared: LW with a mass ratio of 1:1 (LW1:1 ), LW with a mass ratio of 1:3 (LW1:3 ), LW with a mass ratio of 1:1 and added condensed tannin (CT) (LW1:1 /CT), and LW with a mass ratio of 1:3 and added CT (LW1:3 /CT). The solid beech wood lamellas, which were bonded with these adhesive mixtures, were tested directly after bonding, and later on, after 7, 30 and 50 days. The test results indicated greater bonding shear strength in the case of LW1:1 compared to LW1:3. The addition of CT did not contribute to essentially higher shear strength values. The adhesive mixtures LW1:1 and LW1:1 /CT (uncured and cured) were analyzed using FT-IR spectroscopy. No signifi cant differences were observed between the cured LW1:1 and the LW1:1 /CT samples.

Influence of Low Temperature Cycles on the Ultrasonic Behaviour of Pretreated 2024 T3 Aluminium Joints

Many authors have considered the problem of adhesive bond durability over a long period of time or under special environmental conditions, and all have concluded that surface preparation is of paramount importance. Here, 2024 T3 aluminium alloy bonded joints, whose metallic plates underwent phosphoric acid pretreatment prior to bonding, are investigated before and after exposure to ―40°C for 67 hours. This procedure of ageing is repeated several times and the samples are examined, after each cycle by ultrasonic eigen modes of the tri-layer (called Lamb waves in order to traduce the guided form of theses modes). In particular, the position of the cutoff-frequencies of ultrasonic guided waves which propagate into the bonded structure allows us to calculate the stiffnesses of the metal/adhesive interfaces via a rheological model. Thus, after exposure, a progressive decrease in the value of the stiffnesses is observed even for pretreated surfaces.

Influence of low temperature cycles on the integrity of pretreated 2024 T3 aluminium joints by an ultrasonic method

Many authors have considered the problem of adhesive bond durability over a long period of time or under special environmental conditions, and all have conclued that surface preparation is of paramount importance. Here, 2024 T3 aluminium alloy bonded joints, whose metallic plates underwent phosphoric acid pretreatment prior to bonding, are investigated before and after exposure to -40 °C for 67 h. This procedure of ageing is repeated several times and the samples are examined by ultrasonic Lamb waves after each cycle. In particular, the position of the cutoff-frequencies of ultrasonic guided waves which propagate into the bonded aluminum/epoxy/aluminium structure allows us to calculate the stiffnesses of the metal/adhesive interfaces with a rheological model. Thus, after exposure, a progressive decrease in the value of the stiffnesses is observed even for pretreated surfaces. Two complementary mechanical explanations are proposed. First, the cold exposure of the sample and the difference between thermal dilatation coefficients of aluminum and epoxy produce a damage of the interfacial zone. Second, the cooling introduces microcracks in the epoxy then caracterized by a smaller Young modulus.