Durability Of Adhesive Joints Research Articles

Creep Crack Growth Behavior during Hot Water Immersion of an Epoxy Adhesive Using a Spring-Loaded Double Cantilever Beam Test Method.

Double cantilever beam (DCB) tests were conducted by immersing the specimens in temperature-controlled water while applying a creep load using a spring. By introducing a data reduction scheme to the spring-loaded DCB test method, it was confirmed that only a single parameter measurement was sufficient to calculate the energy release rate (ERR). Aluminum alloy substrates bonded with an epoxy adhesive were used, and DCB tests were performed by changing the initial load values, spring constants, and immersion temperatures for two types of surface treatment. The initial applied load and spring constant had no effect on the ERR threshold. In contrast, the threshold decreased with the increasing immersion temperature, but even in the worst case, it was 15% of the critical ERR in the static tests. Using the creep crack growth relationship, it was revealed that there were three phases of creep immersion crack growth in the adhesive joints, and each phase was affected by the temperature. The spring-loaded DCB test method has great potential for investigating the combined effects of creep, moisture, and temperature, and this study has demonstrated the validity of the test method. The long-term durability of adhesive joints becomes increasingly important, and this test method is expected to become widespread.

Simulation of the Durability of Adhesive Joints during Operation of Rubber—Metallic Products

Simulation of the Durability of Adhesive Joints during Operation of Rubber—Metallic Products

Two-functional phase-change pressure-sensitive adhesives based on polyisobutylene matrix filled with paraffin wax

Paraffin wax was used to impart the function of heat accumulation to pressure sensitive adhesives based on polyisobutylene (PIB) and simultaneously to suppress their cold flow. Laser microinterferometry showed 6% solubility of paraffin wax in PIB at 25 °C with achieving complete miscibility of PIB and wax at temperatures above 46 °C. The thermophysical and rheological properties of mixtures containing from 10% to 60% paraffin wax were investigated. According to calorimetry data, wax reduces the glass transition temperature of PIB, which in turn affects the apparent degree of wax crystallinity, shifting it in different directions. Paraffin wax significantly reduces the effective viscosity of the PIB melt and lowers the values of its storage and loss moduli. This simplifies the processing of adhesives and allows them to be used as easily flowable liquids. Nevertheless, the wax crystallizes during cooling, which leads to a multiple increase in the viscosity of adhesives to a level comparable or even greater than the viscosity of filler-free PIB. In this process, the heat is released in relatively larger quantities than during crystallization of pure wax, as additional heat is produced owing to the loss of solubility of wax in the PIB matrix. With an increase in the wax content, the durability of adhesive joints with steel firstly passes through a minimum, which is associated with the plasticizing effect of paraffin wax. However, the addition of 60% paraffin wax makes it possible to increase the durability of adhesive joints by 20 times, simultaneously reducing the melt viscosity of the adhesive by 4 decimal orders of magnitude. A key fact is that the resulting easy-to-process adhesive allows storing heat, i.e. to play two roles at the same time – a reinforced pressure-sensitive adhesive and a phase-change material.

Effects of ageing frequency on the interfacial failure and tensile properties of adhesively bonded Arcan joints exposed to cyclic ageing environments

The strength and durability of adhesive joints are significantly influenced by environmental conditions. When working in a humid environment, the adhesive tends to absorb moisture and this phenomenon can drastically reduce the mechanical performance of the adhesive joints. In practise, joints are usually subjected to cyclic ageing due to moisture absorption and desorption. Accordingly, it is necessary to study the ageing behaviour of the adhesives when they are exposed to environments with cyclic humidity conditions. Accordingly, the current study investigates the mechanical properties of adhesive joints with an epoxy-based adhesive subjected to cyclic ageing conditions using Arcan joint specimens. To this aim, static tensile tests were performed for both cyclic aged, dried, and unaged Arcan joints. The effect of cyclic ageing and drying conditions, such as absorption and desorption mechanisms, on the mechanical properties of the joints were studied. In the numerical part, an experimentally obtained diffusion coefficient (D) was used to simulate the water diffusion in Arcan joint. The results showed that key mechanical properties, such as tensile strength and displacement of the joints are reduced by the number of ageing cycles. The maximum strength degradation of the aged joints compared to the unaged condition was 94% for the third ageing cycle. For the dried condition, the strength of the joints was recovered although it was not fully returned to the initial stage. It was also found that the recovery ratio increases with the ageing cycles. It is shown that a short drying process can significantly recover the mechanical response of the cyclically aged adhesive joints, especially at higher ageing cycles.

The influence of interfacial failure on the tensile S–N response of aged Arcan joints

AbstractThe strength and durability of adhesive joints are significantly influenced by environmental conditions. Humidity absorption can cause deleterious effects on the adhesive joint's performance. The current study investigates the tensile properties of an epoxy‐based adhesive using Arcan joints (which is a kind of butt joint) subjected to different aging levels and loading conditions. To this end, joints with different aging times, as well as reference‐dried samples, were subjected to both the static and cyclic loading conditions. To construct the S–N curves, different cyclic load levels were applied to the joints. The static results showed that the mechanical properties, such as tensile strength of the joints decreased with an increase of the aging time. The fatigue strength and the fatigue lifetime were significantly decreased by the increase of aging levels, mainly due to an interfacial aging phenomenon. The water diffusion in interfacial aging is faster than that of the adhesive aging, which resulted in a premature failure of the joints for both the static and fatigue conditions. Based on the experimental results, the interfacial diffusion coefficient was calculated using an inverse method. According to the results, the rate of water uptake along the interface is more than 30 times higher than that which occurs in the adhesive.

Multiple local hydroxyl groups as a way to improve bond strength and durability in structural adhesives

ABSTRACT Polymer chain-extenders with one (AE, i.e., aminoethanol), two (APD, i.e., 2-amino-1,3-propanediol), and three (tris, i.e., 2-amino-2-(hydroxymethyl)-1,3-propanediol) pendant ethanol groups were used in a model epoxy structural adhesive to investigate their influence on joint strength and durability. While AE and APD showed modest improvements in lap shear strength, the bond durability of adhesive joints was improved dramatically using tris without the need for a chemical surface treatment. Specifically, single lap shear measurements (ASTM D1002 10) using 2024-T3 adherends demonstrated that tris (0.28 − 1.4 wt%) incorporated into a model structural adhesive can improve the lap shear strengths by 50% under dry conditions and by 64% under hot/wet conditions (immersion in water at 63°C for 14 days). The performance under hot/wet conditions is similar to that observed for adherends chemically surface treated with a commonly used silane coupling agent (i.e., 3-aminopropyltriethoxysilane). This enhanced performance of tris is likely a result of improved interfacial interactions because the small amounts of tris additive had an insignificant effect on the mechanical properties of the adhesive formulations themselves based on dynamic mechanical analysis. In addition, X-ray photoelectron spectroscopy measurements on fractured specimens showed that the adhesive remained on the substrate, implying largely cohesive failure in the specimens.

Experimental and numerical analysis of cyclic aging in an epoxy-based adhesive

The strength and durability of adhesive joints in different applications is of special concern where aging can significantly influence the joint permanence. Aging of adhesive joints is very crucial in industries where the joints are exposed to variable environmental conditions during their life. Due to the aging, the mechanical properties of the adhesive layer, interfacial bonding properties and substrates mechanical performance (in case of composite substrate), change. In real applications, the aging conditions is cyclic where the joints frequently experience aging and drying conditions. This article investigates the mechanical behavior and water absorption properties of an epoxy based adhesive in bulk form, subjected to cyclic aging conditions. The effect of cyclic aging on different parameters such as the rate of moisture absorption and desorption, stress-strain curve, glass transition temperature (Tg) have been studied. In the numerical section the parameters of moisture diffusion obtained experimentally were used to simulate the moisture distribution in dog-bone specimens. The experimental results show that in cyclic aging conditions the moisture diffusion constant and the maximum moisture content increase with aging cycles. Also it was found that the mechanical properties such as the elastic modulus and the tensile strength in saturation states decrease with increasing the aging cycles.

Effect of hygrothermal aging and cyclic thermal shocks on the mechanical performance of single-lap adhesive joints

The durability of adhesive joints is potentially affected by the presence of water and thermal shocks. Therefore, the current work intends to study the effect of hygrothermal aging and cyclic thermal shocks degradation on the tensile properties of single-lap adhesive joints. To accomplish this goal, adhesive joints were subjected to several cycles composed of two blocks of 12 h and involving, each block, different temperatures and environments (water and air). Two batches of specimens were used in this study, involving aluminium 6082-T6 adherends with ductile and brittle adhesives. The maximum failure load and ultimate strain was obtained with the ductile adhesive. Higher hygrothermal aging temperatures result in a drastic reduction of the failure load and ultimate strain, irrespective of the adhesive type. The failure load and ultimate strain are marginally affected by the effect of thermal shocks in air, while the failure load decreases significantly with the increase in hygrothermal shocks. However, the combination of water/air was found to be more severe than water/water.

Effect of surface contamination on the durability and strength of stainless steel – polyisobutylene pressure-sensitive adhesive bonds

Cleaning of substrate's surface with a solvent is a standard step in a procedure of adhesive joints preparation while carrying out adhesion tests. However, is cleanliness of substrates really so important? The effect of contamination of substrate's surfaces with vegetable (sunflower) and mineral (naphthenic) oils on the strength and durability of adhesive joints formed by neat and organoclay-filled polyisobutylene-based PSAs with a stainless steel substrate was studied. For the filled composition, the strength of the adhesive joints was higher, even with the contaminated surface, than for the system with the neat PIB. Contamination of the surface leads to the formation of a weak layer of plasticized polymer, which contributes to decreasing of the adhesion strength and durability. These parameters, however, are restored over time, which could be connected with the absorption of the contaminants by the adhesive material, as a result of polymer swelling, and their migration to the bulk of the adhesive. The ability of contaminants that can be absorbed and removed from the surface into the bulk of the adhesive is determined by their solubility in the adhesive. It was demonstrated using laser microinterferometry method that PIB is miscible with naphthenic oil, whereas PIB − sunflower oil system exhibits upper-critical-solution-temperature behavior. These observations provide an explanation to the growth trends of durability and strength of the joints over time in the cases of sunflower and naphthenic oil contamination of the substrate's surface.

Experiment Analysis To Examine The Effects Of Adhesive And Adherent Type Of Geometrical Configuration On Joint Failure Loads

Abstract The intention of trialing’s is to calculate the effects of adhesive and adherent type on CFRP joints and to encounter the relation between the durability of adhesive joints and substantial properties on joint failure loads. The traditional practices to join two metals or any constituents were riveting, welding, brazing, bolting etc., On the other hand, for fibre materials, the above-stated techniques won’t effort out, for fibre materials epoxies are essential. During the extreme loading conditions, (adhesive or cohesive) bonding may bust. This paper is testing the adhesive bonding and cohesive bonding properties between CFRP with diverse conditions such as, varying overlap lengths, loading conditions, pre-treatment process, treating conditions of epoxies. The adhesive bonding is virtuous and captivating maximum load is premeditated. Currently, the analysis of adhesive A: Cold-cure epoxy (Araldite 2021), adhesive B: Toughened Acrylic (F246), adhesive C: Heat-cured toughened epoxy (ESP110), are led through varied loads with distinct lap joints were tested and results were plotted. Adhesive C has high strength compered to all other adhesives and maximum strength of joint depends on pre-treatment, thickness and overlap of joints.

Experimental studies of adhesive joints in four-point static bending

A new type of specimens, being the subject of the patent application in Poland, was used in the studies. The sample consists of two beams: top one (longer) made of structural material such as steel, aluminium alloy and bottom one (shorter), which is part of the glass, which is tempered, layered or traditional glass. The top beam may have any cross-section, e.g. rectangular, square, c-shaped, etc., which is characterized by different values of the moment of inertia. The bottom beam, meanwhile, is made of rectangular glass. The tests were performed under four-point bending conditions at monotonic incremental bending moment values on the Instron 5965 durability machine. The sample allows bending tests to be performed at bending loads while maintaining a constant bending moment in the glued joint area. The new type of specimen has been developed to allow for the testing of glued joints of different structural rigidity, with special emphasis on the steel-glass, aluminum-glass, steel-aluminum and similar connections. The experimental study of the durability of adhesive joints under four-point bending conditions with the monotonic incremental bending moment allows to determine the values of stresses, whose value is related to initiation of damage of the tested joint.

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.

Accelerated Comparative Fatigue Strength Testing of Belt Adhesive Joints

Belt joints are the weakest link in the serial structure that creates an endless loop of spliced belt segments. This affects not only the lower strength of adhesive joints of textile belts in comparison to vulcanized splices, but also the replacement of traditional glues to more ecological but with other strength parameters. This is reflected in the lowered durability of adhesive joints, which in underground coal mines is nearly twice shorter than the operating time of belts. Vulcanized splices require high precision in performance, they need long time to achieve cross-linking of the friction mixture and, above all, they require specialized equipment (vulcanization press) which is not readily available and often takes much time to be delivered down, which means reduced mining output or even downtime. All this reduces the reliability and durability of adhesive joints. In addition, due to the consolidation on the Polish coal market, mines are joined into large economic units serviced by a smaller number of processing plants. The consequence is to extend the transport routes downstream and increase reliability requirements. The greater number of conveyors in the chain reduces reliability of supply and increases production losses. With high fixed costs of underground mines, the reduction in mining output is reflected in the increase in unit costs, and this at low coal prices on the market can mean substantial losses for mines. The paper describes the comparative study of fatigue strength of shortened samples of adhesive joints conducted to compare many different variants of joints (various adhesives and materials). Shortened samples were exposed to accelerated fatigue in the usually long-lasting dynamic studies, allowing more variants to be tested at the same time. High correlation between the results obtained for shortened (100 mm) and traditional full-length (3×250 mm) samples renders accelerated tests possible.

About a possibility of increasing the adhesion strength between mineral glass and polymeric binder under radio-frequency induction plasma treatment

The paper investigated influences of radio-frequency induction plasma treatment on the surface of sheet mineral glasses for household purpose. Discussion for casting the most suitable treatment modes and theirs substantiation is shown. During the investigation the most productive plasma treatment modes for applied binders have been found. It is shown that the durability of adhesive joints between mineral glass and polymeric binder under low-temperature plasma treatment increase to 65%.

An updated review of adhesively bonded joints in composite materials

Continuing interest and more developments in recent years indicated that it would be useful to update Banea and da Silva paper entitled “Adhesively bonded joints in composite materials: an overview”. This paper presents an updated review of adhesively bonded joints in composite materials, which covers articles published from 2009 to 2016. The main parameters that affect the performance of bonded joints such as surface treatment, joint configuration, geometric and material parameters, failure mode etc. are discussed. The environmental factors such as pre-bond moisture, moisture and temperature are also discussed in detail and how they affect the durability of adhesive joints. Lots of shortcomings were resolved during the last years by developing new materials, new methods and models. However, there is still a potential to evaluate and identify the best possible combination of parameters which would give the best performance of composite bonded joints.

Fatigue durability assessment of automotive adhesive joints by an in situ corrosion fatigue test

Fatigue and corrosion damage are the major concerns of automotive adhesive joints, yet literature reports few works about the in situ fatigue durability of adhesive joints in corrosive environment. This study presents an investigation on the fatigue durability of automotive adhesive single lap joints by an in situ corrosion fatigue test. The joints were manufactured with commercial coated AA5754-O aluminum sheets bonded by a toughened epoxy structural adhesive. An in situ corrosion chamber was designed and employed to simulate a humid and corrosive environment by spraying 5% saline solution or distilled water mist around the joints’ overlap area during fatigue testing. The test results show that in the 5% saline solution mist environment, the joints’ fatigue lives encountered a great loss for about an order in magnitude compared to the joints tested in laboratory environment. The difference of fatigue lives between 5% saline solution mist test and distilled water mist test is insignificant. The fracture surface analysis by scanning electron microscope and EDX techniques indicates that the adhesive joints failed interfacially in the corrosive environment, which differs from the cohesive failure mode in the laboratory environment.

RESISTÊNCIA AO CISALHAMENTO DAS JUNTAS ADESIVAS PRODUZIDAS COM TRÊS DIFERENTES ESPÉCIES DE MADEIRAS E ADESIVOS VINÍLICOS PARA APLICAÇÕES NÃO ESTRUTURAIS

Os adesivos utilizados na colagem de madeiras para aplicações não estruturais normalmente contêm uma emulsão de poli(acetato de vinila) (PVAc) estabilizada com poli(álcool vinílico) e alguns aditivos. A ligação adesiva formada com essa classe de adesivo é pobre quando exposta à umidade e à temperatura. Nesse contexto, a classificação prévia dos adesivos utilizados para aplicações não estruturais, com resistência à umidade e à temperatura, é muito importante para a qualidade e durabilidade das juntas adesivas. Neste trabalho, foi estudada a influência de três espécies de madeiras (Fagus sylvatica L., Mimosa scabrella Bentham e Micropholis cf. venulosa Mart. & Eichler) na resistência ao cisalhamento das juntas adesivas preparadas com três adesivos vinílicos, sintetizados com diferentes concentrações do N-butoximetilacrilamida (NBMA). Os ensaios de resistência ao cisalhamento, na linha de colagem, foram realizados sob diferentes ciclos de acondicionamento das juntas adesivas. Os resultados indicaram que há diferenças significativas na resistência de colagem das juntas adesivas e na porcentagem de falha na madeira provocada, tanto pela espécie de madeira quanto pelo tipo de adesivo utilizado. Os adesivos produzidos foram classificados de acordo com a classe de durabilidade, após várias etapas de acondicionamento. Os valores mais altos de resistência ao cisalhamento foram observados nas juntas coladas com as madeiras de Micropholis cf. venulosa Mart. & Eichler e Fagus sylvatica L., com o adesivo AD-3. O menor valor de resistência ao cisalhamento foi observado nas juntas adesivas preparadas com a madeira da espécie Mimosa scabrella Bentham. A madeira Micropholis cf. venulosa Mart. & Eichler mostrou-se mais adequada para a substituição da madeira Fagus sylvatica L.

Influência da estrutura química do co-monômero nas propriedades termomecânicas e durabilidade de uniões adesivas submetidas à ação da água

A caracterização termomecânica, assim como a durabilidade de juntas adesivas usando diferentes polímeros epoxídicos no estado vítreo foram analisadas. Os polímeros foram baseados no prepolímero do éter diglicidílico do bisfenol A (DGEBA) curado com diferentes aminas alifáticas. Análises termomecânicas no modo de torção foram realizadas para monitorar o fator de perda (tan δ), o módulo de armazenamento (G'), e o módulo de perda (G") em função da temperatura. Os ensaios de adesão foram realizados em uniões de simples sobreposição usando substrato de aço quando submetidas à ação da água a temperatura ambiente, e a 80 ºC, com o objetivo de avaliar a durabilidade das juntas adesivas a diferentes temperaturas. As análises termomecânicas evidenciaram diferenças significativas nos valores de tan δ, G' e G" em função da temperatura para as redes estudadas. As melhores propriedades adesivas são obtidas para uniões polímero-substrato que usam polímeros que apresentem estrutura de rede mais flexível. A durabilidade das juntas adesivas quando submetidas à ação da água causa menor prejuízo à formulação com piperidina. Este comportamento foi associado à baixa tendência de absorver água deste polímero, devido à homopolimerização dos grupos epóxi, que originam uma estrutura de rede com baixa concentração de grupos hidroxila.

A Method of Predicting the Stresses in Adhesive Joints after Cyclic Moisture Conditioning

The durability of adhesive joints is of special concern in structural applications and moisture has been identified as one of the major factors affecting joint durability. This is especially important in applications where joints are exposed to varying environmental conditions throughout their life. This paper presents a methodology to predict the stresses in adhesive joints under cyclic moisture conditioning. The single lap joints were manufactured from aluminium alloy 2024 T3 and the FM73®-BR127® adhesive-primer system. Experimental determination of the mechanical properties of the adhesive was carried out to measure the effect of moisture uptake on the strength of the adhesive. The experimental results revealed that the tensile strength of the adhesive decreased with increasing moisture content. The failure strength of the single lap joints also progressively degraded with time when conditioned at 50°C, immersed in water; however, most of the joint strength recovered after drying the joints. A novel finite element based methodology, which incorporated moisture history effects, was adopted to determine the stresses in the single lap joints after curing, conditioning, and tensile testing. A significant amount of thermal residual stress was present in the adhesive layer after curing the joints; however, hygroscopic expansion after the absorption of moisture provided some relief from the curing stresses. The finite element model used moisture history dependent mechanical properties to predict the stresses after application of tensile load on the joints. The maximum stresses were observed in the fillet areas in both the conditioned and the dried joints. Study of the stresses revealed that degradation in the strength of the adhesive was the major contributor in the strength loss of the adhesive joints and adhesive strength recovery also resulted in recovered joint strength. The presented methodology is generic in nature and may be used for various joint configurations as well as for other polymers and polymer matrix composites.

Predicting the Environmental Lifetime of Adhesive Joints under Laboratory Conditions

Adhesives are being increasingly used in civil engineering applications as a means of bonding together similar or dissimilar materials. The prediction of the strength of bonded components is therefore vitally important and different analytical approaches and methods are being used to investigate and predict the durability of adhesive joints. In this work an attempt has been made to predict the durability of butt mild steel adhesive joints subjected to static stresses in the presence of water from data obtained using double-torsion mild steel adhesive joints subjected to similar conditions. In both cases accelerated aging test equipment were built. The first step in developing a test method and model for predicting the environmental fracture data of butt adhesive joints has been proposed that was independent of the detailed butt joint geometry. The model was reasonably successful and accounted for the excessive crack tip blunting that occurred in the adhesives. This is the first time such a model is reported in the literature that may be useful when all variables are included.