International Journal of Adhesion and Adhesives最新文献

Epoxy adhesives are not conductive materials, usually requiring the use of fillers to create electrical bridging between the joint's substrates. This work aims at the implementation of UV fixation, instead of clamping jigs, on doped joints to ensure enough contact bridging pressure during curing. As such, an UV pre-curable adhesive was mechanically characterised in terms of strength – bulk tensile test and TAST (shear) –, and fracture toughness – DCB (mode I) and ENF (mode II) tests –, in the neat state (reference). Afterwards, for the doped configurations – 5%v/v conductive spheres (Sph), 15%v/v aluminium (Al) and 10%v/v graphite (C) – only mode I and II tests were considered accessing the filler's toughening effect. The electrical conductivity of the real joints was assessed through electric discharge machining (EDM). In the end, the Sph's were deemed necessary for bond thickness control. And the Al (mode I +50 % and II +61 %) and C (mode I +25 % and II +42 %) powders presented improvements in toughening the adhesive. However, UV-fixation failed to provide enough clamping pressure, during curing, to maintain the electrical bridging necessary for EDM.

Structural adhesives are widely used across industry sectors and, specifically in oil and gas, they appear as an alternative for structural joining instead of welding, to mitigate the risks arising from sparks in an environment with highly flammable products. In this sense, this article aims to evaluate the mechanical behavior of adhesive joints using the Double Cantilever Beam (DCB - to determine the GIC, mode I interlaminar fracture toughness) test before and after exposing these joints to severe environmental conditions, such as high humidity and high temperature. Also, three different surface treatments (manual sanding with abrasive sponge, solvent cleaning, and peel-ply application) of the adherend (carbon fiber/epoxy composite) are examined, as well as two different thicknesses of the adhesive layer (0.5 and 1.0 mm) to verify possible influences on the GIC behavior before and after conditioning. The results show that reducing manual surface treatment processes is a better option, to reduce the factors that cause greater dispersion in G_IC values. In particular, cleaning the adherend with just isopropyl alcohol (solvent) before applying the adhesive yielded better G_IC results among the tested techniques. Regarding thickness, the findings suggest that a greater thickness of the adhesive layer can lead to an increase in the plastic regions, enhancing the dissipation energy and improving the mode I interlaminar fracture toughness. Hygrothermal conditioning revealed the adverse effects of humidity on the adhesive, resulting in a 20–30 % reduction in G_IC. Differential Scanning Calorimetry (DSC) analyses demonstrate that conditioning caused a notable reduction in the glass transition temperature (T_g) of the adhesive.

The present paper proposes a non-contact ultrasonic testing method for the debonding inspection of metal-based composite structures, utilizing an improved electromagnetic acoustic transducer (EMAT). The enhanced EMAT incorporates a carbonyl iron powder coil backplate and a small butterfly coil to enhance the detecting ability for interfacial bonding. A two-dimensional finite element model is developed to quantify the effectiveness of the carbonyl iron powder coil backplate on increasing the eddy current density and the magnetic flux density in the specimen. An experimental setup was designed using the Ritec SNAP 5000 and the improved EMATs to examine an aluminium-epoxy resin composite structure. Ultrasonic C-scan images of the specimen's bonding interface were obtained from the experiment. Both simulation and experimental results show that carbonyl iron powder coil backplates can increase the efficiency of the EMATs. By investigating the influence of echo number on debonding detection, it was revealed that employing higher-order echoes and utilizing carbonyl iron powder as the coil backplate can enhance the debonding detection capability. The C-scan imaging results indicate that the utilization of high-order echoes enhances imaging quality, and the employment of high-quality miniaturized EMATs enhances the capability for quantitative analysis of debonding defects.

Purpose

To evaluate the effect of adding nano-chitosan on different properties of the adhesive and high-filled flowable composite resin (viewing the graphical abstract is suggested).

Background

Incorporating chitosan might improve the quality of adhesive and high-filled composite resin used in the deep margin elevation (DME) and other restorative methods.

Materials and methods

Two groups of composite disks (without chitosan, with 1 % chitosan) were created to evaluate antimicrobial effects, degree of conversion (DC), solubility and water sorption. Antimicrobial activity was evaluated through biofilm inhibition and disk agar diffusion tests while DC was analyzed using FTIR. For the microshear bond strength test (μSBS), extracted maxillary molars were sectioned 1 mm under the CEJ, undergoing immediate dentin sealing and DME in four groups: control, pretreatment chitosan application, adhesive+1 % chitosan, and composite+1 % chitosan. The forces and the modes of failure were recorded.

Results

Adding chitosan nanoparticles increased the antimicrobial activity, significantly (p < 0.05). The μSBS and DC did not differ significantly between the groups (p > 0.05), and the failures were mostly found in the adhesive mode. The solubility and water sorption increased significantly (p < 0.05), remaining in a clinically acceptable range though.

Conclusion

Adding chitosan could be a potential option to increase the antibacterial effect in the high-filled composite resin without any negative affect on μSBS or DC, and clinically unacceptable effect on solubility and water sorption. (The graphical abstract has been provided).

Clinical significance

Adding chitosan nanoparticles to high-filled flowable composite resin, increases the success rate of related restorative technique by adding the antimicrobial effect without any significant negative influence on other biomechanical properties.

Physicochemical properties of polymerizable composite materials based on styrene-acrylic dispersion Lacroten 244 are considered. It is established that polymerizable gels at coaliscence on magnesium alloys form developed surface structures with good adhesion to metal and paints. The mechanism of formation of such structures and their adhesive properties were investigated by X-ray photoelectron spectroscopy and SEM analysis. It has been shown that the porous structures arise as a result of the chemical reaction of polycondensation between acrylic acid and surface magnesium hydroxides. On low-carbon steel, polymerization of the styrene-acrylic dispersion is accompanied by a strong interfacial interaction with subsequent increase in a uniform polymer coating. It is shown that styrene-acrylic dispersions can be used to obtain cost-effective conversion coatings on magnesium and steel alloys with high protective properties.

Orthotropic deck plates were developed in the 1960s and are a frequently used construction method for steel bridges with large spans. In particular, the early structures of this construction method show increasing damage by fatigue cracks. The reasons for this are, among others, the increased traffic loads but also design deficiencies. Rehabilitation methods such as bolted solutions or crack welding are already in demand. However, these methods weaken the cross-section or have a thermal influence on the base material. Therefore, there is a demand for innovative and flexible strengthening concepts. In the field of adhesive bonding technology, the methods of slack and pre-stressed CFRP have become established as reinforcement (Kasper et al., 2020; Täljsten et al., 2009; Kasper et al., 2020; Do and Lenwari, 2020; Yu and Wu, 2017) [1–5]. Because of the high material costs and the complex structure, especially with pre-stressed CFRP, the application of this reinforcement technology has not yet been established in this fiel. In this case, strengthening procedures with bonded steel patches using structural, cold-curing epoxy resin or polyurethane adhesives are the preferred method for developing solutions in a German research project.

This article presents a new alternative for fatigue crack strengthening using bonded steel patches. The effectiveness of the strengthening variants is analysed on various notch details. For this purpose, the boundary conditions in steel construction are presented and considered, thus enabling a suitable adhesive selection. The fatigue tests were determined by analytical and numerical calculations, validated by static small-scale and component tests on different notch details. Cyclic tests on lap shear samples initially form the basis for the adhesive behaviour. The results of the tests on reinforced standard notch details show a longer service life of the reinforced test specimens compared to the reference tests.

Still, certain feasibility aspects remain open and are part of an ongoing project. The aims are to improve the design, dimensioning, fabrication and assembly results and validate and prepare them for use on the construction site.

Carbon fiber reinforced plastics (CFRP)laminates are widely used in aircrafts. The laminates are often assembled into components by adhesive joints, which will be affected by elevated temperature and humidity during use, resulting in performance degradation. In this study, a compression test of “Outer Single Lap” adhesive joints of CFRP on the rear fuselage of a certain type of navigable aircraft was carried out to investigate the influence of hygrothermal conditions on their performance. The experimental environment includes the elevated temperature and wet condition (ETW) (71 °C, 85%RH) and Room temperature drying (RTD) (23 %, 30%RH). The test results show that RTD specimens have different stages, and the initial stage has good plasticity and no damage. However, when the load reached 50 %, the initial opening pattern damage occurred, which eventually led to the failure of the 20° opening. Compared with RTD samples, the compression properties of ETW samples decreased by 47.7 %, and the opening damage disappeared. Fracture features and stain analysis were performed. The findings suggest the fracture characteristic can change from a brittle fracture to a ductile fracture in different testing conditions, and the influence of the humid and thermal environment on the resin structural adhesive layer itself, the compression state of the carbon fiber laminates, the interface between the carbon fiber laminates and the resin structural adhesive layer should be fully considered in the design.

Electrical generators or engines are based on full surface bonded steel plies. Temperature control is of high relevance to achieve reduced heat dissipations along with improved efficiency. This paper evaluated the effect of service relevant operating conditions (i.e., cooling agents, elevated service temperature and fatigue stresses) on the delamination behavior of electrical steel laminates on specimen and lab level. Therefore, a linear elastic fracture mechanics method and a set-up suitable for superimposed environmental and cyclic fatigue testing was implemented and employed. Two electrical steel laminate configurations were investigated. Pre-treated and un-treated sheets were double side coated with an epoxy varnish. Further, a catalyst was applied on both sides of the coated sheets made from the pre-treated substrate. Double cantilever beam specimens were manufactured by stacking and laminating 6 coated substrates. The fractured surfaces of the fatigue tested specimen were characterized by laser confocal microscopy and infrared spectroscopy in hemispheric reflectance mode. Threshold strain energy release rate values (G_th) ranging from 16 to 62 J/m² were obtained depending on the investigated coated substrates and the environmental conditions. Laminates produced with pre-treated sheets and catalyst exhibited notably enhanced G_th and decreased rates of crack propagation within the stable crack growth regime. A similar crack growth behavior was ascertained in hot air or oil-based cooling agent. The crossover point of the temperature dependent G_th values was indicative for the glass transition temperature of the adhesives. The fractured surfaces presented mainly cohesive failure at higher strain energy release rate values followed by mixed cohesive and interfacial failure when approaching to the threshold regime.

The study examines impact of bondline thickness and overlap length on the performance of single-lap bonded joints by analyzing the dynamic strain distribution using mechanoluminescence (ML) sensing. As the bondline thickness increased from 0.1 to 1.0 mm, the pattern of crack propagation from the top and bottom edges of the bonded region exhibited a marked transition toward rupture. Specifically, the differences in crack propagation behavior were visually identified near one or both bonding interfaces. Additionally, the impact of overlap length on failure modes in lap shear tests, including crack propagation and shear forces, was visually differentiated through ML. Despite its simplicity as a spray-on sensor, ML sensing demonstrated effectiveness in indicating mechanical behavior related to bonding design, such as bondline thickness and overlap length.

In this study, the backface strain (BFS) method applied by digital image correlation (DIC) is used to detect crack initiation and propagation in adhesively bonded single-lap joints (SLJ). By comparing the positive strain, due to the tensile load, and negative strain related to the bending moment, a point, called zero strain point (ZSP), can be detected on the substrate surface of the SLJ. Using the Bigwood and Crocombe analytical model, the presence of the ZSP on the backface is explained and the experimental results are used to detect it. The monitoring of the ZSP reveals useful information about the health condition of the joint. The main aim of this research is to investigate how the ZSP position varies by changing adhesive type (epoxy and polyurethane) and bonding area dimensions both in elastic conditions and damage progression. The results illustrate that the position of the ZSP in polyurethane SLJs is closer to the middle of the joint compared to epoxy SLJs. Additionally, the ZSP is more easily recognizable in epoxy adhesive SLJs when substrates are thicker. Finally, the ZSP showed negligible sensitivity to joint width for both types of adhesive joints regardless of the adhesive type. In conclusion, it is shown that the ZSP can be used as a monitoring index to detect damage initiation and propagation in SLJ specimens.