Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber–Reinforced Phenolic Resin Composite Joints

Energy-dispersive X-ray spectroscopy analysis (EDX) is an easy and exact method for determination of water diffusion coefficients and dynamics. Here we have calculated the water diffusion coefficients and dynamics in adhesive/carbon fiber–reinforced phenolic resin composite joints subjected to different surface treatments with both EDX and elemental analysis. The water diffusion coefficients and dynamics in the adhesive joints determined with EDX analysis are almost the same as those determined with elemental analysis. The durability of the adhesive joints with carbon fiber–reinforced phenolic resin composites subjected to silane coupling agent treatment is better than those subjected to sandpaper burnishing and chemical oxidation treatment.     

A Preliminary Study of the Use of Kynar® Piezoelectric Film to Measure Peel Stresses in Adhesive Joints

A variety of test techniques have been developed to test the performance of adhesives bonded in situ within joints. Most of these techniques measure strength, fracture toughness, or adhesive modulus of the bonded joint. Techniques to measure actual stress or strain values within a bonded joint are quite few in number. The Krieger gage¹ is able to measure the average shear displacement along a 12.5 mm. gage length of a thick adherend joint. It has been used primarily to measure in situ shear moduli of adhesives. Brinson and his colleagues² proposed bonding strain gages within adhesive joints to measure strains within the adhesive. Unfortunately, these gages are only sensitive to the lateral strains and not shear or peel strains. Because the lateral strains are dominated by the behavior of the adherends rather than the adhesive, the information which can be gained is incomplete.     

Stress Distribution in Single Lap Joints with a Cracked Composite Adherend—Part II: Laminated Adherends

The effect of a crack in the overlap region of an adhesive single lap joint is studied on the shear stress distribution in adhesive layer. Each adherend is considered to be a laminated composite material with unidirectional fibers aligned in the direction of the applied load. Crack location is selected to be in the top adherend laminate, in the form of cut fibers and matrix bays. The crack can occur in any layer. The shear-lag model is used to derive the equilibrium equations which are then solved by means of eigenvector expansion. The effects of adhesive thickness, crack size, and location in the adherend, total number of layers in each adherends, volume fraction of fibers, and type of fibers are investigated on the shear distribution in the adhesive as well as load distribution in the intact fiber at the crack tip located in the top adherend. The effect of dissimilar laminated adherends is also investigated on the adhesive shear stress distribution. According to the results, in the presence of a crack, the peak shear stress in the adhesive layer and load concentration in the fibers are very susceptible to the adhesive thickness and number of layers in laminated adherends.     

Stress Distribution in Single Lap Joints with a Cracked Composite Adherend—Part I: Single Lamina Adherends

The effect of a crack in the overlap region of a single step lap joint is studied on the shear distribution in the adhesive layer. Each adherend is considered to be a lamina with unidirectional fibers aligned in the direction of the applied load. Crack location is selected to be in the top adherend, in the form of cut fibers and matrix bays. The shear-lag model is used to derive the equilibrium equations which are then solved using eigenvector expansion. Additionally, a finite element model of the lap joint was prepared and solved using ANSYS. The results of the two methods perfectly match each other. The effects of crack location along the length of the overlap, crack size, edge cracks, adhesive thickness, and type of fibers were investigated on the shear distribution in the adhesive layer and its corresponding peak values. The effect of dissimilar adherends was also investigated on the adhesive shear stress distribution. According to the results, in the presence of a crack, the peak adhesive shear stress is very susceptible to adhesive thickness and type of fibers used in each adherend. Other factors also influence the peak shear stress to some degree.     

Ageing of Adhesive Bonds with Various Surface Treatments,Part 1: Aluminium–Dicyandiamide Cured Epoxy Joints

Ageing studies on adhesive-bonded aluminium–dicyandiamide cured epoxy joints prepared using a variety of different surface treatments were carried out using 100% humidity and cycling the joints between 42–48–42 °C every hour. The pretreatments include a chromic acid, silica/siloxane pretreatment, nonrinse chrome pretreatment, titanium/zirconium (Ti/Zr) pretreatment, and anodised substrate with no pretreatment. Dielectric spectroscopy measurements were used to characterise the rate of the water uptake and monitor the conversion of the surface oxide to hydroxide. These data were correlated with the changes that occurred in the mechanical strength of the bonds. The changes in the surface structure were observed using electron microscopy and elemental analysis conducted using X-ray photoelectron spectroscopy. The dielectric permittivity changes observed were similar for all the different pretreatments, indicating that the predominant process was water absorption. However, small differences were observed that reflect the different surface treatments used. Ageing at an elevated temperature of 70 °C provided definite evidence of hydration of the surface oxide layer. Electron microscopy of the fracture surface indicated oxide-to-hydroxide conversion and was reinforced by X-ray photoelectron spectroscopy. Predominantly, the changes in the mechanical strength observed at low temperature are consistent with the plasticization of the adhesive. However, at the elevated temperature of 70 °C, evidence for weakening of the interfacial layer by hydration becomes evident as a reduction in the mechanical strength. The dielectric measurements allowed the changes in the bond to be followed nondestructively. The mechanical strength of the etched-only pretreatment aged surprisingly well and at the lower temperature of ageing was comparable with the no-rinse chrome and titanium/zirconium pretreatments. The least durable was the PT2Cr-free treatment; however, all treatments showed a significant level of durability at low temperature.     

Numerical Analysis of Heat–Mass Transport and Pressure Build-Up in 1D Unsaturated Porous Medium Subjected to a Combined Microwave and Vacuum System

This article presents one-dimensional numerical analysis of heat-mass transport and pressure build-up inside an unsaturated porous media under microwave energy at a vacuum pressure condition. The unsaturated porous media is composed of glass beads, water, and air. The absorbed microwave power term is computed based on Lambert's law. The finite difference method together with Newton-Raphson technique is employed to predict the heat, multiphase flow, and pressure build-up. Based on the numerical analysis of the effects of vacuum pressure and types of dielectric materials, it was found that the vacuum pressure had a strong effect on temperature, absorbed microwave power, saturation and pressure build-up distribution, and movement of fluid inside the unsaturated porous media during the microwave drying process.     

Use of an Optical–Mechanical Test Combined with Acoustic-Emission Techniques to Study Adhesion in Filled Polymeric Composites

The use of acoustic-emission (AE) techniques integrated with single-particle composite (SPC) mechanical–optical testing is proposed to evaluate and characterize adhesion in particle-filled polymeric composites. It is shown that not only can an intrinsic interfacial strength be determined but also that different types of adhesion mechanisms may be distinguished in terms of straightforward criteria using the wavelet transform (WT) of the acoustic signature, once problems with internal reflections in the test coupon are resolved. The validity of the proposed method is demonstrated with a study of the adhesion of a commercial poly(vinylbutyral) (PVB) to bare and aminosilane-treated glass beads.     

Ageing of Adhesive Bonds with Various Surface Treatments,Part 3: Aluminium–Dicyandiamide Cured Aluminium Filled Epoxy Joints

Ageing of adhesive-bonded aluminium–dicyandiamide cured epoxy alumina-filled joints prepared using a variety of different surface treatments and exposed to elevated temperatures and high humidity are reported. The uptake of moisture was followed using broadband dielectric spectroscopy, and attempts are made to correlate these changes with observations of variations in the mechanical properties and surface structure monitored by electron microscopy. It was found that the absorption of moisture, as indicated by the dielectric measurements, is similar for all the joints. Small differences observed may be ascribed to the influence of the pretreatment on the absorption behaviour. There was no evidence of changes in the oxide layer of the substrate. Detailed electron microscopic examination of the surfaces did indicate, after prolonged exposure, that change in the pretreatment is consistent with small differences in the dielectric data. Predominantly, the changes that were observed in the mechanical strength of the joints are consistent with the plasticization of adhesive in the joint rather than failure at the substrate interface. Ageing at 70°C did, however, indicate that there were changes in the interfacial layer and these can be correlated with the change in the failure mechanism. It was also observed that the titanium/zirconium (Ti/Zr) pretreatment showed signs of being less durable than the others used in this study.     

Adhesive Elastic–Plastic Microcontact Analysis of Truncated Cylinder-on-Flat with Asperities

Adhesion interaction during micro-contacts of deformable rough bodies is characterized in this study using finite element based methodology. The interacting bodies are a truncated cylinder and a flat. Surfaces roughness is simulated by multiple asperities on a cylindrical segment. Lennard–Jones potential methodology is used to calculate adhesion forces by volume integration over the contacting bodies as well as over all asperities, both undeformed and deformed. Cylindrical segment of the asperity is deformed basically in two cylindrical segments. The flat body is deformed the least at the center and maximum at the outer portion of contact width, causing concave bending of the upper body with multi-asperity interfaces. Radius of asperities decreases from the center to outer periphery along the contact width. Adhesion force at each asperity is minimum at the center and maximum at the outer portion of the contact width in the deformed state after complete unloading. The total adhesion force between all asperities and lower body depends on number of asperities, and its maximum value decreases after deformation and occurs at separation distance greater than that for undeformed contact. Its maximum value increases with increasing number of asperities for the undeformed state and decreases with increasing number of asperities for the deformed state. On the other hand, total adhesion force between asperities, truncated cylindrical body and lower body increases with increasing number of asperities for both undeformed and deformed states due to the contribution of truncated segment/lower body interaction, and its location shifts towards the center of contact with increasing number of asperities.     

Adhesive properties of blends of phenol/cardanol–formaldehyde copolymer resin with polychloroprene rubber

This is a continuation of an earlier study on the adhesive properties of neoprene–phenolic resin blends. The phenolic resin used is derived from a mixture of phenol and cardanol, a renewable resource. Having established the utility of cardanol for formulating adhesives, this study investigates the effect of varying the phenol: cardanol ratio in the formulation. The effect of varying the total resin content at various phenol/cardanol ratios is also studied. It is found that a phenol/cardanol ratio of 80:20 is optimum for shear strength of aluminum–aluminum bonds, while a 60:40 ratio is the best for peel properties. For SBR–SBR and SBR–Al bonds, a 60:40 ratio is optimum for both peel as well as shear strength. Further, an 80 phr total resin content in the primer and a 40 phr resin content in the adhesive are found to give the best shear and peel strengths for SBR–Al bonds. The study reveals that the copolymer based on phenol, cardanol and formaldehyde is a better choice for the resin than either of the individual condensation products of phenol or cardanol with formaldehyde.     

Adhesive strength of steel–epoxy composite joints bonded with structural acrylic adhesives filled with silica nanoparticles

This paper reports a study on the effect of silica nanoparticles on the adhesion strength of steel–glass/epoxy composite joints bonded with two-part structural acrylic adhesives. The introduction of nano-silica in the two-part acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strengths of the adhesive joints increased with addition of the filler content up to 1.5 wt%, after which decreased with addition of more filler content. Also, addition of nanoparticles caused a reduction in the peel strength of the joints. Differential scanning calorimeter analysis revealed that T_g values of the adhesives rose with increasing the nanofiller content. The equilibrium water contact angle was decreased for adhesives containing nanoparticles. Scanning electron microscope micrographs revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.     

Study on atmospheric tribology performance of MoS2–W films with self-adaption to temperature

MoS₂ is easily oxidized into MoO₃ at elevated temperature, which leads to a sharp deterioration of lubricity and greatly limits the application. To improve the atmospheric tribology properties of MoS₂ at elevated temperature, the co-deposited MoS₂–W composite films are prepared by magnetron sputtering. Compared with pure MoS₂, the design of three kinds of MoS₂–W composite films not only maintains lower temperature-sensitivity, but also greatly improves the mechanical properties. In particular, the three MoS₂–W composite films embrace good tribology performance at all test temperature, especially 100 °C, at which physical adsorption of H₂O is prominently less than that of 25 °C and the oxidation is relatively slight, compared with that of the higher temperature. Individually, the MoS₂-8.2%W composite film maintains the optimal tribology performance at any test temperature and becomes self-adaptive to temperature variation, which originates from the optimized structure and good mechanical properties.     

Study of Synthesis and Evaluation of Heat-Resistant Coatings Based on Silicon–Boron Carbide–Zirconium Boride–Aluminum Oxide Composite

The effect of nanosized fibers of aluminum oxide on the properties of protective coatings based on the silicon–boron carbide–zirconium boride composite is investigated. The coatings applied on different substrates (graphite and ceramics) are compared and the effect of the thermal treatment conditions on the formed coatings is examined. It is demonstrated that the introduced additives do not weaken the coating’s thermal resistance and allow reducing the cost of the coating, darkening the color, and protecting it from erosion.     

Numerical study of laminar rich hydrogen–air flames with added ethanol

The propagation of fuel-rich hydrogen–air flames with added ethanol has been studied using numerical methods. It has been shown that the inhibition by ethanol is less effective compared to propane and propylene. The addition of ethanol leads to the effect of superequilibrium temperatures, but it takes place only at ethanol concentrations above a certain value. At the flammability limit of fuel-rich mixtures of hydrogen, ethanol, and air, determined by the Le Chatelier rule, the estimated maximum flame temperature is constant. The exception is mixtures with a small addition of ethanol.     

Numerical–experimental method to study the viscous behaviour of ceramic materials

The aim of the work deals with the development of a numerical–experimental method to study the viscous behaviour of ceramic materials and to estimate the viscosity evolution as a function of temperature.The current state of the art regarding the study of viscous behaviour of ceramic materials is carried out by using optical methods able to perform measurements without contact with the sample to be analyzed. The two point bending configuration is the conventional test currently used. Despite the use of the optical technology, the test specimen, because of its viscous behaviour, interferes with the measuring device. The experimental test results are inevitably compromised.The developed numerical–experimental method aims at overcoming the drawbacks of the conventional experimental test configuration and at determining the material viscosity. This method consists of an ad hoc developed experimental test configuration and of a numeric simulation of the experimental test.     

Identification of the Elastic–Plastic Behavior of Adhesively Bonded Structures Under Multi-Axial Loadings: Comparison of a Modified Arcan Test and a Tension/Compression–Torsion Test

Structural bonding is nowadays widespread in the industry. However, characterisation methods and 3D modelling of the adhesives need to be improved. The characterisation requires an experimental procedure to obtain a large experimental database under various loading cases, which represents a significant amount of data. The 3D modelling requires advanced models with several parameters to identify and generally uses inverse identification procedures, which can be time expensive. For a good accuracy, the constitutive models need to take into account the dependency on the hydrostatic stress and be written under the non-associated formalism. In this study, the experimental database is obtained via a modified Arcan test that can cover a wide range of loadings between tension, shear, mixed tension–shear, and mixed compression–shear. A second experimental campaign is realized with a tension/compression–torsion (TCT) test that can cover a greater range of loadings: from tension to compression and mixed tension/compression–shear, with an infinite possibility of mixed loadings. The modified Arcan database is used to identify a 3D elastic–plastic Mahnken–Schlimmer type model, according to an inverse identification procedure developed in a previous study. This model identification is validated on the experimental database coming from the TCT test: a numerical/experimental comparison is realized. This allows the validation of the model and emphasizes the benefits of the TCT test. Indeed, it proves that this test is well suited to characterize adhesive joints and presents several capacities that will be really useful for further studies, like an infinite range of non-proportional loadings available.     

Synthesis and Characterization of Polyindole–NiO-Based Composite Polymer Electrolyte with LiClO4

There has been an increasing interest in synthesizing the novel composite polymer electrolyte (CPE) for use in lithium batteries in recent years. This paper describes the preparation and characterization of CPE containing lithium perchlorate based on polyindole–NiO nanocomposite. NiO nanoparticles were added to the monomer solution before the polymer formation in the presence of a surfactant to get the PInNiO nanocomposite. The thermal properties, surface morphology, and structural studies of the electrolyte were investigated by TGA, SEM, TEM, and XRD. An enhanced conductivity of 2.62 × 10^?4 S cm^?1 at 45°C for the composite polymer electrolyte was determined from impedance studies.     

Interfacial Adhesion of Polyamide 66 Fibres to an Aqueous Polyurethane–Acrylic Hybrid Polymer Adhesive

In this work, the interfacial adhesion between a polyamide 66 fibre, and an aqueous polyurethane–acrylic hybrid polymer adhesive was investigated. Silane and air plasma treatments were introduced to modify the surface of the polyamide 66 fibre. The surface chemistry was characterised using X-ray photoelectron spectroscopy (XPS). There were more oxygen-containing functional groups, –OH or –COOH, introduced by air plasma and silane treatments on the surface of polyamide fibre to increase its chemical activity. The microbond test was used to measure the interfacial shear strength (IFSS) between the waterborne polyurethane–acrylic hybrid polymer adhesive and a polyamide fibre. It has been found that air plasma and silane surface treatments can be used to improve interfacial adhesion. IFSS at 8.7 and 5.9 MPa, respectively, were higher than that of the control, 5.0 MPa. After water immersion at 50°C for 48 h, IFSS dropped to 7.0 MPa for air plasma-treated specimen and to 4.4 and 4.1 MPa for silanised and control specimens, respectively. Air plasma surface treatment is more effective than silane treatment to improve the interface adhesion in the polymer fibre–polymer composite.