Single Lap Joint Tests Research Articles

Addition of Aloe Vera As Corrosion Inhibitor in Self-Assembled Monolayers Systems Designed to Improve Adhesion on Stainless Steel

Surface treatment by phosphatation is widely used in automotive industry and equipment manufacturing [1] because it’s an excellent adhesion primer before painting and due to its lubrication properties with low friction coefficient [2]. It is also known that this treatment offers a good protection against corrosion with a good suitability to be painted. Nevertheless, this process is detrimental for the environment, mostly because of the large amount of waste to be treated, with the presence of concentrated acids, nitrates and nitrites. Moreover, the required thickness is in the range of 2-30 μm, depending of the specifications, and there is a great interest to reduce this value, especially for the fasteners parts.The present work deals with an alternative to steel/phosphate systems by thin organic coating on 304 stainless steel, a low carbon content substrate free of Molybdenum available at affordable costs. To fit with the specification while being as attractive as possible, this alternative would be asked to present a thickness reduced to a few nanometres, environmentally compliant, non-toxic and easy to use. It must keep the main properties of phosphatation i.e. a good adherence or anti-wear functions.A novel process was design, with Self-assembled Monolayers (SAMs) [3] coatings in a first step, followed by a functionalization with Aloe Vera as ecological corrosion inhibitor [4][5]. SAMs are tunable by adjusting either their terminal group or the length of the carbon chain to obtain the desired surface properties such as adhesion or anti-wear. If the addition of Aloe Vera does not bother the tribological behavior of the coating, this is not the case for the systems designed for adherence.To obtain the best compromise, three different terminal groups combined with four carbon chain lengths have been tested. The latest were measured by a single lap joint and three-point bending tests as for result the value of the strength of the bonded joint as a function of the treatments performed. Adhesion results will be presented for different SAM coatings on 304 stainless steel, with a possible application of epoxy layer (polymer used for cataphoresis). The influence of the SAM alkyl chains length and of the terminal groups nature will be checked, as well as the grafting time.Finally, the effect of post-graft rinsing on adhesion as well as corrosion resistance in presence of Aloe Vera or not were evaluated. All findings were supported by surface analysis (SEM, EDS).[1] T. W. COSLETT, Treatment of iron or steel for preventing oxidation or rusting, British patent 8667 and US patent 870937, 1906et 1907[2] J. BOGI, Phosphate conversion coatings on steel, J Mater Sci (1977) 12, 2235-2240[3] A. ULMAN, Formation and structure of self-assembled monolayers, Chem. Rev. 1996, 96, 1533-1554[4] Devarayan, Kesavan, Green Inhibitors for Corrosion of Metals: A Review, Chem Sci Rev Letts, (2012)[5] M. MEHDIPOUR, Electrochemical noise investigation of Aloe plant extract as green inhibitor on the corrosion of stainless steelin 1M H2SO4, J. Ind. Eng. Chem, (2015), 21, 318-327

Comparative Study on the Impact Wedge-Peel Performance of Epoxy-Based Structural Adhesives Modified with Different Toughening Agents.

Epoxy adhesives are widely used in various industries because of their high heat and chemical resistance, high cohesion, and minimal shrinkage. Recently, epoxy adhesives have been applied in the automotive industry as structural adhesives for lightweight vehicles. However, the brittleness of the epoxy is an obstacle for this application, since the automotive industry requires epoxy-based structural adhesives to have a high level of high-speed impact resistance. Hence, we used phenol-terminated polyurethane (PTPU) as a toughening agent for epoxy adhesives and compared the results with those that were obtained with carboxyl-terminated butadiene acrylonitrile copolymer (CTBN). The high-energy impact resistance of the epoxy adhesives was measured by the impact wedge-peel (IWP) test, and the shear strength was measured by the single lap joint test. As a result, the 20 wt % PTPU-modified epoxy adhesive showed remarkably higher total absorbed energy (25.8 J) during the IWP test and shear strength (32.3 MPa) as compared with the control epoxy adhesive (4.1 J and 20.6 MPa, respectively). In particular, the total absorbed energy of the PTPU-modified epoxy adhesive was much larger than that of the CTBN-modified epoxy adhesive (5.8 J). When more than 10 wt % PTPU was added, the modified epoxy adhesives showed stable crack growth and effectively transferred external stress to the substrate. These results were explained by changes in the glass transition temperature, crosslinking density, and morphology due to the toughening agents.

Influence of sample dimensions on single lap joints: effect of interactions between parameters

ABSTRACT The main aim is to understand the effect of adhesive thickness, length and width, and their interactions for highly flexible adhesives on single lap joint tests. Their behavior is completely different from brittle adhesive joints, and their modelling is more difficult with inaccurate results, which makes experimental tests crucial. With this study, future costs will be reduced when working with flexible adhesives since fractional factorial design 2 k allows to reduce drastically the number of tests. In this case, with three factors (adhesive thickness, substrates length, and width) and five specimens for each combination of them, tests were reduced from 300 to 40, with the subsequent cost reduction. The effect on shear stress, strain, Young’s modulus, and absorbed energy by the adhesive joint was studied, using steel substrates with polyurethane adhesive. It has been found that shear stress is mostly affected by the adhesive thickness, the higher the thickness, the lower the stress. In the case of strain, elastic modulus and absorbed energy, the most influent factor is the overlap length. It presents an inverse relation with strain and energy, and a direct one with modulus. With this method the effect of various factors can be known simultaneously.

Mechanical Behavior of Toughened Epoxy Structural Adhesives for Impact Applications

The focus of our study is to identify physical properties of different impact-resistant/toughened structural adhesives and identify/develop an elastic-viscoelastic-plastic model as a function of loading rate by using Ludwik-type equations to be able to predict adhesive behavior at higher loading rates and to make cars more crashworthy. For this purpose, we first characterized eight different commercial toughened epoxy structural adhesives to provide detailed information about their constituents using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDS). Most (but not all) of the model adhesives contained organic tougheners in the form of carboxyl terminated butadiene acrylonitrile (CTBN) copolymer, as well as polyurethane adducts. The main crystalline inorganic phases were found as calcite (CaCO3), wollastonite (CaSiO3) or calcium silicate (CaSiO3), talc (Mg3Si4O10 (OH)2), zeolite which is an alumina silicate based mineral and has many different elements in its composition (M2/nO·Al2O3·xSiO2·yH2O, M can be Mg, Na, Ca, K, Li). The total amount of inorganic fillers was found to be different in each adhesive. Material behavior of the model adhesives were determined via tensile tests and Single Lap Joint (SLJ) tests in shear. Split Hopkinson pressure bar (SHPB) was also used to measure the strain and stress values at higher strain rates in the order of 102 s−1, which is generally encountered in impact related loading situations. Toughness values in the range ~0.5 to ~1.35 MJ/m3 were observed with the model adhesives tested in tensile mode within the ~3 × 10−3 to 0.18 m/m/s strain rate range. The softening behavior of the elastic moduli at higher strain rates observed during tensile testing was also observed with SHPB testing. It is remarkable that, overall, the modulus magnitudes seem to be similar between the tensile test and SHPB specimens within this softening range of the initial bilinear elastic behavior observed. When the results from bulk (tensile) and bonded (shear) specimens were compared, it was clearly seen that the toughness responses of the adhesives to (tensile/shear) strain rates in the bulk and bonded forms, respectively, were different, with the bonded shear toughness values in the ~25 to ~120 MJ/m3 range within ~1.25 to ~25 mm/mm/s shear strain range. The model adhesive which included just inorganic fillers had the lowest tensile toughness at the lowest tensile strain rate, but the highest slope in its tensile toughness regression line, exhibited the second highest bonded shear toughness. When tested at the extension rates of 25 mm/min and 100 mm/min in bonded lap shear, the same adhesive exhibited limited interfacial failure areas, however the dominant failure mode was cohesive failure. When the extension rate increased further, transition to interfacial (adhesive) failure was observed revealing that interfacial failures do not necessarily diminish adhesive bond toughness. Our observations point to the fact that cohesive deformation/failure processes indicating interfacial separations, inter-particle interactions as well as polymer matrix deformation in high deformation loading scenario as in bonded shear loadings may provide the highest toughness. Apparently, a large inorganic filler weight fraction is not necessary to obtain high shear toughness in bonded form since the highest bonded shear toughness was obtained with the adhesive which had the least amount of inorganic fillers among the model adhesives with 14.72 wt %.

Effects of Helical Carbon Nanotubes on Mechanical Performance of Laminated Composites and Bonded Joints

<div class="section abstract"><div class="htmlview paragraph">Most composite assemblies and structures generally fail due to weak interlaminar properties and poor performance of their bonded joints that are assembled together with an adhesive layer. Adhesive failure and cohesive failure are among the most commonly observed failure modes in composite bonded joint assemblies. These failure modes occur due to the lack of reinforcement within the adhesive layer in transverse direction. In addition, the laminated composites fail due to the same reason that is the lack of reinforcement through the thickness direction between the laminae. The overall performance of any composite structures and assemblies largely depends on the interlaminar properties and the performance of its bonded joints. Various techniques and processes were developed in recent years to improve mechanical performance of the composite structures and assemblies, one of which includes the use of nanoscale reinforcements in between the laminae and within the adhesive layer. However, most prior research has been focused on use of straight carbon nanotubes (CNTs) and other nanomaterials in particle forms. The goal of this research was to improve the properties of the adhesive film and the interfacial bonding effectiveness between the laminae. Because CNTs are inert in nature, their interaction with the resin and adhesive polymer molecules is very weak. In this research we have used CNTs with various geometrical configuration (straight and helical geometries) and various weight percentages as additional reinforcements. The objective was to investigate the effectiveness of helical geometries of the CNTs to form interlocking mechanisms with the resin and the traditional microfiber reinforcements to improve the overall performance of the composite structures and assemblies. Single lap joint test specimens and flexural test specimens were prepared based on the ASTM standard D5868-01 and ASTM standard D790 and then tested and analyzed. The experimental results showed that the samples with CNT reinforcements performed considerably better than neat epoxy samples. Among the two different CNT geometries, helical CNTs performed better than the straight CNTs.</div></div>

Formulation and characterization of tamarind (Tamarindus indica L.) seed kernel powder (TKP) as green adhesive for lignocellulosic composite industry

The objective of this study was to investigate the basic properties of eco-friendly adhesives produced from Tamarindus indica seed kernel powder (TKP) and to use them for fabricating particleboard. Four different types of adhesive were manufactured from TKP having certain percentage of polyvinyl alcohol (PVA), citric acid (CA), glucose, acetic acid, sodium bicarbonate, urea and potassium permanganate. Solid content, Gelling time, FTIR, Thermogravimetric analysis (TGA), viscosity and single lap joint test for shear strength of the prepared adhesives were tested. Both the physical and mechanical properties of the experimental particleboards were evaluated followed by ASTM standards. Adhesive type A resulted in the quickest gel time (1.42 min) and the highest bonding strength (5.18 MPa). Adhesive type B having the density of 0.65 g/cm3 showed the highest modulus of elasticity (2108 N/mm2) and modulus of rupture (10 N/mm2). Although dimensional stability of the experimental panels was poor but their overall mechanical strengths properties met the values listed in the standards.

Effect of surface roughness and chemistry on the adhesion and durability of a steel-epoxy adhesive interface

This work focuses on the effect of surface roughness and surface chemistry on the initial adhesion strength and corrosive de-adhesion properties of adhesive bonds. The adherend used in this study is a S690 low-alloy steel whereas the adhesive is a 2-component epoxy-amine adhesive (Araldite 2015). The steel surface is subjected to different surface pre-treatment methods such as mechanical abrasion, grit blasting, zirconium conversion treatment and silane treatment. The effect of these different pre-treatments on the surface morphology, roughness and chemistry is addressed. Single-lap joint tests were performed at ambient conditions to assess the initial bond strength of the joint. Static wedge tests were performed in saltwater immersions to study the environmental ageing of the adhesive joints. Unloaded delamination of adhesive films from the steel surface was studied by means of scanning Kelvin probe (SKP) at high relative humidity. This unique combination of different techniques allows thorough evaluations of the bond performance under different environmental and loading conditions. Experimental results indicate that surface roughening plays an important role in the initial adhesion in the single-lap joint test but a minor role in the durability of the bonded steel surfaces. The improved initial adhesion is mainly attributed to the increased interfacial bond area at higher surface roughness. The presence of complex texture or morphology shows a more profound effect than the average roughness on both the initial adhesion and the durability of the interfacial adhesion. The results from the static wedge test show the large contribution of mechanical interlocking, caused by texturing of the surface, on the durability of the interfacial adhesion. In the absence of complex texture, surfaces with altered chemistry by zirconium- or silane treatment exhibit a significant increase of the initial bonding strength due to enhanced physicochemical interactions across the interface. Assessment of the interfacial delamination kinetics by SKP show that despite the absence of any surface topography, chemically altered surfaces prove to have higher resistance to delamination.

Experimental investigation on strength of stepwise tailored single lap adhesive joint using second-generation acrylic adhesive via shear and low-cycle shear tests

Stress concentration in adhesively bonded joints, which is considered a major factor affecting their strength, can be avoided by tailoring the material properties of the adhesives using a functionally graded adhesive (FGA). The material properties of second-generation acrylic (SGA) adhesives can be simply changed by changing the mixing ratio of the agents. However, the superiority of FGA joints using SGA adhesives has not been experimentally clarified yet. Therefore, in this study, a shear strength test and a constant load low-cycle shear test were conducted on single lap joint (SLJ) specimens tailoring the adhesive layer stepwise. The FGA specimen was compared with the non-tailored specimens using stiff or flexible adhesives. The SLJ test results showed 16% improvement in the joint strength by stepwise tailoring of the adhesive layer. Additionally, the difference in the strain distributions among the different adhesive layers was investigated via a digital image correlation (DIC) method, and the shear strain at the edge of the FGA specimen was more than 40% decreased compared to the non-tailored specimen using the flexible adhesive. The low-cycle test results also showed the superiority of the FGA specimen to the other specimens. The FGA specimen held up more than 4 times the number of cycle of other specimens with an applied load of 18 kN or more. This was attributed to the suppressed plastic deformation at the edges of the adhesive layer owing to the introduction of FGAs.

GFRP-to-timber bonded joints: Adhesive selection

Recent research at the University of Queensland (UQ) has led to the development of a new type of structures called “Hybrid Fiber Reinforced Polymer (FRP)-Timber structures” (“HFT”). In HFT structures, FRP is combined with timber veneers to create high-performance, lightweight, easy-to-construct structural members. These HFT members take advantage (i) of the orthotropic properties of both, timber and FRP to orientate the fiber direction to produce optimal composite properties, and (ii) of the geometry of the cross sections to maximize the load bearing capacity for a given amount of material. While preliminary experimental work has revealed as such the effectiveness of HFT structural members, no work has been carried out so far to investigate the behavior of these HFT structures. Performance of these new HFT members relies significantly on the bond between FRP and timber. This paper presents the results of an experimental study aimed at selecting a suitable commercially available adhesive for glass fiber reinforced polymer (GFRP)-to-timber bonded joints. The experimental program included 393 single lap joint tests covering four different commercially available adhesives, two different curing temperatures, and two test methods (dry and moisture cycle tests). The test results revealed that both, polyurethane (PUR) and cross-linking polyvinyl acetate emulsion (PVAx) performed as the best under dry conditions, while PUR was shown to be superior to all other adhesives when subjected to moisture cycles. Epoxy and phenol resorcinol formaldehyde adhesive (PRF) commonly used in FRP structures and laminated timber structures, resp., were found to be less performing structural adhesives for HFT structures.

The effect of nanospike structures on direct bonding strength properties between aluminum and carbon fiber reinforced thermoplastics

With recent design developments in the automotive industry, it has become necessary to join dissimilar materials such as aluminum and carbon fiber reinforced thermoplastics (CFRTPs). In this study, a nanospike structure is fabricated on the surfaces of aluminum plates and directly bonded to CFRTP laminates. The effect of the nanospike structure on the adhesion strength is evaluated by single-lap joint tests. It is found that the nanospike structure improves the adhesion strength. Furthermore, combining the nanospike structure with a silane coupling treatment results in failure in the aluminum part of the single-lap specimens with an overlap length of 12.5 mm, rather than in the joined region. The average adhesion strength of the single lap joint specimens with an overlap length of 5.0 mm is found to be 24.9 MPa. Scanning electron microscopy observations of the fracture surfaces of the joined region only showed cohesive failure. On the fracture surface of the CFRTP laminate, the matrix exhibits a hairy structure due to the presence of the nanospike structure in some regions and in other regions carbon fibers are exposed due to adherend failure. Thus, in addition to an improved joint strength, the results suggest that the nanostructure will also improve the fracture toughness by causing ductile failure of the matrix.

Failure of elastomeric sealants under tension and shear: Experiments and analysis

The mechanical behaviour of two elastomeric fuel tank sealants was investigated. Laboratory tests were conducted on two sealants, an epoxy cured polythioether and a manganese cured polysulfide. Tensile, planar tension and torsion tests were performed to characterize and understand the response of the sealants under quasi-static loading. Single lap joint tests in tension were also carried out using four different sealant layer thicknesses and two types of adherend (aluminium and steel). The adherends were either primed with an epoxy primer or otherwise conventionally treated (e.g. grit blasted). Experimental results showed a decrease in joint strength with increasing sealant layer thickness. Emphasis was given to the understanding of the failure and the prediction of the strength of the single lap joints. Predicted failure loads were derived by analytical calculations and finite element simulation of the joints.

Physical and mechanical properties of a reversible adhesive for automotive applications

In this work, a hot-melt adhesive used by automotive industries for bonding plastic components has been modified with three different percentages of nanofiller (iron oxide) in order to make the adhesive electromagnetically sensitive and to perform adhesive joint separations. Fe3O4 particles with a weight concentration of 3%, 5% and 10% were embedded in the adhesive matrix. Single Lap Joint (SLJ) tests showed that a slight increase of the maximum load and a more ductile behaviour are obtained. The sensitivity of these modified adhesive performance to the induction heating process was studied with respect to some relevant parameters: the current (or power), the frequency of the electromagnetic induction field and the shape of the coil. Furthermore, the diameter of the hollow copper coil was modified in order to understand whether the coil temperature has an effect on the separation time. The separation time, that is an index of the time needed to reach the melt of the adhesive and the consequent SLJ separation, together with the temperature profile of the adhesives have been used to evaluate the sensitivity of these adhesives to the process parameters. The analysis on the temperature and separation time showed that the most influencing parameter is the frequency of the electromagnetic induction field. As expected, also the shape of the coil influences the separation time, in particular, the adhesive joint separated with the pancake coil showed lower values of the separation time compared to the solenoidal coils. Scanning Electron Microscope (SEM) showed that iron oxide particles tend to form small agglomerate that resulted well dispersed in the adhesive matrix. Thermogravimetric analysis (TGA) was used to verify that the separation procedure do not degrades these modified adhesives.

Effect Of Accelerated Ageing Cycles On The Physical And Mechanical Properties Of A Reversible Thermoplastic Adhesive

ABSTRACT In this work, a polyolefin thermoplastic adhesive has been modified with three different weight percentages, 3%, 5% and 10% of iron oxide powder. The use of this nano-modified adhesive coupled with this technology, offers an improved resistance to applied loads, new opportunities connected with the bonding process and the possibilities to dismantle plastic components for reusing, repairing or recycling at the end of life. In this research activity, the mechanical properties of the pristine and modified adhesive have been assessed. Furthermore, the effect of three different accelerated ageing cycles, currently used by automotive industries, have been studied in relation to the mechanical behaviour and separation time. Three ageing cycles were evaluated that are: hot, humid and mixed cycles. Single Lap Joint tests prove the variations of the mechanical properties and adhesion strength during the accelerated ageing, especially for the hot cycle. Fourier Transform Infrared Spectroscopy has been used and shows that the adhesives exposed to the hottest ageing cycle presented a high value of the oxidation that leads to a partial detachment of the adhesive from the plastic substrates. Joint separations by means of an induction heating system showed that adhesive joints can be separated before and after ageing cycles.

Adhesion properties of poly(ethylene oxide)-lignin blend for nanocellulose composites

In this paper, poly(ethylene oxide)-lignin (PEO-L) blends were prepared for eco-friendly nanocellulose composites and the effect of lignin content on its adhesion property was studied by using single lap joint test. The PEO-L blends were prepared by blending method using 60% methanol. Cellulose nanofiber (CNF) film, chosen as an adherent material of eco-friendly nanocellulose composites, was prepared by casting CNF emulsion, followed by vacuum filtration and drying. The successful formation of PEO-L blends was confirmed from FTIR, DSC and XRD studies. The shear strength of PEO-L blend increased with the lignin content and the 30% lignin case (442 kPa) showed 189% larger shear strength than the pure PEO (835 kPa). This shear strength improvement is associated with enhanced hydrogen bonds between lignin/PEO and CNF film.

Fracture Behavior and Mechanical Properties of Rivet Joint By Using Ultrasonic Vibration with c-Frtp

Fiber Reinforced Plastics (FRP) have been expected to be used for structural materials in various field because of its high specific stiffness and strength. In the case of using FRP for automotive structures, easy and reliable jointing process in a short time must be needed. Most easy jointing processes are adhesive joint with bonding agent or welding joint in the case of FRTP. However mechanical properties of these joint system depend on the interfacial properties between resin and fiber or resin itself, which are relatively poor. In the case of mechanical joint by using bolt and nut, or rivet system with metal materials, whole structure will be heavy. Therefore if FRP parts could be used as a jointing parts instead of rivets, the problems such as a increase of weight and process time of jointing should be overcome.In this study, rivet joint with pultruded c-FRTP (continuous Fiber Reinforced Thermoplastic composite) rods with CF/PA commingled yarns covered with braided GF / PA commingled yarns and were performed by using ultrasonic welding machine with a die forming rivets for a pair of c-FRTP (CF/PA) plates with a joint structure. Mechanical properties of rivet joint were investigated by performing single lap joint test, and fracture behavior was also investigated by stopping the test in each region of the obtained diagram and embedding the sample for cross-sectional observation.

Static and dynamic testing and modelling of aluminium joints with flow-drill screw connections

A new component test suited for quasi-static and dynamic testing of flow-drill screw connections is presented. The component specimen was made of two different aluminium alloys, and included connections with two material combinations. Large-scale finite element simulations were carried out of each test, in which the connections were modelled with a constraint-based macroscopic model. An improvement of the connection modelling technique is presented. The model was calibrated to cross tension, cross mixed and single lap-joint tests, and validated with peeling and the component tests.

Experimental and statistical study of three adherence tests for an epoxy-amine/aluminum alloy system: Pull-Off, Single Lap Joint and Three-Point Bending tests

The mechanical resistance of a bonded joint depends on the adhesive interaction onto the substrate and the mechanical properties of the adhesive itself. Many existing tests can be useful for measuring the adherence or evaluating mechanical adhesive response. All these tests do not provide the same information: in particular, adherence measurements can be split into initiation tests and propagation ones. In this paper, three adherence tests have been considered for the evaluation of the fracture initiation between a poly-epoxide adhesive (a mixture of pure epoxy and amine) and an aluminum surface (AA 2024-T3), namely the Pull-Off, Single Lap Joint (SLJ) and Three-Point Bending tests. Various surface preparation protocols before bonding have been tested and optimized for aluminum substrates, including mechanical and chemical surface treatments, followed by the application of an appropriate primer before bonding. This study paves the way for the future development of adhesive systems as it provides reliable surface preparation protocols for aluminum surfaces and gives an insight into the choice of an adequate adherence test dedicated to high-performance adhesives. The load at break (FMax), the experimental error, the failure mode and statistical studies according to the Weibull model and Principal Component Analysis (PCA) were studied on each surface preparation configuration. It has been shown that the application of a primer, especially a sol-gel product increases the load at break and provides more reliable results. Then, this paper shows that the two tests can quantify the failure initiation and distinguish the different surface preparation efficiency, are the Single Lap Joint test (mode II or mode I + II) and the Three-Point Bending test (mode I), with an increase of the results reliability with the latter one. The Pull-Off test (mode I) is useful as a routine checking, and particularly interesting because its response does not depend on the substrate thickness, even though it cannot highlight the difference between all surface preparations.

Effect of hygrothermal conditioning on the energy release rate and failure mechanism of metal only adherend-glass fibre prepreg co-cured single lap joints

Fibre-reinforced composite materials are extensively used in repair and rehabilitation of oil and gas metal infrastructures which are largely exposed to water and hydrocarbon. An important aspect to this is applying adequate surface preparation to the metal to ensure a durable bond between the composite and metal substrate. In this paper, mild steel surface was prepared using grit blasting and single lap joint (SLJ) test specimens were manufactured and tested to investigate the adhesion in terms of total energy release rate (GT) of the interface between mild steel adherend and glass fibre prepreg. An out-of-water usable epoxy resin primer was incorporated to join mild steel adherend with glass fibre prepreg by curing at a temperature of 55 °C for 48 h. Upon durability testing of the SLJ specimens using hygrothermal conditioning at a temperature of 55 °C for 1000 h, the experimental GT values were seen to reduce significantly. Comparatively lower amount of cohesive failure and increased amount of swelling or delamination of the adhesive was observed for conditioned SLJ specimens when compared to controlled SLJ specimens. Furthermore, the experimental GT values were found to correlate well with an analytical adhesive interface model.

Effect of air dielectric barrier discharge plasma treatment on the adhesion property of sanded polyphenylene sulfide

Air dielectric barrier discharge (DBD) plasma was employed to treat the sanded polyphenylene sulfide (PPS) surface. The plasma-treated PPS samples were bonded with epoxy adhesive, and the adhesion strength was measured by the single lap-joint specimen test. Scanning electron microscopy (SEM), water contact angle analysis, and X-ray photoelectron spectroscopy (XPS) were applied to investigate the effect of the plasma treatment on the PPS surface property. A slight etching trace was detected after the plasma treatment according to the SEM images. XPS and water contact angle analysis indicated that the plasma treatment introduced sulfide oxides (S=O and O=S=O) onto the PPS surface leading to a higher surface energy. A steady improvement of bonding shear strength was achieved with the increase of plasma treatment time or discharge power density, which was consistent with the failure mode study. According to the above analysis, the air DBD plasma treatment could effectively improve the adhesion property of PPS.

Non-destructive inspection of initial defects of PA6.6-GF50/aluminum self-piercing riveted joints and damage monitoring under mechanical static loading

A self-piercing riveting process is used to join a thermoplastic composite sheet of PA6.6-GF50 with an aluminum alloy sheet 5182 O. Two shapes of self-piercing rivet are tested: the countersunk rivet and the button head rivet. Non-destructive inspections by pulse thermography and post-mortem cross-section observations are made to assess the damage that might have occurred during the rivet piercing process. The manufacturing defects are characterized and the possible causes for their emergence are explained. Then, single-lap joint tests were carried out to determine the best joint in terms of its mechanical strength. These tests were also instrumented by various monitoring techniques such as passive thermography, digital image correlation, and acoustic emission to clarify the joint damaging behavior. Non-destructive inspections by pulse thermography are finally correlated with the thermal fields acquired by passive thermography during the mechanical test to improve the understanding of the damage mechanisms and their criticality.