Influence of the mechanical behaviour of different adhesives on an interference-fit cylindrical joint

Hybrid adhesive joining techniques are often used in many industrial sectors to design lightweight structures. A hybrid adhesive joint results from the combination of adhesive bonding with other traditional joining methods such as welding and mechanical fastening, with the aim of combining the advantages of the different techniques and overcoming their drawbacks.This study focuses on the interference fitted/adhesive bonded joining technique. In this application, two cylindrical components are coupled together by inserting one into the other, after having placed an adhesive between them. Generally anaerobic acrylic adhesives, also known as “retaining compound” are used for this application. However the effect of the adhesive nature and of its mechanical and adhesive responses on the performance of the hybrid joint is still unclear. The aim of the present research is to improve the understanding of the behaviour of different adhesives, including rigid epoxies and flexible polyurethanes, in the presence of an interference-fit. Static strength of bonded and unbonded interference fit joints have been compared in order to investigate the role of the different adhesives.     

Effect of adhesive thickness and surface roughness on the shear strength of aluminium one-component polyurethane adhesive single-lap joints for automotive applications

Adhesively bonded technology is now widely accepted as a valuable tool in mechanical design, allowing the production of connections with a very good strength‐to‐weight ratio. The bonding may be made between metal–metal, metal–composite or composite–composite. In the automotive industry, elastomeric adhesives such as polyurethanes are used in structural applications such as windshield bonding because they present important advantages in terms of damping, impact, fatigue and safety, which are critical factors. For efficient designs of adhesively bonded structures, the knowledge of the relationship between substrates and the adhesive layer is essential. The aim of this work, via an experimental study, is to carry out and quantify the various variables affecting the strength of single-lap joints (SLJs), especially the effect of the surface preparation and adhesive thickness. Aluminium SLJs were fabricated and tested to assess the adhesive performance in a joint. The effect of the bondline thickness on the lap-shear strength of the adhesives was studied. A decrease in surface roughness was found to increase the shear strength of the SLJs. Experimental results showed that rougher surfaces have less wettability which is coherent with shear strength tests. However, increasing the adhesive thickness decreased the shear strength of SLJs. Indeed, a numerical model was developed to search the impact of increasing adhesive thickness on the interface of the adherend.     

Experimental Assessment of a Micro-Mechanical Model for the Static Strength of Hybrid Friction-Bonded Interfaces

Anaerobic adhesives are thermosetting acrylic polymers commonly used to improve the performance of most metal joints. Researches on the static strength of hybrid joints, available in the technical literature, show scanty and contradictory results that do not explain the effect of anaerobic adhesive on the hybrid joint behaviour. An early study by one of the authors of the present study formulates a micro-mechanical model describing the shear power of anaerobic adhesives as a function of the intimate properties of adherends and adhesive at the interface. According to the micro-mechanical model, the high local pressure acting on the thin film of adhesive trapped between the crests of the mating surfaces improves the film shear strength upon the adhesive's shear strength at zero pressure. The present work aims to assess this micro-mechanical model through a systematic experimental campaign. The tests are conducted on simple tubular specimens and consider three variables over two levels: adhesive-type (weak and strong anaerobic), pressure level during polymerization (0.5 and 134 MPa), and pressure level during failure test (0.5 and 134 MPa). The results confirm the proposed micro-mechanical model, and highlight that shear strength slightly differs by applying pressure before or after polymerization.     

Enhanced adhesion force based on microphase separation induced by complexation of ferric ions and polyurethane matrix

Waterborne polyurethane elastomer (WPU) has been widely used as a glue, but it still has some drawbacks, including a long cure time and weak adhesive force. In order to overcome these drawbacks, a new composite [PU/ferric ion complexation (Fe/PU)] with high adhesive strength was successfully prepared using ferric ion (Fe³⁺) as a complexing agent. Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, and tensile testing were used to characterize the chemical structure and mechanical properties of the as‐obtained composites. Introduction of the ferric ion induces a certain degree of microphase separation, resulting in better mechanical strength and interfacial adhesion. The mechanical properties of the PU composite with ferric ions are higher than that of pure PU. The adhesive strength of the 25%‐Fe/PU composite is 32.46 ± 3.1 MPa, exhibiting superior adhesive strength. The tensile strength was enhanced 34%, and the elongation was enhanced 23.6% compared to pure PU. Furthermore, the Fe/PU composite, coordinated with ferric ions, exhibits an enhanced storage modulus and reduced loss coefficient compared to PU. We can foresee that Fe/PU composites will play an important role in the building and engineering areas. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46069.     

Analysis of shear strength of cylindrical assemblies with anaerobic adhesives using Weibull statistics

A statistical method to study the reliability of cylindrical anaerobic adhesively-bonded assemblies is presented in this work. An anaerobic adhesive was used to manufacture four groups of bonds with different gaps, but with the same surface pre-treatment and curing position. Shear strength values were obtained and used to determine reliability of all adhesive bonds using the Weibull statistical distribution. Although the Weibull analysis has been widely used in the study of composite materials, its application in adhesive bonds is being explored now. A two-parameter Weibull distribution was employed to execute the Weibull analysis, using an estimator that renders a more realistic Weibull modulus value, as other estimators were found to subestimate or overestimate this value. Weibull modulus values were obtained for adhesive bonds with different gaps to study their reliability, and these results have been compared with the shear strength results.     

Effect of MWCNT filled epoxy adhesives on the quality of adhesively bonded joints

Most adhesively bonded joints exhibit adhesive or cohesive failure, i.e. failure at the adhesive/adherend interface or within the adhesive, respectively. The main objective of this study is to investigate the effect of surface modification of the metal substrate accompanied by modification of the adhesive properties on the strength and failure mechanism of bonded joints. A 5061 aluminium alloy has been used as the metal substrate onto which two types of surface treatments were applied; chemical surface modification and gritblasting. A standard epoxy resin was used as the adhesive medium, in which multi-wall carbon nanotubes (MWCNTs) were dispersed, with a range of weight fraction content (from 0.03% to 0.5%). The resin was fully characterised by mechanical testing in order to determine the optimum weight fraction to enhance its properties. Aluminium to aluminium and glass fibre reinforced polymer (GFRP) composite to aluminium single lap joints bonded with either pure epoxy resin or MWCNT reinforced epoxy resin were subsequently manufactured and tested. The tests show a moderate increase of the joint strength when MWCNTs are added into the adhesive with the failure mechanism changing from cohesive to adhesive. In addition, the comparison between different surface preparation methods shows that gritblasting results in considerably improved adhesive strength over chemical treatment.     

Improved adhesive properties and bonding performance of HTPB‐based polyurethane elastomer by using aziridine‐type bond promoter

Theeffect of two aziridine‐type bond promoters on adhesive and mechanical properties of a hydroxyl terminated polybutadiene‐based elastomeric liner used in solid propellant rockets was investigated by varying the concentration to determine the optimum value. The performance of butyleneiminetrimesoylaziridine (BITA) was compared with that of tris[1‐2‐methylaziridinyl]phosphine oxide (MAPO) in the elastomeric liner of otherwise the same composition. The adhesive performance of the elastomer to the composite was determined by using metal‐elastomer‐composite tensile and peel tests. The adhesive performance of the elastomer to the metal was also determined, this time by using peel and shear tests. The mechanical characterization of the elastomer was done by tensile and hardness tests. A significant enhancement in the bonding performance of the elastomeric liner toward composite propellant and metal case was achieved by optimizing the concentration of bond promoter in the elastomeric composition. All the elastomer compositions with bond promoters BITA and MAPO loadings of 1.0, 1.5, and 2.0 wt % were found to be sufficient for the rocket motor operations because the interfacial adhesive strength of these compositions is higher than the cohesive strength of the composite. Compositions with bond promoter quantities of 1.0, 1.5, 2.0, and 2.5 wt % have better strength values than the others. Liner compositions with the bond promoter BITA give better bonding performance between the composite–metal system and better mechanical properties when compared with the elastomers with the bond promoter MAPO. The best results are obtained in terms of bonding performance and adhesive properties by using the bond promoter BITA in optimized quantities of 1.0 and 1.5 wt % loadings in the elastomer compositions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 806–814, 2001     

电容器瓷套管专用胶粘剂的研究

首先合成了一种低粘度的环氧树脂聚酰胺固化剂——EA6,粘度(25℃)为10 Pa·s,胺值为718 mgKOH·g-1;再将其与CYD128低粘度环氧树脂按质量比1∶3混合,制备了一种电容器瓷套管专用胶粘剂.该胶粘剂具有适用期长、体积收缩率低、抗冲击强度高等优点,适用于陶瓷与金属的粘接,可以同时满足产品的密封与粘接性能要求.     

Synergistic effect of graphene and carbon nanotube on lap shear strength and electrical conductivity of epoxy adhesives

In this study, synergy between graphene platelets (GnPs) and carbon nanotubes (CNTs) in improving lap shear strength and electrical conductivity of epoxy composite adhesives is demonstrated. Adding two-dimensional GnPs with one-dimensional CNTs into epoxy matrix helped to form global three-dimensional network of both GnPs and CNTs, which provide large contact surface area between the fillers and the matrix. This has been evidenced by comparing the mechanical properties and electrical conductivity of epoxy/GnP, epoxy/CNT, and epoxy/GnP-CNT composites. Scanning electron microscopic images of lap shear fracture surfaces of the composite adhesives showed that GnP-CNT hybrid nanofillers demonstrated better interaction to the epoxy matrix than individual GnP and CNT. The lap shear strength of epoxy/GnP-CNT composite adhesive was 89% higher than that of the neat epoxy adhesive, compared with only 44 and 30% increase in the case of epoxy/GnP and epoxy/CNT composite adhesives, respectively. Electrical percolation threshold of epoxy/GnP-CNT composite adhesive is recorded at 0.41 vol %, which is lower than epoxy/GnP composite adhesive (0.58 vol %) and epoxy/CNT composite adhesive (0.53 vol %), respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48056.     

The fracture properties of a fiber metal laminate based on a self‐reinforced thermoplastic composite material

The present research program has studied the fracture properties of a Fiber‐Metal Laminate (FML) system constituted by aluminum alloy and a high‐impact self‐reinforced composite material. Here, the self‐reinforced composite system consists of a polypropylene matrix reinforced with polypropylene fibers. Initial testing has shown that a though adhesion can be achieved between the aluminum layers and the composite material by incorporating a thermoplastic adhesive interlayer at the common interface. The adhesion at the metal–composite interface has been studied under a wide range of strain rate conditions using a Single Cantilever Beam test geometry, and it has been shown that the interfacial fracture toughness is loading rate sensitive. Interlaminar delamination tests of the plain composite have also been studied and it was shown that their fracture toughness is also loading rate sensitive. Additional tensile tests have shown that the tensile strength and moduli of the FMLs are linearly influenced by the volume fraction of their constituent materials as well as are successfully predicted using a simple rule of mixture. Low velocity impact tests have also shown that the FMLs based on a self‐reinforced polypropylene composite yielded specific perforation energies well above the 30 J m²/kg. It was also shown that by increasing the number of metal and composite plies in the FMLs, resulted in hybrid structures capable of absorbing higher specific low velocity impact energies. POLYM. COMPOS., 35:427–434, 2014. © 2013 Society of Plastics Engineers     

聚丙烯酸酯/TiO2-SiO2纳米杂化材料性能的研究

采用具有核-壳结构的纳米TiO2-SjO2与热固性聚丙烯酸酯原位复合，通过溶胶-凝胶法制得了有机-无机纳米杂化材料，并对材料的结构和性能进行了表征。结果表明：聚丙烯酸酯基纳米SiO2包覆TiO2的有机-无机纳米杂化材料在无机组分质量分数低于8％时是透明的；随着TiO2-SiO2用量的增加，纳米杂化材料的附着力是先增后降，而热稳定性则是逐渐增加；拉伸强度和冲击强度随TiO2-SiO2用量的增加都是先增后降，当TiO2-SiO2质量分数为5．10％时，拉伸强度达到最大值，提高了25％；当TiO2-SiO2质量分数为3．45％时，无缺口冲击强度达到最大值，提高了27％。     

Cleavage Strength of Steel/Composite Joints

This paper presents the experimental results of an on-going study to examine cleavage strength, particularly at the interface regions of epoxy adhesive with steel and glass reinforced epoxy (GRE) composite. The adhesion is characterised by mechanical testing of cleavage specimens. A standard specimen was modified to allow testing of hybrid joints. The effects of adhesive thickness and various surface conditions of both adherends were examined. Among key conclusions, the study found that cleavage strength is not strongly dependent upon adhesive thickness and that polished composite gives better adhesion compared with polished steel. Test results were analysed and compared with aspects of numerical analyses. The study has also established a new methodology to test hybrid adhesive cleavage joints.     

Cleavage Strength of Steel/Composite Joints

This paper presents the experimental results of an on-going study to examine cleavage strength, particularly at the interface regions of epoxy adhesive with steel and glass reinforced epoxy (GRE) composite. The adhesion is characterised by mechanical testing of cleavage specimens. A standard specimen was modified to allow testing of hybrid joints. The effects of adhesive thickness and various surface conditions of both adherends were examined. Among key conclusions, the study found that cleavage strength is not strongly dependent upon adhesive thickness and that polished composite gives better adhesion compared with polished steel. Test results were analysed and compared with aspects of numerical analyses. The study has also established a new methodology to test hybrid adhesive cleavage joints.     

Evaluation of adhesion of continuous fiber–epoxy composite/aluminum laminates

Continuous fiber composite/metal laminates (FMLs) offer significant improvements over currently available composite materials for aircraft structures due to their excellent fatigue endurance and low density. Glass fiber–epoxy composite laminae and aluminum foil (GLARE) are commonly used to obtain these hybrid laminates. In this work, FMLs were produced by treating the aluminum foil to promote adhesion bonding by two methods: sulphuric chromic acid etching (SCAE) and chromic acid anodization (CAA). The surface treatments were evaluated by contact angle, roughness and scanning electron microscopy techniques. In order to compare different families of fiber composite/metal laminates, carbon fiber and glass fiber fabrics were used as reinforcements for the hybrid laminates. The adhesion of the hybrid laminates was evaluated by scanning electron microscopy (SEM) and three-point bending test. CAA resulted in better wetting properties. The interlaminar shear strength results for both carbon fiber-epoxy/metal and glass fiber-epoxy metal, were close to the interlaminar shear strength results found in the literature (approx. 40.0 MPa).     

The effects of universal adhesive and innovative fabrication techniques of metal-ceramic restorations on repair strength of porcelain fracture with metal exposure

This study was to evaluate the effects of universal adhesive and innovative fabrication techniques of Cobalt-Chromium (Co-Cr) alloys on shear bond strength (SBS) between the repair material. One hundred forty-four Co-Cr alloys specimens were fabricated by casting (C), milling (M), direct process powder-bed method (CL), and direct metal laser sintering (DMLS) (EL). Each group was then divided randomly into three groups, according to the chemical agent used: alloy primer (Z), universal adhesive (A), or both (AZ). The composite resin cylinders were built on metal specimens. SBSs were determined after water storage and thermocycling, and data were statistically analyzed. The method used for the fabrication of Co-Cr alloy had a significant effect on bond strength (p?=?0.016). AZ (12.077?±?0.575?MPa) groups showed highest SBS values. Co-Cr alloys fabricated with DMLS method have a superior repair capacity. The universal adhesive increased the repair strength when applied with an alloy primer.     

Aluminum/carbon fiber hybrid composites

An effective, economic way of using carbon fiber is to combine it with a resin and another material, either a fiber or a metal, to produce a hybrid structure. Some of the properties of a hybrid beam made by attaching carbon composite to either side of an aluminum channel section are described here. The structure has considerable potential in the orthotics field; the aluminum core assists in the forming of, for instance, orthoses (calipers), modifies the failure characteristics of the carbon fiber composite, and eases the problem of jointing and adjustment of finished articles. Difficulties can arise when combining carbon composites and metals because of differences in thermal expansion behavior. To alleviate these effects a urethane modified epoxide resin matrix, which has very good adhesive properties, was employed. The work covers measurements of strength and modulus, evaluation of the aluminum/aluminum bond strength, and the flexural fatigue performance.     

Thermoplastic bonding to metals via injection molding for macro-composite manufacture

In this work, we explore a new method of in-situ joining of polymers to metals in injection molding to allow direct bonding between thermoplastic and metal parts. Such a method can integrate several downstream steps in product manufacture, allow optimal design of products and joints, and avoid adhesive application, assembly, and associated difficlties. A variety of process parameters and their effects upon the interface tensile strengths were examined. A full factorial experiment was conducted involving four of the critical process parameters identified. The effects upon tensile strength at break of the following process parameters were studied: (1) adherend surface temperature, (2) screw linear velocity, (3) bondline thickness, and (4) pack and hold pressure. The fracture surfaces and the thermoplastic metal interfaces were analyzed. The bonds fabricated with higher adherend surface temperatures have increased mean tensile strength and less adhesive failure. This increase in mean bond tensile strength and less adhesive failure was due to increased polymer penetration of the adherend surface roughness, at the micrometer level, as shown in the analysis of the polymer-metal interface by a scanning electron microscope (SEM).     

A review on direct assembly of through‐the‐thickness reinforced metal–polymer composite hybrid structures

Constant efforts to reduce the structural weight of transportation systems as a solution to control emission levels are currently shaping the way modern cars and airplanes are designed and manufactured. Increased attention has been given to innovative metal–composites multi‐material concepts for the production of lightweight structures. However, the nature of these very dissimilar materials makes their joining a rather complicated task. Recently several technologies have been proposed to overcome process limitation and increase the load transfer between metal and composite in hybrid structures. One of the promising solutions is a new concept known as direct assembling with through‐the‐thickness reinforcements. In this concept, the composite material of a hybrid joint is directly assembled upon a surface‐structured metallic part. Features structured on the metallic part, by a manufacturing phase, act as a through‐the‐thickness reinforcement improving the out‐of‐plane strength and load transfer capabilities of such joints. The current status and state‐of‐art direct assembling technologies are reviewed in this article. Examples of reviewed metal structuring techniques include micromachining, stamping, Surfi‐Sculpt, additive manufacturing, cold metal transfer, and metal injection molding structuring. Direct assembling techniques addressed in this article are vacuum‐assisted resin infusion, resin transfer molding, prepreg/autoclave assembly, and ultrasonic joining. POLYM. ENG. SCI., 59:661–674, 2019. © 2018 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers.     

Adhesive Properties of Epoxy Resin with Chromic Hardener

Cohesive and adhesive properties have been compared of epoxy resins crosslinked either with chromic‐based hardener or with conventional amine‐type hardener. Higher cohesive parameters, such as yield strength, Young's modulus and impact resistance were observed for the material cured with chromic hardener. The adhesive strength of metal‐metal joints (steel‐aluminium) has been also found to be higher for chromic hardener containing epoxy compared to conventional curing systems. The time dependencies of adhesive strength after thermal treatment at 140°C of the joints showed a higher thermal resistance of the epoxy with chromic hardener when compared to the amine cured resin.     

TEM,XPS and thermo-mechanical properties of novel sustainable hybrid coatings

This work contributes to the development of a new generation of protective coatings composed of organic–inorganic materials. A silica based hybrid film was used in this work as high performance materials. The silica sol–gel film reveals enhanced thermo-mechanical properties in comparison with the pure polymer film. Herein, we demonstrate the possibility of employing cheap SiO₂ as prospective nano-fillers for hybrid coatings with active thermo-mechanical properties. Organic–inorganic hybrid coatings based on polyimide and silica were synthesized through a simple physical mixing technique. 3,3′,4,4′-Biphenyltetracarboxylic dianhydride (BPDA), benzene-1,3-diamine (BDA), 3,3′-oxydianiline (ODA) and SiO₂, were used as precursors for the hybrid coatings. These hybrid coatings were deposited via spin coating onto a galvanized iron, aluminum and copper in order to study the adhesive strength. The effects induced by the silica content on the mechanical properties of the coated samples were investigated. The mechanical properties of hybrid composite were found to be enhanced compared to polyimide coating. The main objective was to observe potential improvements in the mechanical and thermal properties of PI–silica hybrid films. Morphology, and structural changes in the composite films were studied as well as adhesion and impact strength and these characteristics were compared with those of unreinforced polyimide films.