Influence of corona treatment on adhesion and mechanical properties in metal/polymer/metal systems

The effect of corona treatment (CT) on the adhesion at the metal–polymer interface was studied. Metal/polymer/metal laminates were manufactured by the laboratory roll‐bonding process with preliminary corona surface treatment of the polymer core: a polyethylene and polypropylene sheet as well as steel sheet. It was treated with corona discharge to increase its surface energy and the adhesion to metal, an austenitic steel. The adhesion, which was measured by T‐peel and shear tests, was increased by 43% of crack peel and 22% of mean peel resistance respectively, after 120 s CT. On the basis of scanning electron spectroscopy observations, improvements in the adhesive properties were attributed to the change in the interfacial morphology. In mechanical tests, yield and tensile strengths were strongly influenced by CT, indicating that these laminates were sensitive to interfacial phenomena. However, elongation at rupture of the composites was found to be unchanged. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Calorimetric Measurements of The Heat Generated by The Peel Adhesion Test

The peel test is a simple mechanical test commonly used to measure the adhesion of flexible films bonded to rigid substrates. When the film is deformed elastically during peeling, the peel force is a direct measure of the strength of the interface. However, when plastic deformation takes place, the work of detachment is much larger than the thermodynamic work of forming the fracture surfaces. Simultaneous mechanical and calorimetric measurements of the work of detachment and the heat generated during the peeling of polymeric films from metal substrates and metal films from polymeric substrates have been made. An energy balance for peeling has been proposed. Most of the work of peeling was consumed by plastic deformation. The peeled polymer dissipated approximately one half of the work of peeling as heat and most of the remainder was stored in the peeled material. The peeled metal dissipated most of the work of peeling as heat.     

Experimental determination of the peel adhesion strength for metallic foils

This work addresses the problem of experimental measurement of peel adhesion in cases where a non-recoverable (plastic) deformation energy of the peeled foil, plus frictional losses, constitutes a significant portion of the total peel energy. In standard tests, when the true adhesion strength is desired, the plastic energy has to be calculated and deducted from the total energy. Several studies have been dedicated to the modelling and calculation of the energy dissipated through plastic deformation so that the net adhesion energy could be deduced. These calculations are cumbersome and impractical for general use. A simple experimental technique for the determination of the net adhesion strength is proposed. Experimental results with ～ 0.1 mm thick foils of stainless steel, nickel, and titanium confirm the theoretical predictions regarding the energy balance during peeling. Using the proposed methodology, there is no need to calculate or otherwise determine the deformation energy losses of the peeled foil or the frictional dissipation. The method is not limited to a particular material and can be used successfully for strain hardening plastic as well as metallic foils. Peel tests on adhesively bonded specimens of stainless steel and nickel and of a thermal spray-coated Ti alloy foil were carried out to demonstrate the applicability of the proposed method.     

Study on integrally molded PA6/304 stainless steel by micro-nano pressing technology

With application of micro-nano pressing technology (MNPT) polyamide 6 (PA6) and 304 stainless steel were integrally molded, and the mechanical properties and structure on the interface of plastic and metal were investigated in the study. The micro structures on the stainless steel specimen surface were achieved by physical and/or chemical surface treatment techniques including polishing and etching methods, respectively. The tensile shear strength and work of fracture for the integrally molded specimen were influenced greatly by the surface treatment on stainless steel. The maximal tensile shear strength and the fracture work for the MNPT molded sample reached up to ca. 11?MPa and 17?KJ/m², respectively. In addition, the interface fractography of the MNPT molded specimen was characterized by scanning electron microscope (SEM) and atomic force microscope (AFM). These results indicated PA6 melt flew into the micro and/or nano holes on the chemical etched metal surface during hot press molding to form micro mechanical interlock structure to prepare strong MNPT molded samples.     

Energy and force distributions during mandrel peeling of a flexible tape with a pressure-sensitive adhesive

Peel tests are commonly used to investigate the strength of adhesive joints. In the mandrel peel test the curvature of the flexible tape within the zone of detachment is controlled by the radius of the mandrel and this, coupled with an energy balance approach, allows separate determinations of the energy terms associated with any plastic or inelastic deformation of the tape and the de-adhesion or peel energy. If, in addition, the force on the mandrel is monitored then the position of the force vector within the separation or de-adhesion zone can be established. This, in turn, permits a closer comparison with predictions from a peel model which allows non-linear behaviour of both the tape and the adhesive layer. The model has been validated by peel tests on cellulose, PVC, aluminium and Teflon tapes carried out at sufficiently low speeds for rate effects within the adhesive to be small. Both the measured values of the de-adhesion energy, which varied from 60 to 160 J/m², and the positions of the force vector within the de-adhesion zone correlated well with those predicted from load-extension tests on samples of the tapes and bulk samples of similar polymeric adhesives carried out at similar rates of deformation.     

PA6/不锈钢热压复合界面性能研究

采用机械抛光、化学刻蚀以及退火分别对304不锈钢表面进行预处理,并利用自制模具将聚酰胺6（PA6）注塑试样与不锈钢进行热压成型。力学性能测试结果表明,经过机械抛光后的不锈钢与PA6热压的搭接强度为3.31 MPa, 而经过抛光、化学腐蚀和退火处理后,复合制件的搭接强度达到17.48 MPa,失效模式由界面失效变为内聚失效;扫描电子显微镜、原子力显微镜观察结果表明,化学刻蚀后的不锈钢表面具有微纳米孔洞,热压时塑料熔体进入金属表面微纳米孔洞形成锚定效果;傅里叶红外光谱分析结果表明,PA6与退火处理后的金属表面氧化物形成了化学键;锚定结构与化学键合有利于提高复合件的力学性能。     

Interfacial adhesion measurement of a ceramic coating on metal substrate

The interfacial adhesion measurement of a ceramic coating on a metal substrate is studied by three-point bending (3PB) technique. In the measurement, interfacial cracks are induced during the 3PB test, and the interfacial energy release rate is calculated from the released energy per unit crack surface area during crack extension under the fixed displacement conditions. A finite element analysis (FEA) model encompassing the plastic behavior of the metal substrate is developed to simulate the 3PB test and extract the energy data. The inputs to the FEA model include the crack length, the maximum and critical loads corresponding to crack initiation, and the mechanical properties of the coating and substrate. A MoB/CoCr ceramic coating/stainless steel substrate system is investigated by the technique for demonstrating the utility of the technique.     

Effects of mechanical and geometrical properties of adhesive and metal layers on low-velocity impact behavior of metal laminate structures

In this study, the effects of mechanical and geometrical properties of the adhesive layers and mechanical properties of the metal layers on low-velocity impact behavior of adhesively bonded metal laminates (ABML) were investigated. The contact force, the transverse displacement, the contact duration, and the dissipated energy were considered as the main structure responses under impact loading. To study the effects of mechanical and geometrical properties of adhesive layers on low-velocity impact behavior of ABML, two different adhesive materials and two different adhesive thicknesses were considered. The results showed that the contact force was more depended on the adhesive thickness and nearly unaffected by the adhesive material, whereas the dissipated energy was more depended on the adhesive material rather than the adhesive thickness in case the overall structure thickness was remained fixed. To determine the effects of material parameters of the metal layers including the yield stress, the elastic modulus, the density, and the tangent modulus on the impact behavior of ABML, finite element analyses were carried out. The results showed that increasing the number of metal layers in a constant total thickness caused decrease of the total contact force and increase of the contact duration and transverse displacement of the structure due to more widespread plastic deformation occurred in the layers. The material yield stress and Young’s modulus were the most influencing material parameters on the mechanical behavior of ABML under low-velocity impact loading. The finite element models were well validated against the experimental and numerical results.     

Quantifying the Relationship Between Peel and Rheology for Pressure Sensitive Adhesives

An attempt is made in this work to model quantitatively the peel force vs. rate behavior of a pressure sensitive adhesive (PSA) tape. The approach follows suggestions of previous authors in modeling the deformation of the PSA as uniaxial extension of individual strands. A debonding failure criterion based on stored elastic energy density is used. In this work, experimental measurements of dynamic mechanical master curves are used to provide the mechanical properties of the PSA in the model. The predictions are compared with experimental peel force vs. rate master curves on tapes made from those same adhesives. The only adjustable parameter for the fitting is the quantity related to the debonding criterion. In this set of natural-rubber-based PSAs, the general shape of the peel master curve and the changes in peel behavior associated with tackifier loading and rubber molecular weight are well explained by the model. The effect of changes in substrate chemistry are not well explained.     

Improving the adhesion of thin stainless steel sheets for fibre metal laminate (FML) applications

Thin stainless steel sheets hold considerable promise for improving several properties of aluminium based fibre metal laminates (FMLs). To allow incorporation of such sheets in FMLs their adhesion to epoxies used in aerospace applications should be at a high level. The present work describes the effects of chemical and mechanical pretreatments to regular and molybdenum-enriched AISI 301 steel sheets. Based on an in-depth knowledge of aluminium pretreatment for FML applications, also aluminium-coated stainless-steel sheets are investigated. Gritblasting was found to yield the best properties. The effect of coating the steel surface with aluminium was found to be promising, but the bond strength between the aluminium and the steel substrate proved insufficient for thin (0.1 mm) AISI 301 steel sheet.     

Ageing of corrosion resistant steel/rubber/composite hybrid structures

One of the major challenges when preparing reliable hybrid structures is the adhesion between different components. Besides enduring the specific stress state, hybrid structures should maintain the required properties in the service environment without degradation. In this study, the environmental resistance of stainless steel/rubber/GFRP (glass fibre reinforced plastic) hybrid structures were tested by exposure to hot, moist and hot/moist environments and after the ageing by peel testing. Two different stainless steel surface finishes and two different rubber grades were investigated. The results were compared with the properties of a mild steel/rubber/GFRP structure. Both mild steel/rubber and composite/rubber structures are used in industrial applications, such as in vibration damping devices and in automotive components.The peel tests showed that with right rubber compounds, stainless steel/rubber and GFRP/rubber interfaces can maintain their properties even in harsh hot/moist environments to such an extent that the interfacial strength of the joint is higher than the cohesive strength of the rubber. This enables the use of rubber's cohesive fracture properties instead of the substrate/rubber interfacial properties when estimating the strength of the steel/rubber/GFRP hybrid structure. In addition, based on the current study, time-consuming stainless steel pre-treatments are not needed but the stainless steel can be in the as-received stage. According to the chemical analysis even before and after the harsh hot/moist exposure used, none of the studied rubber grades had degraded. Thus, we conclude that it is possible to manufacture environmental resistant stainless steel/GFRP hybrid structures with the aid of EPDM rubbers.     

Adhesion of poly(m-, p-phenylene isophtalamide) coatings to metal substrates

The adhesive properties of wear-resistant poly(m-, p-phenylene isophtalamide) coatings to substrates of ferrous and non-ferrous metal materials which are the most common in mechanical engineering were investigated experimentally. The results of measurements of adhesive characteristics taken with the help of such methods as a cross cutting test, a quantitative peel test, a lap shear strength test, a contact angle test and a spreading radius test are discussed in terms of the three most common mechanisms of adhesion: mechanical coupling, molecular bonding, and thermodynamic adhesion. It was established that the adhesive properties of poly(m-, p-phenylene isophtalamide) coatings depend on the content of a ferrite component in the structure of carbon steel substrates.     

Structural effects on dynamic features of sandwich metal/polymer/metal

A theoretical approach to the mechanical coupling between phases in metal/polymer/metal sandwich composites is developed assuming perfect interfaces. Comparisons between experimental dynamic mechanical spectroscopy and theoretical results are made with special attention to the geometrical characteristics. Unexpected results concerning the dependence on the width of the specimen are explained using the strain energy method. The polymer thickness influence is explained only by structural effects instead of the interface effects often found in the literature. The temperature of the sandwich loss factor peak is revealed to greatly depend on the specimen dimensions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2493–2505, 1997     

Effect of acrylic acid on the physical properties of UV-cured poly(urethane acrylate-co-acrylic acid) films for metal coating

UV-cured poly(urethane acrylate-co-acrylic acid) (PU-co-AA) films with five different compositions were prepared by reacting isophorone diisocyanate (IPDI), polycaprolactone triol (PCLT), 2-hydroxyethyl acrylate (HEA), and different weight ratios of trimethylolpropane triacrylate (TMPTA) and acrylic acid (AA) as diluents. Their synthesis and physical properties including gel content, adhesion properties, morphological structure, thermal properties, and mechanical hardness were investigated as a function of the AA content. It was found that the physical properties of the PU-co-AA films are strongly dependent upon the AA content. Crosscut tests showed that PU-co-AA films with lower AA content showed 0% adhesion (0B), and the adhesion of films increased dramatically as the AA content increased to 40–50%. The pull-off measurements showed that the adhesion force of the PU-co-AA films to stainless steel substrates varied from 6 to 31 kg_f/cm² and increased linearly with increasing AA content. PU-co-AA films with higher AA content can be good candidates for UV-curable coating of metal substrates such as stainless steel. However, the thermal stabilities and mechanical hardness decreased with increasing AA content, which results from the relatively linear and flexible structure of AA.     

Effect of Deformation-induced Residual Stress on Peel Strength of Polymer Laminated Sheet Metal

The adhesion between adhesively bonded polymer film and a metallic sheet substrate in a polymer laminated sheet metal (PLSM) subjected to large deformation, such as in a forming process, is influenced by two deformation-induced factors. These are (i) evolution of surface roughness of metallic substrate with applied strain and (ii) development of residual stress in the polymer adherend (polymer film with a thin uniform adhesive layer on one side) arising from significant differences in the deformation behavior of metal and polymeric components. A new experimental methodology was devised in this study to decouple the effects of substrate surface roughness and residual stress on interfacial peel strength (IPS) of uniaxially deformed PLSMs. This methodology was based on 180° peel testing of PLSM specimens prepared under two different lamination conditions, one involving systematic pre-straining in uniaxial tension of the metallic substrate prior to laminations and the other involving post-lamination pre-straining of the PLSM. The role of pre-strain and peel test speed, for the above laminations conditions, were critically analyzed for their effect on IPS of two differently tailored PLSM systems. The IPS results were attributed to the effect of deformation-induced residual stress and metallic surface roughness. The analysis suggests that IPS is strongly dependent upon the residual stress induced by uniaxial deformation but only marginally on substrate surface roughness depending upon the constituents (film and adhesive) of the adherend. The magnitude of pre-strain was inversely and non-linearly related to IPS for both deformed PLSMs. Peel test speed, on the other hand, showed a more complex behavior in terms of IPS for the two PLSM systems.     

Adhesion of Polyethylene to Metals: The Role of Surface Topography

Previous work established the importance of the fibrous substrate topography in obtaining good adhesion of polyethylene to matt black oxide films formed on copper in alkaline solution. In this paper the effect of the very rough surface topography is shown to be general. Anodising treatments for copper and zinc and a high temperature oxidation for steel are described which give a very rough surface consisting (respectively) of fibrous, dendritic and blade-like growths. The peel strength of polyethylene to these substrates is high even under circumstances, for example when the polymer is stabilised with anti-oxidant, where adhesion to a chemically similar smooth surface is low. The high peel strength is associated with large amounts of energy being dissipated during peeling in plastic deformation of the polymer near the interface. It is suggested that this is caused by the development of high shear stress concentration at the fibre ends causing yielding in a large volume of polymer.     

Peel strength improvement of foam core sandwich beams by epoxy resin impregnation on the foam surface

The interfacial adhesion characteristics between foam cores and faces affect much the structural integrity of foam core sandwich structures. The peel strength between the face plate and the foam core is one of the appropriate parameters for the interfacial characteristics of sandwich structures and its peel energy is also measured for the interfacial characterization. The peel strength is the first peak force per unit width of bondline required to produce progressive separation, and the peel energy is the amount of energy per unit bonding area associated with a crack opening. In this study, to improve the peel strength between the foam core and the face plate of foam core sandwich beams, the surfaces of foam core sandwich beams were resin-impregnated. Then the peel strength as well as peel energy of resin impregnated polyurethane foam core sandwich beams were measured by the cleavage peel test and compared with those of the same sandwich beams without surface resin impregnation on the foam surface.     

Contact angle and wettability of hybrid surface-treated metal adherends

Adhesion performance of adhesively bonded metal joints with aluminum and stainless steel was much dependent on the surface treatment of the adherends. This work was aimed at optimizing hybrid surface treatments to improve wettability of metal surfaces and strength of adhesive metal joints, which was a combination of mechanical, chemical, and energetic surface treatment methods. The surface free energies and wettability of hybrid surface-treated metal adherends were measured for different treatment conditions with abrasion, grit blast, sulfuric acid etching, phosphoric acid anodizing, silane treatment, plasma treatment, and flame treatment. The surface morphology and chemical composition of the metal adherends were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy and the bond strengths of the single-lap joints composed of aluminum and stainless steel adherends were measured with respect to hybrid surface treatment conditions. From the experiments, an effective hybrid surface treatment condition was suggested for metal surfaces with super-hydrophilic characteristics. Also, the failure mode of adhesive metal joints was evaluated by photo-surface analysis method.     

Mechanical properties and adhesion of TiN monolayer and TiN/TiAlN nanolayer coatings

In this work, TiN monolayer and TiN/TiAlN nanolayer coatings were deposited on 100C6 (AISI 52100) steel substrate by Physical vapor deposited (PVD) magnetron sputtering system. The morphological characterization was evaluated using an atomic force microscopy. The mechanical properties were determined by nanoindentation test. The adhesion was investigated by both microindentation and scratch test. The results show that the TiN/TiAlN nanolayer coating have the more rough surface and the better mechanical properties and adhesion compared to TiN monolayer coating. The effect of microstructural and mechanical proprieties on the adhesion behavior was further discussed. It was found that the improvement in adhesion of nanolayer system is in part due to the increase in plastic deformation resistance and the enhancement of mechanical properties (hardness and elastic modulus) and to the structure with a small grain size and a high number of interfaces.     

An experimental partitioning of the mechanical energy expended during peel testing

Peeling of polyimide coatings bonded to aluminum substrates was analyzed from a thermodynamic perspective with the intent of determining how the energy expended in separating the bonded materials is consumed. The mechanical work expended and the heat dissipated during peeling were simultaneously measured using deformation calorimetry. The surfaces exposed by peeling were analyzed by electron microscopy and electron spectroscopy. The thermodynamics of tensile drawing for polyimide were studied using deformation calorimetry and thermomechanical analysis. When polyimide coatings were peeled from aluminum substrates at a peel angle of 180°, almost all of the mechanical energy was consumed in propagating the bend through the coating being peeled. The fraction of peel energy dissipated as heat was 48 ± 1.3% and nearly all of the remainder was stored as latent internal energy in the peeled polyimide. When the bend is propagated through aluminum, which has a limited capacity to store latent internal energy, 97-100% of the mechanical energy is dissipated as heat.