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This study assessed the validity of torsion test, by comparing it with shear test, in evaluating the bonding of resin composite core after different surface treatments to both zirconia and resin composite CAD/CAM blocks. In total, 108-resin composite core cylinders (3 mm × 3 mm) were prepared and stored in distilled water at 37 °C/48 h. The cylinders were subjected to no-treatment, sandblasting, or surface grinding. Cylinders from each treatment group were then bonded with either zirconia or resin composite CAD/CAM blocks using dual-cure resin cement and stored for 24 h. They were subjected to torsion (rotational speed, 0.25 rpm until failure) or shear (crosshead speed, 1.0 mm/min) tests (n = 9 for each core/block combination in each test). All fractured surfaces were observed by scanning electron microscopy, and the maximum principal stress (MPS) was assessed using finite element analysis (FEA). In the torsion test, the sandblasted composite core and resin CAD/CAM block showed significantly lower bond strength than the other groups (p < 0.05), but the shear test results showed no intergroup differences. While 39.89% of the specimens showed cohesion failures in the torsion test, 55.56% showed adhesion failures in the shear test. FEA demonstrated an even distribution of MPS from the outer edge to the center of the cement layer during the torsion test; however, MPS was unevenly concentrated at the bottom edge of the cement layer during the shear test. The torsion test was better than the shear test in bond testing because of the uniform tensile stress distribution and unidirectional displacement at the bond interface. [ABSTRACT FROM AUTHOR]

This work studied the effect of the synthesis parameters (i.e. synthesis method and melamine content) on the adhesion of cold-setting melamine-urea-formaldehyde (MUF) resins in wood bonding. Two types of cold-setting MUF resins were synthesized: MUF-A resins with three melamine contents (30, 40, and 50 wt%) prepared by the simultaneous reaction of urea, formaldehyde, and melamine, and MUF-B resins with the same melamine levels but synthesized by a sequential reaction process of melamine with formaldehyde and urea. The curing behaviors of both resins were characterized by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and their adhesion performance in the dry and wet states were compared in block-shear strength (BSS) and wood failure (WF) tests. As the melamine content increased, the viscosity and peak temperature (Tp) of the resins increased. However, MUF-B resins showed lower activation energy (Ea) than those of MUF-A resins. Dynamic and isothermal DMA scans also showed that MUF-B resins also had greater maximum storage modulus (E′max) than those of MUF-A resins in their neat resins and resins/wood composites, indicating stronger interphase adhesion and cohesion. Lower Tp, lower Ea, and higher E′max, of MUF-B resins than those of MUF-A resins resulted in higher BSS and WF of MUF-B resins in wood bonding. In particular, MUF-B resins with 40% melamine showed the highest BSS and WF. These results indicate that the MUF resin synthesis method is closely related to the adhesion performance in wood bonding. [ABSTRACT FROM AUTHOR]

Finite element analysis has been carried in the present research to study individual and combined effect of internal pressure and torsional loading on stress and failure characteristics in case of an adhesively bonded Tubular Single Lap Joints (TSLJ) made of laminated Fiber reinforced polymer (FRP) composite materials. Effect of changing torsional load magnitude on an internally pressurised adhesively bonded TSLJ on interlaminar stresses and onset of different joint fracture modes (adhesion and cohesion failures) has also been studied in the present analysis. Three dimensional stress analysis of the adhesively bonded TSLJ has been carried out through suitable ANSYS Parametric Design Language (APDL) of ANSYS 14.0. Tsai-Wu coupled stress criterion has been used for predicting the onset of joint failures in the TSLJ. It has been observed that stresses (σr, σθ, σz, τrz) induced within the joint region under pure internal pressure loading are least affected through introduction of a torsional loading in the TSLJ. However, the stresses (τrθ and τθz) which are considered to be significant under pure torsional loading get tremendously enhanced due to the varying torsional loading. The interface between the outer tube and adhesive of the TSLJ has been observed to be the most critical bondline interface which is prone to undergo adhesion failure towards the free edges under pure internal loading conditions. However, under pure torsional loading conditions it tends to fracture through adhesion failure towards the clamped edge of the TSLJ. Under combined torsional and internal pressure loading the joint fails towards the clamped edge of the along the critical path which happens to be within the bondline interface, indicating predominance of torsional loading over the pure internal pressure loading. A comparative study based on the magnitude of failure index revealed that torsional loading marginally affects the joint failure as the internal pressure loading improves the compactness of the bonded joint hence improving the resistance of the TSLJ against initiation of joint fractures. [ABSTRACT FROM AUTHOR]

Bi-adhesive (or mixed-adhesive) joint is an alternative stress-reduction technique for adhesively bonded lap joints. In this work, an experimental study was performed to assess the effect of bi-adhesive bondline on the failure load of mono-adhesive and bi-adhesive single-lap joints. The first step in the experimental study related to mono-adhesive joint, the overlap length was checked using the Global yielding criteria. For the selected overlap length, failure loads of AV138, Araldite 2015 and DP-8005 mono-adhesive joints were determined. It was seen that the highest failure load occurred in the Araldite 2015 mono-adhesive joint. Secondly, the bi-adhesive joints were considered as two different adhesive combinations (AV138 + 2015, AV138 + DP-8005). An interesting result was obtained that the considered bi-adhesive joints with two different adhesive combinations (AV138 + 2015, AV138 + DP-8005) give joint strengths higher than the joint strengths of the adhesives used individually, even if ductile adhesive has a joint strength higher than that of the stiff adhesive. In the last step of this study, experimental investigation was then focused on the determination of optimum bond-length ratio for the bi-adhesive joint. Optimum bond-length ratio for bi-adhesive joint was then investigated using three ratios (0.3, 0.5, 0.7). It is concluded that the adhesive type and the bond-length ratio play an important role in the bi-adhesive bondline.Comparisons of the experimentally determined failure loads and shear strengths with available closed-form solutions were also carried out. Experimental failure loads were in good agreement with those obtained from the Volkersen method and Global yielding criteria. [ABSTRACT FROM PUBLISHER]

One of the strengthening methods of composite connection is the employment of reinforcing elements in the adhesive layer. Using of additional elements in the adhesive layer make uniform stress distribution and improves the strength and toughness of the connection. In this paper, metal wires were used to reinforce the adhesive joints of composites. The effects of the number of wires, wire diameter, wire stiffness, angle of wire and the adhesive type on the strength of the adhesive reinforced bonded composite joints were investigated experimentally and numerically. A finite element model was developed to study the stress distribution in the reinforced adhesive joints. The numerical results showed a good agreement with the experimental observation. It was found that increasing the number of wires and wire diameter, choosing a stiffer material for the wire and increasing the wire angle, uniform the stress distribution and reduced the maximum and average stress values in the adhesive layer. For the appropriate reinforcing wire parameters, the joint strength increased more than 90% in this study. It also observed that the using metal wires as a reinforcing element was more effective in the ductile adhesion than the brittle ones. [ABSTRACT FROM AUTHOR]

This experimental work aims to better understand the hardening process of limestone tuff after compaction when water content varies. Indeed, the pavements built with wet calcareous crust or tuff are hardened by the effect of compaction followed by water evaporation but this cohesion after compaction disappears completely by total saturation. In order to classify the materials according to geotechnical specifications related to limestone crusts, tuff from Faidh el Botma area was studied by following the change of compressive strength measured on specimens prepared at different water contents and stored for several days either under air (for fast drying) or in non-hermetic bags (for slow drying). The first series of specimens appeared more resistant than the second one. As explanation of the hardening, the possible precipitation of new phases such as carbonate during the fast drying is discussed based on chemical and microstructural observations as well as the effect of suction than could change the microstructural arrangement of tuff particles when the moisture content varies. [ABSTRACT FROM AUTHOR]

The mechanical and adhesion behavior of cationically polymerized, partially crystalline epoxy networks is presented. For this, a reactive and a nonreactive poly(ɛ-caprolactone) (PCL) were used as the crystalline component for the formation of copolymers and polymer alloys, respectively. The trade-off between toughness on the one hand and glass transition temperature and mechanical strength on the other can be reduced by the presence of nanostructures in combination with small crystalline domains (< 1 μm), as in the case of epoxy/PCL-based polymer alloys. This structure–property relationship reveals that a certain degree of crystallinity leads to enhanced toughness in cationically polymerized epoxy networks. [ABSTRACT FROM PUBLISHER]

Retarded deformation at the bond line edge of a thick, viscoelastic adhesive layer is observed using digital image correlation. Such information is required for proposing physical crack onset/propagation parameters which take into account viscoelastic and viscous mechanisms in the evaluation of dissipated energy. A complex stress/strain redistribution is observed in the early stage after specimen loading. The results illustrate that viscoelasticity dissipates a considerable amount of energy prior to crack nucleation and the lack of predictive models to account for that phenomenon. [ABSTRACT FROM AUTHOR]

To evaluate surface compatibility in wood-plastic composites (WPCs), the dispersion and acid-base components of surface energy of various thermoplastic resins (matrices) and several wood-based reinforcing materials were determined using inverse gas chromatography (IGC). Polypropylene (PP), nylon 6, poly(ethylene terephthalate) (PET), poly(trimethyl terephthalate) (PTT), high impact polystyrene (HIPS), and styrene maleic anhydride (SMA) were used as thermoplastic resins, while wood flour (hot water extracted and un-extracted), microcrystalline cellulose (MCC) (50 μm and 90 μm), α-cellulose (60 μm), and silicified microcrystalline cellulose (SMCC) (60 μm) were used as reinforcing materials. All matrices and reinforcing components were exposed to low vapor concentrations of apolar (decane, heptane, nonane, octane) and polar (chloroform, ethyl acetate, dichloromethane, acetone, and tetrahydrofuran) probes. Methane and helium were employed as reference and carrier gases, respectively. IGC retention times were used to determine the acid-base component of surface energy of the analyzed materials. The corresponding surface energy, work of adhesion, and work of cohesionwere calculated based on the van Oss-Chaudhury-Good approach (acid-base and Lifshitz-van der Waals interactions). Composite performance was analyzed by measuring tensile and flexural strengths according to ASTM standards. The results indicated that for the same type of filler (assuming similar shape and dimensions), the mechanical properties of the composites increased when the ratio of the work of adhesion to the work of cohesion increased. A similar trend was observed when the thermoplastic resin employed to create the composite possessed an acid-base component of surface energy greater than zero. [ABSTRACT FROM AUTHOR]

In this paper, growths of different types of failures including adhesion, cohesion and delamination for a single lap joint (SLJ) of composite laminates were investigated using three-dimensional geometrically nonlinear finite element analysis and by adopting a suitable modeling technique. A unique damage modeling method called sub-laminate modeling was employed for the modeling of damages of different failure modes so as to avoid the oscillatory stress and displacement fields around the damage front. The strain energy release rate (SERR) parameter was used for studying the damage growth and the individual and total components of the SERR along the various damage fronts are evaluated using the virtual crack closure technique (VCCT) based on the linear elastic fracture mechanics (LEFM) approach. This study reveals: that the opening mode is the dominant mode of the propagation for the adhesion and delamination damages, while the sliding mode is dominant for the cohesion failure; that the cohesion failure grows at a faster rate than the adhesion failure; and that the delamination front entrapped within the overlap region in the top adherend of the SLJ grows faster when the delamination damages are present simultaneously in both the adherends. This is particularly true when the delamination centers are exactly aligned with the overlap ends of the joint. [ABSTRACT FROM AUTHOR]

Adhesively bonded metal laminates are used in aerospace applications to achieve low cost, light weight structures in the aerospace industry. Advanced structural adhesives are used to bond metal laminae to manufacture laminates, and to bond stringers to metal laminate skins. Understanding the failure behaviour of such bonded structures is important in order to provide optimal aircraft designs. In this paper, the static failure behaviour of adhesively bonded metal laminate joints is presented. A cohesive zone model was developed to predict their static failure behaviour. A traction-separation response was used for the adhesive material. Three joint configurations were considered: a doubler in bending, a doubler in tension and a laminated single lap. The backface strains and static failure loads obtained from experimental tests were used to validate the results from finite element modelling. The models were found to be in good agreement with experiments. [ABSTRACT FROM AUTHOR]

Inverse Gas Chromatography (IGC) provides a powerful tool for assessing the surface energy of powders by using different chemicals as probes. Finite Dilution Inverse Gas Chromatography (FD-IGC) allows surface energy measurements in a range of probe surface coverages. For heterogeneous materials the relationship between measured surface energy and surface coverage provides information about the surface energy distribution of the material. However, existing methods of analysing FD-IGC data to determine surface energy distributions are based on inappropriate assumptions. Alternative analysis techniques do not determine the material's surface energy distribution but instead provide information about variations in probe-substrate interactions rather than true material properties of the substrate. A more robust method for computing the surface energy distribution of heterogeneous powders is needed. In the pharmaceutical industry, due to the heterogeneous nature of crystalline powders, the surface energy and its distribution plays an important role in the performance of dry powder inhalers, powder mixing, and the cohesion of compressed tablets. Here a new approach for interpreting IGC data, based on more realistic thermodynamic assumptions, is proposed. Using this approach the surface energy distribution of the substrate is determined by fitting the results of simulated experiments to experimental IGC data. The simulation-fitting approach is demonstrated for mannitol and lactose powders. The addition of fines to coarse lactose powder is shown to have a clear effect on the powder's surface energy distribution whilst the surface energy distributions of different particle size fractions of mannitol do not show significant differences in their surface energy distributions. [ABSTRACT FROM AUTHOR]

A computational contact formulation is presented that is suitable for simulating contact interaction problems at very small length scales. The contact model is based on the coarse-graining of the intermolecular forces between neighboring bodies, like van der Waals attraction, into an effective continuum contact description. The model is cast into a nonlinear 3D finite element implementation that is capable of integrating the challenges encountered in the modeling of adhesive systems. The contact model is then applied to the dynamic modeling and simulation of the adhesion and deformation of a gecko seta based on a 3D multiscale approach. The approach spans six orders of magnitude and combines three distinct modeling levels, that describe the effective adhesion behavior at the seta scale, the spatula scale and the molecular scale. The rate-dependent pull-off behavior of adhering setae and spatulae is computed and it is shown that the model is successful in capturing pull-off forces that have been observed experimentally. [ABSTRACT FROM AUTHOR]

Adhesion mechanisms with and without a defect for gripping and releasing objects are proposed, considering the adhesion between a semi-infinite elastic body and a rigid object with a sinusoidal surface roughness. These mechanisms are investigated theoretically. The total energy consists of the elastic term, the interfacial adhesion term, and the mechanical potential energy term due to the external pressure. The grip-and-release process is discussed in terms of the changes in the total energy and the contact width. The gripping stress can be expressed as a function of the elastic modulus. Using polymers with variable elasticity, the grip-and-release process is demonstrated experimentally and discussed in terms of the theory. [ABSTRACT FROM AUTHOR]

Structural adhesives are recognized by the automotive industry as a powerful alternative solution to traditional fastening methods such as welding or riveting. As a new technological solution, they introduce requirements in terms of the evaluation of their mechanical performance. In particular, enhanced safety guarantee requires not only to know the material performance in standard laboratory tests but to be able to predict it under real conditions, in particular for complex shaped parts. This may be done by finite element simulation. Nevertheless, the small thickness and the specific material behavior of the joint make modeling difficult using available numerical tools. This work focuses on the assessment of structural adhesive joints up to their maximal strength using finite element analysis. A complete methodology is proposed which addresses the implementation of a specific non-linear elasto-plastic material constitutive model which is accurate to describe the joint behavior under multi-axial loadings. Experimental tests and an original strategy for the identification of material parameters based on inverse identification are proposed. Finally computational efficiency is addressed using specific interface elements which makes the constitutive model convenient for the simulation of large industrial problems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Adhesion and binding are important properties of nanofibers for a variety of applications in materials for filters, protective devices, and in controlled release of bioactive molecules and tissue engineering. As an overview of researches on adhesion and binding in nanofibrous materials, this article discusses studies in adhesion between micro/nanoparticles and nanofibers, and provides an introduction to research work intended to enhance adhesion/binding between nanofibrous substrates and proteins/cells so as to improve the performance of nanofibrous scaffolds in tissue engineering. [ABSTRACT FROM AUTHOR]

Addition of Cloisite 30B nanoclay particles to a typical ammonium dichromate cured liquid polysulfide elastomeric adhesive leads to very dramatic increase in the aluminum–aluminum joint strength measured by 180° peel test. The increase in adhesive strength could be explained in terms of higher cohesive strength of the nanocomposite adhesives, which has been derived from good interaction between the nanoclay and the polysulfide elastomer. The addition of nanoclay also facilitates the adhesive to dissipate greater amount of energy (by fibrils formation) during the debonding process of the peel test. In addition, the nanoclay aids the low polarity polysulfide elastomer to achieve better molecular contact with the aluminum substrate. The nanoclay particles are very well dispersed (mostly exfoliated) in the polymer matrix even at 8 wt% of nanoclay concentration. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies provide evidences for the excellent dispersion of the nanoclay platelets in the polymer matrix. The results of the mechanical and dynamic mechanical studies confirm the excellent interaction between the nanoclay and the polysulfide elastomer. [ABSTRACT FROM AUTHOR]

The present work investigates the rate-dependent failure behaviour of structural adhesive joints loaded in mode I. Butt joint and tapered double cantilever beam (TDCB) specimens were tested at velocities ranging over more than six orders of magnitude. A rate-dependent extension of the bi-linear cohesive zone model is proposed and implemented into the finite element code LS-DYNA via an user-defined subroutine. The parameters for the implemented cohesive zone model are found directly by evaluation of experimental data. The comparison of simulations with experimental results for different specimen types and test velocities validates the proposed model. The critical energy release rate of adhesively bonded joints is usually measured in (tapered) double cantilever beam tests, and evaluated using the Irwin–Kies equation. In this paper a different evaluation method is proposed, which provides additional information on the energy dissipated during crack initiation. The results of this method agree with the results obtained using the Irwin–Kies equation. The investigations have focussed on thin adhesive layers. Parameter identification and validation have been performed using the crash-optimized adhesive Terokal 5077 from Henkel. [ABSTRACT FROM AUTHOR]

Colloidal forces outside the microscopic probe (particle)–substrate adhesion contact area were analyzed theoretically. Equations describing the van der Waals, electrical double layer, and hydrophobic forces were derived for the non-contact area of a probe–substrate system assuming a simple sphere–flat geometry. Two cases were considered: particles freely resting on the substrate surface and particles pulling off the substrate. The results of modeling presented in this communication suggest that the adhesion of fine particles (microscopic and sub-microscopic particles) to flat surfaces can be affected by the forces acting outside the contact area. However, due to increased distance between the particle and substrate during separation, both the van der Waals and electrostatic forces acting outside the contact area are negligibly small compared to the short-range adhesion forces and they do not contribute to the measured pull-off force to any great extent for most systems. On the contrary, our calculations suggest that the long-range hydrophobic forces can contribute to the strength of adhesion between hydrophobic fine particles and hydrophobic substrates. [ABSTRACT FROM AUTHOR]

Here we present a new method for improving adhesion between natural rubber (NR) and polyester fabric. This is done by in situ grafting of maleic anhydride (MA) onto NR in a two-roll mill. The grafting procedure was followed by infrared spectroscopy (FT-IR). The effect of ultraviolet/ozone (UV/O3) radiation on the stability of the rubber mix as well as on the peel strength of the rubber coated fabric was investigated. Mechanical and spectroscopic analyses as well as light microscopy were used to assess the adhesion properties of the resultant rubber mixes to the polyester fabric. It was observed that the grafting with MA together with UV/O3 treatment improved the peel strength of the rubber coated polyester fabric. [ABSTRACT FROM AUTHOR]

The adhesion and cohesion of micrometer-size particles are governed by complex interactions involving van der Waals and electrostatic forces. For many applications, such as the toner particles used in electrophotographic engines, these interactions are rendered more complex by coating the surfaces of the particles with particulate addenda such as silica nanoclusters. Specifically, nanoclusters may affect either or both the surface forces and/or the electrostatic charge distribution on a microparticle. This can change both its attraction to a substrate as well as the interparticle Coulombic repulsion. This paper explores these interactions and describes their quantitative effects on adhesion and qualitative effects on cohesion. [ABSTRACT FROM AUTHOR]

Since their introduction half a century ago, pressure-sensitive acrylic adhesives have been successfully applied in many fields. They are used in self-adhesive tapes, labels and protective films, as well as in dermal dosage systems for pharmaceutical applications, in biomedical electrodes, and in the assembly of automotive parts, toys, electronic circuits and keyboards. Three properties which are useful in characterizing the nature of pressure-sensitive adhesives (PSAs) are tack, adhesion and cohesion. They are determined, to a large degree, by the kind of monomers, solvent nature, initiator type and amount, molecular weight of acrylic co-polymer, polymerization method, and especially by the type and quantity of the cross-linking agent added to the PSA. There are internal and external cross-linking agents. UV technology is well established in the market and allows the production of a wide range of UV-cross-linkable pressure-sensitive adhesives with interesting features. [ABSTRACT FROM AUTHOR]

Fiber sizing can improve the performance of fiber-reinforced polymer composites. The focus of this work was to determine if the improvement in performance could be ascertained from a micromechanical test for interfacial adhesion on as-processed materials under hygrothermal exposure. Three types of sizings were examined: a carboxyl modified poly(hydroxyether), that is identified as low spread phenoxy (LSP), a poly(vinylpyrrolidone) (PVP) sample and a standard industrial sizing (G′). A nanoindenter was effectively used to obtain interfacial shear strength (IFSS) using a modified micro-indentation technique. The results showed that LSP outperforms the PVP and G′ materials in bulk composite properties, but showed equivalent interfacial shear strength to G′ and experienced hygrothermal degradation in interfacial adhesion that the PVP did not. The LSP composite loses 10% of its original interfacial shear strength after 576 h, while for PVP composite it improves by 25%. The tensile strengths for LSP and PVP composites decrease by 7% and 10%, respectively, at 576 h of hygrothermal exposure. The relationship between tensile strength and interfacial adhesion proved to be weak, but processing defects and other failure processes showed a strong influence of interfacial adhesion on tensile strength of compsites. [ABSTRACT FROM AUTHOR]

Bovine tanned leather without a finish was treated with a one-component urethane prepolymer primer. The changes produced in the leather by increasing the time between the application of the primer and the adhesive joint formation (reaction time) were analyzed by IR-ATR spectroscopy, DMTA, and stress–strain measurements. Adhesion was tested in terms of T-peel strength of PVC/polyurethane adhesive/leather joints. By increasing the reaction time, a higher degree of primer curing was obtained and a higher cohesion was achieved in the leather (i.e., increased mechanical properties). Higher initial and final adhesion values for the primed leather to polyurethane adhesive were obtained by increasing the reaction time, and a higher joint strength was always obtained in comparison to that obtained in the adhesive joint produced with the roughened unprimed leather. Therefore, the application of a urethane-based primer was a good alternative to the current roughening treatment of leather for improving the upper leather to sole bonding in shoe manufacturing. [ABSTRACT FROM AUTHOR]

This study analyses the work of adhesion calculated according to the Young–Dupré equation and the work of adhesion calculated based on the interactions at the interface between the coating material in the liquid phase and the wood. It has been shown that the adhesion of coating materials to wood and their ability to spread over the substrate surface are primarily controlled by interactions between the surface forces at the interface. The values of these interactions confirmed that the tested materials should spread spontaneously over the wood surface. There are also discussed the secondary factors that can significantly influence the interactions between the surface forces and, consequently, the final stability of the examined system. The values of surface free energy for the hardened coating materials were considerably higher than the original values of surface free energy for the corresponding liquid coatings — especially due to the several times higher polar component. We also observed a considerable increase of the work of adhesion of the coating materials to the wood due to the hardening process. This increase resulted mainly from interactions between the polar components of surface free energy of the adjacent phases. The increase in adhesion of the coating materials during the hardening process was accompanied by a decrease in the interfacial free energy at the interface with the substrate. Mechanical testing of the stability of the coating material–wood system showed that the failure in the system always occurred in accordance with the calculated values of the work of adhesion of the coating material to the wood and the work of cohesion of the coating material and of the wood substrate. [ABSTRACT FROM AUTHOR]

The reliability of adhesion performance of bare Cu, as-deposited and surface-hardened black oxide coatings on Cu substrates was studied. The interfacial adhesion with a polyimide adhesive tape and an epoxy moulding compound was measured using the button shear and tape peel tests after hygrothermal ageing in an autoclave, high temperature ageing and thermal cycles. Moisture adsorption and desorption studies at different aging times suggested that the black oxide coating was effective in reducing the moisture adsorption. The bond strengths for all substrates remained almost unchanged after thermal ageing at 150°C for 8 h. Thermal cycling between -50°C and 150°C for 500 cycles reduced by about 20% the button shear strength of the as-deposited black oxide substrate, but it did change much the bonding performance of the bare Cu substrate. Hygrothermal ageing at 121°C/100% RH in an autoclave was most detrimental to adhesion performance because of the combined effect of elevated temperature and high humidity. The reduction in button shear strength after the initial ageing for 48 h was 50–67%, depending on the type of coating. In all accelerated ageing tests, the residual interfacial bond strengths were consistently much higher for the black-oxide-coated substrates than the bare Cu surface, confirming a higher reliability of black oxide coating. Fracture surfaces analysis of tape-peeled bare copper substrates after 500 cycles of thermal loading revealed a transition in failure mechanism from interfacial to cohesive failure. In contrast, the failure mechanism remained unchanged for black-oxide-coated substrates. The observations made from the button shear and tape peel tests were generally different because of the different fracture modes involved. [ABSTRACT FROM AUTHOR]

In conventional offset lithographic printing, it has been well established that the existence of a continuous layer of fountain solution (FS) on the surface of the non-image area is an essential condition to ensure correct operation of lithography. However, the mechanistic function of FS in preventing the ink from being transferred onto the non-image area has not been fully understood. Several major mechanistic interpretations can be found in the literature, which are based either on comparing of static works of adhesion and cohesion of ink and FS, or on the splitting of the 'weaker' FS layer. Although the latter becomes more accepted, direct experimental evidence is difficult to find in the literature. On the other hand, confusing information found in the literature showed that the ink-transfer (or non-transfer) observations reported in many case studies correlate well with simple comparisons of works of adhesion, cohesion and spreading data of ink/FS, ink/plate and FS/plate obtained under the static condition. These results, therefore, imply that, in explaining the function of FS in preventing ink transfer to the non-image area, the ink/FS interfacial adhesion failure would be the dominant mechanism. The work presented in this study covered two specific areas in order to address and better understand the responses of ink and FS layers and their interface to forces encountered during ink transfer. Firstly, an analysis of lithographic plates contaminated with a cationic polymer revealed that the violation of the ink non-transfer condition of the plate non-image area due to contamination could be predicted by traditional criteria of plate wetting and works of adhesion and cohesion. However, these traditional criteria cannot reliably predict the non-transfer condition of the ink on the clean non-image area that was covered by FS. Secondly, in some novel experiments conducted in this study using ice or Teflon as a substrate, the works of adhesion and cohesion were not able to predict ink transfer in most cases. Direct experimental evidence from this work revealed that splitting of the FS layer was involved in the prevention of ink transfer to the non-image areas, and that the thickness of the FS layer was critical in allowing the splitting to occur. [ABSTRACT FROM AUTHOR]

In this work we have studied the effect of adhesion forces on the mechanical parameters between a spherical indenter and human skin surface with an indentation test. To take into account the effect of adhesion on Hertzian contact radius, pressure and strain, a theory of adhesion contact, like that of Johnson, Kendall and Roberts (JKR) or Derjaguin, Muller and Toporov (DMT) must be used. These theories correct the errors induced by the adhesion forces on contact parameters. The change in skin surface lipid film during hydration by water is assessed by analyzing the evolution of the adhesion energy and skin stiffness. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

The effects of an ammonia-based catalyst, surface coverage, organofunctional group and chain length on silane adhesion promoter efficacy were examined at a benzocyclobutene (BCB)/silicon dioxide interface with silanes of varying functionality and chain length. Fracture-mechanics-based techniques, and X-ray photoelectron spectroscopy and contact-angle measurements were used to quantify the adhesion energy and silane surface coverage, respectively. Inclusion of a propylamine catalyst in silane solutions was found to affect both silane surface coverage and the resulting adhesion energy. However, in the absence of the catalyst comparable results were obtained with hydrolysis times in excess of 1 h. Only a weak dependence of adhesion energy on silane surface coverage was observed. After adhesion energy results for silanes with varying organofunctional group were normalized for differences in surface coverage, only the vinylfunctional silane was found to enhance adhesion of BCB to silicon dioxide, due to interaction of the vinylfunctional group with BCB during cure. A trend of increasing adhesion energy with increasing chain length was observed for CH3-terminated silanes (2 ≥ n ≥ 18), while an opposite trend of decreasing adhesion energy with increasing chain length was found for vinyl-terminated silanes (2 ≥ n ≥ 22). The results are compared to existing models of polymer chain entanglement. [ABSTRACT FROM AUTHOR]

This paper reports on the use of an epoxy-coated stud-pull device to perform adhesion measurements on kinetic and thermal spray coatings for metal/metal and metal/ceramic systems. Four different methods were used for testing. The first method used the stud-pull device without a retaining cylinder pushing against the coating. The second method used a retaining cylinder. In the third method the coating was machined by electric discharge machining (EDM) to form a disc-like structure with a diameter identical to that of the epoxy-coated stud. The fourth method replaced the EDM machining by controlled rotary-disc cutting using SiC slurry to machine a disc-like structure in the coating. The first two methods gave a relatively consistent measurement of adhesion, provided the coating thickness is less than 2.5% of the stud diameter. For thicker coatings, both the third and fourth methods are recommended. [ABSTRACT FROM AUTHOR]

On the basis of measurements of the destruction time of a coal sediment column structure, which were described earlier, a further and more detailed analysis of the results of these measurements was carried out. The radius of the contact plane between coal particles in the studied liquids was calculated. The values of the radius decreased with increasing length of the hydrocarbon chain of both alkanes and alcohols. Next, the values of the attachment force of two coal particles through a liquid were calculated and they increased with increasing length of the hydrocarbon chain of both liquids. We have found a linear relationship between reciprocal of the destruction time and the difference in the detachment and attachment forces. From this relationship we concluded that the work of adhesion of the liquid to the coal surface also influenced the attachment force between coal particles through the liquid. [ABSTRACT FROM AUTHOR]

Surface forces between a fractured sphalerite surface and a silica particle in supporting electrolyte solutions were measured using an atomic force microscope. Below pH 8, the long-range surface forces were found to be attractive, decreasing with increasing solution pH. The adhesion force varied from 18 mN/m at pH 4 to 7 mN/m at pH 8. At pH 10, an exponentially decayed repulsive force was measured and no adhesion was observed. The decay length was found to scale with the supporting electrolyte concentration. Although the repulsive force was reduced significantly when up to 0.5 mmol/l calcium ions were added, the surfaces remained non-adhering at contact. In contrast, an attractive force profile was obtained when 0.5 mmol/l cupric ions were added, accompanied by an adhesion force of 16 mN/m. In general, the measured force profile can be accounted for by considering classical van der Waals and electrical double-layer forces for constant surface charge density conditions. The measured force behavior correlates well with the observations in sphalerite-silica heterocoagulationtests. [ABSTRACT FROM AUTHOR]

The design of a combined topography-adhesion--stiffness imaging mode in a scanning force microscope (SFM) based on a digital control system is presented. The digital control system provides for the flexibility in designing the shape of the loading-unloading force waveform and enables a fast rate (up to 1 kHz) of applying the loading-unloading waveform with a pre-defined maximum loading force. Furthermore, flexibility in optimizing the imaging conditions and analyzing the resulting force-displacement data is achieved. The limiting factor for the data acquisition speed appears to be the viscous drag of the working medium exerted onto the SFM cantilever. It is shown that subtracting a no-contact, zero-deflection baseline can compensate for the effects of the viscous drag. The performance of the digital adhesion mapping control system is illustrated by analyzing several different samples: a rigid silicon grid; a molecularly thin block copolymer film; and a thin, heterogeneous polymer film. The remaining problems are related to the cross-talk between the topography and stiffness-related slope. [ABSTRACT FROM AUTHOR]

The use of an embedded-process zone (EPZ) model to investigate the mode I cohesive parameters for plastically-deforming, adhesively-bonded joints is demonstrated in this paper. It is shown that for the particular systems investigated, the cohesive parameters are consistent with an adhesive layer deforming in accordance with its bulk constitutive properties (as constrained by the adherends). In other words, these systems provide examples where the cohesive tractions exerted by an adhesive layer can be calculated simply from considerations of the constrained deformation of the adhesive. Consistent with such calculations, the peak stress in the adhesive layer decreases as the level of the constraint decreases (either with an increase in the thickness of the adhesive layer or with a decrease in the thickness of the adherends). It is also shown that owing to a compensating effect in which the critical displacement for failure varies with the constraint, the energy absorbed by the adhesive layer (the 'intrinsic' toughness of the joint) is essentially independent of the geometry in these systems. [ABSTRACT FROM AUTHOR]

Amorphous silicon-containing diamond-like carbon (Si-DLC) coatings were deposited by Ar+ ion beam-assisted physical vapor deposition of tetraphenyl-tetramethyl-trisiloxane (704 Dow Corning diffusion pump oil) on AISI 4340 low alloy and 440 C high alloy steel specimens, as well as on thin wafers of the same compositions, in order to evaluate residual stresses within the coatings. During annealing in an argon atmosphere at 200°C for up to 30 min, the residual compressive stress, attributed to hydrogen entrapment during deposition, gradually changed to tensile due to loss of hydrogen, and the rate of stress increase decreased with increasing annealing time. The cohesion and adhesion failure loads of the coatings decreased with annealing time, as did the friction coefficient between the coating and a diamond stylus. The specific wear rate, measured by pin-on-disktribometry, increased with annealing time. These properties are affected not only by the change in residual stress state during annealing, but most likely also by devitrification and the accompanying grain growth. If these effects are neglected, then the properties may be correlated directly with residual stresses in the coating. [ABSTRACT FROM AUTHOR]

This article focuses on some information on scanning Probe Microscopy which is published in the special issue of "Journal of Adhesion Science and Technology". This issue is guest-edited by Professor Jaroslaw Drelich. The paper appreciates the initiative, interest and efforts of Dr. Drelich in assembling this issue.