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International audience; The increasing use of adhesives in industry has boosted the search for tests which allow the adherence level to be defined. These tests, depending on the type of load, examine different stresses, failure modes and mixed modes. Furthermore, these tests can be focused either on initiation or propagation of adhesive failure. The subject of this study is the initiation of adhesive failure. The initiation of failure can be determined with the 3-point bending test. Trials of 3-point bending tests were conducted on an aluminum 2024 substrate, with two different thicknesses, in order to understand the impact of the adherend thickness. The aluminum substrate received different types of surface pre-treatment: acetone cleaning, hydrochloric acid etching or aminopropyltriethoxysilane coating. Two adhesives were used: the first one was a mixture of epoxy pre-polymer DGEBA and DETA amine, whereas the second was a commercially formulated adhesive, ELECOLIT 6604. The initiation of adhesive failure was obtained by 3-point bending test and verified with SEM analysis. The failure loads measured enabled the effect of surface treatment on adhesive failure to be revealed: the results indicate that the surface treatment with silane is the most efficient in comparison to hydrochloric acid etching and of course to the simple acetone degreasing. It was assumed that the scatter of the results obtained for each series is due to the variation of the “intrinsic” adherence between the adhesive and the substrate. Furthermore, it was noted that the failure loads for different substrate thicknesses cannot be compared due to the effect of the thickness: it was therefore not possible to simply compare results obtained for different thicknesses of the same substrate for a given substrate-adhesive system. The energy approach proposed in this study makes it possible. The energy requested to initiate the adhesive failure for a given system can then be known, whatever the initial geometry of the 3-point bending test is. However, it was also shown that the thickness of the substrate must be correctly chosen. A thick substrate increases the dispersion and a thin substrate may induce local unwelcome plastic strain. In conclusion, this study allows to define an energy criteria for adhesives failure initiation.

This paper describes the conditions for contact formation between soft elastic hemispheres and softelastic substrates micropatterned with pillars. These microstructured substrates were often proposed inthe two past decades for the control of adhesion. In this study the hexagonal micropillars are arranged inhexagonal arrays and the width L of the pillars as well as the distance D between the pillars (with L¼Dfor a sample) are both varied from one sample to another in order to keep the overall planar surfacefraction of the pillars constant. Additionally, two pillars of heights h¼4 mm and h¼16 mm are consideredhere. As expected from previous studies different contact morphologies are found as a function of theaspect ratio and the contact pressure. The contact may be formed (i) only at the top of the pillar, (ii) bothat the top and between the pillars, or (iii) simultaneously at the top of the pillars and in between thepillars at the centre of the contact for which the pressure is the highest. Unexpectedly it is shown in thislast case that the same contact morphology is obtained with the same pressure if the surface patternaspect ratio L/h is varied homothetically, suggesting a scale invariant behaviour of the contact formationbetween the hemisphere and the soft elastic micropatterned substrate.& 2013 Elsevier Ltd. All rights reserved.

Oxidized and non-oxidized carbon fibers were used to investigate the influence of an oxidation surface treatment on the adhesion strength with an acrylate resin cured by electron beam. For each type of fiber, a complete characterization of the surface properties was done (topography at a nanometric scale, specific surface area, X-ray photoelectron spectroscopy analysis and dispersive and polar components of the surface energy). The adhesion strength was measured by a pull-out test. For comparison, an isothermal UV curing of the matrix was also investigated. The value of the interfacial shear strength, determined by Greszczuk's model, was increased by the oxidation of the carbon fiber surface in the case of UV curing. In the case of electron beam curing, low values were obtained for both types of fibers, which could be explained by an incomplete cure of the matrix at the interface.

Rubber blends of synthetic polyisoprene rubber (IR) and hydrogenated acrylonitrile butadiene rubber (HNBR) are prepared with different compositions. First, DSC results confirm that IR and HNBR are incompatible rubbers. A tensile testing machine equipped with a tack probe test allows us to measure the level of adhesion at rubber blends/glass as well as rubber blends/pure rubber interfaces, for contact times ranging from 0.1 s to a few hours. The adhesive properties of rubber blends were compared with those of pure rubbers. Adhesion energy G of IR/HNBR blends onto glass increases with the IR content in disagreement with a simple law of mixtures because of the influence of bulk properties of blends (morphology and mechanical behaviour). For a given blend, G increases with contact time certainly due to an interfacial reorganisation. Self-adhesion energies G S of pure rubbers and IR/HNBR blends increase also with contact time, thanks to mainly an interdiffusion phenomenon of the rubber chains through the interface. Self-adhesion energy of blends in contact with pure IR follows a simple law of mixtures as a function of IR content. On the contrary, the variation of self-adhesion energy of these blends in contact with pure HNBR is more complex.

Natural rubber (NR), synthetic polyisoprene rubber (IR) and hydrogenated acrylonitrile butadiene rubber (HNBR) were crosslinked by electron beam irradiation at different doses. The adhesion (at rubber/glass interfaces) and self-adhesion (at rubber/rubber interfaces) energies of uncrosslinked and weakly crosslinked rubbers were measured at contact times ranging from 0.1 s to a few hours by means of a tensile testing machine equipped with a tack-probe test. General relationships between these energies and the average molar mass between crosslinks were established in each case.