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International audience; In recent years, natural fibers reinforced composites have received much attention because of their lightweight, recyclable, nontoxic, low cost and biodegradable properties. However, compatibility between hydrophilic natural fiber and hydrophobic polymer is low. One way to increase the fiber/matrix compatibility is to treat the fiber surface, using hydroxyl groups present on the upper layer of the high tenacity viscose. However, hydroxyl groups are not always accessible on the fibers surface due to impurities. It is thus mandatory to study the various possibilities to determine a good cleaning treatment, which furthermore does not have a negative influence on the mechanical properties of the fibers. In this article, (3-aminopropyl)triethoxysilane (APTES) is used to functionalize the fiber surface after cleaning them, in order to prepare the fibers for reactive injection of polyamide-6. In order to determine the influence of each cleaning/treatment on the physical and chemical properties of the fibers and to determine optimal treatments to increase fibers/matrix compatibility, various characterization methods (XPS, FTIR-ATR, SEM, EDX) were combined to theoretical results obtained by a design of experience.

This work aims to study the effect of reactive molding on polyamide-6 (PA6) based micro composites with either glass or high tenacity viscose as fibre reinforcements. For this purpose, microdroplet pullout test was found to be well suited to determine the interfacial shear strength. For pull-out testing, samples are prepared with a common method implying melting polyamide-6 and an innovative method which allows the microdroplets formation by direct wetting in the reactive mixture. Conditions to obtain microdroplet in this new method are close to those of real size composite molding. First, this work focus on the verification of the new sample preparation method using 1 H and 13 C NMR to determine conversion rate and verify the presence of polyamide-6 on wetted fibres bundles. Contact angle are calculated to confirm the NMR analysis conclusions. Both of these analyses confirm that PA6 is effectively formed on fibres when wetting with the reactive mixture. Finally, interfacial shear strength is compared for both glass and high tenacity viscose with these two types of preparation procedures. Obtained values for glass fibres are τ = 25 ± 6 MPa with PA6-melting and τ = 20 ± 3 MPa with reactive mixture wetting. Reactive mixture wetting also allows to avoid high tenacity viscose degradation during PA6 formation, leading to the determination of the interfacial shear strength τ = 12 ± 3 MPa.

The objective of this work is to determine an adequate number of samples for an accurate prediction of tensile strength of fibres using a Weibull distribution. Theory will be compared to experimental results in order to know the effect of experimental errors on the theoretical expectations. The diameter and strength distribution of high tenacity viscose were evaluated. The chosen Weibull distribution was with two parameters. First, the best probability estimator for Weibull was determined using a random selection of experimental datas. Then, in order to be able to predict the number of sample knowing the variation of the Weibull modulus m, different relationship between the coefficient of variation of m and the number of sample n were tested. The relationship CV = 0.78/ $$\sqrt n$$ presented good agreement with experimental datas. The influence of the variation of m on the predicted value of strength was studied in order to determine an adequate number of sample to obtain limited variation of the predicted strength. The last part focus on experimental verification of the points previously developed. It was shown that it is possible to determine the influence of the variation of the Weibull modulus on the predicted strength. However, no correlation was found between the variations of the Weibull modulus and the error on the predicted strength.

International audience; The prior properties of recycled polypropylene depend on the origin of waste deposits and its chemical constituents. To obtain specific properties with a predefine melt flow index of polypropylene, the suppliers of polymer introduce additives and fillers. However, the addition of additives and/or fillers can modify strongly the mechanical behaviour of recycled polypropylene. To understand the impact of the additives and fillers on the quasi-static mechanical behaviour, we consider, in this study, three different recycled polypropylenes with three different melt flow index obtained from different waste deposits. The chemical constituents of the additives and filler contents of the recycled polypropylenes are determined through thermo-physico-chemical analysis. Tensile and bending tests performed at different strain rates allow identifying the mechanical properties such as the elastic modulus, the yield stress, the maximum stress, and the failure mechanisms. The results obtained are compared with non-recycled polypropylene and with few researches to explain the combined effect of additives. Finally, a post-mortem analysis of the samples was carried out to make the link between the obtained mechanical properties and microstructure.

The development of multilayered polymeric/metallic materials by a PM route employing spark plasma sintering (SPS) has been explored. The aim is to produce composites that join a polymer with a metal for structural applications. In a first approach, the consolidation of polyimide-based composites by SPS was studied. For temperatures as low as 350°C, homogeneous mechanical properties were achieved in compression tests. In a second set of experiments, multilayered polyimide/aluminium composites were consolidated by SPS. These polymer-based composites could be used as an interlayer material to join effectively polyimide and aluminium.

The mechanical properties of carbon fibers, especially their tensile properties, are affected by internal and surface defects. In order to asses in what extent the generation of surface defects can result in a loss of the mechanical properties, non-surface treated carbon fibers were oxidized with three different surface treatment processes: electro-chemical oxidation, oxidation in nitric acid, and oxidation in oxygen plasma. Different surface topographies and surface chemistries were obtained, as well as different types and densities of surface defects. The density of surface defects was measured with both a physical approach (Raman spectroscopy) and a chemical approach (Active Surface Area). The tensile properties were evaluated by determining the Weibull modulus and the scale parameter of each reference, after measuring the tensile strength for four different gauge lengths. A relationship between the tensile properties and the nature and density of surface defects was noticed, as large defects largely control the value of the tensile strength. When optimized, some oxidation surface treatment processes can generate surface functional groups as well as an increase of the mechanical properties of the fibers, because of the removal of the contamination layer of pyrolytic carbon generated during the carbonization of the polyacrylonitrile precursor. Oxidation in oxygen plasma revealed to be a promising technology for alternative surface treatment processes, as high levels of functionalization were achieved and a slight improvement of the mechanical properties was obtained too.

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.

The present study deals with the consolidation of an ultra-high performance polymer, the poly(ether ether ketone) (PEEK), for structural applications, using the powder metallurgy (PM) way, and more precisely the Spark Plasma Sintering (SPS) processing. The effects of SPS parameters such as temperature, pressure, and dwell time on density and mechanical properties of PEEK were investigated via a Design of Experiments (DoE). A temperature of 250 °C, a pressure of 40 MPa, and a dwell time of 20 min have been identified as the optimal SPS process parameters. In these conditions, a density of 1.31 g/cm3 was reached and homogeneous mechanical properties in the volume determined by means of compression tests were found with a compressive modulus of 2.75 GPa, a yield strength of 134 MPa, and a maximum compressive strain of 43%. These results are better than those of commercial products obtained by injection molding. The pressure appears to be a significant parameter on PEEK properties and plays positive or negative roles according to the responses of DoE studied. To our knowledge, it is one of the first studies based on the application of the PM techniques for PEEK consolidation showing the possibility to process below its melting point. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44911.

International audience; The purpose of the present article is to evaluate the real fibre surface involved in the practical adhesion of a flax/epoxy system. The difference in practical adhesion evaluated by microbond tests between Hermes (τapp = 22.5 ± 1.5 MPa) and Electra (τapp = 13.2 ± 3.2 MPa) flax fibres varieties/epoxy systems could not be explained by their superficial surface chemistry evaluated by XPS. FTIR spectroscopy highlights a difference in biochemical composition and Laser Confocal microscopy evidences a resin penetration for the two flax fibres systems (1.7 ± 0.7 μm for Hermes and 2.2 ± 0.8 μm for Electra). Thus the effective surface or complex interphase will be by consequence the overall area where the resin and fibre are in contact, i.e. the entire area penetrated by resin.

Thiol functionalities were grafted at the surface of carbon fibers in order to improve the adhesion strength with an acrylate matrix photo-cured by ultraviolet light via a thiol-ene reaction. As revealed by X-ray photoelectron spectroscopy, the grafting was achieved by a reaction between propylene sulfide and the hydroxyl groups located at the surface of the fiber, with the presence of triethylamine. A significant improvement of the interfacial shear strength, measured by a micromechanical test derived from the pull-out test, was obtained (+18%). Generating covalent bonding between the carbon fiber surface and a thermoset polymerizing through a radical mechanism by grafting a chain transfer agent seemed to be an efficient way to improve adhesion strength at the interface.

Acrylate functionalities were grafted at the surface of carbon fibers in order to improve the adhesion strength with an acrylate matrix cured by electron beam. An isocyanate bearing aliphatic urethane acrylate was used as a coupling agent. As revealed by X-ray photoelectron spectroscopy, the isocyanate groups reacted with carboxylic acids and hydroxyl groups located at the surface of the fiber, leading to a covalent bonding of the acrylate groups. The adhesion strength was measured by a micromechanical test derived from the pull-out test. A significant improvement of the interfacial shear strength was obtained (+91%) with an electron beam curing. For comparison, an isothermal cure by UV was also investigated and led to the same level of adhesion strength. The improvement was also proved by an increase in the 90° flexural strength of unidirectional composites (+38%). Grafting functionalities that were compatible with the radical mechanism of the polymerization of the matrix appeared to be a promising strat...

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.

Oxygen plasma was used to modify the surface properties of carbon fibers and their adhesion strength with an acrylate resin cured by electron beam. A characterization of the surface topography and the surface chemistry was carried out (topography at a micrometric and nanometric scale, specific surface area, temperature programmed desorption, and X-ray photoelectron spectroscopy). The topography remained unchanged. Regarding the surface chemistry, carboxylic acids, alcohols, lactones, and ethers were created and their location was at the outer surface of the fibers. A pull-out test was used to measure the adhesion strength with the acrylate resin cured by electron beam. For comparison, an isothermal UV curing was also investigated. The value of the interfacial shear strength was increased only in the case of UV curing. No improvement was observed with electron beam curing, which highlighted the generation of an interphase, the mechanical properties of which are dependent on the processing conditions.

The aim of this study was to analyze the effect of interfacial covalent bonds on the adhesive behavior of an elastomer, a crosslinked polydimethylsiloxane, and a glass substrate. These covalent bonds were created by applying to both materials an appropriate surface treatment by means of plasma polymerization. Adhesion measurements were carried out by analyzing the contact area between a rubber hemisphere and a flat rigid glass plate. The contact was forced under a given compressive loading for different times tc, then the load was removed and the fracture propagation at the interface was recorded as a function of relaxation time tr. Finally, adhesion energies were also determined by means of a probe test using a tensile testing machine.

We have considered in this work the Wilhelmy plate tensiometer to characterize the wetting properties of two model surface textures: (i) a series of three superhydrophobic micropillared surfaces and (ii) a series of two highly water-repellent surfaces microtextured with a femtosecond laser. The wetting forces obtained on these surfaces with the Wilhelmy plate technique were compared to the contact angles of water droplets measured with the sessile drop technique and to the bouncing behavior of water droplets recorded at a high frame rate. We showed that it is possible with this technique to directly measure triple-line anchoring forces that are not accessible with the commonly used sessile drop technique. In addition, we have demonstrated on the basis of the bouncing drop experiments wetting transitions induced by the specific test conditions associated with the Wilhelmy plate tensiometer for the two series of textured surfaces. Finally, the tensiometer technique is proposed as an alternative test for characterizing the wetting properties of highly liquid-repellent surface, especially under immersion conditions.

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.

Two different commercial references of oxidized carbon fibers were used to investigate the influence of different oxidation surface treatments on the interfacial adhesion with an acrylate resin cured by electron beam. For each type of fiber, a characterization of the topography and the chemistry of the surface was done. The 90° flexural strength of unidirectional composites was measured in order to assess interfacial adhesion. Low values were obtained for both types of fibers, which could be explained by the creation of a weak interphase, which was highlighted by a dramatic improvement of the flexural strength after a post-cure. That interphase could be the origin of the low transverse mechanical properties of electron beam cured composites.

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.

The purpose of this study was to better understand the effect of non-rubber substances (mainly proteins and lipids) on adhesion (against glasses) and self-adhesion tack properties of uncrosslinked natural rubber (NR). Various types of NR, with or without non-rubber constituents, were prepared. Synthetic polyisoprene rubber was also used as a reference material. All the rubbers were first characterized by many techniques (FT-IR, DSC, GPC, etc.). Two experimental tests were specially utilized to measure the level of adhesion and self-adhesion: (i) at very short contact times (from a few milliseconds up to 0.1 s) the impact of a pendulum and (ii) for longer contact times (from 0.1 s to a few h) the contact of a probe using a tensile testing machine. The tack energy increased with contact time for all the rubbers studied. Natural rubber which did not contain proteins and lipids exhibited the highest adhesion and self-adhesion tack abilities. In contrast, whole natural rubber, containing both proteins and lipi...

Composites have emerged as a valuable class of engineering materials because they offer many attributes not attainable with other materials. Their light weights coupled with high stiffness characteristics and selectable properties have fostered their use for many years in satellites, high-performance aircraft, world-class sailboats, and even submarines.4,5 Now these materials demonstrate their worth in the mundane but equally demanding consumer, infrastructure, and sporting goods arenas.

Bio-Based Composites: An Introduction Rungsima Chollakup, Wirasak Smitthipong, and Michel Nardin Bio-Based Strategy: Food and Non-Food Markets Rina Singh, Brent Erickson, and Paul Winters Strategy of Bio-Based Resources: Material versus Energy Kuakoon Piyachomkwan, Sittichoke Wanlapatit, Wirasak Smitthipong, and Klanarong Sriroth Bio-Inspired Materials Arkadiusz Chworos and Wirasak Smitthipong Natural Fiber Surface Treatments and Coupling Agents in Bio-Based Composites Potjanart Suwanruji, Wirasak Smitthipong, and Rungsima Chollakup Reinforcement of Polymers by Flax Fibers: Role of Interfaces Christophe Baley, Antoine Le Duigou, Alain Bourmaud, Peter Davies, Michel Nardin, and Claudine Morvan Effects of Reinforcing Fillers and Coupling Agents on Performances of Wood-Polymer Composites Diene Ndiaye, Mamadou Gueye, Ansou Malang Badji, Coumba Thiandoume, Anicet Dasylva, and Adams Tidjani Natural Fiber Polyolefin Composites: Processing, Melt Rheology, and Properties Haroutioun Askanian, Ya Feng, Sophie Commereuc, Florence Delor-Jestin, Kristyna Montagova, Roman Cermak, Valerie Massardier, and Vincent Verney Polysaccharide Bio-Based Composites: Nanofiber Fabrication and Application Jackapon Sunthonrvarabhas, Klanarong Sriroth, and Hyun-Joong Kim Recent Advances in Cellulose Nanocomposites Ali Faghihnejad and Hongbo Zeng Improvement of Damage Resilience of Composites Jiye Chen Lifetime Durability of Bio-Based Composites Vincent Verney, Solene Gaudin, Sophie Commereuc, Haroutioun Askanian, Florence Delor-Jestin, Alexandre Govin, and Rene Guyonnet Mechanical Properties of Natural Fiber-Reinforced Composites Rattana Tantatherdtam, Rungsima Chollakup, and Wirasak Smitthipong Characterization and Strength Modeling of Laminated Bio-Based Composites Peggi L. Clouston, Sanjay R. Arwade, and Alireza Amini Micromechanical Modeling of Bio-Based Composites Michael May and Deborah Mohrmann Life Cycle Assessments of Bio-Based Composites: A Review Thimothy Thamae and Caroline Baillie Bio-Based Composites: Future Trends and Environmental Aspects V.P. Sharma

The present study deals with the optimization of polyimide (PI) mechanical properties, obtained by Spark Plasma Sintering (SPS), by using a method combining Design of Experiments (DOE) with physical, structural, and mechanical characterizations. The effects of SPS parameters such as temperature, pressure, dwell time, and cooling rate on the density, mechanical properties, and structure of PI were investigated. The experimental results revealed that the mechanical properties of the material were optimized by raising the sintering temperature up to 350 degrees C. The optimized SPS processing parameters were a temperature of 350 degrees C, a pressure of 40 MPa, and a dwell time of 5 min. Under these conditions, a relative density of 99.6% was reached within only a few minutes. The corresponding mechanical properties consisted of Young's modulus of 3.43 GPa, a Shore D hardness of 87.3, and a compressive strength of 738 MPa for a maximum compressive strain of 61.8%. Moreover, when working at 320 degrees C and at 100 MPa, an increase in the dwell time was necessary to enhance the properties. Contrary to the other parameters, the cooling rate appeared to be a non-significant parameter. Finally, correlations between the PI structure and the mechanical properties were made to demonstrate the densification mechanisms. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41542.

This article presents two high-temperature thermoplastic powders which were sintered by spark plasma sintering in order to get homogeneous mechanical properties. Dense polyimide (PI) and polyetheretherketone (PEEK) specimens were obtained at temperatures as low as 320°C for PI and 200°C for PEEK, respectively. Relative densities higher than 99% were reached for both materials. In order to characterize their properties, in situ measurements with compression and hardness tests were carried out on sintered samples. This method allowed to obtain polymeric materials with improved mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40783.

Maleic anhydride plasma polymer was deposited at the surface of carbon fibers and functionalized with vinyl and thiol groups to improve its adhesion strength with an acrylate matrix cured by an electron beam. A characterization of the fiber surface properties was done before and after coating (topography, surface chemistry, and surface energy). Sharp improvements of the interfacial shear strength (+ 120%), measured by a micromechanical test derived from the pull-out test, were obtained and, to the best of our knowledge, never reported before. The values were close to the ones obtained with a thermal cure. The comparison of this approach with other types of surface treatments (oxidation, grafting of coupling agents) enabled the establishment of a general strategy for the improvement of the interfacial adhesion in carbon fiber composites cured by an electron beam and potentially the improvement of their mechanical properties. This strategy is based on a high surface density of functionalities that are generating covalent bonding during the polymerization of the matrix and on the insertion of a polymer layer strongly attached to the fiber surface and acting as a buffer between the fiber surface and the matrix to counteract the generation of stress in the interphase.

Naphthalene-based mesophase ribbon fibres were studied in the present work. The fibres were surface treated in a plasma reactor and their mechanical and surface characteristics determined before and after the surface oxidation. The dispersive and non-dispersive components of the surface energy were obtained by contact angle measurements using a tensiometric method, and the surface oxygen content was measured by XPS. The mechanical characterisation was made by single filament tensile tests. The interactions between the ribbon fibres and a polycarbonate matrix were assessed by means of fragmentation tests. The results were compared with those obtained with pitch-based fibres with circular cross-sections.

The acoustic analysis of the morphological evolution, from the surface to the bulk, of a vinylester resin cured in contact with two types of surfaces, i.e. aluminium and air, has been studied. The analysis was also performed as a function of styrene monomer content of the uncured resin. The existence of a thick layer, in which the vinylester network is deeply affected due to the relative variations of polystyrene and vinylester polymer from the interface to the bulk, was first demonstrated by microscopical Fourier transform-infrared spectroscopy. Secondly, this structural evolution was analysed by means of an acoustic scan technique, allowing the variations of the mechanical properties of the vinylester network to be estimated as a function of the distance from the interface. A good correlation was obtained between spectroscopic and acoustic results.

This paper deals with the influence of interphase formation on the stress transfer capacity of the fibre-matrix interface in single fibre composites and constitutes a brief review of our recent work. This influence is studied through the deviation of the experimental results from a recent theoretical analysis relating the interfacial shear strength to the reversible work of adhesion established between the fibre and the matrix. Two examples of interphases are considered: a transcrystalline layer in carbon fibre-PEEK composites and a pseudo-glassy interphase in carbon fibre-elastomer systems. In the former case, the low transverse mechanical properties of the transcrystalline layer lead to a decrease of the interfacial shear strength, whereas, in the latter case, the glassy behaviour of the interphase explains the improved interfacial stress transfer capacity.

The effect on the peeling energy, G, of glass/styrene-butadiene rubber (SBR) assemblies of the length, N, of the alkyl chain, ranging from 4 to 30 carbon atoms, of silane coupling agents is determined. Experimentally, it is shown that G strongly increases with N. Therefore, considering that the rheological model of adhesion (or model of multiplying factors) is valid, G is assumed equal to the product of three terms: the reversible adhesion energy, W. at the interface, the viscoelastic dissipation factor, φ, of SBR and a “molecular factor” to be determined. Finally, it appears that this latter factor depends linearly on N. Such a result should be consistent with an extraction (“suction”) process of the silane alkyl links from bulk SBR during peeling experiments.

The stress transfer capacity of carbon fibre-SBR interfaces is analysed in terms of interfacial shear strength and measured by means of a fragmentation test on single fibre composites. For all the cases studied, the experimental values of the interfacial shear strength are largely higher than theoretically expected. Such a result is explained by the existence near the fibre surface of an interfacial layer in which the polymer chain mobility is greatly reduced. Such an interfacial region of low mobility is pointed out by mechanical spectrometry on unidirectional composites at different fibre contents. This interphase could exhibit a pseudo-glassy behaviour and, in particular, an elastic modulus close to that of the elastomer in its glassy state whatever the temperature.

A round-robin programme has been undertaken to assess the compatibility in the micromechanical techniques used to evaluate the interfacial shear strength of the fibre/matrix bond in composite materials. The tests selected for evaluation were the single-fibre pull-out test, the microdebond test, the fragmentation test and the micro-indentation test. Twelve laboratories were invited to participate in this programme. Each laboratory was supplied with Caurtaulds XA fibre in the untreated condition and with a standard surface treatment, and a quantity of epoxy resin, hardener and catalyst, all from the same batch. Some laboratories were supplied with composite bars made with the same materials. A common cure cycle was chosen for sample preparation. Each laboratory conducted the tests to its own procedures. The results showed that the scatter within each laboratory was acceptable but the scatter between laboratories for a particular test was high. The results are discussed and possible explanations are presented for these observations. The indications are that the fundamental procedures used in each laboratory are sound. The results also suggest that there is great potential for achieving standard procedures and reducing the inter-laboratory scatter. A further round-robin programme is proposed to generate test protocols.

The stress transfer from the matrix to the fibre in composite materials depends to a large extent on the level of adhesion between these materials. In the present study, the work of adhesion between carbon fibres and PEEK polymer is estimated from the surface characteristics of the fibre and the matrix and, more precisely, from the dispersive component of the surface energy and the acid–base character of both material, determined by inverse gas chromatography at infinite dilution. The interfacial shear strength at the carbon fibre/PEEK interface is measured also by means of a fragmentation test on the respective single-fibre composites. For PEEK polymer, it is shown that the acid–base characteristic of fibres and powder are different, indicating that the orientation of the macromolecules near the surface may be affected by the processing of such materials. Nevertheless, as already shown in previous studies for other systems, a linear relationship between the interfacial shear strength and the adhesion at the fibre/matrix interface can be established.

The mechanical and surface characteristics of pitch and PAN-based carbon fibres were studied by tensile testing, XPS, SEM analysis and wetting measurements. The pitch-based fibres had two different geometries, with circular and ellipsoidal (ribbon-shaped) cross sections. Plasma oxidation was used to treat the surface of the fibres. The interfacial characteristics of untreated and treated fibres were measured by fragmentation tests of single filament composites. The effect of the surface treatment on the mechanical, surface and interfacial properties of the fibres was determined and correlated. It was shown that a relationship exists between the ability of the surface to transfer loads and its oxygen content. Finally, the influence of the non-axisymmetry on the interfacial parameters obtained in the fragmentation tests was assessed.

It is now widely accepted that the adhesion between the reinforcing fibre and the polymer matrix is one of the most important parameters governing the performance of a composite material and that the interface could be considered as being the third constituent of the composite material.

Great attention has been recently devoted to the development of fibre reinforced composites of high mechanical performance Obviously, the final performances of a composite material are directly related to the properties of both basic constituents: the fibre and the matrix. The matrix gives materials its cohesion, while the fibres support most of the mechanical stresses. However, it is also well-known that the mechanism of load transfer at the fibre-matrix interface plays a major role in the mechanical and physical performances of composites and, consequently, the fibre-matrix interface can actually be considered as the third constituent of such materials.

The aim of this study is to analyse the influence of the interfacial properties and, more precisely, the adhesion energy, between carbon fibres and PEEK on the final performances of unidirectional composites. First, a linear relationship is established between the interfacial shear strength, determined by means of a fragmentation test on single fibre composites, and the reversible work of adhesion between fibre and matrix. Secondly, a set of mechanical properties, - i.e. interlaminar shear strength, longitudinal tensile and compressive and transverse tensile properties-, of different unidirectional laminates is determined. It is shown that the interlaminar shear strength is constant whatever the type of materials. On the contrary, it appears that the ultimate properties of the laminates increase with the interfacial adhesion energy, whereas the stiffness of these composites remains practically unaffected.

International audience; This paper deals with the development of a novel and predictive finite element method (FEM) model coupling electrical, thermal, and mechanical time-dependent contributions for simulating the behavior of a powdery material submitted to a spark plasma sintering (SPS) treatment by using COMSOL Multiphysics (R) software. The original approach of this work lies in the use of the modified Cam-Clay model to solve the mechanical phenomenon occurring during a SPS sintering treatment. As the powder properties and behaviors are different from the final sintered material and display a nonlinear dependence as a function of temperature and pressure, the model includes the description of the sample densification. In this way, numerical and experimental results obtained on conductive model material (aluminum) such as temperature, stress distributions, and shrinkage, were directly compared. This FEM model demonstrated the ability to predict the powder behavior during temperature-controlled experiments precisely, as they are typically performed in the SPS technique. This approach exhibits a remarkable level of interest because it takes into account the nature of the material and also the specific characteristics of the powder studied.