The wood plastic composites studied in this work are composed of high-density polyethylene matrix and Pinus pinaster wood fibers. Despite some interesting intrinsic properties, this wood plastic composite has limited mechanical properties because of the incompatibility between the polar hydrophilic fibers and the non-polar hydrophobic matrix. In this study, the effects of maleic anhydride-modified polyethylene additive, of carbon chains grafted by acetylation and of wood fiber contents on the tensile mechanical properties of the wood plastic composite were studied. Tensile tests were carried out using digital image correlation as an intrusiveness and robust method for strain measurements. Results showed first that the addition of wood fibers made the wood plastic composite stiffer but less flexible. Acetylation improved the interfacial adhesion properties: the Young modulus was increased and a lower strain at failure was reported. The coupling agent also increased the compatibility but mainly in the case where there was no grafted chain. With regard to the carbon chains, the number of grafts improved the elastic properties while their length did not appear to have any influence. Finally, a scanning electron microscope was used to characterize the post-mortem morphology of the fracture surfaces, the results of which supported the observations obtained from the tensile mechanical properties.

The tensile behavior of wood–plastic composite (WPC) with or without additive is studied using full-field strain measurements by 3D digital image correlation. It is shown that macroscopic values of the longitudinal strain are close to those measured by mechanical extensometer using standard mechanical tests. The modulus of elasticity provided by a Maxwell–Bingham model fitted to the experimental tensile curves is analyzed for several WPC formulations depending on the wood contents and the presence of additive. Color maps of the spatial strain distribution are commented. Moreover, the damage behavior and the degree of heterogeneity are analyzed thanks to the spatial standard deviation of the longitudinal strain field.

The focus of this study has been to fully describe the mechanical properties and behaviour of an extruded Wood Plastic Composite product. The use of plasturgy technologies for the elaboration of lignocellulose reinforced composites raises fundamental questions about the behaviour of these materials. Mechanical properties of a composite depend generally on fibre content, fibre/matrix interface link or added coupling agents. Processes play an important role on the reinforcement distribution in the matrix. The main purpose of this paper is to describe mechanical behaviour of WPC composites which are manufactured using an extrusion process. So, complete set of experiments has been realised: tensile, compressive, bending and shear tests. Longitudinal direction refers to extrusion process directional flow and transverse direction specimens have been tested. Mechanical performances of Wood Plastic Composites depend also on the link of fibre/matrix interface, fracture surface has been analysed using an optical microscope.

L'essai de multifissuration consiste à étudier le réseau de fissures formé dans un revêtement. Le dispositif de flexion 4 points est retenu. Le nombre et la position des fissures sont relevés par microscopie optique en fonction de la déformation. Un traitement statique prenant en compte le caractère aléatoire de la rupture fragile et l'ordonnancement du réseau de fissures sous l'effet de la relaxation de contrainte permet de déterminer deux paramètres fondamentaux: la densité de probabilité de rupture (DPR) qui mesure la fragilité apparente et la taille de la zone relaxée (TZR) dont la valeur renseigne sur la qualité de l'interface entre le revêtement et le substrat pour donner une indication sur l'adhérence. La partie expérimentale concerne plus particulièrement l'étude de films d'alumine (Al2O3) déposés par RMPECVD (Remote Microwave Plasma Enhanced Chemical Vapor Deposition) sur un substrat d'acier inoxydable (316L). Des corrélations entre paramètres de dépôt, préparation de surface et caractéristiques des films sont dégagées. La modélisation de l'essai à l'aide du code Abaqus® permet de visualiser la répartition des contraintes et de mettre en évidence l'influence de la présence de fissures.

Mechanical behaviour of crack coating film Al2O3. The multicraking test consists in studying the cracks network appearing in a film A four point bending test has been chosen. The number and the position of cracks network versus the strain are recorded by optical microscopy. A statistical treatment taking into account the random character of the determination of two fundamental: rupture probability density (DPR) related to the brittleness and relaxed zone size (TZR) linked to the quality of the interface between the film and the substrate which can give indications on the adhesion. The experimental part is devoted to the study of alumina (Al2O3) films deposited by RMPECVD (Remote Microwave Plasma Enhanced Chemical Vapor Deposition) on stainless steel (316L). Correlations have been established between the deposition parameters, surface preparation and mechanical properties. The modelling of this test using the Abaqus (R) code allows to visualise the stress distribution and to show the effect of the presence of cracks.

Alumina samples has been submitted to mild thermal shocks by quenching in a compressed air flow and the critical temperature difference has been determined for increasing thermal shock severities. Then these critical shocks have been numerically simulated by varying the superficial heat exchange coefficient value until the maximal tensile stress reaches the material strength. The combination of experimental and numerical approaches leads to indirect estimate of the heat exchange coefficient values during the tests.

Plasma coating performances and lifetimes may be ruined during service conditions because of uncontrolled residual stress development within the coating. This study presents the results of a CAST3M® thermomechanical numerical model which purpose is to simulate the different residual stresses development within the duplex coating–substrate during the coating built-up and its comparison with the experimental results. To achieve the thermal spray process understanding all the thermal fluxes transferred to a metallic beam and surrounding temperatures were measured so as to provide the CAST3M® model with precise boundary conditions, corresponding to a specific geometry. The residual stresses were experimentally determined by the in situ curvature measurement and, afterwards, by the hole drilling method. The plasma torch stand-off distance, the relative torch/substrate velocity and the substrate material were considered as the parameters of this study. The main results concern the substrate temperature and deflection during the preheating stage, the thermal energy transferred by the molten splats to the substrate together with the quenching stress and the development of thermal stress during the final cooling.