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The present experimental work investigates the response of woven glass fabric reinforced polyamide 6.6/6 subjected to drop weight impact loading. The main objective is the development and the introduction of a new experimental procedure/approach, based on different complementary detection techniques, that aims at investigating the damage induced by impact loading in thermoplastic woven fabric composites. The developed approach is intended to be generalized to other types of composite materials. The main idea is to assess all the experimental results obtained through the developed procedure with a direct investigation method. The latter consists in the Permanent Indentation (PI) measurement providing an indicator of the damage criticality in the composite sample. To this end, several non-destructive testing methods are carried-out and their experimental findings are analyzed and cross-linked. The identification of the different damage mechanisms, caused by the drop weight impact, is performed using X-Ray micro-computed tomography (mCT). C-scan ultrasonic investigation is conducted according to two types: transmission and reflection for the detection of the impact damage and the identification of the induced degradation area. B-scan imaging are then obtained through specific post-processing of the impacted surface to extract the permanent indentation (PI). The latter is validated through surface flatness measurement using the highly resolved 3D optical profilometry. The correlation between the X-Ray tomography results and the permanent indentation measurement is then established. It correlates the PI level with the damage mechanisms of a barely visible impact damage (BVID) in woven glass reinforced polyamide 6.6/6 composite. The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The present work is co-funded by Groupe PSA and ANRT. It is made in the framework of the OpenLab Materials and Processes involving Groupe PSA, Arts et Metiers (ENSAM) and Georgia Tech Lorraine.

The paper proposes a new experimental methodology, based on ultrasonic measurements, that aims at evaluating the anisotropic damage in woven semi-crystalline polymer composites through new damage indicators. Due to their microstructure, woven composite materials are characterized by an anisotropic evolution of damage induced by different damage mechanisms occurring at the micro or mesoscopic scales. In this work, these damage modes in polyamide 6.6/6-woven glass fiber reinforced composites have been investigated qualitatively and quantitatively by X-ray micro-computed tomography (mCT) analysis on composite samples cut according to two orientations with respect to the mold flow direction. Composite samples are initially damaged at different levels during preliminary interrupted tensile tests. Ultrasonic investigations using C-scan imaging have been carried out without yielding significant results. Consequently, an ultrasonic method for stiffness constants estimation based on the bulk and guided wave velocity measurements is applied. Two damage indicators are then proposed. The first consists in calculating the Frobenius norm of the obtained stiffness matrix. The second is computed using the phase shift between two ultrasonic signals respectively measured on the tested samples and an undamaged reference sample. Both X-ray mCT and ultrasonic investigations show a higher damage evolution with respect to the applied stress for the samples oriented at $$45^{\circ }$$ from the warp direction compared to the samples in the $$0^{\circ }$$ configuration. The evolution of the second ultrasonic damage indicator exhibits a good correlation with the void volume fraction evolution estimated by mCT as well as with the damage calculated using the measured elastic modulus reduction. The merit of this research is of importance for the automotive industry.

IF=2.63; International audience; A torsion delamination test was developed to characterize the interfacial cohesion of multilayer organic coatings. It consists in applying an increasing torque on a hexagonal plot directly glued on the coating until delamination occurs. The test is quantitative and allows the calculus of the shear stress that generates delamination. This torsion test was successfully used to test the adhesion of multilayer car coatings. The delaminating interfaces were directly observed via optical and electron microscopy. We have shown that the critical delaminating shear stress and the delaminating interface are dependent of both the primer and of the curing temperatures respectively. Furthermore, an interpretation of the delamination process is proposed.

© 2016 Elsevier Ltd.The aim of this study was the elaboration of thermoplastic and biobased nonisocyanate polyurethanes (TNIPUs) based on different aromatic-aliphatic architectures. A rigid aromatic bis(cyclic carbonate) was synthesized from terephthalic acid, and subsequently used with various diamines for the preparation of TNIPUs. A two-step method was investigated to design advanced macromolecular architectures. All TNIPUs and corresponding intermediates were fully characterized. The influence of various parameters such as the ratio between the constituting building blocks and the chemical structure on NIPU properties was studied. Thermal and mechanical results show that the TNIPUs presenting the highest molar masses and the highest properties were synthesized from dimer diamine prepolymers. A high content of terephthalic acid and short-chain diamine increases the glass transition temperature and leads to good performances, with a balance between elongation and tensile strength properties. The final TNIPUs present biobased content up to 76%.

International audience; The behaviour of the 6% Al magnesium alloy AM60 in aqueous acid fluoride solutions was studied in situ by electrochemical techniques and the surface chemistry of the resulting film was examined by monochromatized XPS. The evolution of the corrosion potential and cyclic voltammograms showed that the aggressiveness of the solutions is mainly driven by their fluoride concentration, the pH having almost no detectable influence. The more concentrated and acidic fluoride solutions led to a higher degree of fluoride coverage of the surface. The surface film is composed of magnesium hydroxide and hydroxyfluoride Mg(OH)2−xFx which approaches MgF2 with increasing fluoride concentration in the film. The parameters governing the film evolution and their relation to surface reactions are discussed.

International audience; Electrochemical rest potential and cyclic voltametry were used to investigate the behaviour of the 6% Al magnesium alloy AM60 in various zirconium or titanium fluoride aqueous acid solutions. These solutions have a wide range of aggressiveness with respect to AM60 due largely to fluoride concentration and in some cases to their highly acidic nature. The morphology and composition of the resulting film have been determined by Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray spectroscopy (EDX). The film nucleation is promoted by a pH increase due to water reduction and is thus more likely to occur on the cathodic parts of the surface. Correlatively, film formation on the anodic primary solid solution occurred in only one solution.