Identification d'un modèle d'endommagement à l'échelle du pli composite grâce à des essais hors-axe d'orthotropie

Theidentification of the mechanical properties of composite materials is usually performed on specimens with well suited ply stackings. The industrialists designing CMCs parts face high production costs, and difficulties in producing tailor-suited specimens without compromising the representativeness of the manufacturing process. The frame of this work is the mechanical characterization and modelling of a Carbon / Crbon Composite (CCC) material, with no possibility of performing tests on different ply stackings. The in-plane shear properties of composite materials are usually measured by performing simple and standardized tests, such as the (±45°)ns ply stacking tensile tests. These methods cannot be put in place for the characterization of the studied CCC because it is not posible to adapt the manufacturing process to produce this kind of specimens. To palliate this issue, an off-axis tensile test fixture, greatly inspired by the works of [2], [3] and [4], has been designed to allow the measurement of the shear properties of the CCC. This fixture allows the rotation of the grips in the testing plane, with a center of rotation on the border of the effective area of the specimen. These boundary conditions allow the edges of the specimen to rotate freely during the test, which guarantees more uniform strain and stress fields despite the off-axis loading. The identification of the virgin shear modulus of a unidirectional (UD) Carbon / Epoxy composite using this fixture has been presented in [1]. The results were considered satisfying, with a 5% difference relative to standard (±45°)ns tests, which shows the fixture is working for the measurement of the elasticity parameters. These works are extended here, with a new experimental campaign in order to validate the f ixture use for the identification of the parameters of a damage model coupled to inelastic strains for UD composites [5]. Out of axis tensile tests (45°) allow, thanks to the presented fixture, to measure the shear G12 and transverse E2 moduli during the same test, using strain measurements in three different directions. Load-unload cycles allow the computation of the damage variables associated to the variations of the moduli, but also the measurement of the inelastic strain during the test. Tests performed on the rotating fixture, with a 45° off-axis configuration, are compared to standard tests on (±45°)ns and (90°)n, completed with tensile tests on (±67.5°)ns to identify the transverse / shear coupling [6]. To put it in a nutshell, a new ouf-of-axis tensile fixture is presented again, and is tested for the identification of the non-linear transverse and shear behavior of UD composites.