This paper describes a new approach of Nondestructive Evaluation (NDE) using fibrous sensors inserted inside composite reinforcements during their weaving. A flexible piezoresistive fibrous sensor has been developed and optimized for in situ structural deformation sensing in carbon composites. The sensor was inserted, in the weft direction, in three-dimensional warp interlock reinforcement during the weaving process on a special weaving loom. The reinforcement was then impregnated in epoxy resin and was later subjected to quasi-static tensile strain. It was found that the sensor was able to detect deformations in the composite structure until rupture since it was inserted together with reinforcing tows. The morphological and electromechanical properties of the fibrous sensors have been analyzed using scanning electron microscopy, tomography and yarn tensile strength tester. An appropriate data treatment and recording device has also been developed and utilized. The results obtained for carbon composite specimens under standard testing conditions (NF EN ISO 527-4 Plastiques, CEN, 1997) have validated in situ monitoring concept using our textile fibrous sensors.

Composite materials reinforced with 3D layer-to-layer angle-interlock fabrics are increasingly employed due to their significant resistance to delamination and impact damage, which is not observed in classical 2D laminated composites. However, the prediction of the mechanical behavior of such composites is challenging due to the intricate fibrous architecture. The structure is intimately linked to its history of manufacturing which induces changes in the reinforcement geometry. The purpose of this work is to assess the equivalent membrane and bending elastic moduli of the shell-type structure by an asymptotic homogenization procedure on a periodic unit cell, in the framework of the Love-Kirchhoff plate theory. A specific Python program using Abaqus software package is developed, allowing for parameterized geometrical modeling and mechanical analysis in a systematic and efficient way. This modeling and simulation tool enables to consider the real composite architecture after infusion and the yarn damage during weaving. The effective properties are finally validated using numerical computations on 3D heterogeneous plates and by comparison with experimental tests.

A self-piercing riveting process is used to join a thermoplastic composite sheet of PA6.6-GF50 with an aluminum alloy sheet 5182 O. Two shapes of self-piercing rivet are tested: the countersunk rivet and the button head rivet. Non-destructive inspections by pulse thermography and post-mortem cross-section observations are made to assess the damage that might have occurred during the rivet piercing process. The manufacturing defects are characterized and the possible causes for their emergence are explained. Then, single-lap joint tests were carried out to determine the best joint in terms of its mechanical strength. These tests were also instrumented by various monitoring techniques such as passive thermography, digital image correlation, and acoustic emission to clarify the joint damaging behavior. Non-destructive inspections by pulse thermography are finally correlated with the thermal fields acquired by passive thermography during the mechanical test to improve the understanding of the damage mechanisms and their criticality.

The drape behaviour of the dry textile structure is tremendously important to ensure a homogeneous distribution of tows and to control the fibre volume fraction inside a composite material. The composite forming operation into a 3D shape is directly linked to the capability of the 3D fabric to deform. Some difficulties like the interply slip may occur in the thickness direction with multiple layers stacked in different planes which are partially linked by interlinking yarns. This can lead to interply slip which directly affects mechanical performance of the final composite material. Thus, the use of specific warp interlock structure both enables inter ply slip between layers of the fabric, necessary to the production, and also maintains a homogeneous distribution of fibrous material in all the directions. Different warp interlock structures have been designed, produced and tested in order to estimate the influence of mouldability on mechanical performance.

Tartaric Sulfuric Anodizing (TSA) and γ-glycidoxypropyltrimethoxysilane silanization (ɤ-GPS) were tested as treatments of Al-2024 and Al-2198 aluminum alloys for promoting adherence and corrosion protection of the Al/CFRP interface in CFRP/Al co-cured hybrid materials, and compared to Chromic Acid Anodizing (CAA). The corrosion resistance and the durability of the Al/CFRP interface was investigated and discussed. Polarization curves and Evans Diagrams were achieved in NaCl solution, and the adhesion and durability of the interface was evaluated by mechanical tensile test on single lap joint specimens before and after salt spray exposure. The results are discussed and compared to CAA in order to evaluate the proposed treatments as CAA substitution candidate in the REACH European regulation. It was found that TSA and ɤ-GPS can provide as good adhesion as CAA before salt spray exposure, but a mechanical higher strength depletion of the interface is obtained after long term salt spray exposure compared to CAA. This depletion was attributed to an insufficient long term corrosion resistance of TSA or ɤ-GPS compared to CAA.