Experimental methodology of study of damage initiation and development in textile composites in uniaxial tensile test

Damage in textile composites is closely connected with the internal micro- and meso-geometry of the reinforcement, and reveals features, which are not present in the damage processes in classical laminates. This paper proposes a test sequence intended to characterise damage in textile composites – its initiation and development different scale levels: (1) Tensile tests on samples cut in characteristic directions of the textile reinforcement (machine, cross and bias), accompanied with acoustic emission (AE) registration and full-field strain measurement on the surface. The test produces stress–strain diagrams and identifies characteristic strain levels for post-mortem investigation: just after first damage ε1; well-developed damage ε2; just before the final fracture of the sample ε3. Full-field strain measurement highlights the relation between strain concentrations (linked with the damage initiation) and the reinforcement structure. (2) Samples loaded up to ε1…3 are examined with CT and X-ray. This reveals the damage pattern and allows quantitative characterising of the damage development. (3) Optical and SEM examination of cross-sections through the damage sites, determined with X-ray, identifies local damage modes. The same strain levels are further used for setting up fatigue tests. The experimental protocol is applied for triaxial braided and quasi-UD composites.