The fatigue behaviour of [0°/±45°] triaxial braided composites is investigated. Tension-tension and compression-compression loading is chosen to study main damage mechanisms and their effect on the stiffness degradation. In both cyclic loading cases a high stiffness degradation can be observed shortly after the start of cyclic loading. Inter-fibre fractures in the braid yarns with subsequent delaminations are responsible for this behaviour during tension-tension loading. Compression-compression loading leads to kink band formation in the axial yarns favoured by yarn undulations. In consequence of the observed material degradation, S-N curves based on a defined level of stiffness degradation are proposed for fatigue dimensioning instead of load cycles to fracture.
A comparative study of various joining techniques fatigue behaviour focusing on stiffness degradation