TECHNOLOGY behaviour Fig. 4: Fatigue curves for various composite materials Fig. 5: Damage types in a composite material (Trovalet) The ability to evaluate the life cycle of a composite part requires a full understanding of the damage mechanisms in the structure (Figure 5) depending on the material's composition and the characteristics of the forces applied (damage tracking with acoustic emission, fractographic analysis of the specimens and parts tested, see Figures 6 and 7). Other phenomena to be taken into consideration The residual stresses from the preparation of the composite, which combine with the external mechanical stresses, should also be taken into account in this forecast, focusing on life cycle but also on service performance. Paired mechanical/physico-chemical phenomena (e.g. water diffusion) also need to be considered. Cetim is currently developing methods to determine fatigue behaviour laws faster under various environments by combining calculations, tests and measurements, and is also working on fatigue post-processing codes for the fatigue design of composite parts. More information: nolwenn.leray@cetim.fr sophie.toillon@cetim.fr 118 jec composites magazine / No111 March 2017 Fig. 6 : Damage monitoring in a composite structure by acoustic emission (AE) Fig. 7 : Fatigue grooves in a carbon/ epoxy composite [0°] - Mode I interlaminar fatigue rupture (S.E.M. examination)http://www.wickert-presstech.com