Discrete modeling strategies for aeronautic composite structures: from failure scenario to certification
Résumé
During the last two decades, the composite group of Institute Clement Ader has developed some very efficient modeling strategies based on refined phenomenological analysis of failure in composite structures. It started by a discrete modeling of Nomex honeycomb core which was able to predict accurately the impact and compression after impact of sandwich structures. This idea was recently extended to a discrete modeling of foam with a change of scale. Both frontal and razing impacts on helicopter composite rotor blades were studied using a semi-continuous approach. The right scale of modeling of the front spar or the thin woven skins was the scale of bundles. This approach is robust enough to be used now for design and certification. One major concern with aeronautic composite structures is low-velocity low-energy impacts on UD laminates. The Discrete Ply Modelling (DPM) is based on a mesh following the orientation of the plies. This complex mesh allows taking into account naturally the coupling between intra and inter laminar damages but also splitting. Moreover, it is based only on 13 “true” parameters. This approach was applied successfully for impact and crash on laminates, CAI, residual dent computation, pull-through, edge impact and impact on tapered laminate. This approach was recently extended successfully to in-plane issues like open hole tension, scaling effects and large notches. So the confidence in these discrete models is high and the next step is to move from the scale of coupon under uniaxial loading to the scale of technological specimens under complex loadings. This investigation was made through the VERTEX research program. A significant step to Predictive Virtual Testing was achieved and a new pyramid of tests for the certification of aeronautic composite structures can be proposed