This paper presents a multiscale hybrid approach for predicting damage and failure of laminated composite structures based on the thermo-mechanical properties (stress/strain behaviour and strength) of the unidirectional plies. This kind of approach is thus predictive for different stacking sequences. The approach introduces viscosity of the matrix in order to obtain an accurate description of the mesoscopic behaviour, especially the non-linearity under shear loading. The failure criterion used is based on physical principles and introduces micromechanical aspects (such as the effect of the local debonding on the non-linear failure behaviour) at the mesoscopic scale. The main improvements, over those proposed in the second world-wide failure exercise, are related to (1) the evolution and effects of the mesoscopic cracks and (2) the coupling between those cracks and delamination (inter-ply damage). This approach has been implemented in an implicit finite element code in order to predict the strength of composite structures, exhibiting different levels of complexity (unnotched plates, open-hole plates) and subjected to complex loadings (membrane or bending loadings). All the 13 Test Cases of the third world-wide failure exercise have been solved.

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Conventional' or certified repair procedures for impacted composite structures (i.e. patches) are time consuming, and must be performed by highly qualified staff. In this paper, a cost effective and simple repair method by liquid resin infiltration is studied. As damages on aircraft structures are generally due to impact, this kind of damage is characterised and compared to quasi-static indentation with ultrasonic inspection and micrographic cuts. The repair by liquid resin is used to fill in the very special damage pattern region organised as a crack network (delamination and transverse cracks). In order to study this new repair method, an experimental set-up has been manufactured and different configurations have been studied. Mechanical testing (CAI, DCB and ENF) was then performed to evaluate the strength of this repair. As good results were achieved, further exploration under complex loading should be performed to ensure the quality of the repair for an industrial application.

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