Computational fracture mechanics for reliability of composites at the micro and macro scales

In recent years, an increasing use of composite materials inaerospace and aeronautical applications has taken place. Fibrereinforced composites materials (FRCs) present high specificstrength and stiffness ratios, which can be consideredas remarkable advantages with respect to metallic materials.One of the main problems associated with the internal arrangementof fibre reinforced materials regards the numerousand complex failure mechanisms that can occur at differentscales of observations. Stemming from these reasons,at present, the analysis and study of fracture in fibre compositesconstitutes a relevant and recurrent area of researchdue to the actual needs for the achievement of a higher levelof understanding of such fracture phenomena. Within thiscontext, this dissertation presents a new model to simulatefracture in FRCs with the aim of designing safe and durableaircraft structures, for instance: shells, plates or thin filmsubstratestructures. The fundamental computational modelused in the present thesis was proposed in (14), devising aseminal combination of the Phase Field approach for brittlefracture and a Cohesive Zone Model for interface failure.In the current research, this computational framework is examinedand validated through the numerical simulations ofdifferent applications at the micro- and macro-scales: (i) themicro-mechanical inter-fiber failure of composites, the subsequentpropagation of failure through the thickness of the laminatesarising a macro-crack and (ii) several macro-mechanicalapplications concerning advanced composite structures (shells,thin film-substrates and Functionally Graded Materials). Derivedfrom the current predictions, it is possible to argue thatthe current numerical methodology is very suitable for thesimulation of fracture in composites at different length scalesand allows the preclusion of intricate remeshing techniquesor crack tracking algorithms in conjunction with minimizingthe mesh-dependent pathology due to its non-local character.