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Title: Understanding and modelling the mechanical response of woven composites
Author: Vieira De Carvalho, Nelson
ISNI:       0000 0004 2729 1274
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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The present work focuses on improving the understanding and modelling of the mechanical response of woven composites. It comprises of original experimental observations together with novel numerical and analytical developments. The experimental work focused on the investigation of damage initiation and propagation under compression. Detailed microscopy shows that damage is controlled by the individual failure of the load-aligned tows through kink-band formation. Moreover, both weave architecture/internal geometry and support provided by the adjacent layers are seen to affect damage location and morphology, suggesting that, to capture the failure mechanisms in compression, they should be explicitly modelled. Subsequently a theoretical framework to derive periodic boundary conditions for the mechanical analysis of periodic structures, using domains smaller then the unit cells, is presented. These domains, named reduced Unit Cells, lead to significant gains in efficiency, which enable the use of refined numerical/analytical models. The framework mentioned above was used to develop a detailed nonlinear numerical model of a 2D woven composite. Weave architecture was modelled explicitly and the effect of the support provided by the adjacent layers was taken into account. The constitutive response and ultimate strength values predicted numerically agree well with experimental results for both tension and compression. Additionally, the model was used to investigate the effect of the biaxial loading ratio on the failure strength. Finally, an analytical model to predict the compressive and tensile response of woven composites is presented. The load-aligned tow was modelled as an Euler-Bernoulli beam supported by an elastic foundation. The properties of the latter are fully derived from kinematic models for the deformation of the weave, providing great insight into the deformation mechanisms of woven composites. The analytical predictions agree well with both experimental and numerical results. Overall, its flexibility offers an alternative and valuable addition to detailed numerical models, particularly when performing sensitivities studies.
Supervisor: Robinson, Paul ; Pinho, Silvestre Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral