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Dimensionnement en fatigue des structures ferroviaires en composites épais

Abstract : This PhD work is devoted to the development of design tools able to be used in an industrial context by design offices. Even if we notice an increase use of composites materials in many fields, applications are limited when the stresses supported by the structures and the request security need accurate design providing high safety. Further if we increase the safety factors, the gain weight due to the use of composite materials and the cost attached to these materials, rapidly reduce the interest inherent of these materials. Avoiding such over-design needs a good knowledge of these materials both in their linear domain but in their non-linear domain too. That means a good understanding of damage mechanisms and damage tolerant analysis for damages susceptible to occur. In this context and through a partnership with ALSTOM industry, we studied carbon epoxy textile composites for bogie parts application. The objective was to characterize these materials and to analyze their damage modes when submitted to static and fatigue loadings and then to propose constitutive laws coupling stiffness and damage and accurate strength criteria. These models when introduced in finite element codes have to allow the design of structures with high gradients parts. The other objective was to study the influence of thickness in a context of increasing numbers of plies to support high stressed zones. The major reason is that composite materials are no more confined to secondary parts which only have to support low stresses but are now used for primary parts which contrary to secondary parts have to carry out high stresses with gradients. This is the reason why the thicknesses of laminate structures have notably increased. If we can always mention a good fatigue strength for composite materials, a high ratio between the fatigue limit and the tensile strength, it is necessary to verify such assessment when the thickness increased. In fact laminate structures develop out of plane stresses with the increase of the thickness the main consequence of them is to initiate delamination through the thickness. This type of damage can be very critical for the lifetime of these structures and has then to be considered during design phase.
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Submitted on : Friday, October 1, 2010 - 10:36:30 AM
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  • HAL Id : pastel-00522605, version 1

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Pongsak Nimdum. Dimensionnement en fatigue des structures ferroviaires en composites épais. Matériaux. École Nationale Supérieure des Mines de Paris, 2009. Français. ⟨pastel-00522605⟩

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