A Family of Prediction Tools for Fine Ceramic Fibers Subcritical Cracking

Abstract : Ceramic Matrix Composites reinforced with long fibers are potential candidates for high-temperature structural applications. Their lifetime is mainly controlled by the fibers. The rupture mechanism of fibers under environmental conditions and mechanical stress is the environmentally assisted propagation of their surface defects toward their core. The analysis of cracks subcritical propagation is called static fatigue, because most works use a Paris-like law relating the crack's velocity to the crack's stress intensity factor. This law, depending on temperature, agrees fairly well with experimental results for constant environmental conditions. However, is not directly suitable to varying ones, as it is the case in real composites. The approach to subcritical propagation introduced here relies on classical fracture mechanics, in which the environment only modifies the damage zone at the crack's tip. The model does not explicitly depend on temperature, but only on the total oxygen flux reacting at the crack's tip. Consequently, this model is valid for any temperature and oxygen pressure, which can vary along time, as long as the environment is modelled properly. For Hi-Nicalon fibers up to 1000°C in dry atmosphere, we introduced the chemical phenomena observed through simple diffusion/reaction models in order to define the true oxygen flux reacting at the crack's tip. The resulting identified model is validated on experimental data.
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Martin Genet, Pierre Ladevèze. A Family of Prediction Tools for Fine Ceramic Fibers Subcritical Cracking. 7th International Conference on High Temperature Ceramic Matrix Composites (HTCMC7), Sep 2010, Bayreuth, Germany. ⟨hal-01274846⟩

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