Abstract
The present paper investigates the static fatigue behavior of Hi-Nicalon fiber-reinforced SiC–SiC minicomposites at high temperatures in the 900–1200 °C range, and under tensile stresses above the proportional limit. The stress–rupture time relation was analyzed with respect to subcritical crack growth in filaments and fiber tow fracture. Slow crack growth from flaws located at the surface of filaments is driven by the oxidation of free carbon at the grain boundaries. Lifetime of the reinforcing tows depends on the statistical distribution of filament strength and on structural factors, which are enhanced by temperature increase. The rupture time data were plotted in terms of initial stresses on reinforcing filaments. The effect of temperature and load on the stress–rupture time relation for minicomposites was investigated using results of fractography and predictions of minicomposite lifetime using a model of subcritical growth for critical filaments. The critical filament is the one whose failure by slow crack-growth triggers unstable fracture of the minicomposite. This is identified by the strength–probability relation provided by the cumulative distribution function for filament strength at room temperature. The results were compared to the fatigue behavior of dry tows. The influence of various factors related to oxidation, including multiple failures, load sharing, and variability, was analyzed.
Highlights
Continuous fiber reinforced ceramic matrix composites (CMCs) exhibit a combination of superior properties over monolithic ceramics that make them attractive for high temperature applications
This multiscale scheme is illustrated in the present paper, which analyzes the static fatigue behavior of SiC/SiC minicomposites, with respect to the delayed failure of reinforcing filaments and tows
The present paper proposes a multiscale approach to the static fatigue of Hi Nicalon reinforced SiC/SiC minicomposites at high temperatures in air
Summary
Continuous fiber reinforced ceramic matrix composites (CMCs) exhibit a combination of superior properties over monolithic ceramics that make them attractive for high temperature applications. The CMCs are endowed with a remarkable versatility, which means that the behavior of CMCs can be designed with respect to expected performances, through the selection of fiber and matrix types with appropriate properties This multiscale scheme is illustrated in the present paper, which analyzes the static fatigue behavior of SiC/SiC minicomposites, with respect to the delayed failure of reinforcing filaments and tows. CMCs like SiC/SiC, which consist of an SiC matrix reinforced by SiC fibers, exhibit high mechanical properties at high temperatures and in severe environments [1,2]. They were developed initially for military and aerospace applications. They are being introduced into new fields, such as stationary gas turbines for the co-generation of heat and power, and their range of applications will grow when their cost is lowered significantly
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