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Elastic, thermo-mechanical oxidation and microstructural properties of the C/C-SiC CMCs

A set of ageing tests on all the SCHUNK and DLR materials developed and on the BoraSiC coating system were performed to evaluate the loss of weight and the decrease of the flexural strength.

Additional high temperature, up to 1500°C, flexural and compression on C-Ring short term tests were performed. The strength results for filament winded materials at RT were evaluated by Weibull statistical analysis, finding relatively high Weibull moduli.

The coating seems to be, generally, suitable for medium term oxidation environment.

The presence of delaminations and voids inside the bulk of the CMCs render the strength and oxidation results quite spread.

Some materials show a brittle failure mode (es. DLR BE5) in all testing conditions.

A set of interlaminar shear strength (ILSS) by compression of notched specimens tests were performed on Schunk fabric based materials. The shear strength is quite high.

The slow crck growth (SCG, dynamic fatigue) tests indicate that the CMC material isn’t significantly sensitive to sub-critical crack propagation, and there is no significant environmental influence on MOR at RT, in air.

No significant cyclic fatigue damage is measurable up to 100000 cycles and at max. load below 70% of static MOR of the CMC. The damage at higher loads close to the failure can be indicated by change of the stiffness and increase of accumulated strain. Fatigue limits seems to be at high % of MOR.

The cyclic fatigue damage on instrumented flanged and end capped tubes is negligible at pressure close to rupture, since the failure is mainly determined by strength limit at geometric discontinuities (flanges).

The SCG and cyclic fatigue results were used to set up a life time prediction model of the tested materials.

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