Damage Progression and Stress Redistribution in Notched SiC/SiC Composites

The stress fields adjacent to machined notch roots were examined during tensile tests of woven SiC/SiC composites using thermoelastic stress analysis. As expected, the stress-concentration factor (SCF) at the notch roots increased with increasing notch lengths. Damage-induced stress-relief was not evident in these composites. In fact, the redistribution of stresses onto isolated fiber tows adjacent to the notch root caused an increase in the apparent SCF. Lastly, the SCF increased with mean stress. This was assumed to occur as a result of opening matrix cracks that are typically closed due to residual compressive stresses in the matrix material at near zero loads.