AN EXPERIMENTAL INVESTIGATION OF THE FAILURE MODES IN HYBRID CERAMIC-MATRIX COMPOSITES

A material system has been developed that employs the benefits of both fiber and whisker reinforcement in the strengthening and toughening o f ceramics. Testing was performed on this hybrid material system in th ree-point flexure using a combination of acoustic emissions analysis a nd microscopy techniques for damage analysis. It is shown that the hyb rid material system will withstand a higher stress before microcrackin g occurs in the matrix and has improved transverse strength. In the lo ngitudinal direction, microcracking occurred at 121 MPa for the hybrid composite, compared to 47 MPa for composites reinforced solely with f ibers. The transverse flexure strength was 62 MPa for the hybrid, comp ared with 24 MPa for fiber-reinforced composites. The hybrid composite also had higher stiffness and better damage tolerance in both the Lon gitudinal and transverse directions. Material properties are presented for three material systems: a whisker-reinforced cordierite composite , a fiber-reinforced cordierite composite, and a fiber/whisker hybrid- reinforced cordierite composite.