Functionally graded ultra-high temperature ceramics: From thermo-elastic numerical analysis to damage tolerant composites

To maximize the toughening contributions due to fiber bridging and residual stresses upon layering, ultra-high temperature ceramics containing variable amounts of short carbon in functionally graded stacking sequences were designed characterized. Stress fields evaluated by finite element model on (AB)nA more complex asymmetric architectures compared experimental fracture toughness pointing an effective increment those structures where notch fell zones compression. For best composite, at room achieved 7 MPa·m0.5 further increased 10 when tested 1500 °C within a light ZrB2-based composite with density below 4 g/cm3. According numerical simulations microstructural features composites, main guidelines for realization simultaneous failure tolerance ablation resistance established.