Functionally graded ultra-high temperature ceramics: from thermo-elastic numerical analysis to fracture tolerant materials

temperature ceramics containing variable amounts of short carbon fiber in functionally graded stacking sequenceswere designed and characterized. Stress fields evaluated by finite element model on (AB)nA and morecomplex asymmetric architectures were compared to the experimental fracture toughness pointing to an effectivetoughness increment in those structures where the notch fell in zones of residual compression. For the bestcomposite, toughness at room temperature achieved 7 MPa·m0.5 and further increased to 10 MPa·m0.5 whentested at 1500 °C within a light ZrB2-based composite with density below 4 g/cm3.According to the numerical simulations and the effective microstructural features of the composites, the mainguidelines for the realization of ceramics with simultaneous failure tolerance and ablation resistance were established.