Evaluation of improved work of fracture in the mullite/cordierite laminate composites with transformation weakened cristobalite layers

The strength and work of fracture for the laminate-type composites of β-cristobalite and mullite/cordierite mixtures in 60:40 wt.% were evaluated by 4-point flexural test and numerical analysis. The fracture test was investigated, with laminates densified by hot-pressing, at different thickness ratios between mullite/cordierite and β-cristobalite. The β-cristobalite had critical grain size effect on the fracture behavior. The grain size of the β-cristobalite was controlled by annealing at 1300 °C. A load-deflection curve for the hot pressed sample annealed for 10 h showed a significant work of fracture (2.38 kJ/m2) with a strength of 131 MPa at the thickness ratio of cristobalite to the mullite/cordierite layer of 1:5. The improved work of fracture in the laminate was attributed to the matrix crack deflection by thermal and shear-induced phase transformation in the weakened cristobalite layer. Additionally, a numerical simulation performed by using quadrilateral 8-nodes curved layered shell element of DIANA supported the thickness ratio effect of the test results.