A Damage-Based Fatigue Model of Braided Ceramic Matrix Composites at Elevated Temperature

Abstract Ceramic matrix composites (CMCs) play an increasingly significant role in the modern aerospace industry due to their excellent high-temperature mechanical properties. Fatigue property at elevated temperatures is an essential issue for their application, especially for the turbine blades of aircraft engines subjected to cyclic loading under extreme conditions. A progressive fatigue damage approach was established to predict the damage initiation and evolution of braided SiC/SiC CMCs under tension-tension cyclic loading. The main framework was achieved via a user-material subroutine UMAT in ABAQUS with FORTRAN code. Different damage initiation criteria are introduced for fiber bundles, matrix and interface. Related experimental results reveal that the main reasons for the failure of composites under cyclic loading are the loss of bearing capacity of the matrix, the decrease of fiber strength in high-temperature oxidation environment and the interface wear. Hence, the stiffness and strength degradation of matrix and fiber bundles as well as the interfacial shear stress reduction are used to describe the fatigue damage in this method. And a specific proportion of failure elements on the loading surface is regarded as the symbol of the eventual failure of the composites. Damage evolution of different constituents during the fatigue process can be simulated with this method. Subsequently, the simulation results of static and fatigue analysis were compared with relevant experimental results at 1300°C. It indicates that the predicted static tensile strain-stress curve, and curves of maximum strains vs cycles in the fatigue analysis are in good agreement with that measured during the experiments. Besides, the predicted fatigue life also exhibits an acceptable consistency.